Transcript stages of plant maturation

OBJECTIVES
The student will be able to…
• Differentiate
between annual,
biennial, and
perennial plants.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
OBJECTIVES
The student will be able to…
• Describe the processes and steps in seed
germination.
• Enumerate the traits that differentiate plant
juvenility from maturity.
• Describe the steps in the flowering process
in plants.
• Define the stages of dormancy, senescence,
and abscission.
• List four plant hormones and their principal
effects.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
• In a typical life cycle, plants pass through two states:
– Growth and rest.
• Growth occurs in suitable environmental conditions.
– Temperature, rainfall, etc.
– Characterized by flowering, shoot lengthening, and leaf
production.
• Rest, (dormancy) also reflects environment.
– Cold, drought, or inadequate light.
– Characterized by slowed/stopped growth, leaf drop,
and/or death of above-ground parts of the plant.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
• To understand importance of growth & dormancy,
classify plants according to the length of time
they live.
– Plants fall into one of four botanical groups.
• Annual, biennial, perennial, and monocarp.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Annual
• An annual plant reproduces itself by seed, grows to
maturity, flowers, produces seeds, and dies during
one growing season.
– It experiences dormancy only as a seed.
Figure 3-1a Annual plant life cycle. Drawing by Bethany Layport.
• To most gardeners an annual is a frost-tender
flowering or vegetable plant grown in summer.
– In mild climates there also are winter annuals that
are planted in fall to bloom through the winter.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Annual
• Exception must be made for plants that would live
more than one year in their warm native climate.
– These plants, not able to survive winter in cold regions,
are not true annuals but function as annuals because of
climate.
• Tomatoes, lantana & impatiens, when grown in cold areas.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Biennial
• A biennial plant completes its life cycle in 2 years.
Figure 3-1b Biennial plant life cycle. Drawing by Bethany Layport.
• A biennial…
–
–
–
–
–
Is grown from seed.
Produces leaves in rosette form for one season.
Becomes dormant during winter.
Resumes growth in spring.
Produces a vertical flower stalk (bolts), and dies.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Biennial
• Biennials are relatively uncommon among
cultivated plants.
– Hollyhocks, parsley, and sweet William.
• Some vegetable crops are biennials, harvested
prior to entering winter dormancy.
– Cabbages and carrots.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Perennial
• Perennials live for more than two growing seasons.
Figure 3-1c Perennial plant life cycle. Drawing by Bethany Layport.
• Technically trees, shrubs & bulbs all are perennial.
– In horticulture, the term often refers to flowers such as
daylilies & iris, that grow back from the roots each spring.
• Perennials typically reproduce by growing new
plants from the mother plant (vegetatively).
– In addition to by seed.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
PLANT LIFE CYCLES
Monocarp
• A monocarp can live for many years but will flower
only once in its lifetime and die afterward.
Figure 3-1d Monocarp plant life cycle. Drawing by Bethany Layport.
• Bromeliads and century plants (Agave spp.) are
two examples of monocarpic plants.
– These plants bloom after several years of active growth.
• The tops then die, and new plants are produced by the root
system of the old plant.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
• Regardless of how long a plant lives, it usually will
pass through four stages of maturation.
– Germination, juvenility, maturity, and senescence.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• Germination starts when a seed absorbs water
– Ends when the primary root emerges.
• After germination, the seedling
goes through establishment.
– Until it is independent
& photosynthesizing.
Figure 3-2 Germination of a bean seedling.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• A seed must contain…
– An embryo to develop into a new plant.
– A source of energy to supply the
embryo during germination
and establishment.
• Carbohydrate, fat, or protein.
A covering
called the
seed coat
helps prevent
injury & drying.
Figure 3-2 Germination of a bean seedling.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• In many dicot seeds, carbohydrates for germination
are stored in two cotyledons.
– These resemble leaves & are
sometimes attached to the
stem when the seedling
emerges from the ground.
Frequently
called seed
leaves, as
opposed to
true leaves,
produced later.
Figure 3-2 Germination of a bean seedling.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• Cotyledons may serve as storage sites as well
as photosynthesizing organs & transfer
tissue between the endosperm
and the embryo.
Figure 3-2 Germination of a bean seedling.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• Cotyledons may serve as storage sites as well
as photosynthesizing organs & transfer
tissue between the endosperm
and the embryo.
In other species carbohydrates are
mainly stored in an endosperm, a
single organ.
Figure 3-3a Corn grain showing enlarged endosperm.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
Figure 3-2 Germination of a bean seedling.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• For a seed to germinate and establish a new plant,
correct environmental conditions are necessary.
– Water must be present.
– Oxygen must be available.
– Temperature must be in acceptable range to that species.
• Uptake of water, the first process, causes the seed
to swell & triggers many chemical reactions.
– Including an increase in the cellular respiration rate.
• Oxygen is necessary for cellular respiratory process.
– Without it, cellular respiration will not begin and
the seed will not germinate
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• Suitable temperature is essential for germination.
– Temperatures either too high/too low will kill the embryo.
• Or prevent germination from proceeding.
• After sufficient swelling and cellular respiration have
taken place, the radicle, or primary root, will emerge.
– It grows down into the soil, beginning the absorption
process, and soon afterward the shoot emerges.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Germination
• The first shoot of most dicot plants will emerge
from the soil in an arch, with the stem
of the young plant forming a
loop called the hypocotyl.
Once exposed to sunlight, the
arched part of the hypocotyl
straightens, pulling cotyledons
and other delicate tips of the
young plant through the soil.
Figure 3-2 Germination of a bean seedling.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Juvenility
• After germination, most plants enter juvenility.
– May last from several weeks to years.
• The plant will grow rapidly but not begin reproduction.
• Pruning, temperature alteration & applications of
growth-regulating chemicals can change a plant
from juvenile to the mature state, and back again.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Juvenility
• Some plants have recognizable traits that signal
that the plant is in a juvenile state.
– Leaf Form - different from that found on the mature plant.
– Growth Form - variation in form also distinguishes
juvenile from mature plants.
Juvenile branch form is sometimes found on young fruit trees
as whip-like vertical shoots, usually arising from the base of
the trunk, they are called suckers, or water sprouts.
– Thorns - a third common characteristic of juvenility.
– Leaf Retention - A tendency for juvenile parts of a
tree to hold leaves throughout the winter is the fourth
characteristic.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Juvenility
Plants may indicate juvenility by
other than visible characteristics.
In propagation, juvenile parts
almost always root faster than
mature portions.
Figure 3-4 An oak tree retaining its dead leaves
in winter, a characteristic of juvenility. Courtesy
of Dr. Claud L. Brown, University of Georgia.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Maturity is the third stage in plant growth, during
which sexual reproduction takes place.
– Flower Induction - the first indication of maturity.
• The first of the three phases of flowering.
– Flower Initiation - the second phase of flowering.
– Flower Development - length of time from induction to
bloom may vary from several weeks to 6 or 8 months.
– The opening of the flower is the final stage of
development, after which the flower is generally
receptive to pollination.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Induction of flowering is sometimes caused by
environmental factors such as temperature or
night length.
– In nature these factors program flowering into a seasonal
pattern so that it occurs at the same time each year.
• People can simulate these conditions to induce flowering
at a pre-selected time.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Cool temperature is a crucial environmental factor
that causes flowering of many plants.
– Some plants that grow/flower well in northern climates
die or grow only vegetatively in warmer locales.
– They must be vernalized (subjected to cold temperatures)
before they can be grown successfully.
– In addition to certain fruit trees, biennial plants may
also require vernalization for flowering.
• Cold received during the winter following the first season
of growth induces flowering to complete the life cycle
of the plant.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Cabbages, carrots, and beets all are biennial plants
that require vernalization.
– Because they are raised for their roots & leaves, and
harvested the first year, vernalization is not important.
• Vernalization of bulbs such as tulips, hyacinths, and
crocuses is important as they are grown for flowers.
– In warm climates bulbs of these plants are sold prechilled.
• Vernalized by refrigerated storage.
– They flower the following spring regardless of climate.
• They will not bloom more than 1 year unless growing in
a climate where they receive yearly natural vernalization.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Daily night duration is a second environmental
factor that can control flowering in plants.
– Nights are longest in winter, shortest in summer.
• Intermediate in spring and fall.
– The further north or south of the equator, the more
extreme the difference between the shortest summer
night and longest winter night.
• Plants that respond to these changes in the night
length are called photoperiodic.
– Common in all but tropical climates near the equator.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Two main types of photoperiodic plants have been
studied intensively.
– Commonly called short-day and long-day plants.
• Actually it is the length of the night that triggers flowering.
• The confusing designation stems from the first
research on photoperiod.
– It was mistakenly believed length of light rather than
darkness caused flowering.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Short-day plants flower only when the daily light
period is less than their critical photoperiod.
– For example, 12 hours.
• Long-day plants will flower only if the light period
is more than their critical photoperiod.
– Or by cutting the dark period into two shorter periods.
– They can also flower under continuous light.
• Or during a long dark period interrupted by a short light period.
– In an otherwise long night, a short period of light has the
effect of cutting the dark period into two shorter periods.
• If each half is less than the critical period, the plant responds as
if it were exposed to only short nights & flowering takes place
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
Figure 3-5 The flowering responses of long-day plants to varying dark/light ratios.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• The way in which night length triggers flowering
involves a pigment called phytochrome.
– Alternates between two forms, each with sensitivity to
differing wavelengths of light in the red to far-red range.
• Light intensity can also control flowering.
– Plants that are day neutral and not affected by night
length frequently respond to intensity.
• Greater light intensity is required to induce flowering
than is sufficient to keep a plant growing vegetatively.
– Many houseplants bought for their blooms never flower
again after being moved from a greenhouse to indoors.
• The light intensity is simply too low to induce flowering.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Like induction, flower initiation is invisible to the
naked eye.
– Changes are taking place in microscopic parts of the plant.
• During this phase, vegetative meristems at the
stem tips or leaf axils change to flower meristems.
– Capable of developing into blossoms.
• This change takes place over several days or weeks.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
Small knobs of cells
emerge in a spiral
around the center.
These are the
beginnings of
petals, stamens,
& other flower
parts.
The meristem stops
lengthening, but
development
continues.
Figure 3-6 Electron microscope photograph of a developing flower meristem of an Easter lily.
Photo courtesy of Dr. H. Paul Rasmussen, Logan, Utah.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• The final stage of development is opening of the
flower, after which it is receptive to pollination.
– Whether it pollinates itself (self-pollination) or is
cross-pollinated by another plant will affect the
resulting seeds.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• During pollination, dust-size pollen
grains released from the anthers
are deposited by wind or insects
on the stigma.
– Like seeds, they germinate & grow
downward toward the ovary where
the eggs are located
– After reaching the ovary, the uniting
of sperm (contained in the pollen)
and eggs (in the ovary) occurs in
the process of fertilization.
Figure 3-7 Germinating pollen grains growing toward the ovary.
These female parts of a flower are collectively called the pistil.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• After reaching the ovary, the uniting of sperm
(contained in the pollen) and eggs (in the ovary)
occurs in the process of fertilization.
• In some instances pollen produced by a flower may
be unable to fertilize eggs produced by that flower.
– Self-incompatibility is in about 40% of cultivated plants.
• In some cases the pollen grain simply never germinates, and in
others it germinates but grows poorly, never reaching the egg.
• Thus cross-pollination is quite common.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Cross-pollination can be a hindrance as well as an
advantage…
– Sweet corn & field corn can cross-pollinate.
• Making the sweet corn taste like corn raised for grain.
– Sweet and hot peppers also will cross-pollinate.
• Growing a mild pepper with hot-tasting seeds or other changes.
• Although egg fertilization usually must occur before
a fruit will develop, in some cases it is not necessary
– As in when the sperm does not fertilize the egg, but the
fruit still develops, resulting in a seedless fruit.
• Seedless fruits formed in this way are called parthenocarpic.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Parthenocarpy can be caused by growth-regulating
chemicals or specific environmental conditions.
– Excessively warm temperatures during pollination can
cause seedless tomatoes to form.
• Parthenocarpic seedless fruits also form by spontaneous
death of the seed embryo in early developmental stages.
• A majority of cultivated fruits need living seeds are necessary
for the fruit to develop normally.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• If only half the eggs in an
apple are fertilized, only
one side will grow, which
produces misshapen fruit.
Cucumbers can have this problem,
with a portion staying small while
the remainder develops normally.
• In cases where the fruit
contains only one seed,
fruit will drop prematurely
if the embryo dies.
Figure 3-8 A greenhouse-grown cucumber that was not fully pollinated & failed to develop normally.
Courtesy of the Cooperative Extension Service of the University of California.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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STAGES OF PLANT MATURATION
Maturity
• During fruit development, sugars photosynthesized
in the leaves constantly flow into the fruit.
– Supplying energy for the developing ovary, which will
become the fruit.
• When a fruit reaches the end of its enlargement
period, ripening begins.
– Caused by the production of ethylene gas, a hormone
produced by the fruit.
• It may become soft or change color.
• Flavor can change from sour to sweet.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
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STAGES OF PLANT MATURATION
Maturity
• Softening of fruits is the result of the breaking down
of compounds called pectic substances, which
strengthen cell walls and cement cells together.
– In over-ripening, mushiness occurs because too much
pectic substance has been lost.
• Mealiness in apples results from such over-ripening.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Maturity
• Color changes result from the breakdown of
chlorophyll & accumulation of other pigments.
– Chlorophyll decreases & other pigments increase intensity.
• Carotene is a pigment that gives orange color to fruits
such as oranges and persimmons.
• Anthocyanin is the pigment responsible for the red color
of ripe strawberries and apples.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Senescence
• Senescence is aging of a plant or any of its parts.
– Part of the natural life cycle of the plant, or as a result
of environmental factors.
• Natural life span often determines when senescence begins.
• Characterized by dramatic changes in metabolism:
– Increased respiration.
– Decreased photosynthesis.
– Breakdown of larger molecules into smaller ones.
• Fats, proteins, or carbohydrates.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Senescence
• Annual plants begin senescence at flowering, and
will die soon after seed formation is complete.
• Senescence after reproduction also happens in
monocarps that live several years before flowering.
• Senescence of perennial plants is frequently called
decline.
– Asparagus is a perennial that suffers from decline.
• Productive life of asparagus plants is generally 20 to 25 years.
• As plants reach this age, yield drops off & the bed is replanted.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Senescence
• An entire plant need not die for the term senescence
to be applied.
– Top portions of herbaceous perennials & bulbs
senesce annually, but the root system remains alive.
• A colorful show of leaf senescence occurs during the
fall when trees turn color.
– Coloring is due to the same pigment changes that
occur with the ripening of fruit.
• Shortening of day length in fall & cooler temperature
trigger this senescence.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Senescence
• The dropping of leaves, flowers, fruits, or other plant
parts is called abscission.
– Involves the manufacture hormones and the formation
of a zone of abscission.
In simple leaves, this
zone is formed at the
point where the petiole
connects to the stem.
Figure 3-9 A leaf just prior to abscission.
• In compound leaves, the main abscission zone is
also at the point where the petiole reaches the stem.
– Individual leaflets may form abscission layers & drop.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Senescence
• Flower abscission is often related to pollination.
– Pollen contains auxin, which it carries to the pistil,
triggering abscission of the flower parts.
• As petals, stamens, stigma & style are no longer
needed, their abscission diverts more carbohydrate
to the developing fruit.
– Fruit abscission can occur at any point in development
but is most common after ripening.
• Dropping of ripe fruit is a type of seed dispersal, with an
abscission layer generally forms before a fruit drops.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Dormancy
• Dormancy is a stage of plant development in which
growth slows or stops, affecting all life stages from
seed to maturity.
– Important in adapting plants to environment & ensuring
survival.
• Dormancy occurs during periods not suitable for
plant growth, and is usually seasonally related.
– Winter dormancy is found in plants in cold-winter areas.
– Dry-season dormancy is found in areas of distinct wet
and dry seasons, such as California.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Dormancy
• While photosynthesis can happen at temperatures
below freezing, dry winter air can cause plant
damage or death.
– Especially if groundwater is frozen and unavailable.
• Limited surface area of many evergreen leaves has
adapted them to minimize water loss.
• In other plants, leaf abscission is an indicator of
dormancy, signaling the onset of winter.
– Leaves of these plants cannot withstand subfreezing
temperatures, so they abscise in autumn.
• New leaves survive as buds.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Dormancy
• The changeover from dormancy to active growth is
called breaking dormancy.
– Normally results from changing environmental conditions.
• Seeds usually enter dormancy just prior to fruit
abscission, or senescence of the parent plant.
– Conditions needed to break dormancy & start germination
are specifically geared to ensure seedling survival.
• Many seeds require winter vernalization.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Dormancy
• Simulated vernalization is sometimes used to break
dormancy in commercial nursery crop production.
– Called stratification, it involves storing moist seeds at
temperatures near freezing for one or more months.
• Peach & apple tree seeds are stratified before planting.
• Heat can break dormancy in some seeds.
– Forest fires destroy existing trees, but also trigger the
germination of dormant pine seeds.
– Only intense forest fire heat will weaken seed coats
of some pine seeds that are woody and thick.
• Most seeds require less drastic measures to break dormancy.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
STAGES OF PLANT MATURATION
Dormancy
• Usually the seed coat erodes enough by weather to
permit germination.
– It can also be weathered artificially by scarification.
• Cutting, scraping, or otherwise injuring the seed coat
enough to allow water absorption & germination.
• Chemical scarification can weaken the seed coat,
such as through the swallowing of seeds.
– Acid of the stomach eats away at the seed coat, and the
seed is deposited along with the feces of the animal.
• A sort of built-in fertilizer.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
• Plant hormones are chemicals, made within the
plant, that produce changes in growth.
– Cause root formation, seedless fruit formation, leaf drop,
and stem lengthening.
• Plant growth regulators are synthesized chemicals
like plant hormones, which have the same effects.
– May be chemically quite similar to hormones.
• But they do not occur naturally.
• Nine groups of plant hormones have been identified.
– It is likely that others will be discovered eventually.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
• Scientists researching plant hormones encounter a
number of difficulties.
– Effects of hormones are not the same, species to species.
– Slight changes in hormone concentrations can alter their
effects completely.
– Two or more hormones are frequently found together.
• It is difficult to determine which chemical is responsible for a
particular effect.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
See the entire list on
page 41 your textbook.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Auxins
• Auxins, the first hormones discovered have such
diverse effects as…
– Promotion of rooting.
– Formation of underground tubers and bulbs.
– Prevention of fruit formation, defoliation.
– Prevention of abscission of leaves and fruits.
– Auxins promote juvenility.
– Auxin made in the terminal bud is responsible for
suppressing the sprouting of axillary buds further
down the stem of a plant.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Auxins
• Synthetic auxins, available in garden centers,
have a number of practical home uses.
– Powders sold to encourage rooting of cuttings are
composed of manufactured auxins in a talcum base.
– 2,4-D, sold to control lawn weeds is an auxin which kills
many plants at high concentrations.
• At very low concentrations, it is a growth enhancer.
– High auxin concentrations can prevent fruit on ornamental
trees when it is an undesirable feature.
• In commercial agriculture, synthetic auxins defoliate
plants before harvest, prevent sprouting of potatoes
in storage, and prevent premature orchard fruit drop.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Gibberellins
• Activity associated with gibberellins:
– Stem elongation
– Breaking dormancy of seeds, buds, and tubers.
– Increases in flower, leaf, and fruit size.
– Inducing flowering in plants that normally require
vernalization or a specific photoperiod.
• Gibberellins are used in greenhouses to...
– Form tall tree-form fuchsias and geraniums from cuttings.
– Increase the size of grapes by elongating flower parts.
– Substitute for vernalizing azaleas and fruit trees
in the South.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Cytokinins
• Cytokinins are believed to work in conjunction with
light to increase cell division and enlargement.
– Also been shown to prevent chlorophyll degeneration
and break axillary bud dormancy.
• Their only commercial horticulture use is in tissue
culture, where they stimulate callus growth.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• Synthetic and natural growth retardants are sold
under the trade names A-Rest®, B-Nine®, Bonzi®,
Sumagic®, and Cycocel® .
– Used on florist crops such as poinsettia & chrysanthemum.
• They slow elongation of stems, making sturdier, fuller plants.
– On fruit crops they improve color, firmness & storage life.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• Growth retardants can be used on hedges and
lawns to slow growth and decrease maintenance.
TREATED
UNTREATED
They can also be used
to maintain bedding
plants in a compact
size, giving plants a
neater appearance
in formal landscapes.
Figure 3-10 A shrub treated (left) and
untreated (right) with Atrimmec® growth
retardant. Courtesy of PBI/Gordon
Company, Kansas City, Mo.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• Abscisic acid (ABA) is a growth retardant that may
induce abscission and does induce dormancy and
inhibit seed germination.
– Its action can be counteracted by growth-inducing
chemicals such as auxins, gibberellins, and cytokinins.
• Appears to be very involved with stress resistance.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• A number of growth retardants have also been used
to control lawn growth & reduce mowing frequency.
– Maleic hydrazide & mefluidide reduce growth or stop
flowering.
– EPTC and amidochlor reduce growth or flowering.
• But cannot stop it completely.
• These chemicals must be used carefully, and the
results are not always predictable.
– Unacceptable color loss, injury and lessened ability
of the turf to recover from disease & pest problems
can result.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• Ethylene is a retardant, with use dates to Chinese
practices of ripening fruits in incense-filled rooms.
– Later determined to be ethylene gas given off in
the fumes that caused the accelerated ripening.
• Ethylene is also produced by the ripening fruits
themselves, wounded plant parts or by cut flowers.
– It can be manufactured.
• Ethylene also ages plant parts such as flowers,
causing them to abscise, and induces flowering
in a limited number of species.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Growth Retardants
• Pineapples and other members of the bromeliad
family will bloom when treated with ethylene.
– In commercial greenhouses, the product used for
ethylene generation is Florel® or ethephon.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Pinching Agents
• Pinching agent chemicals are used commercially
to kill terminal vegetative buds.
– To promote branching & a more bushy, attractive plant.
• OffShoot-0® & Atrimmec® are mainly used for this purpose.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Vitamins
• Vitamins are sold occasionally as stimulants for
plant growth and for use after transplanting.
– The same vitamins sold for human use.
• But act more as hormones in plants.
• Particularly B vitamins.
• Vitamin effectiveness has not been determined fully.
– When used on bean seeds, limited experiments have
shown improved germination rates.
• And decrease the time from seed sowing to harvest.
– Increases in yield have been reported on some species.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
HORMONES & GROWTH-REGULATING CHEMICALS
Vitamins
• Overall, it is very possible that vitamins do improve
plant growth in some cases.
– They should never be used in place of fertilizers or
proven-effective chemicals sold for use on plants.
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458
END OF
CHAPTER
Practical Horticulture 7th edition
By Laura Williams Rice and Robert P. Rice, Jr.
© 2011, 2006, 2003, 2000, 1997 Pearson Education, Inc.
Pearson Prentice Hall - Upper Saddle River, NJ 07458