Transcript Power Point - Texas A&M University

Learn to Think Like a Plant
Then You Can Talk to Them
David Wm. Reed
Department of Horticultural Sciences
Texas A&M University
Plants are “schizophrenic hermits” !
They “live alone” and “talk to themselves”
Plants “talk” using:
 Hormones
 Moving photosynthates, nutrients, etc. from “sources”
to “sinks”
 Sensing their environment (day vs. night, day length,
length of winter, temperature, rainfall, structures they
touch, gases in the air, chemicals in the soil, etc.)
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They possess the senses of sight, touch, smell and taste
To the best of my knowledge, they cannot hear?
Learn Plant Language
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We must learn the “language” plants use.
Plants don’t use “words” or “nerve impulses”.
Rather they use hormonal signals, chemical signals,
and environmental signals that “trigger metabolism”
and “turn genes on and off”.
If we learn their “communication logic”, then we can
“talk” to them and “dictate “ what they do.
We’re Going to Talk About
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How plants “see”
Their “favorite temperature”
How they know when they are “cut”
How and why they sometimes “kill’
themselves or parts of themselves
A little about their “sexual preference”
Let’s “talk” to plants with
Light
How do plants “see”?
Plants “see” with:
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Chlorophyll
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Carotenoids
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absorbs light for photosynthesis
also absorbs light for photosynthesis
protects plants from high light and sunburn
Phytochrome
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determines when the sun rises and sets
assists in determining day length (photoperiod)
(actually plants measure night length!)
Why are leaves green?
Chlorophyll & Carotenoid
Absorption Spectrum
(these are the colors of light that power photosynthesis)
Plants primarily use red and blue light for photosynthesis
Plants are “partially color blind” to green light.
Emission Spectrum of
Artificial Lights
Each light has a unique color spectrum
Which light is the best match
for photosynthesis?
Let’s “talk” to plants with
Temperature
Photosynthesis – Respiration
Interaction
From: http://ecosys.cfl.scf.rncan.gc.ca/dynamic/photosyn_e.htm
Photosynthesis – Respiration
Interaction
At optimum temperatures:
photosynthesis greatly exceeds respiration
“net food storage”
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As temperature increases:
 respiration increases (especially night time)
photosynthesis deceases (some enzymes inactivated)
At high temperatures:
respiration approaches or exceeds photosynthesis
“net food depletion”
and the plant starts starving
Cool Season Crops in the South
Optimum Temperature = 65 to 75 oF
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Grow great during fall, winter and spring
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Because their photosynthesis greatly exceeds
respiration
In the heat of late spring and early summer
Respiration approaches or exceeds their photosynthesis
The plants may begin starving to death.
Cool Season Plants in the South
Over-seeded ryegrass
Daffodil
Cool season plants die in summer because:
1) non-adapted species may not store sufficient food to come
back the next year (ex. tulip)
2) adapted species will store sufficient food in underground
storage organ and only the top dies (ex. ephemerals, daffodil)
3) set seed and “kill” themselves (winter annual, ex. rye)
Warm Season Crops in Texas
Optimum Temperature = 80 to 90 oF
 Grow great during early and late summer
 Because their photosynthesis exceeds respiration
Texas Summers
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Upper 90s oF most of July & August
In mid-summer, their photosynthesis & respiration are
more equal
Therefore, even some warm season plants don’t grow very
much in the heat of the summer in Texas
Many warm season plants only have a flush of spring
growth; and may not flush again in late summer/early fall
Many plants actually go into quiescence in mid-summer
in Texas
High Night Temperatures
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High night temperatures that are most critical.
High night respiration rates “burns-up”
photosynthates produced during the day.
Cool-season crops
starve to death
Warm-season crops
go into a summer quiescence
By the way, it is what also ruins our fall color!
Winter Dormancy or Rest
A strategy for temperate perennial plants
to survive winter.
Trigger?
short days & decreasing temperatures.
Cause?
> inhibitors (ABA) & < promoters (auxin, GA)
Overcome?
2-8 weeks constant cold storage @ 32 to 45 oF
200-1,200 cumulative hours outdoors @ 32 to 45 oF
How do you “tell” a plant to come
out of winter dormancy or rest?
Stratification
Required for most temperate plant seeds.
Match Chilling Requirement & Chilling Zone
Required for most spring flowering
temperature perennial fruit trees,
ornamental trees & shrubs
Match Chilling Requirement with
Chilling Zone
Peach
Cultivar
Chilling Hour
Requirement
Red Haven
Red Globe
Sentinel
June Gold
Rio Grande
EarliGrande
950
800
750
650
450
250
Let’s “talk” to plants about
Death
and
Decapitation
Plant Suicide
Plants often kill themselves or part of themselves.
On a routine basis! And, on purpose!
 Summer & winter annuals
 Leaf abscission (drop)
 Flower petals
 Fruit
Usually, the
signal is the
“death hormone”
ethylene
Horticulturist Murder Plants
Horticulturist often kill plants
by causing inadvertent
exposure to the
 Cut flowers and fruit
stored enclosed
“death hormone” ethylene  One rotten apple can
spoil the whole barrel or
the whole bouquet
 Not “emasculating”
flowers
 Improperly adjusted
heaters
Ethylene is Dr. Jekyll and Mr. Hyde
Ethylene is not
always the bad
guy “Mr. Hyde”
Ethylene can also
be the good guy
“Dr. Jekyll”
Ethylene as “Dr. Jekyll”
 stimulates bromeliads to
flower
 stimulates the formation
of pistillate (female)
flowers on monoecious
plants
 stimulates adventitious
roots on some plants
 can be used as a defoliant
for transplanting
Plant Decapitation
What happens when you
decapitate a stem?
 Auxin is produced by
the young leaves
around the shoot tip.
 Auxin is responsible
for apical dominance.
 Decapitation alters the
flow of auxin down the
stem.
What happens when you decapitate a stem?
Adventitious Root Formation
Auxin accumulates at the cut
which stimulates adventitious
root formation
Lateral Buds Break Dormancy
Apical dominance is removed
because the flow of auxin down
the stem is stopped.
How do you “tell” a plant to
look ugly?
Dehorning or Pollarding
You can be
convicted of
“crape murder”
for doing this!
Let’s “tell” a plant how to grow
into an attractive, pleasing and
functional shape.
Pruning to Direct Growth
thinning-out vs. heading-back
Let’s let the plant “tell us”
exactly where to make the
“surgical cuts”
Target Pruning
 A technique developed by Dr. Alex Shigo
 When a limb is cut, plants will seal-off the
inside of the xylem (e.g. wood).
 This is called “compartmentalization”
 Target pruning is a “surgical cut” along the
line of compartmentalization
 Anatomically, the “surgical cut” is made
along a straight line just outside the “bark
ridge” to the top of the “branch collar”
Target Pruning
From: www.clemson.edu/crapemyrtle/pruninginstructions.htm
From: www.rittenhouse.ca/hortmag/images/oak.jpg
If you cannot see the branch collar,
roughly it is from just outside the
bark ridge at a downward and
slightly outward angle.
Target Pruning
Target pruning according to Alex Shigo
Prune Weak Crotches
Selectively remove weak
crotches, i.e.
narrow crotch angles
with bark inclusions
Prune Weak Crotches
Selectively remove weak
crotches, i.e. narrow
crotch angles
This must be done when
the tree is young;
even if
it disfigures the tree!!!!
Remember, trees are
pruned for the
next generation!
Let’s “talk” to plants about their
Sexual Preference
Sexual Preference in Plants
Monoecious Plants
possess both staminate (male) and pistillate
(female) flowers on the same plant
cucurbits
begonia
corn
pecan
oak
papaya*
* Actually papaya are sexually confused, they can “go every which way”
“Why are all my cucumber flowers
falling off?”
No ovary, i.e. “baby
cucumber” at base
of flower.
These are staminate
(male) flowers.
“Well mame, it’s because those “useless” male flowers
that emerge early in the spring don’t make babies!!!!!”
Pistillate
(female)
cucumber
flowers
Ovary, i.e. “baby
cucumber”
“Don’t worry mame, your cucumber plants will start
making female flowers a bit later in the spring.”
“Let me tell you how you can “talk” your
cucumbers into making more female flowers.”
Sexual Preference in Plants
The sex of some monoecious plants can be
manipulated with hormones
Ethylene
Favors pistillate (female) flower formation
Gibberellic Acid
Favors staminate (male) flower formation
Finally
My wish for today is that
I said at least one thing that
“rocked your world”