Transcript Ch 38- Plant Nutrition

Ch 38- Plant Nutrition
By:Team GS
Nitrogen Fixation
•A process performed by certain bacteria found in the
nodules of leguminous plants, which make the resulting
nitrogenous compounds available to their host plants.
•Important because plants need ammonia to build
amino acids, but most of the nitrogen in the atmosphere
is in the form of Nitrogen gas
•Most plants lack the biochemical pathways (which
includes the enzyme nitrogenase) necessary to convert
nitrogen gas to ammonia
•Bacteria have the capacity to convert nitrogen
gas to ammonia live close to plant roots. Others
are located in plant tissues called nodules
•Hosting these bacteria costs the plant to lose
energy
•To conserve energy, legume root hairs will not
respond to bacterial signals when nitrogen levels
are high
A root hair of Alfalfa is invaded by Rhizobium
•Extensive signaling between bacteria and the legume lets
each organism know the other is present and checks
whether the bacteria is the correct species for the specific
legume
•These highly evolved symbiotic relationships depend on
exact species matches
•Different legumes have their own specific symbiotic
Rhizobium
Carnivorous Plants
• Carnivorous plants have the ability to obtain nitrogen
directly from other animals
• They often grow in acidic soils that lack organic nitrogen
(bogs)
• By capturing and digesting small animals directly, these
plants obtain adequate nitrogen supplies
• Carnivorous plants have modified leaves to lure and trap
insects and other small animals
• The plants digest their prey with enzymes secreted from
various types of glands
• Pitcher plants attract insect by the
bright colors within their leaves
and their sugar-rich secretions
• Once inside,insects slide into the
cavity of the leaf, which is filled
with water and digestive enzymes
• Asian pitcher plant, Nepenthes
• Complex communities of
invertebrates and protists inhabit
the pitchers
Pitcher Plant
Venus Flytrap
• The Venus flytrap has three sensitive
hairs called trichomes on each side of
each leaf that, when touched, trigger
the two halves of the leaf snap together.
The enzymes secreted from the leaf
surfaces digest the prey
• These use a growth mechanism to close
and open
• As a result, they can only open and
close a limited amount of times
Ancestry
• The Venus flytrap and the Sundew share a common
ancestor that lacked the snap-trap mechanism
characteristics of flytraps
• Glandular trichomes secrete both sticky mucilage (traps
small animals) and digestive enzymes. They close slowly.
• Molecular phylogenic studies indicate that Venus flytraps
are sister species to of the Sundews, forming a sister clade
• The snap-trap mechanism evolved only once in decedents
of the Sundew ancestor
Aquatic waterwheel
• An even closer ancestor to the flytrap is the
Aldrovanda vesicular, the Aquatic waterwheel
• The waterwheel is a rootless plant that uses trigger
hairs and a snap trap mechanism like the flytrap to
capture and digest small aquatic animals
• The waterwheels ancestor must have been a terrestrial
plant that made its way back into the water
Mycorrhizae
• While symbiotic relationships with nitrogen-fixing bacteria
are rare, symbiotic associations with mycorrhizal fungi are
found in about 90% of vascular plants
• The fungi in mycorrhizae associations function as
extensions of the root system
• This dramatically increases the amount of soil contact and
total surface area for absorption
• When mycorrhizae are present, they aid in the direct
transfer of phosphorous, copper, zinc and other nutrients
from the soil into the roots
• The plant supplies organic carbon to the fungus. The
system is an example of mutualism
Parasitic Plants
• Parasitic plants come in photosynthetic and
nonphotosynthetic varieties
• At least 3000 types of plants are known to tap into
the nutrient resources of other plants
• Adaptations include structures that tap into the
vascular tissue of the host plant so that nutrients
can be siphoned into the parasite
• The Dodder is a parasitic plant which looks like
brown twine wrapped around its host
• The Dodder lacks chlorophyll and completely relies
on its host for all its nutritional needs.
• The Indian pipe, Hypopitys uniflora also lacks
chlorophyll and hooks into host trees through the
fungal hypae of the hosts mycorrhizae
•This is called a saprophyte because it
lacks chlorophyll and depends
completely on decaying organic
matter for all its nutrients. Indian
pipes are found in forests of the
northeastern United States
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