plant phys exam 5

grazing

(cattle, bison) less discriminate eating of grass and bulk tissue because their

ruminant digestive system efficiently extracts nutrients. Refers to eating ground

Large native grazers can benefit plant communities by increasing plant diversity in two ways

1) Grazing dominant species thus reducing their competitive exclusion of subdominant species

2) creating habitat or niche space heterogeneity in which many species can coexist

Novel herbivory regimes

driven by introduction of exotic

 grazers or unprecedented increases in population size

 can lead to chronic herbivory that degrades plant communities

browsing

(deer) nipping meristems and leaves to feed on most nutritious

tissues because their digestive system is less efficient at extracting nutrients. Refers to eating leaves

more targeted

granivory

(rodents): seed predation

Insect herbivory strategies

• stem borers: (bark beetles) wound entry for pathogens, high mortality rates

• leaf chewers: (caterpillars, beetles) severe damage/defoliation

• phloem feeders: aphids cause little damage but can introduce viruses

impact of herbivory varies on 3 factors

How much and what part of the plant is being consumed?

Roots: resource uptake affected

Leaves: photosynthetic ability reduced

Flowers: reproduction reduced

Twigs: competitive ability lost

Meristems: altered growth form

What is the life stage of the plant?

Seeds: embryo death

Seedlings: high vulnerability to death

Mature plant: less sensitive

How frequently does it happen?

Chronic herbivory is a situation where a plant is repeatedly being consumed which can result in impaired function or death

three general strategies plants use to deal with herbivory

Resistance

Tolerance

Avoidance

resistance

prevent being eaten using physical or chemical protection

       Why are plants sharp? Physical protection from herbivores 

       Why are plants toxic, or not nutritious? Chemical protection, make tissues toxic bitter or of poor nutrient quality

Tolerance

Resource storage in woody tissue as an investment in regrowth after herbivory (cherry tree)

Avoidance

grow in such a way that herbivores cant access tissues. For example,

Vertical escape

examples of plant physical defenses

spines

woody tissue

cuticle

plant secondary metabolism

Diverse array of organic compounds that generally don’t have any direct function in growth and development but increase survival and reproductive success

three general functions of secondary
metabolites

  1) Deterrence (toxicity, palatability, decrease nutritive value) of herbivores/pathogens 

  2) attractants (smell, color, taste) for pollinators, seed-dispersing animals

  3) allelopathy: impair the germination/growth of plant competitors

three major groups of secondary
compounds

Terpenes

Phenolics

Alkaloids

Terpenes

composed of 5 C monomers

-GA and ABA are plant hormones

-Carotenoids are critical accessory pigments in photosynthesis

Herbivore defense

Pyrethroids (insecticide)

Cardenolides: toxic to mammals

Phenolics

contain a phenol group (aromatic ring)

1) Structure and protection, gives rigidity to wood – Lignin

2) Defense compounds- phenolic glycosides, tannins

3) Allelopathy- catechin

4) attraction: petal and fruit pigments- flavonoids

Alkaloids

nitrogen containing secondary compounds

Alkaloids in high enough concentrations are toxic to many animals often by interfering with

  nervous system function

Several have medicinal properties, others alter brain function and in high enough concentrations they are deadly

patterns of defense chemistry
expression

Constitutive

Inducible

Targeted

Constitutive defense

defenses are always expressed because risk is high

 best suited to prevent herbivory that is moving rapidly

Inducible defense

activated in response to herbivory but takes time

Targeted defense

tailor defense to specific enemy based on saliva chemistry

how plants sense herbivory

Defense induction can be activated by wounding or elicitors in herbivore saliva

Volicitin

Volicitin

signaling molecule that induces defense response

three general strategies for plant defense signaling against insects

1. Systemic defense signaling: single plant

2. Plant population defense signaling: individuals within a population

3. Community defense signaling

Systemic defense signaling

  Herbivory perceived in wound sites and signals

   sent out within the plant to elicit a defense response

Jasmonic acid travels from damaged leaf

   through phloem activating defense genes

   in undamaged leaves

Plant population defense signaling

volatile signals (jasmonate) are transported through the air between plants to warn of herbivory

Community defense signaling

volatile signals are sent into the air in response to herbivory that attract the herbivores predator

sexual reproduction in plants and their benefits and
tradeoffs in different environments

diploid cells of parent plants undergo meiosis leading to gamete production (genetic combination of the parents)

-metabolically expensive

-generates genetic diversisty that can increase population fitness in variable environments

flower paradox

flowers are so expensive……why is it so common?

asexual reproduction in plants and their benefits and tradeoffs in different environments

genetically identifical offspring through mitosis:

1. suckering

2. rhizomes

3. stolons

4. fragmentation

-rapid regeneration allows fast growth that creates a competitive advantage

-environment stable

floral anatomy

processes of pollination

pollen grains are carried on wind or by pollinators

if they land on stigma they germination and grow a pollen tube down through the style to the ovary

double fertilization

one sperm fertilizes the egg which will become the embryo

the other sperm fertilizes two polar nuclei cells (3n) which divides miotically to form endosperm (embryo food)

self-pollination

risk: low genetic diversity of offspring

reward: high probability of success

cross pollination

risk: depedent on pollinators or wind and it is metabolically expensive (to produce showy smelly flowers for pollinators or produces LOTS of seeds for pollen for wind pollination)

reward: genetic diversity

traits plants have developed to increase cross-pollination

1. self-incompatibility: stigma recognizes self-pollen and inhibits pollen tube growth

2. dioecious flowering strategy: unisexual flower produced on different plants so self pollination isn’t possible

3. male and female flowers are developmentally staggered on the same plant so pollen is released at a different time than the female flower is ready to be pollinated and fertilized

wind-pollinated plants anatomy and environment

abundant pollen

small and lack color, scent and nectar

more abundant in open habitats where wind can effectively disperse

animal pollinated plants anatomy and environment

product of co-evolution with their pollinators

diversification of flower characteristisics that plays to the pollinators senses and passions

nectar: energy

pollen: protein

plant strategies developed to optimize pollinators visits relative to nectar removed

nectar and pollen rewards

amount of nectar offered

time of day

smells and scents

flowers with female pollinator phermones to attract males.

risks/benefits of specialist

one or just a few pollinator species

efficiency high, but vulnerability if that species goes extinct

risks/benefits of generalist

simple flowers that can be visited and pollinated by dozens of very different pollinators

pollen gets transferred, but not very efficiently

pollination deception

mimicry: an organisms evolves shared characteristic with other organism

visual: flower appears like nectar providing flower but has no nectar

chemical: flower produce female pollinator pheremones to attract males

visual sexual: flower anatomically looks similar to a female been which attracts males wasps, transferring pollen

seed and fruit development from the female flower parts

1. pollination transfers a sperm cell from stamen to an egg cell inside an ovule contained in the ovary at the base of a female flower

2. flower ovaries may contain only one ovule that develops a single seed per furit or hundreds of ovules

3. if a sperm cell successfully fertilizes an egg cell an embyro will develop and the ovule will well into a seed as it fills with endosperm to feed the seedling when the seed germinates

4. fruit develops from the swelling of the ovary wall

types of seeds

structure of seeds

seed coat: protects embryo and controls germination timing

endosperm: embryo food in the form of starch and oils

function of seeds

seeds nourish and protect developing embryo (baby plant)

types of fruit

-fleshy fruits: ovary wall becomes soft during ripening

-dry fruits: ovary wall is dry at maturity. dehiscent (split open at maturity to shed seeds) and indehiscent (remain closed at maturity)

structure of fruit

function of fruit

1. protect the embryo from drying out

2. serves as fertilizer for germinating seeds as it decomposes

3. seed dispersal: animal involvement: eating or attachment

patterns of wind dispersal

wind: fruits are optimized for dispersal distance (lower mass and greater surface area)

floating: disperses far, annual

fluterring: closer to parent trees, woody

seed masting and its benefit to plants

production of many seeds by a plant episodically in regional synchrony across its population

seed production timing is reponsive to resource availability (climate) and is synchronized with pollen production and pollinator and disperser populations

-masting increases animal caching behavior and reduces seed predation (granivory avoidance)

patterns of animal dispersal

-larder hoarding: seed caching of larger number in a single space

-scatter hoarding: caching individual or few seeds in different places

seed banks

viable embryos in seeds in the soil

can also be in serotinous fruit or cones that are shut by resins (anti-herbivory) and only open in response to fire

soil pathogen and seed predators kill seeds, reducinf seed bank size

seed banks vary in germination timing increase plant population success

hydrothermal accumulation time: seeds in a hydrated state progress towards germination with increasing temp

strategy used by
annual plants to disperse seeds and develop seed banks that increase their
success.

annuals: long lived seeds (annuals need a back up)

strategy used by perrenial plants to disperse seeds and develop seed banks that increase their success.

perennials: short-lived seeds

species in the seed bank are often different than the plant community above them

nitrogen cycle as an example of nutrient cycling between plants and microbes and plant uptake of nitrogen.

driven by bacteria and fungi through decomposition (ammonification), nitrification and root symbiosiis

sources of bioavailable nitrogen in the environment.

nitrogen-fixing soil bacteria: ammonification makes ammonium

nitrification from nitrifying bacteria: ammonium to nitrites to nitrates

reactions of biological nitrogen fixation by nitrogenase

nitrogenase converts N2 into NH3 to nitrate (redox reactions)

N2 + 8e + 8H + 16 ATP —> 2NH3

N fixation requires anaerobic condtions: leghemoglobin binds oxygen to keep its concentration low

process that forms nodules in legume roots

plants exude isoflavanoids and betanes from their roots which signal migration of compatible bacteria toward roots to activate NodD gene in the bacteria

bacteria signaling molecules that activate hormonal development of the nodule on the roots of the legume host

1. infection thread forms from golgi vesicles in response to Nod factors

2. infection phase: cell wall degrades, bacteria enter the cell

3. transport phase: infection thread moves inward transporting bacteria

4. nodule fomration: nodule forms with vascular connections to xylem and phloem

mycorrhizal root symbiosis

ectomycorrhiza

the root is covered in a fungal sheath calle dthe mantle and resource exchanged occurs in the Hartig net

endomycorrhiza: arbuscle

sequence of transformations for the Nitrogen cycle

N2--> NH4--> NO3-->plant uptake