Plant Science Final exam

Type of plant defenses

Physical barriers: Waxes, bark,cork

Chemical Defenses: 3 major groups

Pathogen-specific compounds: SAR and phytoalexins

1st tier

waxes

Cuticle of the epidermis

waxy layers in the root: endodermis

bark is heavily waxy to prevent bacteria and bugs from attacking the plant

2nd tier

chemical compounds

defense cpds

3 groups: N2 containing cpds, terpenoids, phenolics

N2 containing compounds

alkaloids, cyanogenic glycosides, glucosinolates expensive to make( in terms of ATP and N, remember N is hard for plants to get)

Alkaloids

>6000 known alkaloids

about 20% of flowering plants make these anti insect compounds

nicotine
caffeine
codeine
cocaine
capsaicin

Cyanogenic Glycosides

25 known
>2600 plant species know to produce cyainde gas

components kept separate until herbivore damage occurs

cassava

crabapples

cherries

apples

glucosinolates

cabbage family (broccoli,cabbage)

composed of 2 parts a and b

terpenoids

made of 5 paired carbon units called isoprenes

menthol

pyrethroids

gossypol

made from acetyl-coa or compunds found in respiration pathways

are the largest group of secondary metabolites

GA is a diterpene, carotenoids are tetraepenes, and ABA id sesquiterpene

are toxins and feeding deterrents

phenolics

made of long chain phenol groups

make plants bitter tasting

aspirin

tannin

lignin

3rd tier

specific responses

Hypersensitive response: dead tissue response

pathogenesis-related genes; activated when pathogen proteins bind to receptor protein and activate genes for systemic acquired resistance (pheromone stimulates salicylic acid production in other plants), phytoalexins ( antimicrobial compounds; cant be detected until infection occurs)

Plant stress physiology

stress reduces crop yields by up to 75%

major stressors: heat, cold, water, salt

heat stress

destablizes lipids of phospholipid bilayer, allowing permeability to increase dangerously enzymes shut down

heat shock protein (HSP) stabilizes these enzymes

how do plants get rid of potential heat load

for sun leaves heat load is very high

it has been calculated that a 0.3mm thick leaf would heat up to 100 degree C every minute if the light absorbed was not converted into sugars and heat

ways to get rid of heat from plants

re emission as red light

evaporative heat loss

by isoprene production (stabilize photosynthetic membranes under hotter conditions inside the leaf)

xanthophylls (yellow accessory pigments) can cycle by conversion from one to another, resulting in a dissipation of heat rotate their chlorplasts up and down to longer palisade cell

cold stress

Ice crystal formation causes damage; crystal formation inside the cell is less damaging than between cells

At cold temps, membranes solidify. Some plants produce anti-freeze compounds that keep membranes from solidifying

water stress effects

leaf expansion

turgor decreases

cell wall chemistry/ structure changes

leaf abscission

increased root expansion

stomatal closure due to ABA production ( thus carbon intake stops)

salt stress

salts can change water potential so that water moves out of plant to soil

halophytes pull salt ions out of incoming water before that can affect the plants biochemistry

weather

short term

snapshot of current conditions

climate

long term

decades/centuries of measured weather conditions

climate components

atmosphere: air flow, 78% nitrogen, 21% oxygen

Hydrogen: water flow/presence

Geosphere: Earth crust/volcanoes

Biosphere: influence of the biological processes

Cryosphere: influence of the ice/snow/glaciers

Sources of ancient climate data

tree rings can gice us O16/O18 ratios, C12/C13/C14 ratios

Ice cores from glaciers

coral reef cores

cave deposits

effects of a warming earth on crops and livestock

Nitrogen and carbon cycles are altered by increased CO2

Increased nitrogen efficiency use by crops by 19%

biological nitrogen fixation increase of 55%

lower nitrogen fertilizer requirements

higher CO2 levels save water in crop plants

Higher CO2 levels are predicted to: increase the efficiency of carbon uptake by crop plants, save water as plant gets carbon, doesn’t have to leave stomata open as long

Effects on pathogens

All pathogen groups are predicted to increase substantially, both in numbers and in range locations

increase in the number of pathogens and new ranges will offset any increase in crop yields