Lecture 2: Plants II (nutrition, transport, and alternative photsynthesis)

Autotrophs

nearly all plants → derive the carbon they need from the air via fixation of atmospheric CO₂, they derive low energy electrons they need from water, releasing O₂, they derive oxygen they need for electron transport from atmospheric O₂

Micronutrients

trace minerals that act as cofactors in respiration and photosynthesis (iron and copper)

Hydroponic growth

allows us to identify the nutrients that plants need, remove thing from the defined medium and see what presents a problem without it

Essential

when the absence of an element severely hinders growth or reproduction

Ion exchange

makes soil nutrients available to plants → most articles in a soil carry a net negative charge → this causes these particles to bind cations dissolved in the soil → these cations must be released in order for plants to make use of them

Ion exchange process

active transport of protons out of root (increases proton content in soil), release of CO₂ which reacts with water to form carbonic acid, H⁺ displaces cations bound to soil particles

Anionic nutrients

more mobile in the soil solution and can be absorbed directly

Secondary active transport

energy source for transportation is the electrochemical gradient

rhizobia

bacterial mutualists, nitrogen fixing bacteria that have formed a mutualism with legumes, colonize the roots of plants

symbiosome

specialized compartment in a host cell that houses an endosymbiont in a symbiotic relationship (rhizobia encased in plant derived symbiosomes)

Ways to replenish nitrogen in a soil

shifting agriculture, organic fertilizers, and inorganic fertilizers

shifting agriculture

do not farm on the depleted soil, move elsewhere, weathering of the parent rock will naturally replenish nutrients over time

Organic fertilizers

add organic materials like compost or manure

Inorganic fertilizers

ammonium containing substances chemically manufactured added to soils, allows for more efficient use of land at the cost of being more energy intensive

hemiparasite (mistletoe)

partially parasitic, performs some photosynthesis on its own, but obtains water and other nutrients from its host

holoparasite

type of total parasitic plant that cannot produce its own food and relies entirely on its host for nutrition

mycorrhizae

fungal mutualists that recognize and recruit strigolactones into the roots

arbuscules

where nutrient exchange occurs, formed by the penetration of fungal cells of the outer layer of cells in the root

water potential

determines the movement of water, two components

solute potential

more solutes mean lower concentration of water which means greater tendency to take up more water

pressure potential

when closed compartments fill with water, they swell and resist the addition of more water.

turgor pressure

when a cell has positive pressure potential, helps plants stand upright

aquaporins

proteins through which water moves into the roots

transpiration-cohesion-tension mechanism

process that moves water upward in pants → as water evaporates from the leaves, it creates tension that pulls a continuous column of water upward through the xylem. Because water molecules stick together, the entire column is pulled from the roots to the leaves

transpiration

process by which water is lost in leaves through stomata → diffusion of water out of the leaf into the atmosphere

phloem

conducts sugar throughout a plant, requires living cells in order to function, source of food for many insects including aphids

pressure flow model

sucrose is actively transported from sources into the phloem → higher sucrose causes water to enter those areas → this pushed liquid down due to turgor pressure → sucrose is unloaded actively in sinks, water exits via diffusion

stomata

pores in leaves through which transpiration occurs, open or close based on water availability, allow CO₂ to enter the leaf

CAM pathway

minimizes water loss, photosynthesizes during the day but only have stomata open at night. accomplished via PEP carboxylase → stores CO₂ as a 4-carbon organic acid at night. during the day, the stomata are closed but the organic acids are broken down to yield CO₂. the products of the light reactions drive the Calvin cycle during the day without having the stomata open; temporal separation of steps to avoid water loss

photorespiration

a wasteful biochemical reaction catalyzed by rubisco due to its dual affinity for CO₂ and O₂

C3 photosynthesis

normal photosynthesis → RuBP is combined with CO₂ to yield a short lived six carbon compound that breaks down into two three carbon compounds

Closed stomata

the relative concentration of CO₂ goes down relative to O₂ in the cells

High temperatures

gases become less soluble in water → CO₂ solubility decreases more rapidly than O₂ solubility as temperatures rise → CO₂ to O₂ ratio gets smaller

C4 photosynthesis

favored in hot climates, uses PEP carboxylase → 4C molecule transferred to the bundle sheath where it is broken down into CO₂ and where rubisco is sequestered → concentrates CO₂ in the bundle sheath well above normal levels; spatial separation of steps to avoid photorespiration

PEP carboxylase

much greater specificity for CO₂, yields a 4-carbon molecule