What does a plant need to ‘eat?’

CO2 (PS) + H2O (PS + hydraulic structure + TS)andessential elements

To synthesize all that it is:

cellulose and wall polymerscytoplasm (including proteins)membranes (lipids, fatty acids)vitamins, co factors, ions and solutesregulators

The source of all plants’ food is from soil solution and atmosphere, where required compounds are present in VERY dilute quantities ---

plants have to scavenge, and concentratenutrients before building their bodies

Essential elements are required fora plant to complete its life cycle.

They were discovered by hydroponic culture and experimentsleaving proposed essential elementsout of the nutrient solution

Deficiency symptoms can be categorized by showing up:

1) in lower (older) tissues first, if so, the element is a mobile ion such asK+, NO3-, and Mg+ and is transportedfrom older to younger tissue when the soil does not provide enough for plant growth;

2) in upper (younger) tissues first,if so, the element is an immobile ion suchas Ca++ and other divalent cations, onceincorporated into tissue, not easily extracted.

C HOPKNS CaFe Mg

a mnemonic for remembering the essential macronutrients

Fe is an exception

Clay particle

Sand grain

Organic matterOrganicmatter

Root hair

Clay particle

Clay particle

Sand grain

Anions usually dissolve in soil water;they are readily available forabsorption by root hairs

Cations often interact with negativecharges on the surface of claycations are present

in soil bound ionically to soilsurface = “cation bank”

pH of soil determinescation availability

acid soils arecation-depleted

liming + fertilizerrestores nutrientcontent of soil

anions do not bind and thus areeasily lost from the soil solution during too muchrain/flooding

Most nutrients are taken up by root hairs. Ions are dissolved in solution – the solution travels apoplastically through the cell walls to the endodermis (Casparian Strip) where it has to enter the symplast.

H+H+

H+

H+H+

H+

H+

H+H+

ATP

ADP

K+A-

The Nernst equation helps us know whether ion/solute distributionis passive or active:

(Nernst potential) EN = 2.3 RT X log Co [2.3RT ~ 59]z F Ci

The Nernst equation states that at equilibrium, the differencein concentration of an ion between two compartmentsis balanced by the voltage differencebetween the two compartments.

EN (Nernst potential) is themembrane potential that would allow passive distribution at a give concentration gradient

EN predicts the concentration gradientthat would allow the membrane potentialto equal ENwith passive flux of that ion/solute

Most plants are associated with fungi;together fungal hyphae and roots makeup mycorrhizae. These structures:

• increase the surface area of the nutrient gathering membranes;

• assist in digesting organic materials in the soil for uptake into the plant;

• increase water uptake• possibly ‘fertilize’ soil with CH2O from

their host plant

Uptake of N is a special case, and in the case of legumes, is accomplished bysymbiosis with Rhizobium

Trappedinsect

Many plants obtain nutrition from digesting animals, and some plants parasitize others