What does a plant need to ‘eat?’ CO2 (PS) + H2O (PS + hydraulic structure + TS) and essential elements To synthesize all that it is: cellulose and wall polymers cytoplasm (including proteins) membranes (lipids, fatty acids) vitamins, co factors, ions and solutes regulators 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 concentrate nutrients before building their bodies Figure 38.1 An Early Experiment on the Role of Soil in Plant Nutrition.

Essential elements are required for a plant to complete its life cycle. They were discovered by hydroponic culture and experiments leaving proposed essential elements out 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 as K+, NO3-, and Mg+ and is transported from 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 such as Ca++ and other divalent cations, once incorporated into tissue, not easily extracted. Figure 38.3 Hydroponics Is Used to Study Nutrient Deficiencies.

C HOPKNS CaFe Mg a mnemonic for remembering the essential macronutrients Fe is an exception

Table 38.1a Essential Nutrients

Table 38.1b Essential Nutrients

Table 38.1c Essential Nutrients

cations are present in soil bound ionically to soil surface = “cation bank” pH of soil determines cation availability acid soils are cation-depleted liming + fertilizer restores nutrient content of soil anions do not bind and thus are easily lost from the soil solution during too much rain/flooding Cations often interact with negative charges on the surface of clay Organic matter Organic matter Clay particle Sand grain Root hair Clay particle Figure 38.7 Cations Tend to Bind to Soil Particles; Anions Stay in Solution. Clay particle Sand grain Anions usually dissolve in soil water; they are readily available for absorption by root hairs

Most nutrients are taken up by root hairs 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.

ATP H+ H+ ADP H+ H+ H+ H+ H+ H+ K+ H+ A- The Nernst equation helps us know whether ion/solute distribution is 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 difference in concentration of an ion between two compartments is balanced by the voltage difference between the two compartments. EN (Nernst potential) is the membrane potential that would allow passive distribution at a give concentration gradient EN predicts the concentration gradient that would allow the membrane potential to equal ENwith passive flux of that ion/solute ATP H+ H+ ADP H+ H+ H+ H+ H+ H+ K+ H+ A-

Most plants are associated with fungi; together fungal hyphae and roots make up 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 by symbiosis with Rhizobium

Trapped insect Many plants obtain nutrition from digesting animals, and some plants parasitize others Figure 38.18 Sundews Have Modified Leaves with Sticky Surfaces That Catch Insects.