plant phys-quiz 2

What distinguishes macronutrients from micronutrients? Provide three examples of each.

macronutrients: elements required in high concentration in dry matter; Nitrogen(N), Potassium (K), Phosphorus (P), S, Si, Ca, Mg

micronutrients: elements required in low concentration in dry matter; Chlorine (Cl), Iron (Fe), Boron (B), Mn, Zn, Cn, Ni

What are the four biological/physiological groups that essential elements are found in? Give an example for each group.

• Group 1:

• Group 2:

• Group 3:

• Group 4:

• Group 1: most abundant, nutrients that are a part of carbon compounds and found in macromolecule subunits, key role for interaction with ATP (energy); N, P, S

• Group 2: cell wall structure/integrity; B, Si

• Group 3: important as ions; K, Ca, Mg, Cl, Zn, Na

• Group 4: redox reactions; Fe, Mn, Cu, Ni, Mo

After examining your plants, you discover that the younger leaves are chlorotic, but the older leaves appear to be healthy. Is the nutrient in question mobile or immobile? Explain how you know.

The nutrient is immobile, if it was mobile then the older leaves would be chlorotic. immobile nutrients do not spread (stays where it is first used), mobile nutrients do not (move from old to new growth).

Describe the principle of cation exchange and how it promotes nutrient uptake from the soil.

Soil is generally negative so cations will stick to the soil, cation exchange will occur to get less positively charged soil particles, that can then displace cations to be used. Negative charge of soil prevents cations from being washed away.

Protons from roots can also promote this

Briefly describe each of the following root zones:

1. Root cap:

2. Meristematic zone:

3. Quiescent Center:

4. Elongation Zone:

5. Maturation Zone:

1. Root cap: secretes mucigel to protect the apical meristem of the roots

2. Meristematic zone: rapid cell division except for in the quiscent center: all undifferentiated cells

3. Quiescent Center: slow cell division in center of root, within meristematic zone, likely due to limited nutrients

4. Elongation Zone: region of elongation and no new cell division

5. Maturation Zone: most of the cells differentiate

Nutrient uptake at apices:

highest demands, nutrient most concentrated in unexplored, creates conc. grad. for new nutrient diffusal

Explain the symbiotic nature of mycorrhizal interactions. How does each organism benefit?

Fungi get carbs/other organic molecules from the plant, while the plant gets more nutrients by virtue of increased surface area because of having more hyphae. Most plants in nature have a relationship with fungi.

Compare and contrast arbuscular and ectomycorrhizae. Describe how each interacts with the roots (ie, what does the symbiosis look like?).

arbuscular: mostly internal and more common; hyphae will grow out of spores then penetrate through the epidermis and spread through the cortex (do not penetrate the endodermis). important for phosphates;

have fast growth, efficient nutrient absorption and rapid translocation of nutrients

ectomycorrhizae: mostly external; fungi forms a mantel/sheath covering the outer surface of root and if it penetrates it will stay in the cell wall. Transfer of nutrients mostly happens at epidermis, thicker and more branched hyphae, and grows more slowly

What are the nitrogen sources for plants and how are they generated in the soil?

nitrate and ammonium, acquired through atmospheric fixation (lighting and photochemical rxns) to make nitrate and biological fixation (free-living, symbiotic) to make ammonium

reaction of Nitrate Reductase:

NO₃^- + NADH/NADP + H⁺→ NO₂^- + NAD⁺/NADP⁺ + H₂O

reaction of Nitrite Reductase:

NO₂^- + 6 Fd_red + 8 H⁺→ NH₄⁺ + 6 Fd_ox

reaction of Glutamine Synthase

NH₄⁺ + glutamate + ATP → glutamine + ADP + P_i

reaction of Glutamate Synthase (GOGAT)

glutamine + 2-oxogluterate + NADH/FD_red → 2 glutamate + NAD⁺/Fd_ox

reaction of Glutamate Dehydrogenase

NH₄⁺ + 2-oxoglutarate + NADH/NADPH → glutamate + NAD⁺/NADP⁺ + H₂O

reaction of Aspartate aminotransferase

glutamate + oxaloacetate → 2-oxogluterate + aspartate

reaction of Asparagine synthetase

glutamine + aspartate + ATP → glutamate + asparagine + AMP + PP_i

Describe the regulatory mechanisms for each of the following, and why they make sense in terms of resource management:

1. Nitrate reductase:

2. Nitrite reductase:

3. Asparagine synthase:

1. Nitrate reductase: regulated by light, nitrate and carbohydrates, high levels of all of these factors will cause NR to be actived by dephosphorylation; low light, nitrate and high magnesium inhibits NR, needs nitrogen containing compounds, needs to do nitrogen assimilation to provide necessary nutrients; high energy will invest in protein biosynthesis

2. Nitrite reductase: upregulated by light and nitrate, want to convert toxic nitrite into ammonium

3. Asparagine synthase: regulated by energy conditions, high energy promotes GOGAT and inhibits AS (will result in bigger carbon molecules) and low energy(low light) favors AS (results in assimilation of more ammonium per carbon); based on priority/needs of plant

Describe the process of nodule formation, including a discussion of the role of nodulin and nodulation genes.

plant sends out chemoattractant, get expression of nod genes once recepted. nod genes biosynthesize nod factors, they bind to receptors, initiating signaling cascade to induce gene expression (Ca2+ build up, Ca2+-CaM activates, CaMK activates TF to induce nodulin gene expression)
Nod factors induce root hair curling, enclosing the rhizobia allowing it to fuse to the plasma membrane. golgi secretes vesicles forming infection thread that rhizobia travel w/o going though vascular tissue. root cortex begins to differentiate to form module primordium. infection thread grow and fuse w/ primordia to make symbiosome (vescile wl rhizobia). bacteria take over symbiosome, rapidly divide until signaled to stop and then start nitrogen-fixing (now called bacteriod). nodule!!

Briefly describe how each of the following is assimilated in plants:
1. Sulfur-
2. Phosphorus-
3. Iron-

1. Sulfur-roots absorb sulfate from soil (weathering/breaking down of matter), transfer to leaves via xylem. assimilated into cysteine, used elsewhere and glutathione through phloem to rest of plant tissue.
2. Phosphorus-inorganic phosphate in the soil (H2PO4 or HPO3-) assimilated into ATP and transferred to other things; important for nucleotides and used as high energy
3. Iron-ferric (Fe3+/insoluble, cofactor for a lot of enzymes) and ferrous(Fe2+/lower charge so more soluble at neutral pH). 1) H+-ATPase acidify soil make ferric more soluble (released from soil/water-due to lower charge);iron chlorate reductase reduces Fe3+ to Fe2+ and oxidizes NADH 2) siderophores promotes release of Fe3+ from soil particle and uptaked into cell, assimilated in leaves by porphyrin rings (important as heme group, cytochrome C in photosynthesis)

Compare and contrast

Passive/simple diffusion:
Facilitated diffusion:
Active transport:

Passive/simple diffusion: molecules move down in chemical potential, no channel or carrier or energy needed
Facilitated diffusion: no energy, molecules move down chemical potential, needs a carrier or channel (transporter)
Active transport: molecules move up in chemical potential, needs energy and a transporter

What four factors determine or contribute to chemical potential?

sum of: concentration, electrical and hydrostatic/pressure potential, and the correction factor/chemical potential at neutral pH

If a membrane was selectively permeable, such that K+ could diffuse but Cl- could not, would a concentration gradient of KCl ever come to equilibrium? If so, how?

yes, K+ diffuses to form charge potential difference and will slow down until reach equilbrium (nernst potential-electrical voltage to stop specific ions from moving, pull of electrical gradient matches push of concentration gradient)

Do channel transporters have absolute specificity for their solute? What about carriers? Explain.

channel transporters specify based on pore size (certain ions are bigger vs smaller) and charge (inside charged amino acids, no like charges), regulated by gating (voltage or ligand)
carriers are more specific and slower, binding site specific, facilitated or active transport

Compare and contrast
Primary active transport:
Secondary active transport:

Primary active transport: energy comes from ATP hydrolysis, redox rxns, light
Secondary active transport: couple uphill transport (positive chemical potential) of one solute to downhill transport (negative chemical potential) of a second

symport vs antiport (primarily secondary, can be primary)

both solutes in same direction vs solutes in opposite direction

Why do carriers display kinetic profiles similar to enzymes?
Why do observed transport of molecules like sucrose show two different stages?

carriers have binding sites for solute and behave like enzymes where they need to undergo physical changes to complete the process (Vmax-rate at saturating conc (infinite conc.), want to be higher) or substrate , Km-binding affinity (solute conc. results in ½ Vmax, want to be lower)
dual affinity transport systems, high-affinity by carriers (low conc) and low-affinity by channels (high conc, H+-sucrose symport diffusion)

Describe the physiological mechanism for how blue light promotes stomatal opening?

guard cells will swell under blue light, causing stomata to open, and overal growth (cell explansion); blue light stimulates proton pumping through H+-ATPase, get hyperpolarization of membrane, activating a voltage gated K+-influx channel, get influx of K+ and chloride into vacuole, vacuole is hypertonic and water influx causes swelling
inhibited by orthoranadate(blocks ATP)

what way can transport occur w/o carrier or channel?

apoplastic and symplastic transport

how to make mutations, what we look at, and intensity of effects

expose plant tissue to mutation (physical-x-ray, gamma rays, fast neurons, ion beams; chemical-ethylmethane sulfonate (EMS), dimethylsulfate and sodium azide); insert gene or gene seq into RNA, use transposon, T-DNA tagging
freeze plant (liquid nitrogen) to prevent changes an RNAse inhibitors to prevent changes, grind and then mix with chemicals into liquid
can be silent, beneficial or harmful