Plant Physiology Exam 2

What is a plant hormone?

Organic compounds that are messengers

In what general ways are plant and animal hormones similar and different?

• Act in very small amounts

• Produce physiological actions away from site of synthesis

What are the five “classical” plant hormones?

Gibberellin, cytokinin, auxin, ethylene, abscisic acid

What are the four “newcomers” (relatively recently discovered) plant hormones?

Brassinosteroids, salicylic acid, strigolactones, jasmonates

What are the main functions of these hormones?

• Auxin: Lateral organ initiation, maintaining meristematic cells in root, mediated by changes in gene expression, genes control cell growth, signaling, response pathways

• Cytokinin: Cell division, control of leaf senescence, controls nutrient allocations, root nodule development (like nitrogen fixation nodules), maintenance of meristematic cells, regulate auxin action

• Abscisic acid: Response to abiotic stress, seed maturation

• Ethylene: Flowering, sex determination, induction of fruit ripening, leaf and petal senescence, cell division and elongation, root growth, stress responses

• GA: Seed germination (such as barley for beer)

How does auxin regulate phototropism?

Auxins are biosynthesized on the shade side and produce elongation of the cells on the shaded side.

What are the commercial applications of controlling ethylene synthesis and response?

Control ripening and flowering timing (like for pineapples)

What are the main hormones responsible for the stress response?

Biotic stress: Jasmonic, salicylic acid

Abiotic stress: Abscisic acid (ethylene to an extent)

What are the main hormones responsible for reproductive control?

GA, ethylene, abscisic acid

What are the main hormones responsible for vegetative growth?

Auxin, cytokinin, strigolactones, GA, brassinosteroids

Name different types of plastids, in which plastid does photosynthesis take place?

• Chloroplast (most important, light harvesting)

• Aminoplast

• Leucoplast

What type of components do plastids store?

Chloroplasts store starches

Aminoplasts store chromoplasts, plastids, and pigments

What are the primary pigments of the chloroplasts?

Chloropyll

What are the functions of chlorophylls and carotenoids?

• Chlorophyll: Captures light and gets excited

• Carotenoids: Photoprotection, maximizing light throughout the spectra

What is the driving force of electron flow in photosynthesis?

PSII and PSI

What is the linear electron flow (Z scheme)? What are the donor and the receiver of electrons?

• Involves PSII and PSI

• Donor is water, receiver is NADPH

Name the main photosystems and electron carriers, and what are their main functions?

• PSII: Breaks down water to produce oxygen

• PSI: NADP ot NADPH

• ATP

• Cytochrome: Receives electrons from the photosystems, in charge of pumping more protons into thylakoid membrane

• Plastoquinone: Carries electrons in the electron transport chain

• Plastocyanine: Cytochrome → PSI

Where are they located? [Photosystems and electron carriers]

PSII and PSI (Thylakoid membrane)

What is the oxygen-evolving complex, and where is it located?

• Contains manganese

• Splits water (water oxidation)

• Located in PSII

How do the chloroplasts generate ATP?

• PSII breaks down oxygen into protons and oxygen 

  • ATPase (like a lollipop) 

  • Z style (PSII excitement, calm down, and PSI excitement )  

  • Cytochrome is pumping protons into thylakoid lumen 

  • Protons go through at synthase 

  • As protons leave, ATP is produced 

• Cyclic style: PSI and cytochrome no ATP production

What are the two main products of the electron flow?

ATP and NADPH

What is the cyclic electron flow? What is/are the main products?

Cyclic electron flow means that the electrons go back into the cytochrome instead of ending in the NADPH when there isn’t any NADP to receive the electrons. Product is ATP

What is the water-to-water electron flow? And when does it happen?

Occurs when there isn’t enough NADPH and the option is to use oxygen to receive electrons producing water. Happens when the stomatas have closed and there is no carbon fixation.

Where do the light-dependent reactions take place?

Thylakoid membrane

Where does the carbon fixation reaction occur?

Stroma

What is the ribulose carboxylase/oxygenase enzyme (Rubisco), and what is its primary function?

An enzyme involved in the Calvin cycle

Bind to carbon → fixes CO2

What is the Calvin cycle? What are the main parts of the cycle?

Carbon fixation with Rubsico → Reduction → Regeneration of RuBP

What is photorespiration?

Rubisco binds to oxygen and creates a toxic oxygen reactive (phosophoglycolate) that needs to be recycled, which uses up energy and loses carbon dioxide. It’s a waste of plant resources.

Why is photorespiration energy costly for the plant? What are the disadvantages?

Plant needs to spend energy to neutralize products of photorespiration. In the case of C3 plants, they use 30% more energy to convert products of photorespiration.

What are C3, C4, and CAM carbon fixation mechanisms? In C4 and CAM plants, how do cells share the loads of fixing and assimilating CO2?

Carbon dioxide is more concentrated in cells of C4 plants, but there is no photorespiration (so it’s more efficient!)

What plants are more efficient at fixing carbon dioxide? C3 or C4? Explain why.

C4 cycle occurs during the night so there is less chance of water loss in regions that are hotter. Advantage over C3 plants because of an enzyme to fix carbon dioxide into a 4-carbon molecule.

What is the ecological significance of the CAM plants?

• Can be studies to potentially make commercial C4 plants survive/create more yield in changing climate, warmer with high CO2 levels and higher drought occurrence

• Manage water more efficiently

• Acid metabolism

What is the primary form of carbon transport through the phloem?

Sugar

Where are starch and sucrose synthesized and stored?

• Starch is synthesized in the chloroplasts

• Sucrose is synthesized in the cytoplasm

What is a source and a sink?

• Source: Where sugars are produced within a plants (leaves, photosynthesizing cell)

  • Sometimes root (create carbs and the plant uses this energy to create leaves, who then become the source) (mostly winter/early spring, before photosynthesizing leaves come in)

• Sink: Fruit, roots, shoot (stem)

Name three chemical components transported by the phloem.

Sugars, hormones, minerals

Explain the accepted model of phloem transport, the pressure flow hypothesis, and how it is related to the xylem and the overall solute transport throughout the plant.

• ATPase moves protons out of cell. This accumulation of protons is used by the co-transporters (when potassium enter through proton gradient)

• Casparian strip → those minerals are forced to cross the plasma membrane (through those transporters, indirectly by the energy used by ATP proton pumps)

  • Pumps take protons out, leaving a strong gradient for minerals to enter

• Pressure flow hypothesis: water moves through phloem due to sugar, high and low pressure placements in phloem

What is the primary electrogenic plant plasma membrane pump?

Pumps protons (H+) out of cytosol (Mineral or sugar, electron gradient helps move different minerals)

Are protons usually more abundant in the cytoplasm or the apoplast?

Apoplast

Pumps need energy (ATP) to pump elements from soil

Explain how the electrochemical gradient of pumps determines the movement of ions across membranes.

• Ions will go from an area of high concentration to an area of low concentration. If energy is used to pump protons into an already high area, this will create an electromotive force that will move other elements

• There is a gradient of protons, when protons go back to cytosol, it is used to transport other elements

Potassium is an unusual essential element in that it does not form covalent bonds within plants. Describe three critical functions of potassium (K).

• K+ will replace protons removed by ATP pump

• Potassium inside cell contributes to osmotic potential (accumulation of potassium = water will follow)

What are macronutrients?

Nutrients needed in high quantities

What are the three most important macronutrients for plant growth?

NPK

Name the functions of each macronutrient.

• Nitrogen: Nutrient and water uptake, makes up proteins & nucleic acids

  • Needs to be reduced by the plant. Soil source of nitrogen is nitrate, the microorganisms turn naturally found nitrogen sources into nitrates. Enzyme implants will produce ammonium ions, which can be incorporated into plant molecules (ex. Amino acids)

• Phosphorus: Energy and selective membrane

• Potassium: Maintains turgor and reduces wilting, contributes to cell expansion and movement

• Bonus! Magnesium: Cofactor for many enzymes and central to chlorophyll

• Sulfur: Enzyme and protein formation, chlorophyll production, synthesis of amino acids, energy transfer, ATP synthesis

• Calcium: Structure of cell walls, strength

What are micronutrients?

Nutrients needed in small quantities

What are mobile and immobile nutrients?

Mobile nutrients: Can be transported through xylem and phloem (ex. nitrogen)

Immobile nutrients: Cannot move through plants, deficiencies observed in new growth (ex. calcium)

How is the plants' lack of a mobile and immobile element visualized during scarcity? How is it related to phloem transport?

Mobile nutrients are displayed through deficiencies in older leaves and immobile nutrients are displayed through deterioration of younger leaves during scarcity. If nutrients can be loaded/transported through phloem then it’s mobile.

Name two non-essential elements

Cadmium and arsenic