Plant Hormones

General Botany EXAM 5

Where are auxins synthesized in plants?

In the shoot apical meristem (SAM) and root apical meristem (RAM)

How is auxin transported within cells?

Enters the cell by passive diffusion in its protonated form (IAA+) and as an anion (IAA-) via AUX1 carriers.

How is efflux facilitated?

PIN and ABCB proteins

Name a synthetic auxin and its agricultural use

2,3-D is a synthetic auxin used as a weed control agent in dicots

What is the role of auxins in apical dominance?

Basipetal auxin distribution inhibits axillary bud growth, maintaining apical dominance. Removal of the apex induces lateral growth.

What are cytokinins, and where are they found?

They are growth regulators similar to adenine, found in actively dividing tissues, bleeding sap, wounds, and cracks.

How do cytokinins affect plant tissue culture?

They stimulate cell division and induce shoot bud formation in tissue culture

What is the antagonistic relationship between cytokinins and auxins?

High auxin-t-cytokinin ratio induces root formation, while high cytokinin-t-auxin ration induces shoot formation.

What is ethylene’s role in plants?

Ethylene promotes fruit ripening, senescence, abscission, and rapid stem growth in some plants

How does ethylene affect sex expression in plants like squash?

It promotes femaleness, while gibberellins promote maleness in some monoecious plants.

What is the function of abscisic acid (ABA) during water stress?

It promotes stomatal closure to conserve water

How does gibberellin break seed dormancy?

It triggers the production of enzymes like amylases, which breaks down starch into sugars for cellular respiration and embryo growth

What role do brassinosteroids play in plants?

They promote cell division, elongation, vascular differentiation, flower and fruit development, and stress resistance

How does auxin affect vascular tissue in developing leaves?

It influences the differentiation of vascular tissue and promotes regeneration of injured vascular traces.

What is the role of auxin in lateral root formation?

Basipetal auxin transportation from the parental root to lateral roots promotes their formation

What is the effect of high auxin concentration on growing roots?

High auxin concentrations inhibit the growth of already growing roots

How does auxin promote the formation of parthenocarpic fruits?

When applied to carpels, auxin can stimulate the production of seedless fruits

Where are cytokinins synthesized, and how are they transported?

They are synthesized in root tips and transported to sinks via the xylem

How do cytokinins delay senescence?

They prevent chlorophyll degradation, thereby delaying leaf aging.

What is the effect of cytokinins on lateral bud growth?

They induce lateral bud growth even in the presence of auxin

What is the role of ethylene in flooded plants?

It promotes air space formation by generating cortical parenchyma, aiding in gas exchange

What is the commercial importance of ethylene in fruit production?

It promotes fruit loosening in cherries, blackberries, peaches, and prunes

How does ethylene interact with auxin in leaf abscission?

It promotes leaf abscission by dissolving cell walls, while auxin reduces sensitivity to ethylene in the abscission zone

How does ABA affect seed dormancy?

ABA promotes dormancy by preventing premature germination. Declining ABA levels break dormancy

What happens in viviparous mutants lacking ABA?

Seeds germinate prematurely because the embryo cannot undergo dormancy

How is ABA transported in plants?

ABA travels via xylem or phloem to target tissues

How do gibberellins promote germination in barley seeds?

Gibberellins stimulate amylase production in the aleurone layer, breaking down starch into sugars for embryo growth.

What is the role of gibberellins in the Green Revolution?

Dwarfing genes linked to gibberellin response reduced vegetative growth, making crops resistant to wind and rain damage

How are gibberellins used commercially?

Gibberellins are used to break dormancy, enlarge fruits, and loosen fruits in clusters like grapes

What is the dual transport nature of brassinosteroids?

Brassinosteroids can act locally or be transported via the xylem when applied exogenously.

How do brassinosteroids affect stress resistance in plants?

They enhance stress tolerance and delay senescence under unfavorable conditions.