plant hormones week 3

What is another term used interchangeably with plant hormone?

Phytohormone.

Why must plants be highly adaptable to their external environment?

Because they cannot move.

What are three examples of seasonal processes regulated by plant hormones?

Dormancy, germination, and flowering.

What are three examples of environmental factors plants respond to via hormones?

Light, temperature, and wind.

At what typical concentrations are plant hormones effective?

Low concentrations, from micromolar to nanomolar.

Where are plant hormones typically synthesized?

In small amounts, often in specific tissues.

How do plant hormones reach their site of action?

They are transported, often concentrated by specific transporters.

What cellular components perceive plant hormones?

Specific receptors or binding proteins.

What process is triggered immediately after a hormone binds to its receptor?

Signal transduction.

What are the two primary cellular targets altered by signal transduction?

Gene expression and protein activity.

What is phototropism?

Plant growth or movement in response to light.

What is gravitropism?

Plant growth or development changes in response to gravity.

Who published the foundational 1880 study on plant movement?

Charles Darwin and his son Francis Darwin.

What experimental plant structure did the Darwins use to study phototropism?

The coleoptile of a canary grass seedling.

What happens to a phototropic response if the shoot tip is decapitated?

The plant does not bend toward the light.

What happens to phototropism when the shoot tip is covered with an opaque cap?

The plant does not bend.

What happens to phototropism when the shoot tip is covered with a transparent cap?

The plant still bends toward the light.

What happens to phototropism when the site of curvature is covered by an opaque shield?

The plant still bends.

Which part of the plant perceives light during phototropism?

The shoot apex (tip).

What did the Darwins propose was sent from the tip to cause bending?

A mobile influence.

What was the first plant hormone identified using these phototropism assays?

Auxin.

What was Fritz Went's hypothesis regarding shoot curvature?

The shoot apex produces a diffusible factor that promotes curvature in response to light.

How did Fritz Went capture the diffusible growth factor from shoot tips?

By placing excised shoot tips onto semi-solid agar blocks.

How did Went test the agar blocks for the growth-promoting substance?

He placed them off-center on decapitated shoots to see if they induced bending.

What does the degree of shoot bending correlate with in Went's assay?

The concentration of the plant hormone auxin present in the agar block.

What is the scientific name of the prototypical, most active natural auxin?

Indole-3-acetic acid (IAA).

What is 2,4-D?

A synthetic auxin used as a potent herbicide that disrupts normal plant growth.

How does auxin promote cell elongation according to the acid growth theory?

It acidifies and relaxes the cell wall, allowing turgor pressure to expand the cell.

How does the GUS reporter system visualize auxin activity?

An auxin-responsive promoter drives GUS expression, producing a blue pigment in high-auxin areas.

Where is auxin highly concentrated in developing juvenile leaves?

In the actively developing vascular tissue (xylem and phloem).

What is the hypocotyl phenotype of mutants with elevated auxin (IAA) levels?

They develop a much longer hypocotyl due to increased cell elongation.

What is the root phenotype of mutants with elevated auxin (IAA) levels?

They produce a high number of rapidly developing lateral roots.

What is the function of PIN proteins?

They transport the hormone auxin across cell membranes.

What is the phenotype of the pin-formed (pin) mutant in Arabidopsis?

A leafless, flowerless, unbranched inflorescence stem due to defective auxin transport.

Where is auxin normally concentrated at the very tip of a vertically growing root?

In the columella cells.

How does auxin distribute in a root tip when a plant is turned horizontally?

It accumulates differentially on the lower side of the root tip.

How does asymmetric auxin accumulation cause a root to bend downward?

High auxin on the lower side inhibits cell expansion, while the top side keeps expanding.

What is apical dominance?

Auxin produced by the shoot apex represses the outgrowth of lateral axillary buds.

What happens to lateral buds when a plant is decapitated?

They are released from repression and grow out rapidly into lateral branches.

How can lateral bud outgrowth be prevented in a decapitated plant?

By applying auxin directly to the cut surface of the decapitated stem.

How do different plant tissues (roots, buds, stems) respond to the same auxin concentration?

They have different sensitivities; a concentration that promotes stem growth may inhibit root growth.

What are undifferentiated plant cells growing on agar media called?

A callus (plural: calli).

What substance did early researchers add to synthetic media to promote cell division?

Coconut milk extract.

What was the first individual cell-division-promoting molecule discovered, and what was its source?

Kinetin, derived from autoclaved herring sperm.

What is the naturally occurring cytokinin typically found in most plants?

Zeatin.

To which nucleotide base are kinetin and zeatin structurally related?

Adenine.

What are the primary physiological roles of cytokinin in plants?

Promoting cell division, delaying senescence, and promoting axillary bud growth.

In which plant regions is cytokinin typically found concentrated?

Roots, developing fruits, and wounding sites.

How does cytokinin affect leaf senescence?

It delays senescence, keeping leaves green and active for longer.

What bacterium causes tumor-like galls on plants by transferring DNA?

Agrobacterium.

What is the name of the plasmid and the specific region transferred by Agrobacterium?

Ti plasmid, specifically the T-DNA region.

What plant hormones do the transferred Agrobacterium T-DNA genes encode?

Auxin and cytokinin.

How do varying ratios of auxin and cytokinin affect tissue culture development?

High auxin promotes roots; high cytokinin promotes shoots.

What is micropropagation?

Rapidly propagating identical plants in vitro using tissue culture.

Why is micropropagation preferred over seed propagation for specific crop varieties?

It produces genetically identical clones without diluting desirable genetics through sexual reproduction.

What Japanese rice disease led to the discovery of gibberellins?

Bakanae (foolish seedling disease), where plants grew tall, spindly, and fell over.

What fungus was identified as the cause of Bakanae disease in rice?

Gibberella fujikuroi (also known as Fusarium moniliforme).

What is lodging in agricultural crops?

The falling over of plants because they are too tall and spindly to support themselves.

What is the internodal distance on a plant stem?

The distance between successive leaves on the main stem.

How many carbon atoms typically form the ring structure of gibberellins?

19 or 20 carbons.

How are different gibberellins distinguished in scientific nomenclature?

By numbers, such as GA1 and GA3.

Why are seedless grapes sprayed with gibberellic acid (GA)?

To produce larger, plumper fruit by replacing the growth signals normally sent by seeds.

What is malting in the context of brewing?

Germinating grain to release sugars, then halting the process before sugars are consumed.

What embryo-released hormone triggers the germination process in cereal grains?

Gibberellic acid (GA).

Which cell layer in a seed responds to GA to start enzyme synthesis?

The aleurone layer.

Which enzyme does the aleurone layer produce to break down stored starch?

Alpha-amylase.

What is the molecular defect in Gregor Mendel's classic dwarf pea plants?

A mutation in the gene encoding GA 3-beta-hydroxylase, preventing active GA synthesis.

What chemical conversion is blocked in Mendel's dwarf pea plants?

The conversion of inactive GA20 to active GA1.

What are the two general physiological causes of a dwarf plant phenotype?

Deficiency in GA synthesis or insensitivity to GA signaling.

Why are reduced height (RHT) wheat varieties short despite having normal GA levels?

They are insensitive ("blind") to gibberellic acid signaling.

Who received the 1970 Nobel Peace Prize for breeding dwarf wheat varieties?

Norman Borlaug.

Why do semi-dwarf wheat and barley varieties resist lodging under high fertilization?

They do not over-elongate their stems in response to nitrogen.

What agricultural era was driven by dwarf genetics and synthetic nitrogen fertilizers?

The Green Revolution.