The redistribution of auxin during gravitropism in maize roots

Developmental effects of auxin

¤ Regulate apical dominance

¤ Promote lateral and adventitious root formation

– even though auxin inhibit the primary root elongation

¤ Delay the onset of leaf abscission

¤ Regulate the floral bud development

¤ Promote fruit development

¤ Induce vascular differentiation

Developmental effects of auxin

¤ Regulate apical dominance

¤ Promote lateral and adventitious root formation

– even though auxin inhibit the primary root elongation

¤ Delay the onset of leaf abscission

¤ Regulate the floral bud development

¤ Promote fruit development

¤ Induce vascular differentiation

Regulate apical dominance– apical bud inhibits the growth lateral buds

+ TIBA (efflux inhibitor) in

lanolin placed below the shoot

apex Axillary bud formation

Direct-inhibition model

Auxin is synthesized in the shoot apex and is transported basipetally to the axillary buds

( [auxin] gradient)

axillary buds are more sensitive to auxin than other shoot tissues

+ IAA inhibits the growth

of lateral buds

However¤ After decapitation 4 h, the level of IAA is 5-fold increase

¤ Applied auxin directly to terminal bud, [auxin]shoot, axillary bud outgrowt

h

¤ radiolabeled auxin does not enter basipetal the bud

¤ axr1 mutant (unable to respond to auxin), much branching phenotype

¤ Transgenic plant (02):

auxin-responsive promoter + luciferase (LUX) gene

decapitated the expression of LUX increase in and around the axillary buds

¤ After decapitation, an increase in cytokinin imported from root via xylem,

Add cytokinin in axillary buds bud growth

(but bud growth prior to the increase of cytokinin)

¤ After decapitation, ABA level decrease, in some species.

¤ Carotenoid cleavage product

¤ Grafting studies

Root signals interact with auxin in the xylem ongoing research

Web Essay 19.4

Auxin induce vascular differentiation– is polar and occurs from leaves to roots

Auxin

Cytokinin

Xylem and phloem differentiation: high auxin conc.

Only phloem differentiation: low auxin conc.

Auxin promote fruit development

produce auxin

The commercial uses of synthetic auxins

¤ prevention of fruit and leaf drop

¤ promotion of flowering

¤ induction of parthenocarpic fruits – seedless fruits

¤ thinning of fruit

¤ rooting of cutting

¤ herbicide for dicot weeds