Chapter 23 Abscisic acid (ABA): ¤ a seed maturation

dormin: a growth inhibitor was purified from sycamore leaves collected in

early autumn, when the trees were entering dormancy

long-term development: the change of gene expression

abscisin Ⅱ a substance that promotes the abscission of cotton fruits [Ironically] ABA-induced abscission of cotton fruits is due to ABA’s ability to stimulate ethylene production

ABA appears to promote senescence (the events preceding abscission)

¤ antistress signal

inhibit growth and stomatal opening, particularly when the plant is

under environmental stress

short-term development: the alternation of ion flux across membranes

is still active for long-term responses

enantiomer

ABA assay: Gas chromatography (10-13 g) High-performance liquid chromatography Immunoassy

ABA biosynthesis takes place in chloroplast and other plastids

direct pathway

9-cis-epoxy-carotenoid dioxygenase (NCED), is rapidly induced by waterstress, in thylakoid

MW 264

ABA glucoside

ABA-deficient mutants: can be corrected by the application of exogenous ABA.

ABA-deficient vp14 mutant:

vp: maize mutant

Vivipary (preharvest sprouting):

precocious germination of seeds in

the fruits

* ABA is transported by both the xylem and the phloem, but rich in phloem

sap

* ABA synthesized in the roots can be transported to the shoot via the xylem

* ABA acts as a root signal that helps reduce the transpiration rate by

closing stomata in leaves

* Stomatal conductance is often much more closely related to soil water

status than to leaf water status, and the only plant part that can be

directly affected by soil water status is the root system. (p.675R)

* ABA redistribution – “anion trap” concept

the steepness of the pH gradients across membrane

the specific uptake carriers