Abscisic Acid: correlations with abscission and with development in the cotton fruit.

Abscisic acid was measured in developing cotton fruit (Gossypium hirsutum) by means of gas-liquid chromatography. High levels of abscisic acid occurred in correlation with abortion and abscission of young fruit, with low germination of immature seed, and with senescence and dehiscence of mature fruit. Declining or low levels of abscisic acid occurred in correlation with the period of most rapid fruit growth and with high germination of immature and mature seed. Young fruit of cultivar Acala 4-42 contained about twice as much abscisic acid as young fruit of cultivar Acala SJ-1, and this difference is correlated with a higher rate of young fruit abscission in Acala 4-42. Young fruit abscising late in the fruiting season contained about twice as much abscisic acid as young fruit abscising early in the fruiting season.

Phaseic acid: Occurrence in cotton fruit; Acceleration of abscission.

Phaseic acid was tentatively identified in cotton fruit; this is the second report of its natural occurrence. It was found in cotton fruit of all ages, from very young to fully mature fruit. It accelerates abscission in the excised nodes of cotton seedlings, but has only about one-tenth of the abscission-promoting activity of abscisic acid.

Applied auxin gradients and abscission in explants.

The influence of applied auxin on abscission in explants (excised cotyledonary nodes) of cotton was investigated.Proximal applications to the stem stump accelerated abscission with all concentrations applied. Distal applications to the petiole stumps retarded abscission with all concentrations applied.Simultaneous applications to petiole and stem stumps accelerated, retarded, or were without effect on abscission depending on the relative amounts applied. Relatively high concentrations proximal on stem stumps accelerated abscission whereas relatively high concentrations distal on petiole stumps retarded abscission. The abscission rates from various combinations resulted in a multiphasic abscission response curve as the amounts applied were increased.Consideration of these and related data in the literature indicates that many factors can have profound effects on the nature of abscission responses to auxin.

Gas-liquid chromatography of trimethylsilyl derivatives of abscisic Acid and other plant hormones.

This paper describes a new method for qualitative and quantitative assay of abscisic acid and other acidic plant hormones, such as indoleacetic acid and the gibberellins, by the gas-liquid chromatography of their trimethylsilyl derivatives. Interfering substances in plant extracts were largely removed by preliminary column chromatography with carbon-celite and elution of the abscisic acid with 60% acetone, permitting direct determination of abscisic acid by gas-liquid chromatography using a flame ionization detector. (A level of 0.65 mg/kg fr wt was found.) This method enables measurement of amounts of abscisic acid as low as 0.025 mug. In impure samples collected by gas-liquid chromatography the abscisic acid recovered could be measured quantitatively by use of its ultraviolet absorption maximum at 260 mmu.

Environmental factors in the physiology of abscission.

This paper reviews the physiological effects of the principal environmental factors which can influence the process of leaf abscission. The factors include temperature, light, water, gases, mineral elements, soil conditions, and parasitic organisms. These factors influence a variety of internal physiological conditions and processes which in turn may either accelerate or retard the process of abscission. The most important internal factors include A) sugar, pectin, cellulose, and other carbohydrates; B) energy-yielding respiration; C) enzymic reactions; D) amino acids, purines, and other nitrogenous substances; E) levels of plant hormones; and F) the molecular biological pathway. The current information is consistent with the hypothesis that the environmental factors act in leaf abscission via direct or indirect influences on the synthesis or reaction rate of enzymes.

Auxin and gibberellin effects on cell growth and starch during abscission in cotton.

An increase in starch content of cells in the abscission zone of the cotton explant appeared correlated with an increase in number of cells. A large increase in the number of cells in the abscission zone, concomitant with an increase in starch content, followed treatment with gibberellin as compared to auxin. In the final stages of abscission starch was hydrolyzed in the cells of the separation layer. Some starch remained after the petiole abscised.A positive phloroglucinol-hydrochloric acid reaction in the cells of the petiole distal to the line of separation indicated the presence, not of lignin, but of soluble sugars and uronic acids. This reaction was especially intense following gibberellic acid treatment.It was concluded that gibberellin in accelerating abscission leads to (1) an increase in cell number and starch content in the abscission zone, (2) the hydrolysis of starch in the separation layer just before abscission, and (3) the breakdown of polysaccharides and the release of soluble sugars and uronic acids. Auxin, an abscission retardant, either delays or prevents these events.