Changes in Abscisic Acid and Indoleacetic Acid before and after Anthesis Relative to Changes in Abscission Rates of Cotton Fruiting Forms

Abstract

Cotton (Gossypium hirsutum L.) fruiting forms exhibit pronounced changes, with age, in their probability of abscission. Large floral buds rarely abscise, but after anthesis the young fruits (boils) have a high probability of abscising. Abscission rate reaches a peak about 5 to 6 days after anthesis and then gradually decreases. An experiment was conducted to try to determine the reason for the rapid and pronounced increase in probability of abscission just after anthesis. Cotton was grown in the field and fruiting forms of various ages from 9 days before to 9 days after anthesis were all harvested the same day and subsequently analyzed for ABA and UIA. The concentration of ABA decreased slightly at anthesis and increased gradually thereafter. In contrast, the concentration of IAA was high before anthesis and then decreased at anthesis to about onefifth the previous concentration. IAA remained low for at least 4 days after anthesis and then increased rapidly between 7 and 9 days after anthesis. The high concentration of IAA in floral buds before anthesis is probably a major factor in their resistance to abscission. Likewise, the low concentration of IAA at anthesis and for about 4 days thereafter may promote fruit abscission during the young boll stage.

Changes in Amide-Linked and Ester Indole-3-Acetic Acid in Cotton Fruiting Forms during Their Development

“…Cotton (Gossypium hirsutum L.), cv Deltapine 61,' was grown in a field at the Western Cotton Research Laboratory in Phoenix as reported earlier (18). Flower buds were harvested 9, 6, and 3 before anthesis; flowers were harvested at anthesis; and bolls were harvested 2, 4, 7, and 9 d after anthesis.…”

“…it then decreased as free IAA increased. Because these changes in free IAA were inversely correlated with changes in fruiting-form abscission, we suggested that the high concentration of IAA in large flower buds inhibited abscission before anthesis, whereas the low concentration at and for 4 d after anthesis promoted abscission of young bolls (18).…”

“…Because exogenous IAA delays or prevents abscission (2, 7), we measured the concentration of free IAA in fruiting forms from 9 d before until 9 d after anthesis (18). The concentration of free IAA decreased about 80% during the 6 d before anthesis, remained low for the next 4 d, and then increased rapidly between 7 and 9 d after anthesis.…”

The Effects of Figaron and Water Deficit on Seed Yield of Two Soybean Cultivars

“…Several investigators have reported that any kind of water stress in soybean tends to accelerate abscission of reproductive organs resulting in decreased yield (Kato, 1964;Doss et al, 1974;Ashley and Ethridge, 1978;Korte et al, 1983). Water deficiency also changes the status of internal hormonal balance in the plant (Mcmichael et al, 1972;Guinn, 1976;Guinn and Brummett, 1988;Guinn et al, 1990). It enhances the rate of ethylene production (Guinn, 1976), increases abscisic acid (ABA) content in young cotton bolls and decreases the free indole-3-acetic acid (IAA) content (Guinn, 1982;Brummett, 1987 and1988).…”

“…Water deficiency also changes the status of internal hormonal balance in the plant (Mcmichael et al, 1972;Guinn, 1976;Guinn and Brummett, 1988;Guinn et al, 1990). It enhances the rate of ethylene production (Guinn, 1976), increases abscisic acid (ABA) content in young cotton bolls and decreases the free indole-3-acetic acid (IAA) content (Guinn, 1982;Brummett, 1987 and1988). In sesame, abscission could be manipulated by altering the level of IAA and ethylene (Sexton and Roberts, 1982) .…”