ABA and IAA Concentrations in Young Bolls and Abscission Zones in Relation to Boll Retention

Gene Guinn and Donald L. Brummett


 
ABSTRACT

A deficiency of photosynthate decreases boll retention. Earlier research showed that a nutritional stress increases ethylene production in young bolls, and provided a partial explanation for the increased boll shedding that occurs when the demand for photosynthate exceeds the supply. Experiments were conducted to test the hypothesis that a deficiency of photosynthate affects the amounts of ABA and IAA in bolls and their a scission zones. Photosynthesis was increased by thinning to permit better light penetration into the plant canopy. The demand for photosynthate was decreased by removing all bolls from the remaining plants the day they were thinned (about 3 weeks after first flower). Control plants were neither thinned nor defruited. Bolls and their abscission zones were harvested 3 days after anthesis three times during an irrigation cycle. Plants wilted severely before the third harvest. Thinning and defruiting increased boll retention, but boll retention decreased with time as boll load increased and as water stress developed. Thinning and defruiting slightly decreased the ABA content of bolls, but did not affect the ABA content of abscission zones. Water deficit, however, caused large increases in the ABA contents of bolls and their abscission zones. Thinning and defruiting had little effect on the IAA content of bolls, but increased the IAA concentration in abscission zones (where IAA inhibits abscission). Water deficit decreased IAA concentrations in bolls and their abscission zones and greatly decreased boll retention. Earlier results also showed that water deficit increases ethylene production in young bolls. Combined with the earlier data on ethylene, the results indicate that stresses (shortage of photosynthate or water) that increases boll shedding do so by changing the concentrations of hormones that regulate abscission.



Reprinted from 1986 Proceedings: Beltwide Cotton Production Research Conferences pp. 88 - 89
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998