THE INTERNAL CONTROL OF FLOWER ABSCISSION IN SOYBEANS

KATHY ANNE BECKMANN, Purdue University

Abstract

Soybeans are known to abscise 26 to 72% of their flowers and pods. High temperatures, long photoperiods, inadequate water, low nitrogen, carbohydrate availability, insects and disease have all been shown to affect abscission. The physiological understanding of how such effects induce changes in abortion of reproductive structure is not known. The development of the vascular connections in the flower peduncle, the level of ABA in the nodal region and the application of ABA and IAA to leaves of flowering soybeans that differ significantly in the abortion of reproductive structures were examined and their potential as effectors is discussed. The mediation of the carbohydrate contribution to premature abscission could reside in the vascular development of the flower pedicel in the area. The physiological understanding for how such effectors induce changes in reproductive abortion is not known. The development of the vascular connections in the flower pedicel. The concentration of ABA in the nodal regions and the application of ABA and IAA were examined in intermediate and determinate cultivars with different percentage abscission. Three soybean cultivars were planted at 3.8 and 15.1-cm plant spacings in the field as a randomized-complete-block design. The abscission of reproductive structures in the determinate cultiver, Fuji (58%), was significantly greater than that of the indeterminate cultivars, Williams (17.94%) and Amsoy '71 (18.40), for nodes 10-15. Nodal regions, peduncles, buds, and flowers were obtained from growth-chamber grown Amsoy '71 soybeans. Plant tissue was prepared in paraffin using standard techniques. Longitudinal and transverse sections 8 to 10 (mu) thick were examined. It was apparent that all flower primordia developed vascular connections with the central axis of the peduncle. No transfer cells were observed in regions where the peduncle merges with the stem. The absence of transfer cells limit the available assimilates to the flowers at that node. Concentrations of ABA were analyzed in nodes 5, 6, 8, 9, 11, and 12 of Fuji and Williams. Field-grown plants were randomly selected at initial flowering, one week, two weeks, and four weeks later. Tissue was extracted in methanol, dried in-vacuo, and the quantity of ABA (free and conjugated) determined by radioimmunoassay. ABA concentrations in the nodal tissue of Williams were higher than Fuji throughout the sampling period. Two patterns of changes in the concentration of ABA were found. Pattern 1 began at low concentration (15-25 ng ABA/GFW) before declining (3-20 ng ABA/GFW). Pattern 2 began high (up to 140 ng ABA/GFW) and then decreased 3-40 ng ABA/GFW). The Patterns were not statistically correlated with cultivar, node or abscission. Three concentrations of IAA and ABA (control, 10('-6)M, 10('-3)M or 10('-4)M, respectively) were applied to leaves of field grown Amsoy '71, Fuji and Williams at nodes 9, 10, 11 and 12 at anthesis. Applications were made every other day until flowering ceased at these nodes. Abscission of reproductive structures in the cultivars, Fuji, Williams and Amsoy '71, were statistically different (79%, 53%, and 29%, respectively). Abscission at node 11 in Fuji and Williams was statistically lower (48%) than the other three nodes (ranging between 53 and 57%). IAA at 10('-3)M increased abscission significantly (15%).

Degree

Ph.D.

Subject Area

Agronomy

COinS