ASGSB 1998 Annual Meeting Abstracts

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GRAVITROPISM AND PHOTOTROPISM OF FLOWER STALKS IN ARABIDOPSIS. S.E. Weise and J.Z. Kiss. Department of Botany, Miami University, Oxford OH

Relatively little work has been done on the tropistic responses of Arabidopsis inflorescence stems (flower stalks). Previous research in our laboratory has assayed gravitropism of both the roots and hypocotyls of a wild-type (WT) Arabidopsis and three starch-deficient strains. In the present study, the time course of curvature of the inflorescence stems of Arabidopsis WT a starchless mutant (ACG 21), and two reduced starch mutants (ACG 20 and ACG 27) was used to study gravitropism. Short inflorescence stems (1.0 - 2.9 cm) were less graviresponsive compared to the long stems (3.0 - 6.0 cm). In both studies, the WT initially had the greatest response and the starchless mutant had the least response, while the reduced starch mutants exhibited an intermediate response. Growth rates for all four strains were approximately equal. Approximately 8 hours after reorientation, flower stalks of all four strains returned to a position parallel to the gravity vector. Therefore, it appears that statoliths play an important initial role in gravitropism, accelerating the response of the inflorescence stem. However, after longer time intervals, the three mutant strains had a full gravitropic response similar to that of the WT. In addition, results of phototropism experiments show a high degree of variability, which we attribute to a large amount of nutation in the flower stalks. Taken together, our study suggests that, in flower-stalks, the longer term response to gravity is independent of the total mass of the statoliths. (Financial support was provided by NASA grant NAG 2-1017 and the Summer Scholar & Howard Hughes programs at Miami University.)

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