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The Effects of PHYC and PHYD on Tropistic Responses of ARABIDOPSIS.   C.E. Montgomery, P. Kumar and J.Z. Kiss  Miami University, Oxford, OH.

   Plants constantly adjust their architecture in order to optimize their growth in response to a variety of environmental stimuli including light and gravity. In seedlings, primary roots are positively gravitropic and negatively phototropic while shoots are positively phototropic. Plants sense light using the red-light-absorbing phytochromes and the blue-light-absorbing cryptochromes and phototropins. The five members of the phy family (PHYA to PHYE) have been shown to be involved in the orientation of the shoots and roots of Arabidopsis. As the phyC mutant has been isolated only recently, studies on the role of PHYC on tropistic responses are incomplete. Thus in this project we studied the role of PHYC in growth and tropisms by using the mutants phyCD and phyD and compared them to the wild type Wassilewskija (WS WT). Four-day-old seedlings were grown on half-strength MS salt in 1.2% agar, and experiments were conducted on seedlings grown either in continuous white light (70 µmol m^-1s^-1) or darkness. In general, growth of the mutants was robust and comparable to the WT. The most significant differences were found in experiments with light-grown seedlings. Roots of both the phyCD and phyD mutants were impaired in negative blue-light induced phototropism compared to the WT. Thus, our results suggest that both PHYC and PHYD play a role in root phototropism.

(Supported by Miami University Undergraduate Summer Scholar Program.)