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The Role of Phytochrome C in Tropisms.  Kumar, P., Montgomery, C.E., Kiss, J.Z. Miami University, Oxford, OH 45056.

Light and gravity are among the most important environmental stimuli that influence plant form and development.  Plants sense light using the red-light-absorbing phytochromes and the blue-light-absorbing cryptochromes and phototropins.  The phytochromes, which are a molecular family consisting of PHYA-E, have been shown to be involved in both phototropism and gravitropism.  Phytochrome C is considered one of the more minor forms, and very little is known about the role of PHYC in plant development.  In this project, we studied the role of PHYC in growth and tropisms by using the mutants, phyCD and phyD, and comparing them to wild-type, Wassilewskija (WS) plants.  Gravitropism and blue-light-induced phototropism were examined in young seedlings and in mature plants.  The most significant differences were found in experiments with inflorescence stems, and PHYC modulated both gravitropism and phototropism in these organs.  Phytochromes play an important role in helping plants sort through the constant bombardment from environmental stimuli and in determining the final growth form of the plant.  (Supported by NASA Grant NCC2-1200).