Modulation of phototropism by phytochrome E and attenuation of gravitropism by phytochromes B and E in inflorescence stems

Light is one of the most important environmental parameters for a plant and plays a critical role throughout the life cycle. Plants sense light using the red-light-absorbing phytochromes and the blue-light-absorbing cryptochromes and phototropins. In this report, we examine the role of phytochromes in phototropism and gravitropism in inflorescence stems of Arabidopsis thaliana. Tropisms and growth responses were assayed in wild-type (WT) plants, and these responses were compared with those of the mutants phyA, phyB, phyAB, phyD and phyE. After considering growth differences, we found that phototropism of the phyE mutant is significantly less (P < 0.05) and that gravitropism of phyB and phyE is significantly greater (P < 0.05) compared with the WT responses. Interestingly, while phyE plays a positive role in phototropism, this pigment (along with phyB) attenuates gravitropism in inflorescence stems. This study adds to the growing literature demonstrating that phytochromes can play a role in blue-light-mediated responses such as phototropism.