Poster: Tropisms

Abs # 400: Chloroplast Movement is Simultaneous with Para- and Diaheliotropic Leaf Movement in Peanut

Presenter:	Schmalstig, Judy G, jschmals@rollins.edu
Authors	Schmalstig, Judy G (A)   Vasicek, Laina M (A)   Razor, Jill A (A)
Affiliations:	(A): Rollins College

Chloroplast movement and leaf orientation in peanut were measured in response to increasing irradiance levels to understand the contributions of each factor to efficiency of light absorption and photoprotection, and to look for any possible interactions. Chloroplast movement occurred simultaneously with both paraheliotropism and diaheliotropism. As irradiance increased, there was a progressive increase in the percentage of cells with no chloroplasts present on upper margin of the cell, reaching a plateau of 90 % at 900 μmolm-2s-1. Leaves reoriented their blades perpendicular to light fixed at a 45 degree angle (diaheliotropism) at irradiances up to 600 μmolm-2s-1, and turned upward from the horizon at irradiance above 900 μmolm-2s-1 (paraheliotropism). Between 600 and 900 μmolm-2s-1, movement seemed to be a compromise between the diaheliotropic movement, perceived on the blade, and paraheliotropic movement, perceived on the pulvinus. Paraheliotropism and diaheliotropism appear to occur via separate mechanisms acting independently, based on the site of light perception, and the different responses to light irradiance. Chloroplast movement during diahelioptropism seems to counter the strategy of leaf tracking, but photosynthesis was not reduced by the chloroplast movement until irradiance reached 900 μmolm-2s-1. Chloroplast movement during paraheliotropism may be an additional mechanism for photoprotection.