Poster: Tropisms

Abs # 654: Phytochromes A and B may play a role in modulating blue-light-induced chloroplast movements in Arabidopsis thaliana

Presenter:	DeBlasio, Stacy , sdeblasi@bio.indiana.edu
Authors	DeBlasio, Stacy  (A)   Mullen, Jack  (A)   Luesse, Darron  (A)   Hangarter, Roger  (A)
Affiliations:	(A): Indiana University Bloomington

Although red light alone does not induce chloroplast movements in angiosperms, we investigated the possibility that phytochrome co-activation may be required for blue-light-induction of the responses in Arabidopsis thaliana. Photometric analysis of chloroplast movements in various phytochrome mutants revealed that phyA, B, and D are not required for chloroplast movements since the appropriate changes in RL transmittance induced by chloroplast migration still occurs in these mutant. However, phyB and to a lesser extent phyA deficiency resulted in an enhancement of the avoidance responses induced by fluence rates of blue light above 15 µmol m^-2 s^-1. Overexpression of PHYA and PHYB resulted in an enhancement of the low light response while the high light response remained unaffected. Closer analysis of chloroplast movements within the range of blue light intensities in which we observed a transition accumulation response (>1.5 and <15 µmol m^-2 s^-1) revealed these responses to be biphasic. WT leaves continuously irradiated with 10 µmol m^-2 s^-1 of blue light exhibit an initial increase in RL transmittance before transmittance decreases to a value lower than that measured prior to the blue light treatment. A biphasic response was not observed for phyABD leaves exposed to the same fluence rate of blue light suggesting that phytochrome may play a role in modulating the transition between chloroplast accumulation and avoidance under intermediate light conditions. This is the first report demonstrating phytochrome involvement in the blue-light-induced chloroplast movements of a higher plant.