Phototropism of Arabidopsis thaliana inflorescences under natural radiation is mediated by photosensory systems alternative to phototropins

SERRANO, A; GIORDANO, CV; ARANA, MV

Congreso; 16th International Congress of Photobiology; 2014

  Flower bending towards light, described by phototropism and heliotropism processes have been studied worldwide through contrasting natural scenarios [1-2] mainly from ecological perspectives. However, the underlying physiological mechanisms of these responses are still unclear. Recently, a study conducted under controlled conditions and artificial light sources demonstrated that, as for vegetative organs, blue light signalized by the phototropin family of photoreceptors (PHOT1 and PHOT2) induces phototropism of inflorescences in Arabidopsis thaliana [3].   Our aim was to characterize inflorescence movements in Arabidopsis thaliana under natural radiation, evaluating the relevance of blue light and of phototropins in these responses.   We measured inflorescence bending of WT-Col vs. phot1phot2 double mutants, (lacking both photoreceptors) during 48h under natural radiation. We found that, unlike other species studied [2-3], WT inflorescences tracked the sun only from the noon to the evening but not in the morning (Fig.1). Unexpectedly, mutants also exhibited inflorescence bending in contrast to what is reported under artificial conditions [3]. Fig.1- Inflorescenc e orientation of WT and phot1phot2 mutants of A.thaliana.   We compared the inflorescence bending between plants exposed to an array of acetate filters which inverted the natural blue light gradient and plants exposed to a neutral filter control treatment (Fig.2A). We found that plants under the inverted blue gradient re-directed their inflorescences following the new gradient, while control plants returned to the original position after a brief disorientation period (Fig.2B). Fig.2- Blue light conditions generated by filter arrays (A). Re-orientation of inflorescences after applying filter treatments.   Our results indicate that blue light is the main signal for inflorescence bending. In contrast with blue light phototropism reported for inflorescences under controlled conditions, photosensory systems alternative to phototropins are mediating this response in natural environments.   [1] C.Galen, Ecophysiology. 2006,148,195 [2] S.Patiño, J.Grace, Plant, Cell and Environment. 2002,25,41 [3] T.Kagawa, M.Kimura, M.Wada, Plant Cell Physiol. 2009,50(10),1774