Poster: Photomorphogenesis

Abs # 511: Primary inhibition of hypocotyl elongation requires a phototropin1-dependent increase in cytoplasmic Ca²⁺

Presenter:	Spalding, Edgar P, spalding@wisc.edu
Authors	Spalding, Edgar P (A)   Lieg, Erin J (A)   Durham Brooks, Tessa L (A)   Folta, Kevin M (A) (B)
Affiliations:	(A): University of Wisconsin
Web Site:	http://www.botany.wisc.edu/physiology/spalding.html

The phototropin photoreceptors transduce blue light signals into several physiological and developmental responses in plants. A transient rise in cytoplasmic Ca²⁺ that begins within seconds of phototropin 1 (phot1) excitation is believed to be an important element in the transduction pathways leading to one or more of the phot1-dependent responses. The goal of the present work was to determine whether the Ca²⁺ response was necessary for 1) the inhibition of hypocotyl elongation that develops within minutes of the irradiation, and 2) hypocotyl phototropism (curved growth of the stem in response to asymmetric illumination.) After determining that pulses of light delivering photon fluences of between 1 and 1000 μmol m^-2 induced growth inhibition mediated by phot1 without significant interference from other photosensory pathways, the effect of blocking the Ca²⁺ rise was assessed. Treatment of seedlings with a Ca²⁺ chelator prevented the rise in cytoplasmic Ca²⁺ and prevented phot1-mediated growth inhibition. However, the same chelator treatment did not impair phot1-mediated phototropism. Thus, it appears that the early, transient rise in cytoplasmic Ca²⁺ is an important intermediary process leading to the onset of hypocotyl growth inhibition but not phototropism. The signal transduction pathways leading to these two phot1-dependent processes therefore diverge within several seconds of blue light irradiation.