Poster: Tropisms

Abs # 663: Light can modulate circumnutation of Arabidopsis flower stalk

Presenter:	Someya, Nobutaka , someya@postman.riken.go.jp
Authors	Someya, Nobutaka  (A)   Niinuma, Kanae  (A)   Yamaguchi, Isamu  (A)   Hamamoto, Hiroshi  (A)
Affiliations:	(A): RIKEN Plant Science Center

The influence of light on the circumnutation of Arabidopsis thaliana flower stalk was investigated using time-lapse video monitoring. Under continuous white light condition, the flower stalk exhibited a uniform nutation frequency (approx. 4.0 nutations / 6h) with low degree of the flower stalk curvature (<20 degrees). Under dark condition, the nutation frequency reduced after 12h (approx. 1.5-2.0 nutations / 6h after 24h dark treatment) and the flower stalk curvature increased (>45 degrees). On re-exposure to white light after 24h dark treatment, the flower stalk maintained the same high degree of curvature as in the dark, while the nutation frequency increased to white light level immediately. It is suggested that the nutation frequency is independent from curvature development. It is also observed that the nutation frequency is modulated by a dose dependent manner under white, blue and red light conditions. When the plants treated under dark condition for 24h are exposed to blue and red light, the nutation frequency increased similar to white light re-exposure. However, the recovery of the nutation frequency was not observed by the re-exposure to far-red light condition. These experiments revealed two significant points, i) light is an important external factor controlling circumnutation and ii) curvature and the nutation frequency behaved differently and independent to each other during these experimental conditions. Contrary to the belief that the circumnutation is an autonomous movement, which is not influenced by external stimuli, we conclude that changes in light can modulate circumnutation, including both the nutation frequency and curvature in Arabidopsis flower stalk.