Abstract:

Aims The aim of this study is to investigate the effect of different light qualities on circumnutation of cowpea (Vigna unguiculata) seedlings.

Methods The behaviors of cowpea seedlings were observed in a black box, which fixed with two infrared cameras on the top and a side, respectively. The motion was recorded as photos taken at an interval of 5 min, in a 3-dimensional space coordinate under different light qualities (such as white, red, blue, and red-blue with opposite direction) for 48 h. The coordinate values of cowpea seedling growth point (CPGP) were read on a computer screen.

Important findings The results showed that in the dark condition, the CPGP movements had two types, one was a spiral rising anticlockwise circulation, and the other was swinging up irregularly. The spiral rising anticlockwise circulation lasted 18.3 h, then turned to swing up irregularly. It takes (82.7 ± 4.2) min spiraling a circle on average, with the maximum range of swing 2.0 cm and the minimum 0.5 cm. Under white light condition, the CPGP movements tended toward light source with a swing up irregularly. The range of swing changed from decrease to increase, with the maximum range of swing 0.6 cm and the minimum 0.1 cm. Under red light condition, the CPGP movements showed two stages, in which one was a tending toward light source directly for (21.9 ± 1.6) h, the other was swing up perpendicular to light direction for (8.8 ± 0.5) h. The maximum range of swing was 3.5 cm, and the minimum was 2.0 cm. Under blue light condition, the CPGP movements showed a swing up with “Z” trajectory tending toward light source, alternating 2 durations with (110.0 ± 5.8) min and (223.5 ± 4.9) min. under red-blue light with opposite direction conditions, the CPGP movements tended toward blue light source for (12.0 ± 3.8) h, then toward red light source slowly. The order of CPGP within 48 h decreased under different light quality with red, dark, blue, white and red-blue. The seedlings of cowpea could move with circumnutation in dark conditions, suggesting that circumnutation does not need light induction. However, the light quality could change the movement direction and speed. CPGP movements showed different patterns under different light qualities, but the movements tended toward light source in general.

Key words: circumnutation, light quality, 3-dimensional space coordinate, Vigna unguiculata