Phytochrome control of turion formation in Spirodela polyrhiza L. Schleiden

Turion yield in Spirodela polyrhiza, strain SJ, is increased by increasing the daily light period. This effect is more pronounced in autotrophic than in mixotrophic conditions. Night-break irradiation (15 mins) increased turion yield by 150 % under the conditions of an 8-h daily light period. Besides the effect of night-break irradiation, end-of-day far-red irradiation decreased turion yield with increasing photoperiod, whereas end-of-day red irradiation was without any effect. This demonstrates the promoting effect of the Pfr form of phytochrome on formation of light-grown turions. Formation of dark-grown turions was increased by about 240% by a single red light pulse and was reversed by an immediately applied far-red light pulse. Consequently, under heterotrophic conditions phytochrome modulates the turion formation process.