Modifications in Aster response to long-day conditions caused by overexpression of phytochrome A or B

Abstract

We studied the role of phytochromes A and B in the regulation of critical day length, night-break signal and the quantitative effects of sunlight on inflorescence development, a long-day induced process, in Aster. We used transgenic plants overexpressing either PHY A or PHY B, different natural daylight conditions, and day extension and night break treatments by low-fluence-rate fluorescent or incandescent lighting with a red to far-red ratio of 7.3 and 0.6, respectively. Wild-type plants had a higher sensitivity to day extension with fluorescent than incandescent lighting and a quantitative response to natural daylight conditions. Their response to a day extension with either incandescent or fluorescent lighting and to a night break with incandescent, but not fluorescent, lighting was subject to the quantitative effect of daylight conditions during the natural short day. Overexpression of PHY A shortened the critical day length for inflorescence development from 14 to 8 h. Overexpression of PHY B shortened the length of the night break needed to induce inflorescence development from 2 h to 15 min. Overexpression of either PHY A or B reduced the quantitative effect of natural daylight. For Aster plants grown under commercial conditions, from autumn through spring, the overexpression of either PHYA or PHYB substantially increased the yield of flowering shoots.