Phytochrome‐membrane interactions as a factor in stomatal opening

Red light enhances stomatal opening in Commelina communis L. This light effect is reversed by far‐red irradiation. Pretreatment with filipin, which competitively inhibits phytochrome binding to membranes, also inhibits light‐enhanced opening. The pretreatment with filipin is more inhibitory if preceded by red irradiation, than after far‐red irradiation. Similar results are obtained with cycloheximide and low temperature, which retard phytochrome synthesis more than its degradation. This result may indicate an enhanced release of phytochrome in the Pfr form from binding sites rather than release of phytochrome in the Pr form. This points towards the possibility that phytochrome degradation and its release from binding sites are coupled.