Effect of blue and red radiation on cycling stomata of bean.

Differences in the effect of blue and red radiation of low radiant flux density on sustained stomatal cycling were studied in Phaseolus vulgaris cv. Vroege Wagenaar. Stomatal behaviour in a constant environment was observed indirectly by recording the differences between leaf and air temperature. In radiation with equal radiant flux densities of 1.75 W/m2 and with equal estimated absorbed quantum flux densities of 0.73 nE/cm2 s of both colours, cycling was more rapid and peak-to-trough differences were smaller in red than in blue radiation. Blue radiation from below caused more rapid cycling with larger peak-to-trough differences than radiation from above. In red radiation the direction of radiation had a much smaller influence on period and peak-to-trough difference. To explain these qualitatively different effects of both colours on cycling stomata, the hypothesis is proposed that blue light increases the osmotic pressure in the guard cells more effectively than red light. In blue light the permeability for water transport of the guard cell membranes is lower than in red light. (Abstract retrieved from CAB Abstracts by CABI’s permission)