STOMATAL RESPONSES OF TRADESCANTIA-ALBIFLORA TO CHANGING AIR HUMIDITY IN LIGHT AND IN DARKNESS

Tradescantia albiflora has green variegated and white leaves. Its stomatal apparatus consists of the guard cells and two pairs of subsidiary cells. Investigations were carried out by observing the stomata microscopically by means of a video system in situ in a CO2 exchange chamber and by simultaneously measuring the gas exchange of the leaves. In response to air humidity changes, stomatal movements in T. albiflora begin, owing to turgor changes, in the polar and lateral subsidiary cells. The stomatal response of green leaves to changes of air humidity showed typical transient and oscillatory phases prior to steady-state reactions. In darkness, stomata closed when air humidity decreased; however, they did not reopen when air humidity was raised again. Stomata of illuminated white leaves responded like those of green leaves in darkness. With increasing soil water stress stomata responded to changing air humidity with reductions of the transient phases and a decreasing tendency to reopen when air humidity became high again. CO2 deficiency of the air caused the stomata to open in the dark, and interacted with the air humidity effect in such a way that stomata of green leaves responded to air humidity changes in darkness in a similar way as they did in light.