Light‐Induced Stomatal Movements in Wheat Leaves Recorded as Transpiration Experiments with the Corona‐Hygrometer

Stomatal Physiology

“…The final steady-state aperture is determined by the energy flux. The final aperture is to some extent independent of intensity, however, for the same steady-state opening is reached in continuous light of 32,000 m-c and in intermittent illumination with 64,000 m-c (5 sec light, 5 sec darkness) (53). Virgin (53) has also obtained evidence that the product law may occasionally hold for a fairly wide range of apertures.…”

“…The final aperture is to some extent independent of intensity, however, for the same steady-state opening is reached in continuous light of 32,000 m-c and in intermittent illumination with 64,000 m-c (5 sec light, 5 sec darkness) (53). Virgin (53) has also obtained evidence that the product law may occasionally hold for a fairly wide range of apertures. One can hardly expect the product rule to hold ideally, for the epidermal resistance to movement is variable and water deficit may increase during opening, caus ing a closing movement.…”

“…When the light is switched off, closing starts immediately. Closing is the more rapid process (55) and may be measurable 15 sec after the beginning of darkness (53). Recently (56), it has been reported for Pinto beans (Phaseolus vulgaris) that closing is much slower than opening.…”

“…At each intensity the aperture reaches a steady-state value which is characteristic for that intensity provided the water defi cit of the leaf is small. The higher the intensity is, the greater the fi nal opening (41,44,53,58,59) up to an in tensity which causes maximal opening. The saturating intensity is around 105 erg cm-2 sec-1 for incandescent light sources (47,60).…”

“…When a turgid leaf which has been kept in darkness for a few hours is exposed to light, the stomata open after a short time lag (53,54). When the light is switched off, closing starts immediately.…”