EFFECT OF THE MESOPHYLL ON STOMATAL OPENING IN COMMELINA-COMMUNIS

The effect of a number of factors on the opening of stomata in the intact leaf and in the isolated leaf epidermis of Commelina communis has been investigated. Stomata in the intact leaf opened wide in the light and closed rapidly on transfer to the dark. They were also sensitive to CO2. In contrast, stomata in isolated epidermis floated on an incubation solution containing 100 mol m-3 KCl responded neither to light nor CO2. They opened as widely as those in the intact leaf when treated with fusicoccin. Stomata in isolated epidermis opened almost as wide as those in the intact leaf when they were incubated with isolated mesophyll cells in the light. The solution in which the mesophyll cells were incubated was separated by centrifugation. The medium from cells previously incubated in the light caused the stomata in isolated epidermis to open but that from cells kept in the dark had no effect. A similar effect was observed when isolated chloroplasts were incubated with the isolated epidermis. However, the supernatant from the chloroplast suspension had no significant effect on stomatal opening. These results indicate that the mesophyll plays an important role in stomatal opening in the light. The mesophyll appears to produce in the light, but not in the dark, a soluble compound which moves to the guard cells to bring about stomatal opening. The experiments with isolated chloroplasts suggest that this substance is a product of photosynthesis.