Abstract
Experiments were carried out to elucidate the temporary after-effect of a period of water stress on the opening potential of stomata of tobacco (Nicotiana tabaccum) and beans (Vicia faba). Stomatal aperture was measured on floating leaf discs or epidermal strips after a period of time in light under controlled conditions; direct effects of leaf-water deficit were thus avoided. The responses of the two species were not qualitatively different. Only a minor part of the post-stress damage was located in the mesophyll in beans, the major part (approximately two-thirds) being located in the guard cells themselves. The CO1 compensation point for tobacco leaves showed no after-effect of stress. However, the response of stomata to normal and CO1-free air in both species suggested that a minor part of the after-effect on stomatal opening, presumably that part arising in the mesophyll, may be explained by elevated CO1 concentrations in the stomatal cavity. The nature of that part of the after-effect arising within the guard cells themselves was not clarified. Guard-cell starch content was apparently unaffected by stress in both species; in tobacco, epidermal-cell starch content was reduced in the stress and post-stress condition. Stomatal responses to the short-term addition of energy-supplying metabolites (ATP, glycolate, and glucose-1-phosphate) showed no interaction with the post-stress condition. Similarly responses to the addition of stomatal inhibitors (sodium azide, dodecenylsuccinic acid, atrazine, and phenylmercuric acetate) did not indicate the exact nature of the after-effect, although there was a marked increase in the sensitivity to atrazine in post-stress leaf discs. In tobacco leaf discs an examination of the process of elimination of this after-effect, as distinct from studies directly on its nature, suggested that complete recovery involved at least two steps, together lasting 2 to 3 days. One step required time and was independent of light; the other required light of at least 1 klx for a day or more and did not occur in CO2-free air. Stomata recovered almost completely in 2 days without light when discs were floated on 005 M glucose-1-phosphate.