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