The effect of water stress on the leaf area of Cucumis melo
Matthews, Lisa R
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Greenhouse and field-grown Cucumis melo, cantaloupe vines were grown under irrigated and water stressed conditions. In addition, the stressed plants were rewatered after stress had resulted in a reduction in leaf area, providing a water stressed/recovered condition. The upper surface of the leaves was examined with a scanning electron microscope to determine if the primary cause of reduced leaf area was a decrease in cell number or cell size. The reduction in leaf area induced by water stress was due to a decrease in mitotic activity of the epidermal cells, which caused a reduction in the total number of cells per leaf. Leaves that first appeared during water stressed conditions exhibited the most severe decrease in cell division. Leaves that first appeared under irrigated conditions but developed under stressed conditions exhibited relatively normal cell division as well as normal leaf size. This indicated that most cell division occurred during and immediately following leaf initiation. Cell size did not appear to be affected by water stress, but was affected by the age of the leaf. There was a recovery of leaf area after the stressed plants were rewatered that resulted from a corresponding recovery of cell division and a concomitant increase in the total number of cells per leaf. This finding contradicts the majority of the literature which suggests that cell turgor is most affected by water stress which, therefore, causes a decrease in cell expansion. Measurements of plant water status of the greenhouse grown plants revealed an increase in diffusive resistance during water stress and a decrease in relative water content during water stress with a recovery of both upon rewatering. It is concluded that, under the conditions used in this study, cell division was more sensitive to water stress than was cell enlargement. Further, cell differentiation, as judged by the relative number of upper leaf surface cells, was found to be increased in the guard cells but unaltered in the epidermal cells and trichomes.