The Effects of Inhibition of Cotyledon Photosynthesis on Seedling Development in Cucumis sativus L.

The period during which cucumber cotyledons function purely as storage organs is very brief and this role is supplemented and superseded shortly after emergence by their photosynthetic function. Inhibition of cotyledon photosynthesis by DCMU during the early post emergence phase prevented further plumule development although some cotyledon expansion still took place before seedling death occurred. Seedlings did not survive DCMU application to the cotyledons if the treatment was made before the first leaf was expanded. Reduction of the incident light intensity at the cotyledon surface to about 10 per cent of the control reduced the rate of growth of the seedlings but they did not die. Shading one cotyledon substantially reduced the weight and area of that cotyledon and of the seedling as a whole. There was little indication that the untreated cotyledon either increased its photosynthetic rate or its output of photosynthate-nor did it supply the inhibited cotyledon with assimilates. There was some indication that sucrose applied to the cotyledon surface was able to compensate for light to a small extent especially when only one cotyledon was shaded. However, in full light, sucrose tended to be inhibitory. After emergence cotyledon reserves are sufficient only for limited cotyledon development. Survival and growth of the seedling beyond this stage is dependent upon cotyledon photosynthesis.