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

The period during which cucumber cotyledons function purelyas storage organs is very brief and this role is supplementedand superseded shortly after emergence by their photosyntheticfunction. Inhibition of cotyledon photosynthesis by DCMU duringthe early post emergence phase prevented further plumule developmentalthough some cotyledon expansion still took place before seedlingdeath occurred. Seedlings did not survive DCMU application tothe cotyledons if the treatment was made before the first leafwas expanded. Reduction of the incident light intensity at the cotyledon surfaceto about 10 per cent of the control reduced the rate of growthof the seedlings but they did not die. Shading one cotyledonsubstantially reduced the weight and area of that cotyledonand of the seedling as a whole. There was little indicationthat the untreated cotyledon either increased its photosyntheticrate or its output of photosynthate-nor did it supply the inhibitedcotyledon with assimilates. There was some indication that sucroseapplied to the cotyledon surface was able to compensate forlight to a small extent especially when only one cotyledon wasshaded. However, in full light, sucrose tended to be inhibitory. After emergence cotyledon reserves are sufficient only for limitedcotyledon development. Survival and growth of the seedling beyondthis stage is dependent upon cotyledon photosynthesis.