Effect of Sink-Source Manipulations on the Photosynthetic Rate and Carbohydrate Content of Cucumber Cotyledons |
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Authors: | MAYORAL, MARIA LUISA PLAUT, ZVI REINHOLD, LEONORA |
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Abstract: | Mayoral, M. L., Plaut, Z. and Reinhold, L. 1985. Effect of sink-sourcemanipulations on the photosynthetic rate and carbohydrate contentof cucumber cotyledons.-J. exp. Bot. 36 15511558. The photosynthetic rate of cucumber cotyledons (Cucumis sativuscv. Dahla) reached a maximum value of 12 mg dm2 h1,10 d after emergence. In 12-d-old seedlings removal of one cotyledondoubled the CO2 fixation rate of the other, as observed 3 dafter treatment. When the primary leaf was removed, the photosyntheticrate of the cotyledons was decreased by 33%. At this stage ofgrowth elimination of the roots as a sink for assimilates bygirdling the hypocotyl affected neither the photosynthetic ratenor the carbohydrate content of the cotyledons. By contrast,in 18-d-old seedlings removal of the first leaf brought abouta 42% increase in the photosynthetic rate of the cotyledons.The simultaneous removal of the first leaf and one cotyledondoubled the rate of CO2 fixation of the remaining cotyledon.Girdling the hypocotyl lowered the photosynthetic rate of thecotyledons by 73%. In both 12- and 18-d-old seedlings a decreaseor increase in the sink-source ratio was correlated with anincrease or a decrease respectively in the carbohydrate contentof the cotyledons. The stomatal resistance of the cotyledonswas not affected by any of the treatments. The effect of sink-sourcemanipulations on photosynthesis and on the level of carbohydratespresent in the cotyledons was more evident in those seedlingsgrowing under high light intensity (580 µE m2 s1),than in those exposed to 300 µE m2 s1 Key words: Sink-source relationship, cotyledons, photosynthesis |
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