Effect of sink source manipulations on the photosynthetic rate and carbohydrate content of cucumber cucumis sativus cultivar dalila cotyledons

Mayoral, M.L.; Plaut, Z.; Reinhold, L.

Journal of Experimental Botany 36(171): 1551-1558


ISSN/ISBN: 0022-0957
Accession: 005269587

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The photosynthetic rate of cucumber cotyledons reached a maximum value of 12 mg dm-2 h-1, 10 d after emergence. In 12-d-old seedlings removal of one cotyledon doubled the CO2 fixation rate of the other, as observed 3 d after treatment. When the primary leaf was removed, the photosynthetic rate of the cotyledons was decreased by 33%. At this stage of growth elimination of the roots as a sink for assimilates by girdling the hypocotyl affected neither the photosynthetic rate nor the carbohydrate content of the cotyledons. By contrast, in 18-d-old seedlings removal of the first leaf brought about a 42% increase in the photosynthetic rate of the cotyledons. The simultaneous removal of the first leaf and one cotyledon doubled the rate of CO2 fixation of the remaining cotyledon. Girdling the hypocotyl lowered the photosynthetic rate of the cotyledons by 73%. In both 12- and 18-d-old seedlings a decrease or increase in the sink-source ratio was correlated with an increase or a decrease, respectively, in the carbohydrate content of the cotyledons. The stomatal resistance of the cotyledons was not affected by any of the treatments. The effect of sink-source manipulations on photosynthesis and on the level of carbohydrates present in the cotyledons was more evident in those seedlings growing under high light intensity (580 .mu.E m-2 s-1), than in those exposed to 300 .mu.E m-2 s-1.