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Plant Physiology 85:592-597 (1987)
© 1987 American Society of Plant Biologists

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Environmental and Stress Physiology

Regulation of Photosynthetic Carbon Metabolism in Cucumber by Light Intensity and Photosynthetic Period 1

N. Suzanne Robbins2 and David M. Pharr

Department of Horticultural Science, North Carolina State University, Raleigh, North Carolina 27695-7609

The effects of photosynthetic periods and light intensity on cucumber (Cucumis sativus L.) carbon exchange rates and photoassimilate partitioning were determined in relation to the activities of galactinol synthase and sucrose-phosphate synthase. Carbon assimilation and partitioning appeared to be controlled by different mechanisms. Carbon exchange rates were influenced by total photon flux density, but were nearly constant over the entire photoperiod for given photoperiod lengths. Length of the photosynthetic periods did influence photoassimilate partitioning. Assimilate export rate was decreased by more than 60% during the latter part of the short photoperiod treatment. This decrease in export rate was associated with a sharp increase in leaf starch acccumulation rate. Results were consistent with the hypothesis that starch accumulation occurs at the expense of export under short photoperiods. Galactinol synthase activities did not appear to influence the partitioning of photoassimilates between starch and transport carbohydrates. Sucrose phosphate synthase activities correlated highly with sugar formation rates (sucrose, raffinose, stachyose + assimilate export rate, r = 0.93, {alpha} = 0.007). Cucumber leaf sucrose phosphate synthase fluctuated diurnally in a similar pattern to that observed in vegetative soybean plants.

2 This work is a portion of a thesis submitted by N. S. R. in partial fulfillment for the Ph.D. degree.

1 Paper No. 10962 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7601.






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Copyright © 1987 by the American Society of Plant Biologists