STIMULATION OF PHOTOSYNTHETIC STARCH FORMATION BY SEQUESTRATION OF CYTOPLASMIC ORTHOPHOSPHATE

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SUMMARY

Photosynthetic starch formation in leaf discs of spinach beet and related species can be increased more than ten fold by the presence of exogenous mannose at 10−2 M. In these species, carbon from mannose is not incorporated into starch to a significant extent and the stimulation is believed to be an indirect effect resulting from the sequestration of cytoplasmic ortho-phosphate as mannose phosphate. In species such as tobacco, there is substantial incorporation of carbon from mannose into starch and into soluble compounds other than mannose-6-phos-phate.

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