Photosynthetic patterning: a mechanism for sun tracking

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Abstract
Vectorial light detection, a major process in reversible sun tracking (unexplained by phototropic growth responses) is attributed to photosynthate differentials in the leaf. Evidence is provided that movements of the leaf of Lavatera cretica L. (Malvaceae), directly mediated by turgor changes in supporting tissues, are triggered by photosynthate gradients across the pulvinar phloem. These solute asymmetries are inferred from starch deposition asymmetries found in the lamina after oblique illumination. Starch patterns correspond precisely with characteristics of leaf-surface topography which cause incident light effectiveness for photosynthesis to change differentially with light direction.