DIFFERENTIAL STARCH DEPOSITION: A ‘MEMORY’ HYPOTHESIS FOR NOCTURNAL LEAF MOVEMENTS IN THE SUN‐TRACKING SPECIES LAVATERA CRETICA L.

Abstract

SummaryOblique illumination of the lamina of Lavatera cretica produces asymmetrical deposits of starch as a function of light‐shadow patterns owing to surface irregularities. Asymmetrical deposits, produced immediately after sunrise each day, are believed stored until shortly before the next sunrise. During daytime tracking, deposits are evenly symmetrical. Overnight conversion of these even deposits is believed to continue for most of the night. Shortly before sunrise, however, only residual asymmetrical deposits remain to be converted. Resulting solute asymmetries in the translocation stream are believed to trigger turgor gradients in the pulvinus, so producing anticipatory movements just before dawn. Pre‐dawn movements thus actually repeat those accompanying the previous post‐dawn oblique lighting. Changing solute gradients across the pulvinar phloem, originating from shifts in sunlight direction, are cited as the probable cause of normal tracking adjustments.