Abstract
The stomatal response to blue light is an intrinsic component of the sensory transducing processes mediating light-stimulated stomatal movements. Guard cell chloroplasts have a specific blue light response with an action spectrum that resembles the action spectrum for blue light-stimulated stomatal opening, suggesting a role of guard cell chloroplasts in the sensory transduction of blue light. The xanthophyll, zeaxanthin has recently been identified as a blue light photoreceptor in guard cells. The inhibitor of zeaxanthin formation, dithiothreitol, inhibits zeaxanthin formation and the stomatal response to blue light in a concentration-dependent fashion. In greenhouse-grown leaves, guard cell zeaxanthin content closely tracks incident radiation and it is positively correlated with stomatal apertures. The sensitivity of guard cells to blue light co-varies with guard cell zeaxanthin content. A zeaxanthin-less mutant of Arabidopsis is devoid of a typical stomatal response to blue light. At constant light and temperature, changes in ambient [CO 2 ] in a growth chamber caused large changes in stomata aperture and in guard cell zeaxanthin. The aperture-zeaxanthin changes were linearly related over a wide range of [CO 2 ]. Experiments with detached epidermis showed a similar relation among [CO 2 ], stomatal apertures and guard cell zeaxanthin, and DTT inhibited the CO 2 response in the light without altering the CO 2 response in the dark. These results indicate that blue light sensing by guard cell zeaxanthin has a regulatory role in the light response of stomata. Zeaxanthin also appears to mediate light-CO 2 interactions in guard cells.
Published Version
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