Starch Hydrolysis Induced by Polarized Light in Stomatal Guard Cells of Living Plants

It was reported in 1930 (2) that exposure to polarized light had been found to induce hydrolysis of starch grains in the mesophyll of living leaves. Similar action on starch grains in vitro has also been observed (1, 3, 6). The present paper gives an account of some experiments on the hydrolyzing influence of polarized light when applied to foliar stomata. In many plant forms the guard cells of leaf stomata are more easily observed in the living condition than are other starch-containing cells. Also, guard cells are specially attractive for studies on turgor or changes in relation to starch formation and starch hydrolysis, for turgor changes influence the opening and closing of the stomatal apertures. All of these tests were made with bright sky light or direct sunshine, polarized by means of a Nicol prism, or sometimes by means of reflection from a glass-covered ferrotype plate. The list of plant forms studied included Hyacinthus orientalis, Convallaria majalis, Pancratium fragrans, Tradescantia fluminensis, Hemerocallis fulva, Crinum americanum, Lactuca sativa, Tropaeolum polyphyllum, and Rheum rhaponticum. These plants were chosen because their foliar stomata are relatively large and are essentially confined to the lower (or abaxial) leaf surface. In healthy leaves of all these forms, or in pieces of still living epidermis stripped from the leaves, polarized light was found to induce or accelerate the disintegration and hydrolysis of the starch grains of the stomatal guard cells.