Ultrastructure des mitochondries des stomates de maïs; cas d'une ouverture photoactive

Young intact maize plants were placed in an experimental chamber specially designed to allow continuous measurement of transpiration and photosynthetic rates in defined environmental conditions. After two circadian periods, leaf samples were collected at the end of the night period and after 150 min of light exposure. Samples were immediately immersed in fixative bath and prepared for ultrastructural examination. In darkness, when stomata were closed, most of the observed guard cell mitochondria exhibited the characteristic morphology of the resting state, while the others appeared in the respiring state. In subsidiary cells, the distribution showed an inverse pattern. After photoactive stomatal opening, all mitochondria of the guard cells were in the resting state 3 configuration, but in subsidiary cells they were in active state 4 configuration. These differences in mitochondrial ultrastructure corresponding to their location in guard cells or subsidiary cells during photoactive stomatal opening provide information about energy expenditure in the cells of the stomatal complex. Subsidiary cells appear to play a role more important than merely an ionic reservoir.