Abstract
The guard cells of Vicia faba and Nicotiana tabacum contain numerous mitochondria, elements of endoplasmic reticulum, spherosomes, and peroxisome‐like microbodies. A full ribosomal complement appears in young but not in fully mature guard cells. Numerous small lipid droplets external to the plasmalemma were noted in mature Vicia guard cells. Chloroplasts were found in both epidermal and guard cells of both species. Full photosynthetic capacity was indicated by the grana fretwork of guard‐cell chloroplasts. A specialized peripheral reticulum was observed in the guard‐cell chloroplasts of Vicia. Plasmodesmata were observed in both walls between sister guard cells and between guard and epidermal cells. In the latter case plasmodesmata were found primarily in pit fields of transverse walls. It is postulated that the small volume of guard cells allows them an osmotic advantage over larger neighboring cells in generating turgor.
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