The modified stomata of the floral nectary ofVicia faba L. 1. Development, anatomy and ultrastructure

Abstract

This study of the floral nectary ofVicia faba L. focusses on the modified stomata through which nectar flows, and on the question of whether they can regulate their stomatal pore aperture. The floral nectary ofV. faba consists of a disk which surrounds the gynoecium. As the flower bud matures, a tapered projection arises by cell divisions and expansion at a position opposite the free stamen. Modified stomata develop from pentagonal guard mother cells on this projection, and are often contiguous, but because development of modified stomata is asynchronous, many stages can occur in a local area. Plasmodesmata, which connect guard mother cells and guard cells of developing modified stomata with adjacent cell types, become covered by cell wall material on the guard-cell side in mature modified stomata. The numerous small vacuoles of guard mother cells and young guard cells are replaced by a single large one as the guard cells expand. Pore development occurs concurrent with this expansion as the ventral walls separate at a designated location leading to rupture of the inner, and then outer, cuticles, to reveal the pores of mature modified stomata.