Ultrastructural study on degeneration of tapetum in anther of snap bean (Phaseolus vulgaris L.) under heat stress

Pollen sterility was induced by heat stress applied about 10 days before fl owering in the snap bean Phaseolus vulgaris L. Cytohistological changes in the tapeturn during early development of the anther were studied to identif y the tissues most sensitive to high temperature stress. The first distinct structural abnormalities were detected in the distribution pattern of the rough endoplasmic reticulum (RER) in the tapetum at the early microspore st age under high temperature conditions. Stacks of RER were frequently observ ed in the tapetum under optimal conditions, but rarely occurred under high temperature conditions. Various patterns of endoplasmic reticulum (ER) arra ngement - linear, wavy, looped or circular - were observed in the tapetum. Two types of circular ER were observed at the microspore stage under high t emperature conditions, RER with ribosomes on the surface and smooth endopla smic reticulum (SER) lacking ribosomes. The tapeturn underwent degenerative changes under high temperature conditions earlier than under optimal condi tions. The structural abnormalities of the microspore were associated with tapetal degeneration. We concluded that high air temperature affected the E R structure and blocked its function in the tapetum, and then induced earli er than usual degeneration of tapetum. Pollen sterility is associated with tapetal degeneration.