Effect of heat stress on calcium ultrastructural distribution in pepper anther

Potassium antimonate was used to locate loosely bound calcium in the pepper (Capsicum annuum) anther under normal and heat stress environments. In the microspore mother cell, a few calcium precipitates were deposited on the surface of the cell, a few in the cytoplasm and almost no precipitates were formed in the nucleus. After 12 h at 40 degreesC, antimonate calcium deposits increased in the cytoplasm and the nucleus and many emerged on the inner surface of the vacuole membrane. After 24 h heat stress, some cells were partly deformed, numerous calcium precipitates appeared in the cytoplasm and deposited on the surface of the vacuole membrane and in the vacuoles. Compared to the pollen mother cell, there was a significant increase in calcium deposit quantities on the surface and in the cytoplasm of the tetraspore. By heat stressing for 24 h, precipitates obviously increased in the cytoplasm and nucleus of the tetraspore in contrast to the control. In the microspore, many calcium precipitates were formed on the baculae, the inner surface of plasma membrane, vacuole membrane, but only a few in the cytoplasm and nucleus. After 12 h heat exposure, precipitates on plasma membrane became abundant, a few in the cytoplasm and the peripheral nucleus, while no precipitates were seen on the vacuole membrane. As for the anthers exposed to 24-h heat stress, precipitates increased on the inner surface of the plasma membrane, cytoplasm and nucleus. In mature pollen, there was a layer of calcium-induced precipitates on the pollen wall, but few in the cytoplasm and plasma membrane. No obvious calcium changes occurred on mature pollen after 12 or 24 h heat exposure. The relationship between heat stress and calcium distribution was discussed. (C) 2002 Elsevier Science B.V. All rights reserved.