Apoptosis-like degradation of pollen grains in siberian squill related to the lack of low temperatures during their development

Low temperature is necessary for completing the cycle of anther development in early-spring ephemeroids. Pollen grains were investigated in Scilla sibirica L. growing under natural conditions in a park and taken to a greenhouse for the cold season. In control plants grown in the open ground, the development of microspores was normal. The plants transferred to the greenhouse sharply differed from control material. By the middle of November, the aggregations of condensed chromatin were formed near the nucleus envelope of their generative cells. In some mitochondria, the system of cristae was reduced. In December, all the mitochondria showed a reduced system of cristae. In the matrix of some mitochondria with ruptured envelopes, rather large vesicles were detected. In the vegetative and generative cells, autophagic vacuoles were formed. They also occurred in the nucleus itself; as a result, the cells of pollen grains became much more vacuolated. In January, only the products of protoplast lysis were detected in all the pollen grains. It was concluded that the lack of low temperatures induced apoptosis-like degradation of the cells of Siberian squill pollen grains.