The study of microsporogenesis and pollen development in Amentotaxus formosana Li (Amentotaxaceae)
Date Issued
2008
Date
2008
Author(s)
Hsu, Chia- Mei
Abstract
Amentotaxus formosana Li (Amentotaxaceae) is an endemic and rare species of gymnosperms in Taiwan. In this study, the ultrastructural changes of its microspores by means of LM, SEM, TEM, fluorescent microscopy, and histochemical analysis during microsporogenesis were investigated. uring meiosis, both simultaneous and successive cytokinesis occurred in the same microsporangium. In addition, most tetrads were rhomboidal, tetrahedral or tetragonal in shape; only a few were, decussate, linear and T-shaped. At the middle tetrad stage, many structures with double-membrane appeared in the nucleus, while many organelles, such as mitochondria, plastids, dictyosomes, and endoplasmic reticula appeared in the cytoplasm. Meanwhile, the lamellated endexine accumulated on the plasma membrane, and the granular ectexine subsequently appeared on the surface of lamellated endexine. Shortly before the microspores were released from the callose wall, the location of tetrad germinal pore moved from the proximal pole to the distal one, which suggested a rotation of the tetrad microspores. At early free microspore stage, starch grains accumulated but then disappeared toward the late stage, suggesting that the starch grains were possibly consumed as carbon and energy sources. The Ubisch bodies which appeared on the surface of the inner tangential wall of the tapetum were either spheroidal or elongated beak-shaped. All of the Ubisch bodies had a core with low electron density material and were enclosed by round, high electron density sporopollenin. This was a result of the exocytosis of Ubisch bodies from the degenerating tapetal cells. At the vacuolated stage, the ectexine continued to increase in its volume, while the endexine ceased to increase in its number of layers. Subsequently, the microspore divided into a vegetative cell and a generative cell. At the bicellular stage, the lamellate endexine was highly compressed, while the intine swelled rapidly and differentiated into a smooth outer layer and a wavy inner layer, respectively.t the mature pollen grain stage, the Ubisch bodies occurred on the surface of pollen grains. The water content of mature pollen grain was 38.5%. When those pollens grains were tested with FCR reaction, they had 69.3% viability. After 1hr rehydration in distal water, the exine and intine of the pollen grains split and expanded respectively and presented more than 90% viability. The results demonstrated the high viability of A. formosana pollen. Within the conservation test, fresh pollen grains were stored respectively at 4℃ and -20℃ for 1 and 2 months. The viability tests showed 1 month-stored pollen grains under two kinds of temperature treatments both had 90% viability after 4 hrs rehydration. However, viability of 2 months-stored had a higher value under -20℃ preservation than under 4 ℃ preservation. In addition, the pollen grains under -20℃ preservation increased gradually to 60.3%. The results suggested that the -20℃-stored pollen had better preserving ability.e firstly observed the inversion of microspore during microsporogenesis in A. formosana and presumed that this phenomenon resulted from a differential dissociation time of callose.
Subjects
Amentotaxus formosana Li
callose
microspore rotation
Ubisch body
exocytosis
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