The Study of Microsporogenesis and Pollen Development in Calocedrus macrolepis Kurz var. formosana (Florin) W. C. Cheng & L. K. Fu
Date Issued
2007
Date
2007
Author(s)
Yen, Hsiao-Jung
DOI
zh-TW
Abstract
Calocedrus macrolepis Kurz var. formosana (Florin) W. C. Cheng & L. K. Fu is an endemic conifer in Taiwan. Its wood is precious and valuable. The low seed setting ratio resulted the underproduction of seeds of this plant. Therefore, the development of reproductive organs, especially the male cones, was worth to study. This purpose was investigated by fluorescent microscopy, confocal laser scanning microscopy, light microscopy, scanning and transmission electron microscopy, histochemical analysis, and FCR test, respectively.
Leaves of this plant are decussated and scale-like with decurrent base. Three to six microsporangia at abaxial side of microsporophyll arranged decussately as phyllotaxy. Buds of male cones located at the end of the branches initiated differentiation at end-August.
At microsporogenous tissue stage, the microsporangium wall could be recognized as epidermis, middle layer and tapetum from outside to inner. During microsporogenesis, simultaneous cytokinesis occurred immediately after meiosis at the end of December. When cytokinesis completed, multiform tetrads were emerged in a microsporangium, including rhomboidal, tetrahedral, and tetragonal tetrads. Tapetum cell began the process of programmed cell death. Then, callose wall dissolved, and four haploid microspores freed into microsporangial locule. Free microspores which were released by dissolved of callose contented of many starch grains in cytoplasm. Within this stage, tapetum was degenerated totally from microsporangial wall and released into microsporangial locule. Development of ectexine, endexine, and intine of microspores was occured immediately. Then, the microspore became vacuolized gradually and middle layer disappear synchronically. However, only one single epidermis layer remained as microsporangial wall. Finally, microspores passed through an asymmetric cell division. A large vegetative cell and a small generative cell were formed in each pollen grain. Function of epidermis at there was similar with endothicium, which radial thickening for anthesis. A mature pollen grain dispersed at next end-February.
Each pollen grain had a single pore and ectexine with many adhered Ubisch bodies, and the ectexine not enclose the whole pollen grain. Cytoplasm of mature pollen grains used polysaccharide to be storage material. The water content of mature pollen grains was low (38.5 %), and the cytoplasm was condensed as star-like shape at the central of pollen grain. The percentage of viability of these fresh and dry pollen grains was as low as zero. After partial rehydration in distal water for 1 hr, the cytoplasm was round up, and the intine was compressed by the expansive cytoplasm. Subsequently, the compressed intine made exine split and peel off abruptly. When the pollen grains were continuously rehydrated in vitro, the cytoplasm became egg-shape and the intine was thickened unlimitedly. After rehydration of pollen grains for 24hrs, the maximal percentage of viability with 70% was calculated. After completed hydration of protoplast, outermost part of intine shed off, too.
This detail process of this microsporogenesis in this study may support the preliminary and robust information for either further or future male-sterily study in Calocedrus macrolepis var. formosana.
Subjects
柏科
小孢子發育
花粉發育
Calocedrus macrolepis Kurz var. formosana (Florin) W. C. Cheng & L. K. Fu
Cupressaceae
microsporogenesis
pollen development
Type
other