Author: Chen Zu-keng, Wang Fu-xiong Wang Fu-hsiung and Zhou Fu
J Integr Plant Biol 1987, 29 (5): -.
The development of the tapetum in Pinus bungeana may be divided into five stages for the convenience of description. (1) Stage of the microspore mother cells: The organelles of the tapetal cell, consisting of amyloplasts, Golgi vesicles, lipid bodies, and endoplasmic reticulum are abundant and prominent. (2) Stage of the meiosis h During this period the amount of rough en- doplasmic reticulum (RER), ribosomes, and Golgi vesicles is prominently increasing, in the meanwhile the Golgi vesicles move up and contact with the plasmolemma and then pass over them. On the other hand, the outer tangential wall of the tapetal cell begins to be disintegrated. Then a number of sporopollenin bodies with various shape and size occur outside of the plas- molemma and move gradually into the locule of the microsporangium. In addition, there are a large number of starch grains aggregation in anelectron-dense matrix of the cytoplasm. (3) Stage of the meiosis Ⅱ: The cytoplasm of the tapetal cell has receded, and the plasmolemma has also withdrawn in some degree from the callose wall, even forming the cmbayment-like structure. The pro-Ubisch body can be found in the small embayments, and was usually accompanied with a number of Golgi vesicles, h is interesting to note that the lipid bodies are gradually dec- reasing during meiosis Ⅰ and Ⅱ. On the contrary the pro-Ubisch bodies and sporopollenin bodies are continual!y aggregated outside the plasmolemma. Moreover, the volume of starch grains within the amyloplast also increases. The above fact shows that the synthesis of carbohydrate is still proceeding. At the moment the amount of endoplasmic reticulum and ribosomes has reached the peak. (4) Stage of microspore formation: The cytoplasm of the tapetal cells begins to break down and becomes vacuolated, At this stage, the various organelles are disintegrated to different degrees and the degenerative process of RER and mitochondria is rather slow. (5) Stage of bicellular pollen grain: The cytoplasm of tapetal cell breaks down almost entirely, but the RER and mitochondria can be still recognizable. And there is a prominent, acetolysis-resistant peritapetal membrane as well as certain sporopollenin bodies in the outer tangnential wall. During the process of meiosis of microspore mother cell, the function of the tapetal cell in Pinus bungeana may be summarized as follows: (a) The decrease of lipid bodies within cytop- lasm of the tapetal cell is accompanied by the increase of the pro-Ubisch bodies outside the plasmolemma. This phenomenon may be shown that the precursor of pro-Ubisch bodies is close related to the activity of lipid bodies. As has been reported by Carniel (1967), Rowley & Erdtmen (1967) and Echlin & Godwin (1968), the lipid droplets or grey spheroidal bodies are possibly the procursors of the pro-Ubisch bodies. (b) There are a large number of Golgi vesicles in the cytoplasm Of tapetal cell at this stage. It may be explained that the precursors of pro-Ubisch bodies or sporopollenin bodies resulted from the activity of lipid bodies subsequently are trans- ferred to outside the plasmolemma via the Golgi vesicles. Perhaps we could consider that these procursors of the osmiophilic materials are carried away in soluble state, then aggregated in the invaginations of the plasmolemma. (c) At the same time, the ribosomal population rises very sharply and the starch accumulation in the amyloplast reaches the peak of their activity. In view of the above situation, the synthesis of the protein and the deposition of carbohydrates are very active. Thus the amount of the pro-Ubisch and sporopollenin bodies are greatly increased during the dyad and tetrad stages in Pinus bungeana. This is the inevitable outcome of the activity of the tapetal ceils.