ON THE CONDITIONS FOR THE INDUCTION OF RICE POLLEN PLANTLETS AND CERTAIN FACTORS AFFECTING THE FREQUENCY OF INDUCTION

The present paper deals with the factors affecting the induction, formation, dif- ferentiation and the frequency of induction of rice pollen plantlets cultured in vitro. We have obtained the following results. 1. If the suitable stage of the development of pollen (late uninuclear stage at the verge of first mitosis) is ascertained, pollen callus may be obtained on a simple medium containing 2,4-D (2mg/1) and sucrose (6%). The gorwth substance, the source of carbon and the osmotic pressure are the necessary conditions for triggering the first division of the pollen. The complex medium consisting of minerals, trace elements, vitamins, sucrose and growth substances is not necessary for the initiation and the early growth of pollen callus, but all these factors in the medium are beneficial for the further deve- lopment of the callus. 2. Sucrose in the medium plays a significant role in the regulation of osmotic pressure. Excessively high concentration of sucrose inhibits callus formation. 3. Coconut milk, casein hydrolysate, mononucleotide and some other organic sup- plements are obviously beneficial to callus formation and the subsequent differentia- tion of the organs. 4. If the culture medium is supplemented with 2-chlorethvl-phosphonic acid (8 ppm, 40 ppm) or when the raceme of the rice is pretreated at 10℃, for 48 hours, the frequency of the formation of the pollen callus will be greatly promoted. 5. The age of the pollen callus affects the ability of the organ differentiation; the older the callus is, the lower the induction frequency of the pollen plantlets. The causes and the mechnisms of the above mentioned results have been dis- cussed.