Physiological and biochemical studies on the sink and source capacities in different orguns of crop plants

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Purpose of this research is to elucidate the determination mechanism of sink and source capacities of photosynthetic assimilatesin crop plants.1.It was shown that Q enzyme, a starch degradation enzyme, was the key enzyme to starch accumulation in the leaf sheath which was the main accumulation organ of starch in rice. Moreover, it was also found that the expression of Q enzyme activity expression was regulated by the supply of sucrose to the leaf sheath.2.The low grain filling mechanism in the New Plant Type (NPT) rice varieties developed in IRRI as the high yielding varieties was examined. It was found that the NPT varieties lacked in apical dominance, and allocated assimilates uniformly into all the grains in a panicle. This was supposed to be the main reason for deficiency of difference of superior and inferior grains in a panicle.3.The mechanism of falling down of the flowers and pods locating in the upper part of racimes of soybean plantswas studied. It was indicated that indoleacetic acid like plant hormone produced in the base of racime was responsible to the falling down of the pods.4.It was shown that inhibition of Rubisco formation in the source organs by Na ions is not so great in salt tolerant rice varieties, compared with intolerant varieties. Moreover, in salt tolerant rice varieties, competitive inhibition of K ion absorption by Nais little compared with intolerant varieties.5.It was suggested that there was a barrier in the transportation of Al ions to the leaf blades in acid soil tolerant rice varieties. This might maintain the photosynthesis in the leaf blades at high level in the acid soil tolerant rice varieties.