Interorgan Mobilization of Phosphorus, Their Relative Contribution to Grain-Filling and Induction of Sequential and Non-Sequential Senescence in Rice Cultivars

The analysis of ³²P export from the fed leaf (source) to other leaves (sink) of four rice (Oryza saliva L.) cultivars (Ratna, Jaya, Masuri and Kalojira) indicates that the export of ³²P was a function of proximity relatiooship from source to sink leaf at the grain formation stage. But at the grain development stage, this relationship was not maintained by the third leaf, regardless of cultivar. Among the leaves, the third leaf exported minimal ³²P to the grains in all the cultivars. Maximal ³²P was exported to the culm and the grains from the flag leaf of Ratna and Jaya in either development stage, from the second leaf of Masuri and Kalojira at the grain formation stage but from the flag leaf at the grain development stage. This study brings out the fact that despite uniform amount of ³²P having been applied, the relative export from fed leaf is different in different cultivars and that induces differential patterns of leaf senescence (sequential and non-sequential) in different rice cultivars.