[Cytokinin changes of root exudates, leaves and grains in inter-subspecific hybrid rice]

Using inter-subspecific hybrid rice of IIyou 2070 and IIyou 419 , their restorer lines 2070 and Zhong419, the various forms and levels of root-derived cytokinins(CTKs) in root exudates, and changes of various forms of cytokinins in rice flag leaves and grains were analyzed by HPLC and ELISA after initial heading stage. The results indicated that zeatin had 62.8% to 89.1% of total cytokinins and was the dominant form of cytokinins in root exudates during early grain filling, whereas, the contents of diHZ and diHZR greatly increased during milk ripening. This change was consistent with the dynamic changes of ZRs (Z+ZR)and diHZRs (diHZ+diHZR)in flag leaves of IIyou 2070 and 2070. Different from main cytokinin composition in root exudates, IPAs took high proportion of total CTKs in leaf and grain. We suggested that there were changes of various forms and activities of root-derived cytokinins in root exudates, and this change was related to catabolic enzymes of cytokinins and the different expression of enzyme genes. Meanwhile, the relationship between cytokinin changes of vigorous and weak spikelets and grain filling was disscused.