The use of the genetic resources of rice plants is another approach for the improvement of the productivity and quality of rice. If the role of GS1 in senescing organs and that of NADH-GOGAT in developing organs were also true for indica and javanica, some differences in the contents of these enzymes would be expected, because of their great biomass productions. When several indica and javanica cultivars of rice plants were grown in a greenhouse at Sendai, located in northern Japan, typical characteristics of morphology were observed.31 Indica and javanica cultivars generally show the characteristics of high productivity of biomass, i.e., large plant height, great leaf length and weight, or large numbers of tillers, when compared to those of Sasanishiki or Nipponbare, typical culti-vars of japonica.
Relative contents of the GS1 protein in the lowest senescing leaf blades of most indica cultivars were much higher than those of Sasanishiki, when the contents were calculated on the basis of leaf fresh weight.31 When the relative amounts of GS1 protein were plotted against the total leaf nitrogen on a unit of leaf dry weight, to roughly eliminate the effect of leaf age,5 cultivars of japonica and two cultivars of javanica were plotted as one regression line
(Obara et al, unpublished). Four cultivars out of a total of eight indica cultivars contained approximately twice as much GS1 protein as the japonica and javanica on the basis of total leaf nitrogen, although a regression line was not drawn for these indica cultivars. On the other hand, relative contents of NADH-GOGAT protein in unexpanded developing leaf blades of most indica cultivars were significantly lower than those of japonica and javanica. Cellular localization of GS1 and NADH-GOGAT proteins were identical among all cultivars tested. These results indicate that several indica cultivars possess an enhanced capacity to export leaf nitrogen, whereas japonica and javanica cultivars have an efficient system to utilize glutamine transported via vascular tissues.
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