Studies On The Relationship Between The Nitrogen Distribution And The Nitrogen Physiological Efficiency In Oilseed Rape

The environmental pollution by the loss of N fertilizer has brought about greatconcern all over the world (Raun et al., 2002). As a result, how to raise the N fertilizerefficiency has become a central issue in the plant nutrition fields. With the continuousimprovement of cultivation measures, focus has been turned to plant itself, with efforts toraise N fertilizer use efficiency through crop breeding. This paper compared the differenceof N efficiency of some seed rape genotypes and preliminarily studied their mechanism forproviding a scientific basis in the management of N nutrient, and selecting and breeding ofhigh N efficiency varieties.Two seed rape varieties (742, huiyou50) were used in our experiments. The dynamicchange in phloem juice content during the later growing period and the active of the keyenzyme (PE, GS, GOGAT) which lead to the difference of nitrogen use efficiency, werestudied under the sand culture of complete nutrient solution condition with normal nitrogensupply. And the differences of organic nitrogen redistribution in vegetative of oilseed rapevarieties with different nitrogen physiological efficiency were studied using ¹⁵N tracemethod during the later growing period.The active of the proteolytic enzyme (PE) and the glutamine synthetase (GS) inblades and the active of glutamate z-oxoglutarate aminotransferase (GOGAT) in seeds atdifferent time were determined during the later growing period, and the content of freeamino acid and L-Glutamine in phloem juice were also determined in the experiment. Theresults suggested that with senescence of the plant during the period after blooming, theactive of proteolytic enzyme in blades decreased, though it fluctuated. The GS active inblades decreased first, then increased and finally decreased again; The GOGAT active inseeds increased gradually, reaching the maximum during the later period of seeds and thendecreased. Comparing the actives of the three enzymes in two varieties, the experimentaldata indicated there was little difference between the actives of proteolytic enzyme in twobreeds. The GS active in 742 was higher than that in Huiyou 50 during the earlier period of seeds, but it was the opposite during the later period of seeds. The GOGAT active inHuiyou50 was high but it only sustained for a short period; However, The GOGAT activein 742 was low but it sustained for a longer period.The contents of free amino acid and L-Glutamine in phloem juice were measuredduring the growing period. The results showed that the content of free amino acid inphloem juice were unsteady, while the content of L-Glutamine appear to be rapid declinedin the two breeds. The difference in free amino acid between breeds was large, and thecontent of L-Glutamine in 742 is higher than that in Huiyou 50.The differences of organic nitrogen redistribution in vegetative of oilseed rapevarieties with different nitrogen physiological efficiency during the later growing periodwere studied using ¹⁵N trace method under the sand culture of complete nutrient solutioncondition. Results showed that high nitrogen physiological variety(variety 742) had largeramount of organic nitrogen redistribution, compared with the low nitrogen physiologicalefficiency variety(variety Huiyou50). The speed of organic nitrogen redistribution wasslow at first and then fast, the amount of nitrogen redistribution toward seeds and itsproportion was larger, the amount of nitrogen redistribution toward siquilin and itsproportion was smaller. The amounts of nitrogen loss by plant and its proportion weresmaller, and the velocity of nitrogen loss is slower. As a result, the nitrogen physiologicalefficiency and nitrogen harvest index of variety 742 were higher than that of varietyHuiyou50. By comparing the amount of nitrogen redistribution and its proportion duringthe four growing periods, the results showed that the largest redistribution amount ofnitrogen absorbed by plant and its proportion was found in stem elongation stage, thesmallest redistribution amount and its proportion at siliquing stage, while those werebetween them at seeding and flowing stages.