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Pak. J. Bot., 46(5): 1789-1795, 2014.

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MECHANISMS OF NITROGEN RE-DISTRIBUTION IN RESPONSE TO ENZYME ACTIVITIES AND THE EFFECTS ON NITROGEN USE EFFICIENCY IN BRASSICA NAPUS DURING LATER GROWTH STAGES

ZHENHUA ZHANG^1,2*∆, WENMING WANG^1∆, CHUNYUN GUAN³, QIANG LIU^1,2, XIANGMIN RONG^1,2, YONGLIANG HAN^1,2, JIANGWEI PENG^1,2, QIONG LIAO¹, YING YU¹ AND HAIXING SONG^1,2*

Abstract: In order to investigate the mechanisms of nitrogen (N) re-distribution in response to proteolytic enzyme (PE), glutamine synthetase (GS) and glutamate synthetase (GOGAT) activities and the effects on N use efficiency (NUE). Two oilseed rape genotypes were grown in sand culture in a greenhouse under normal (15.0 mmol L^-1 NO₃^-) and limited-N (7.5 mmol L^-1 NO₃^-) levels. Isotope (¹⁵N) labeling and enzyme inhibitors against the PE, GS and GOGAT enzymes were used. We found that, when the two genotypes were subjected to specific inhibitors of PE, GS, and GOGAT, the activities of these enzymes were significantly decreased, resulting in reduced N re-distributed from leaf to grain, as well as reduced NUE. L-glutamine and free amino acid contents in the phloem sap were primarily influenced by PE and GS activities, whereas grain yield was primary regulated by GOGAT activity during the later growth stages. These findings suggest that PE, GS, and GOGAT are key enzymes for the regulation of N re-distribution in plant tissues during later growth stages, with grain yield and NUE of oilseed rape being positively regulated by PE, GS and GOGAT activities.

Key words: Nitrogen (N) redistribution, N use efficiency, Proteolytic enzyme (PE), Glutamine synthetase (GS), Glutamate synthase (GOGAT)

¹College of Resources and Environment Sciences, Hunan Agricultural University, Changsha 410128, China;

²National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resources; College of Resources and Environment, Hunan Agricultural University, Changsha 410128, China;

³National Center of Oilseed Crops Improvement, Hunan Branch, Changsha 410128, China

^∆These authors contributed equally to this work

^*Corresponding author’s e-mail: zhzh1468@163.com, shx723@163.com, Tel: +86-15873141718