ENZYMES OF N METABOLISM AS INFLUENCED BY AM FUNGI AND AZOSPIRILLLIM INOCULATION IN MULBERRYK. KUMUTHA, S.P. SUNDARAM AND J. SEMPAVALAN
This study examined the impact of inoculation of arbuscular mycorrhizal fungi (AM) and Azosordlum on the enzyme activities in relation to nitrogen metabolism of mulberry cultivar MR 2 under pot culture with the application of 3 levels of nitrogen (0,45,60 Kg ha-1). The enzyme assays and mycorrhizal colonization were studied at 30 and 45 days after transplanting. N application causes no reduction in arbuscular mycorrhizal colonization and the inoculation of A. brasilense MAZ 5 had expressed their stimulatory effect on AM fungi colonization as evidenced by the increase in (native) mycorrhizal colonization. Inoculation resulted significant increase in nitrate reductase (NR) activities of plants at all levels of N and it was relatively higher in N2 level. Combined inoculation almost doubled the NR activity and recorded 9.2-49.9 % increase over A. brasilense alone. AM fungi or Azospirillum inoculation either alone or in combination significantly increased the GS, GOGAT and GDH activities. GS and GOGAT activities were found higher in N, level and the degree of response was decreased with higher level of N application (N2) GS activity was higher than GOGAT. Higher GDH was recorded with N application as well as increase in age of the crop and it was lower than GS and GOGAT. The enhanced P status in mycorrhizal plants might have increased these enzyme activities and also the increased enzyme activities are due to the contribution of functional GS-GOGAT system in mycorrhizal plants. Also it indicates that coupled enzyme complex of GSGOGAT system is the route of ammonia assimilation in mulberry. This study further indicated the role of AM fungi in increasing the assimilation of nitrogen.
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