Abstract
A full understanding of the interdependence of leaf nitrate (($No_3$￣) metabolism and symbiotic nitrogen($N_2$) fixation in legume crops is needed to help maximize the use of both N sources as well as to improve forage quality through the inhibition of leaf nitrate accumulation. The present work examines the effects of added nitrate, the level of which are 0,2,4,8 and 12mM, on the nodule formation and leaf nitrate utilization and on the possibility of inducing nitrate-toxicity to livestocks in two alfalfa varieties, ' Vernal ' of grazing type and ' Victoria ' of hay type. Higher level of exogeneous nitrate resulted in the increased above-ground dry weight. Nodulation was inhibited severely when more than 8mM NO$_3$￣ was supplied to alfalfa plants, and leaf nitrate reductase reached a maximunm at 4mM nitrate supply. The $V_{max}$of nitrate reductase in leaves of Vernal was similar to that of Victoria, whereas the $K_m$ of Vernal was higher than that of Victoria. High accumulation of leaf nitrate, $4{\times}10^{-5}$ g/g leaf fresh weight, was shown at 12mM nitrate supply, which was thought to be not enough to induce nitrate-toxicity to livestocks.icity to livestocks.
알팔파 방목형 품종 Victoria와 건초형 품종 Vernal을 공시하여 실산태 새소 농도 0,2,4,8, 12mM의 다섯 수준으로 급여하여 파종 6주후 초기 생육시기에 지상부 부위별과 뿌리혹 건물증, 엽중 질산태 질소 환원 능력 및 축적 정도를 조사하였으며, 그 결과는 다음과 같이 요약된다. 1. $NO_3$￣ 수준이 높아짐에 따라 지상부 건물중이 증가하였으나 NO($NO_3$) ￣ 의 8mM과 12mM간의 차이는 없었다. 2. 두 품종 모두 8mM 이상의 NO$_3$￣ 수준에서 뿌리혹 착생이 현저히 억제되었다. 3. 엽 생체중당 nitrate reductase 활성은 $NO_3$￣ 수준이 증가함에 따라 높아졌으나 4mM이상에서는 차이가 크지 않았다. 4. 엽중 질산태 질소축적은$NO_3$￣ 의 12mM 처리시 크게 증가하였다.
