Antisense inhibition of NADH glutamate synthase impairs carbon/nitrogen assimilation in nodules of alfalfa (Medicago sativa L.)

被引:30
作者
Cordoba, E
Shishkova, S
Vance, CP
Hernández, G
机构
[1] Univ Nacl Autonoma Mexico, Ctr Invest Fijac Nitrogeno, Cuernavaca, Morelos, Mexico
[2] Univ Minnesota, Dept Agron & Plant Genet, St Paul, MN 55108 USA
[3] ARS, USDA, Plant Sci Res Unit, St Paul, MN 55108 USA
关键词
NADH-glutamate synthase; antisense transgenic alfalfa; S. meliloti-alfalfa symbiosis; C/N metabolism in nodules; symbiotic N fixation;
D O I
10.1046/j.1365-313X.2003.01686.x
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
Legumes acquire significant amounts of nitrogen for growth from symbiotic nitrogen fixation. The glutamine synthetase (GS)/NADH-dependent glutamate synthase (NADH-GOGAT) cycle catalyzes initial nitrogen assimilation. This report describes the impact of specifically reducing nodule NADH-GOGAT activity on symbiotic performance of alfalfa (Medicago sativa L.). Four independent transgenic alfalfa lines, designated GA89, GA87, GA88, and GA82 (for GOGAT antisense), containing an antisense NADH-GOGAT cDNA fragment under the control of the soybean leghemoglobin (lbc3) promoter were evaluated. The GA plants were fertile and showed normal growth in non-symbiotic conditions. The NADH-GOGAT antisense transgene was heritable and the T-1 plants showed phenotypic alterations - similar to primary transformants. Clonally propagated plants were inoculated with Sinorhizobium meliloti after rooting and the symbiotic phenotype was analyzed 21 days post-inoculation. Nodules of each GA line had reduced NADH-GOGAT activity, ranging from 33 to 87% of control plants, that was accompanied by comparable decreases in RNA and protein. Plants from the GA89 line, with the lowest NADH-GOGAT activity (c. 30%), presented a strikingly altered symbiotic phenotype: concomitantly activities of key enzyme for carbon and nitrogen assimilation decreased; nodule amino acids and amides were reduced while sucrose accumulated. Antisense GOGAT plants were chlorotic, reduced in fresh weight, and had a lower N content than control plants. Photosynthesis was also impaired in antisense plants. Specifically, reducing NADH-GOGAT in nodules resulted in plants having impaired nitrogen assimilation and altered carbon/nitrogen metabolic flux.
引用
收藏
页码:1037 / 1049
页数:13
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