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This article in CS

  1. Vol. 27 No. 4, p. 627-631
     
    Received: Jan 24, 1986
    Published: July, 1987


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doi:10.2135/cropsci1987.0011183X002700040003x

Variation for Activity of Nodule Nitrogen and Carbon Assimilating Enzymes in Alfalfa1

  1. D. L. Jessen,
  2. D. K. Barnes,
  3. C. P. Vance and
  4. G. H. Heichel2

Abstract

Abstract

The nodule enzymes glutamate synthase (GOGAT) and phosphoenolpyruvate carboxylase (PEPC) are important in the assimilation of symbiotically fixed N in alfalfa (Medicago sativa L.). The objectives of this study were: to evaluate several alfalfa germplasm sources for variability in nodule GOGAT and PEPC activities, and to determine the relationships between N2 fixation and plant yield traits with nodule GOGAT and PEPC enzyme activities. Approximately 160 plants from each of six alfalfa germplasms were grown in sand culture in the glasshouse and assayed for nodule GOGAT and PEPC enzyme activities. Twenty-four genotypes (four from each germplasm) were selected to represent a range in GOGAT and PEPC activities. These genotypes were evaluated in glasshouse and field clonal studies for GOGAT and PEPC activities per gram nodule fresh weight, acetylene reduction activity (ARA), nodule mass, nodule color, nodule soluble protein concentration, and plant yield. Variability for nodule GOGAT and PEPC activities within each of the six germplasms was large and normally distributed. The 12 high GOGAT genotypes (2 from each germplasm) were 44% greater GOGAT activity than the 12 low genotypes. The 12 high PEPC genotypes were 27% greater in PEPC activity than the 12 low genotypes. Both groups of high enzyme activity genotypes were significantly greater than the low genotypes in ARA, nodule soluble protein concentration, and field shoot yield. Both GOGAT and PEPC activities were positively correlated (r=0.61**, significant at the 0.01 probability level). Also, GOGAT and PEPC were each correlated with ARA (r=0.43*, significant at the 0.05 probability level, and 0.45*, respectively), nodule color score (r=0.46** and 0.73**) soluble protein concentration (r= 0.77** and 0.90**). Plant yield and N2 fixation measured in the field were not correlated with nodule GOGAT and PEPC activities measured in the glasshouse. The relationships between GOGAT and PEPC with other plant traits indicated that these enzymes are associated with the host-Rhizobium meliloti Dang. symbiosis and should be explored as possible selection criteria to include in an alfalfa breeding program.

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