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Variation in RuDPCase Activity in Barley¹

Seasonal patterns of ribulose 1,5-diphosphate carboxylase (RuDPCase), EC4.1.1.39, activity from leaves and awns, specific leaf weight, and total above-ground dry matter accumulation rate were determined for two barley (Hordeum vulgare L.) genotypes. In general, RuDPCase activity was greatest in young, fully expanded leaves and was lower in each subsequent leaf down the culm. for a given leaf, RuDPCase activity also decreased sharply with increasing age. Specific leaf weight (SLW) did not change with leaf age but upper leaves on a culm had greater specific leaf weights than did lower leaves. The RuDPCase activity in the total plant canopy and in the youngest expanded leaf for both varieties was significantly and positively correlated with the rate of aboveground canopy dry matter accumulation.

Twelve barley cultivars chosen to sample a relatively broad genetic background were grown in two controlled environments and a greenhouse. Genotypes differed significantly in RuDPCase activity (dm² leaf) ^–1 and (g dry wt) ^–1 and in SLW. Only RuDPCase activity (dm² leaf) ^–1 and SLW were significantly affected by environment. There were no significant genotype by environment interactions for RuDPCase activity (dm² leaf) ^–1, for activity (g dry wt) ^–1, or for SLW. Heritability estimates using the components of variance method were 0.67, 0.56, and 0.74 for RuDPCase activity (dm² leaf) ^–1, for activity (g dry wt)^–1, and for SLW, respectively. The correlation coefficients for SLW vs. RuDPCase activity (dm² leaf) ^–1 and vs. activity (g dry wt)^–1 were 0.83, and 0.06, respectively. It was concluded that RuDPCase activity of barley leaves might be increased in two ways: 1. by selecting for high RuDPCase activity (g dry wt) ^–1 and 2. by selecting for high SLW.

Key Words: Photosynthesis • Specific leaf weight • Dry matter accumulation • Genotypic variation

² Former gradnate research assistant (current address: Pioneer Hi-Bred International, Box 85, Johnston, IA 50131) and professor, respectively.

Received for publication March 1, 1975.