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Development of Photosynthetic Activity following Anaerobic Germination in Rice-Mimic Grass (Echinochloa crus-galli var oryzicola) ¹

Department of Horticulture and Landscape Architecture, Washington State University, Pullman, Washington 99164

Shoots of anaerobically germinated Echinochloa crus-galli var oryzicola are nonpigmented whether germinated in light or dark, and chlorophyll synthesis is minimal for the first 12 to 18 hours of greening after exposure to ambient conditions. When chlorophyll development is compared between greening anoxic and etiolated shoots, there is a 100-fold difference in chlorophyll levels at 8 hours, an 8-fold difference at 24 hours, but roughly equal amounts at 60 hours. The chlorophyll a/b ratio approaches 3 earlier in greening anoxic shoots than in greening etiolated shoots, relative to total chlorophyll. The long lag in chlorophyll synthesis can be shortened by giving dark-grown anoxic shoots a 24-hour midtreatment of air before light.

Development of photosynthetic activity in etiolated shoots, determined by CO₂ gas exchange, ¹⁴CO₂ uptake, and activity of carboxylating enzymes closely parallels development of chlorophylls. However, development of photosynthetic capability in greening anoxic shoots does not parallel chlorophyll development; ability to fix carbon lags behind chlorophyll synthesis. A reason for this lag is the very low activity of RuBP carboxylase during the first 36 hours of greening in anoxic shoots. The activity of phosphoenolpyruvate carboxylase is also delayed, but its kinetics more closely match those of chlorophyll development.

¹ Supported by National Science Foundation Grant 80-10598 and a Grant-in-Aid of Research from Sigma Xi. Scientific Paper No. 6311, College of Agriculture, Washington State University, Pullman, WA 99163.