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Amylolytic Activity of Orchardgrass and Starch and Sucrose Contents of Orchardgrass vs Pangola Digitgrass Leaf Blades as Influenced by Night Temperature and Gibberellic Acid¹

This study was made to determine differences in sucrose and starch contents and amylolytic activities between Orchardgrass (Dactylis glomerata L.) and ‘Pangola’ digitgrass (Digitaria decumbens Stent.). This information could help explain why growth of tropical grasses is severely reduced by suboptimal night temperature (IOC) whereas temperate species are much less affected.

Orchardgrass and Pangola were treated with gibberellic acid (GA) and subjected to 30 or IOC 12-hour nights with SOC days, after which sucrose and starch were determined. The starch-degrading enzymes of Orchardgrass leaf blades were separated by means of polyacrylamide gel electrophoresis. Amylolytic enzyme activity was determined from densitometer tracings and by a colorimetric assay. In the case of Orchardgrass extracts, densitometer tracings of gels negatively stained by starch-iodine showed the presence of 18 bands regardless of plant treatment. This was hi contrast to similar data previously obtained for Pangola. The temperate grass was found to contain more amylolytic isozymes and greater total amylolytic activity than Pangola. Neither the IOC night regime nor GA application affected total amylolytic activity or starch content of Orchardgrass, whereas both treatments affected amylolytic activity and starch content of Pangola. GA application did not affect the number of amylolytic isozymes in the leaf blades of either plant. Sucrose appeared to accumulate in leaves of both grasses during IOC exposure, in the presence and in the absence of GA. In the case of Orchardgrass, GA appeared to reduce leaf sucrose content at SOC.

Key Words: Dactylis glomerata L. • Starch degradations • Polyacrylamide gel electrophoresis • Digitaria decumbens Stent. • Invertase • Amylases

² Research Technologist and Associate Plant Physiologist, Agronomy Department, and Assistant Dean of Research, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611, respectively.

Received for publication July 20, 1973.