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Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 1/10/1996 Publication Date: N/A Citation: N/A Interpretive Summary: The primary forage crops in the southeastern U.S. are warm-season grasses. These grasses enter dormancy during late fall and have significantly reduced yields until early spring. We are studying the contributions of chilling temperature to low forage yields during this "winter dormancy". We have previously shown that degradation of the leaf starch reserves in the chilling-sensitive forage grass Digitaria eriantha (pangolagrass) is inhibited during exposure to chilling night temperatures. We also showed that the activity of specific carbohydrate metabolizing enzymes (starch phosphorylases) was altered in response to this chilling treatment. In this paper we describe the purification of pangolagrass leaf starch-phosphorylase enzymes and the leaf-cell-specific l Our results show that at least four different active forms of leaf GPs are present. Three of these four appear to exist in two forms, suggesting modifications that regulate the activity of these enzymes. This would be the first report of this type of regulation of plant GP activity. Further analysis of how these enzymes are regulated will provide information on how the plant responds, at the cellular level, to chilling temperatures, and how we may alter plant metabolism to increase forage productivity during chilling temperature exposure. Technical Abstract: We have previously identified four major à-glucan phosphorylase (GP) enzymes in crude leaf extracts from pangolagrass (Digitaria eriantha Stent.). One co-isolates with the chloroplasts (cGP) while the other three are extrachloroplastic (eGP). In this report we present further characterization and leaf cell-type localization of the eGP enzymes. In contrast to observations in maize, all of the pangolagrass GP enzymes were present in isolated bundle sheath and mesophyll cells. Ion exchange column chromatography separated the leaf GPs into three peaks: A, B and C. Peak A was the most active and contained three eGP active bands separable by native polyacrylamide gel electrophoresis (NPGE). Peak B GP enzymes migrated identically to peak A enzymes during NPGE. Peak C contained a single cGP. The two major eGPs in the peak A fraction co-purif could be separated by IEF-column chromatography. Kinetic properties of these peak A eGP enzymes were similar to those of other plant eGP enzymes, with the exception that the pangolagrass eGP is not inhibited by dinucleotide sugars. The co-localization of the leaf GP enzymes in both bundle sheath and mesophyll cells, and the separation of the eGPs into two pools (peaks A and B) during ion exchange chromatography are unique characteristics not previously described for plant leaf Gps. |
