Relationships of Soluble Carbohydrates and Freeze Tolerance in Saltgrass

Abstract

Information is lacking regarding the changes of endogenous soluble carbohydrates of saltgrass [Distichlis spicata (L.) Greene] during cold acclimation. The objective of this study was to quantify soluble carbohydrates and their relationships to freezing tolerance in six saltgrass accessions (A65, A29, C66, 32, 55, and 48). The study was performed at monthly intervals under natural acclimation in two consecutive winter seasons (October 1999–April 2000 and October 2000–April 2001) at Fort Collins, CO. Concurrent with LT50 (subfreezing temperature resulting in 50% mortality) assessment, soluble carbohydrates, including sucrose, fructose, glucose, raffinose, and stachyose were measured by gas chromatography (GC). Results indicated significant differences among accessions and sampling dates in LT50 and carbohydrate content. Sucrose was the predominant sugar, but did not show a clear seasonal trend and had no correlation with freezing tolerance. Fructose, glucose, raffinose, and stachyose exhibited clear seasonal changes, reaching highest concentrations during midwinter. In December of both seasons, higher concentration of fructose and glucose were observed in 48 and 55 as compared with other accessions. Accession A29 had the highest concentration of raffinose in December and January in both seasons. A29 also had the highest stachyose content in midwinter of 1999‐2000. Higher fructose, glucose, or raffinose concentrations were frequently observed in accessions of 48, 55, and A29, which coincided with their lower LT50 as compared with the other accessions. In contrast, C66 had the lowest sugar concentrations, which related to its sensitivity to low temperatures. These results indicate that fructose, glucose, raffinose, and stachyose may play important roles in saltgrass freezing tolerance.