Differences in freeze tolerance of zoysiagrasses: II. Carbohydrate and proline accumulation

Cold hardiness among zoysiagrass (Zoysia spp.) genotypes varies, but the physiological basis for cold hardiness is not completely understood. The objective of this study was to determine the relationship of carbohydrate (starch, total soluble sugars, total reducing sugars, sucrose, glucose, and raffinose family oligosaccharides) and proline concentrations with the cold acclimation of zoysiagrass and the lethal temperature killing, 50% of the plants (LT50). Thirteen genotypes of zoysiagrass were selected with contrasting levels of winter hardiness. Plants were grown for 4 wk of 8/2 degrees C day/night cycles and a 10-h photoperiod of 300 mu mol m(-2) s(-1) to induce cold acclimation. Rhizomes and stolons were sampled from nonacclimated and cold-acclimated plants and used for carbohydrate and proline analysis. Concentrations of soluble sugars and proline increased during cold acclimation, while starch concentrations decreased. Starch, sugar/starch ratio, glucose, total reducing sugars, and proline in cold-acclimated plants were correlated (r = 0.61, -0.67, -0.73, -0.62, and -0.62, respectively) with LT50. These correlations indicate that higher concentrations of total reducing sugars, glucose, and proline are positively associated with zoysiagrass freeze tolerance, whereas' higher concentrations of starch appeared detrimental to freeze tolerance.