Differential Accumulation of Carbohydrates in Alfalfa Cultivars of Contrasting Winterhardiness

Abstract

Soluble sugar composition and starch reserves are significantly altered during cold hardening of alfalfa (Medicago sativa L.). We characterized the relationship between carbohydrate composition of the crown and freezing tolerance in cultivars of contrasting winterhardiness during their acclimation to low temperature under controlled (two cultivars) and natural hardening conditions (three cultivars in 1991–1992 and six cultivars in 1992–1993). During hardening under environmentally controlled conditions, freezing tolerance and crown levels of soluble sugars increased significantly with a concomitant decrease in starch. Differences in freezing tolerance between a cold‐tolerant and a cold‐sensitive cultivar were closely associated to the accumulation of the oligosaccharides raffinose and stachyose but were not related to the levels of sucrose. Incubation of prehardened plants at subzero temperatures (−2°C) increased freezing tolerance and promoted higher accumulations of sucrose, raffinose, and stachyose and further reduction in starch levels. Under natural hardening conditions, sucrose concentration in crowns was poorly related to the differences in midwinter levels of freezing tolerance between cultivars. Stachyose and raffinose accumulated later in fall than sucrose and reached higher levels in winterhardy than in nonhardy cultivars. Our results show that the accumulation of sucrose, stachyose, and raffinose and the decrease in glucose, fructose, and starch levels are temporally related to the development of freezing tolerance in alfalfa. However, differences in the maximum level of freezing tolerance between nonhardy and winterhardy cultivars are better related to the capacity of the plants to accumulate stachyose and raffinose than to accumulate sucrose.

Estimation of Rhizome Composition and Overwintering Ability in Perennial Sorghum spp. Using Near-Infrared Spectroscopy (NIRS)

“…Similar to fat, starch concentrations were negatively correlated with overwintering. This is in agreement with several previous studies [24,41,42]. Lower starch concentrations could reflect the breakdown of starch into sugars, which may be necessary for cold acclimation [25] and would be expected to decrease the freezing potential of the cells.…”

Iron-Superoxide Dismutase Expression in Transgenic Alfalfa Increases Winter Survival without a Detectable Increase in Photosynthetic Oxidative Stress Tolerance

“…This may have enabled the transgenic plants to allocate more sugars to the root compared with the control plants, and therefore further increase root carbohydrate levels during cold acclimation. Since soluble carbohydrate levels in the roots of alfalfa have been correlated with the level of freezing tolerance across different cultivars and across stages of acclimation (Castonguay et al, 1995(Castonguay et al, , 1997, this would predict increased winter survival in the transgenic plants. Our results do not support this mechanism of action for SOD in these transgenic plants.…”

Quantitative effects of alfalfa extract supply on rice straw degradation, fermentation and biomass synthesis by rumen microorganisms in vitro

“…One must stress that the additional amounts of non structural sugars supplied by alfalfa extract can be considered as negligible. It was estimated from published data on alfalfa intracellular carbohydrates [8] that at its maximal rate, alfalfa supplementation supplied the fermentation broth with only 0.4 g . [20].…”