Morphogenesis and Physiological Basis in Wheat Cultivars with Different Levels of Cold-Resistance during Cold Acclimation and Freezing Period

Abstract

"Dongnong dongmai 1" is the released cultivar of winter wheat (Triticum aestivum L.) in Heilongjiang province in China. However, the physiological metabolism in the over-wintering process of the cultivar is unclear. In this study, the plant morphological characters were investigated and several physiological parameters were measured with comparisons of three winter wheat cultivars, Dongnong Dongmai 1 (cold tolerant), Dongnong 705 (semitolerant to coldness), and Jimai 22 (cold susceptible), the objective was to understand the physiological adaptation to low temperature of Dongnong Dongmai 1. The numbers of leaf, tiller, and tiller leaf as well as water content in plant were investigated from 3 Oct. to 8 Nov. at a 5 d interval. Leaf, sheath, and tiller nod were sampled from 22 Oct. to 22 Dec. at a 10 d interval. The numbers of tiller and tiller leaf were significantly higher in Dongnong Dongmai 1 than in other cultivars before frozen period. Under cold stress, water content decreased in all parts of culti- vars. Dongnong Dongmai 1 had the largest reduction of water content in leaf, but the water content in tiller nod declined slower and maintained the highest level among the three cultivars. In contrast, Jimai 22 had relatively higher water content in leaf and sharp reduction in tiller nod. The electric conductivity measurement indicated that leaves died at 30, 20, and 0 d after the frozen day in Dongnong Dongmai 1, Dongnong 705, and Jimai 22, respectively. The total soluble sugar content in leaves and leaf sheathes was the highest in Dongnong Dongmai 1, and the lowest in Jimai 22. Similarly, during frozen period, the content of total soluble sugar in tiller nod was the highest in Dongnong Dongmai 1 and the lowest in Jimai 22. Superoxide dismutase (SOD) in leaf was inactivated at 20 d after the frozen day in Dongnong 705 and Jimai 22, but maintained the certain activity even at 40 d after the frozen day in Dongnong Dongmai 1. Moreover, the activities of SOD in all parts of Jimai 22 were lower than those of other cultivars. During frozen period the activities of peroxidase (POD) were higher in sheath and tiller nod in Dongnong Dong-mai 1, it was higher in tiller nod and lower in leaf sheath in Dongnong 705, and cignificantly lower both in sheath and tiller nod in Jimai 22.The results suggest that high resistance to coldness in Dongdong Dongmai 1 is probably related to the translocation of total soluble sugar from leaf to sheath and tiller nod. Low water content in plant and relative high activities of SOD and POD in sheath and tiller nod are also contributed to the cold-resistance of Dongnong Dongmai 1.