| In order to identify the roles of carbohydrates, proline, and active oxygen metabolism in moderate freezing tolerance, the physiological or biochemical basis of differential responses of crowns (stolons for centipedegrass), leaves and roots to cold acclimation in tall fescue [Festuca arunginacea (Shreb.)] and centipedegrass [Eremochloa ophiuroides (Munro) Hack. ], changes in LT50 (Showing by the temperature at which 50% lethal plants or leakage of cell electrolyte occurred), content of carbohydrates, proline and their kinetics in response to 10 days' cold acclimation treated in 4/2C or field natural overwintering were monitored in crowns (stolons for centipedegrass), leaves or roots independently in tall fescue and centipedegrass and the characteristics of active oxygen metabolism during cold acclimation, under and after freezing moderate stress and their roles in survival of tall fescue and centipedegrass suffering from moderate freezing stress were also studied in this paper.Results showed that, leaves had a capability of quick response, while crowns a relative slow and steady one, but roots could not be acclimated at all in tall fescue. Nevertheless in centipedegrass, -stolons were the only organ responded to cold acclimation among the leaves, roots and stolons thus determined the its freezing tolerance and overwintering ability. Large differences in crowns (stolons), leaves, roots of tall fescue and centipedegrass in response to cold acclimation were partly due to the differences in content and changing of carbohydrates and proline, and relative proportion of sucrose, fructose, starch and proline. Compared with other organ such as leaves and roots, crowns of tall fescue and stolons of centipedegrass had a moderate ratio of total soluble carbohydrates to starch, which enable them prepared both for improving freezing tolerance and the carbon resources needed in regenerating after suffered from lethal freezing damage to leaves and roots, or the regrowth process after overwintering. We suggested that, as far as carbohydrates were concerned, the differential responses of crowns, leaves and root in tall fescue to cold acclimation had their profound physiological basis, differential changes in the content of carbohydrates might be one of them.Decreasing in LT50 kept pace with increasing in total soluble carbohydrates which mainly composed of sucrose and fructose in crowns and leaves, but not roots of tall fescue in response to control cold acclimation, a remarkable correlativity were existed in them.Although there was an increasing in proline during control cold acclimation, closing comparisons showed that changes in proline may had nothing to do with the increasing of freezing tolerance in tall fescue. Control cold acclimation could not improve the freezing tolerance of crowns, leaves and roots in centipedegrass seedlings without adult stolons because of the limitation in accumulation soluble carbohydrates of those organs. Despite of some differences in quantity and components, results of natural field overwintering experiment of tall fescue and centipedegrass, particularly in stolons of centipedegrass in which a retard about a week after increasing in carbohydrates then following improving in freezing tolerance were observed, proved again carbohydrates do play a important role in enhance the freezing tolerance.Although 10-days' cold acclimation caused increasing in active oxygen generating rate, moderate repressing in anti-oxygen enzymes' activity and slight damage to biomembrane (show by the increasing in MDA) both in tall fescue and centipedegrass, it could enhance the stability of structure and metabolism in tall fescue, not in centipedegrass. Compared with those in normal temperature, the leaves and roots in tall fescue suffered from moderate freezing stress after 10 days cold acclimation showed relative low increasing rate in active oxygen generating rate and decreasing rate in anti-oxygen enzymes activity, activity of some anti-oxygen enzymes such as POD even showed a remarkabl...
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