Effects Of Inoculated Nodule Bacteria On Low-temperature Tolerance In Alfalfa(Medicagosativa L)

In this research, alfalfa with nodules(NA) and alfalfa without nodules(NN) were used as experimental materials for cold treatment, alfalfa plants were performed at-6℃ with 0 h,2 h, 4 h, 6 h, 8 h, 10 h and 12 h with regard to the control at 25℃ and then determined the physiological indexes: relative water content(RWC), osmotic potential(OP),relative conductivity of leaves(TDS),chlorophyll a, chlorophyll b, total chlorophyll,the ratio of chlorophyll a and b, vitamin C(VC), glutathione(GSH), Superoxide anion free radical(O2-)and hydrogen peroxide(H2O2). In order to get the relationship between alfalfa inoculated nodule bacteria and cold tolerance of alfalfa, the result is as follows:1. The relative water content of NA was higher than NN in low-temperature stress. The relative water content of the two groups under cold stress was lower than that under control condition. Along with the time of low-temperature stress, RWC in both groups increased, and then decreased when alfalfa was exposed to low temperature for 10 h.2. The osmotic potentials decreased in the shoot of NA and NN. But NA declined faster than NN. The osmotic potentials of NA and NN had not significant difference(P<0.05) under normal condition. However, the osmotic potentials of the former was lower than the latter and there were significant differences between the two treatments in long time of low-temperature stress.3. Under control condition, electric conductivity was 0.393 in NA and was 0.390 in NN. With the increase of low temperature stress time, electric conductivity of NA and NN was higher than the electric conductivity under normal condition. The electric conductivity of NN rose, and then declined and continuously increased at last. The trend of electric conductivity in NA gradually rose then decreased. There was significant difference between NA and NN in 10 and 12 h low-temperature stress. Electric conductivity of NA was lower than that in NN during cold stress except for 4h.4. The contents of chlorophyll a,chlorophyll b and total chlorophyll in NA and NN decreased at cold stress. At the beginning of the cold stress, the contents of chlorophyll a,chlorophyll b and total chlorophyll in NA were lower than that of NN. However, the contents of chlorophyll a,chlorophyll b and total chlorophyll in NA were higher than NN in the later stage. the ratio of chlorophyll a and b of NN showed an increasing trend from 0 h to 6 h, and then decreased from 6 h to 12 h, while the ratio of chlorophyll a and b of NA showed a decreasing trend under cold stress.5. Vitamin C content in the shoot of NN rose at first and then decreased. Vitamin C in the root of NN fell and then declined and increased at last. The Vitamin C content in shoot and root of NA rose at first and then decreased. At the beginning of cold stress, the Vitamin C content in NA was lower than NN. But in long low-temperature stress, the opposite trend appeared. There was significant difference between the root of NA and NN during the whole cold stress except for 2 h and 4h(P<0.05).6. The glutathione contents in the shoot and root of NN reduced at low-temperature stress. The glutathione contents in shoot of NN rose and then decreased; the trend in the root of NA declined and then increased and declined at last. The glutathione contents in the shoot of NA was lower than that in NA from 0h to 6h, but during the time of 6h to12 h low-temperature stress, the glutathione content in the shoot of NA was higher than that without nodules. The glutathione content in the root of NA was higher than that NN and there was significant difference between root of NA and NN during the process of cold tolerance except for 2 h and 4h.7. The contents of H2O2 in NN decreased first and then increased. H2O2 in shoots of NA fluctuated along with the cold stress. H2O2 in roots of NA decreased first and then increased. However, the contents of H2O2 in NA were higher than NN in the later stage.8. The content of O2- in the shoot of NN declined and then rose. O2- contents in shoot and rood of NA declined and then increased and declined at last. The content of O2- rose and then decreased and increased at last in the root of NN. After exposed to cold stress for a long time, NA showed lower O2- content than that in NN.These results indicated that NA showed a stronger antioxidant capacity, osmotic adjustment ability and level of photosynthesis. Furthermore, nodule could alleviate the low-temperature damage to alfalfa,thus enhanced the cold tolerance of alfalfa.