Study On The Cold Tolerance Mechanism Of Atriplex Centralasiatica Iljin

Temperature is an important environmental factor that restricts plant growth and development,causes plant biomass decline,and affects its ecological distribution.Due to many external factors such as seasonal changes,most plants often experience cold stress during their growth and development.Most C₄ plants are heat tolerant,yet cold sensitive.Of which Atriplex centralasiatica Iljin is found to be cold tolerant.This paper mainly explored the cold tolerant mechanism in Atriplex centralasiatica by comparing its changes of physiological and biochemical indexes with those of two other cold-sensitive C₄ plants Amaranthus tricolor L.and Zea mays L.under cold stress.The results are as follows:1.The critical chilling temperature for Atriplex centralasiatica,Amaranthus tricolor and Zea mays.Under cold stress,as the temperature continued to decrease,the?PS??ETR?Fv/Fm?PIabs??Eo??Ro of Atriplex centralasiatica,Amaranthus tricolor and Zea mays would decrease accordingly.When the temperature dropped below the critical chilling temperature,the value of?PS?,ETR,Fv/Fm,PIabs,?Eo and?Ro of the plants decreased sharply.The values of?PS??ETR?Fv/Fm?PIabs??Eo??Ro of Atriplex centralasiatica decreased significantly at 1?,-2?and-5?,and those of Amaranthus tricolor and Zea mays decreased significantly at 4?,7?and 10?.According to the experimental results,the critical chilling temperature of Atriplex centralasiatica is about 3?,while that for Amaranthus tricolor and Zea mays is about10?and 14?respectively.Therefore,Atriplex centralasiatica has stronger cold tolerance than Zea mays and Amaranthus tricolor.2.Effects of different temperatures on light response models of Atriplex centralasiatica,Amaranthus tricolor and Zea mays:Light is essential for photosynthesis.The photosynthesis-light response curve can reflect the ability of plants to use light.It is also an important tool for determining the relationship between photosynthetic capacity and environmental factors.The accuracy of the photosynthesis-light response curve model is relatively high.We used non-rectangular hyperbolic model and modified rectangular hyperbolic model to fit the photosynthetic rate with light intensity to get the light response curves of the three plants under cold stress and normal conditions,by this way we obtained key photosynthetic parameters which may reflect the cold tolerant ability of the plants.The results showed that the initial slope of the light response curve???of Atriplex centralasiatica,Amaranthus tricolor and Zea mays decreased at 10°C compared with those grown at 25°C.As compared with Amaranthus tricolor and Zea mays,the initial slope?of Atriplex centralasiatica decreased less significantly,indicating the quantum yield of Atriplex centralasiatica decreased least under cold stress.Furthermore,the maximum net photosynthetic rate?Pmax?and light saturation point of the three plants also decreased under 10?,but Amaranthus tricolor and Zea mays showed drastic decrease compared with that of Atriplex centralasiatica,indicating Atriplex centralasiatica can still use high light intensity and photoinhibition is under control.Moreover,the light compensation point and dark respiration rate of Atriplex centralasiatica,Amaranthus tricolor and Zea mays all increased significantly compared with that at 25?,with Atriplex centralasiatica increased the least of the three.The initial slope of the light response curve of the relative electron transfer rates???of Atriplex centralasiatica,Amaranthus tricolor and Zea mays decreased at 10°C compared to those grown at 25°C,with the initial slope?decreased more dramatically in Amaranthus tricolor and Zea mays.The maximum electron flow?Jmax?of Atriplex centralasiatica,Amaranthus tricolor and Zea mays also dropped down under 10°C,with the former dropped the least of the three.At 10?,the light saturation point of Atriplex centralasiatica,Amaranthus tricolor and Zea mays all decreased,with a similar trend to Jmax.All the results suggested Atriplex centralasiatica still owe high electron yield efficiency and transport rate under high irradiation and low temperature.3.Effects of different temperature treatments on physiological and biochemical indexes of Atriplex centralasiatica,Amaranthus tricolor and Zea mays:The results showed that cold stress has different degrees of inhibiting effects on all the plants.For example,the net photosynthetic rate?Pn?,stomatal conductance?Gs?,transpiration rate?Tr?,maximum photochemical efficiency of PSII?Fv/Fm?and actual photochemical efficiency of PSII??PSII?all decreased in the plants,but compared with Amaranthus tricolor and Zea mays,Atriplex centralasiatica is the least affected.Meanwhile we found that PEP carboxylase activity,pyruvate phosphate dual kinase activity of Amaranthus tricolor and Zea mays all decreased sharply under low temperature,while those of Atriplex centralasiatica kept relatively high,which is in agreement with the high Pn under cold stress.Furthermore,Atriplex centralasiatica showed high AOX respiration rate,high–SH content and high index of unsaturated fatty acids than those in Amaranthus tricolor and Zea mays under low temperature,indicating these biological changes are key to the cold tolerance in Atriplex centralasiatica.On the other hand,SOD activity and MDA content all increased under cold treatment in all plants,but the MDA content and SOD activity is lower in Atriplex centralasiatica,suggesting the membrane is less injured and the degree of membrane peroxidation is relatively lower in Atriplex centralasiatica,while SOD does not play an important role in its cold resistance.