Study Of Mechanism And Effect Of Cold Acclimation On The Leaves Nitrogen Allocation In Chorispora Bungeana And Arabidopsis Thaliana

Nitrogen is the necessary macroelement for the growth and development of the plants.The nitrogen in leaves mainly exists in the form of protein,free amino acid,NO^3-and NH⁴⁺etc.The plant will control the photosynthesis process through changing distribution patterns of the various kind of nitrogen in leaves,so,the leaves at different positions and with different functions may have different nitrogen distribution patterns.Cold acclimation will affect the leaf nitrogen distribution.However,there were few studies on the laws of the nitrogen distribution in various leaf positions.Consequently,It‘s significant to study the nitrogen distribution in the different leaf positions,in particular,the relationship between distribution law and the response to the low temperature stress under stress.Taking the new leaves?A leaf position?,mature leaves?B leaf position?and old leaves?C leaf position?of the Arabidopsis and Chorispora bungeana as materials and combining with molecular biology and Plant physiology,this paper studied the nitrogen distribution laws of different leaf positions,regulation mechanism and the stress response changes such as the frost-resistance and explored the relationship between the development and growth of the plant and the resistance cost balance.The main results are as follows:1.The total nitrogen content in Chorispora bungeana under normal temperature showed A=C>B while the pattern of A>B=C appeared under low temperature.Cold acclimation reduced the total nitrogen content in C leaf position.The pattern of A?B>C remained the same under both normal and low temperature.Cold acclimation reduced the total nitrogen content in both the A and B leaf positions.However,there was no significant change in the total nitrogen content tendency of both plants.2.There was a decrease tendency in the protein content from A to B to C under both the normal and low temperatures.Cold acclimation increased the protein content in A and C leaf positions of the Chorispora bungeana and decreased the protein content in A leaf position of Arabidopsis.After the cold acclimation,the chlorophyll content in B leaf position of the Chorispora bungeana increased significantly while those in A and C leaf positions of the Arabidopsis had some decrease.The amino acid content was stable in Chorispora bungeana under normal and low temperature.However,the cold acclimation significantly increased the proline content in A and B leaf positions of the Arabidopsis with an 18-fold change.Moreover,the total free amino acid content in Chorispora bungeana was much higher than that in Arabidopsis.3.There was no difference in nitrate and nitrite contents in A,B,C leaf positions of the Chorispora bungeana under normal temperature.The largest content was in A while the least was in C under low temperature.The contents both in B and C leaf positions decreased significantly after cold acclimation.The pattern of the nitrate content in Arabidopsis was C>B>A under normal temperature.And the content in A was very little.Under low temperature,the pattern turned to B>C>A.The cold acclimation significantly increased the nitrate contents in all three leaf positions.The nitrite content was consistent in A,B,C leaf positions under normal temperature while the pattern turned to B>A>C under low temperature.Cold acclimation increased nitrate contents both in A and B leaf positions.In conclusion,cold acclimation have no significant effect on the total nitrogen tendency in both plants but have significant effect on the various forms of nitrogen distributed to different leaf positions.4.In the mRNA level,corresponding to the decreased nitrate and nitrite contents,the NR,NiR expression of the Chorispora bungeana increased after cold acclimation.However,though the NiR and nitrite content had similar ascendant tendency,the NR had no change in Arabidopsis after cold acclimation.This indicated the NR and NiR expressions were not the main factors that caused the changes of the nitrate and nitrite contents.5.The NR and NiR specific activity corresponded to the decreased nitrate and nitrite contents in Chorispora bungeana and increased content in Arabidopsis,which was not completely consistent with the expression amount and showed there was indeed a complex regulation process between mRNA expression and enzymatic activity.Moreover,combining the NRT1.1,NRT1.7 expressions and nitrate content of the plant under normal temperature,we could gain the above result of A=B>C as to nitrate content in Chorispora bungeana under low temperature.Similarly,the above result of B>C>A as to nitrate content in Arabidopsis under low temperature also could be achieved.6.Cold acclimation increased the conductivity in the C leaf position of Chorispora bungeana,making it higher than that under normal temperature,which indicated the C leaf position suffered more from the low temperature and the cells were most severely damaged,reflecting the low frost-resistance.However,there was no significant difference in the conductivity of all leaf postitions under normal and low temperature,indicating the frost-resistances of A,B,C leaf positions were matched.The result of amino acid also suggested the proline contents in all leaf positions of Chorispora bungeana did not have significant change.The conductivity in A leaf position of the Arabidopsis was lowest at-10?under both normal and low temperature.Lower conductivity in A leaf position appeared after cold acclimation,showing extremely significant frost-resistance compared with B and C leaf positions.The result of amino acid also showed there was an 18-fold increase in the proline content of the Arabidopsis after cold acclimation.However,the overall conductivity of Chorispora bungeana is significantly smaller than Arabidopsis,and the overall content of proline is much higher than Arabidopsis,which also indicates that Chorispora bungeana has a very high resistance to low temperature stress in the Arabidopsis.In addition,at ambient temperature and low temperature,the water content of each leaf position of the Chorispora bungeana is more balanced.Only the C leaf bit is higher than a at room temperature.Arabidopsis at normal temperature and low temperature are A?B=C leaf position,it may be indicated that Arabidopsis under duress will accumulate more dry matter in the newborn leaves.The reactive oxygen staining also showed that the color of the leaf of A,B and C in the Chorispora bungeana at ambient temperature and low temperature was gradually deeper,cold acclimation did not make a significant change,but the Arabidopsis at room temperature A,C slightly deep,low temperature c slightly deeper,cold acclimation makes A leaf position is significantly lighter,indicating that superoxide anion at low temperature significantly decreased,may help plants to resist low temperature stress.This study clarified that there was no significant difference in the total nitrogen trend of the two plants after cold acclimation,but the distribution of nitrogen in different leaf position was changed under the regulation of NR,Nir and NRT.After cold acclimation,there was no change in the leaf position protein content and proline,but the content of leaf protein in Arabidopsis decreased rapidly and proline doubled.The change of the above nitrogen distribution may be caused by cold acclimation of Chorispora bungeana leaf position antifreeze balance,the reason of the high frost resistance of Arabidopsis A is that the Chorispora bungeana is more inclined to take care of all the leaves and the Arabidopsis leaves are preferentially protected under low temperature stress.The experiment also provides basis for the physiological and ecological mechanism of alpine ice and model plants adapting to adversity.