Study On The Mechanism Of Calcium-calmodulin Signaling Pathway Involved In Potassium Uptake In Tobacco Seedlings Under Low Potassium Stress

Potassium is one of the most demanded nutrients for plants growth,it can directly participate in a variety of physiological and biochemical reactions,and is also a recognized quality element for tobacco.However,the potassium content of tobacco leaves in China is seriously affected by potassium deficiency and low utilization efficiency of potassium fertilizer are conmom in tobacco planting soil.Therefore it is important to study the key factors regulating potassium uptake in tobacco plants under low potassium stress.Numerous studies have shown that calcium signaling is one of the main factors in signal transduction under low potassium stress in plants,and it is also an important substance that affects the translocation of potassium uptake in plant root system.Calmodulin（Ca M）is an important calcium sensor that binds calcium ionsto form a Ca²⁺-Ca M complex,which is involved in biotic and abiotic stresses by regulating the activity of downstream target proteins.In this study,indoor hydroponic experiment was conducted with tobacco variety K326 as the test materia.The main research was :（1）The effects of different calcium ion concentrations on the growth and development of tobacco seedlings and potassium uptake under low potassium stress.（2）Effects of calcium signaling inhibitors on photosynthetic characteristics and potassium uptake in tobacco seedlings under low potassium stress.（3）Effects of calmodulin antagonists on the physiological characteristics and potassium uptake of tobacco seedlings under low potassium stress.The main results are as follows:1.The growth and potassium uptake in low potasium seedlings were significantly affected by different calcium concentration.The fresh weight and dry weight of shoot and root,soluble protein content of leaf and root,root activity,antioxidant enzyme activity and potassium content of all parts treated with normal potassium were significantly higher than those treated with low potassium level,regardless of the calcium ion concentration.With increasing calcium ion concentration at the same potassium level,the changes of dry and fresh weight,physiological characteristics and potassium content in different parts of the tobacco plant were firstely increased and then decresed.The growth condition,physiological characteristics of root and leaves and potassium content of the low-potassium plants reached a peak when calcium ion concentration was 5 mmol/L,and the root potassium content of the tobacco plants was significantly higher compared to the other treatments,with the maximum value of 7.323 mg/g.Lower calcium ion concentrations in hydroponic solution can promote plant growth and development and potassium absorption,and the inhibitory effect is produced at higher concentrations.The relationship between calcium and potassiumwas antagonistic.when the calcium concentration in the hydroponic solution was 5 mmol/L,it was most favorable for tobacco growth and development and theabsorption and accumulation of potassium.2.Effects of low potassium stress on photosynthetic characteristics and potassium uptake in tobacco seedlings were aggravated by calcium signaling inhibitors.Under low K stress,the relative conductivity of leaves and the accumulation of reactive oxygen species in tobacco plants treated with calcium channel inhibitors or chelators increased significantly,and the expression of antioxidant enzymes and antioxidant enzyme-related genes,chlorophyll content,NADPase content in root,calcium ion content in root and leaf,root calmodulin content decreased significantly,and photosynthetic characteristics（except water vapor pressure saturation deficit）decreased significantly.Under low potassium stress,potassium content inshoot and root of tobacco plants treated with calcium channel inhibitors or chelators was significantly lower than that of control,and the average decrease range was 25.54% and 53.36%,respectively.The relative expression levels of potassium channel genes NKT2,Nt KC1 and transporter protein genes Nt HAK1 and Nt HAK5 decreased by an average of 60.60%,50.62%,38.61% and 69.79%,respectively,in the low-potassium roots,and the relative expression levels of calcium channel-related genes NtCNGC3 and NtCNGC10 in the roots decreased by an average of 85.26%and 87.38%.Under low K stress,the three calcium-inhibiting treatments inhibited the expression of genes related to potassium uptake in roots and potassium uptake in tobacco plants by reducing soluble protein content,root activity,antioxidant enzyme activity and relative expression of related genes and inhibiting chlorophyll synthesis photosynthesis of tobacco plants.3.Calmodulin antagonists also intensified the effects of low k stress on physiological characteristics and potassium uptake of tobacco seedlings..At low potassium level,six indexes of potassium content,antioxidant enzyme activity,chlorophyll content and photosynthetic characteristics（except water vapor pressure saturation deficit）in all parts of the plant were significantly decreased after exogenous calmodulin antagonist was applied.Under low potassium stress,the calmodulin content of leaves,potassium content of all plant parts,expression of root potassium uptake related genes,total chlorophyll content and photosynthetic characteristics（except water vapor pressure saturation deficit）,and leaf calmodulin content were significantly decreased in the calmodulin antagonist treatment compared to those without calmodulin antagonist.The potassium content in shoot and root decreased by 23.69% and 60.00% on average.The relative expression levels of NKT2,Nt KC1,Nt HAK1,Nt HAK5,NtCNGC3,and NtCNGC10 genes in roots deceeased by 82.84%,94.18%,52.44%,86.55%,64.29%,and 48.88% on average.Addition of calmodulin antagonists under low K stress could inhibit calmodulin content,hinder the formation of Ca²⁺-Ca M complex,affect signal transduction and ultimatelylead to the decrease of antioxidant enzyme activity and photosynthesis in leaves,the decrease of genes expression of K⁺ uptake related in the roots,and inhibit K⁺ uptake and accumulation in plants.