The Expression Analysis On Ca²⁺ Transport And Response Genes Under Calcium Deficiency Condition In Different Resistance Plants

Chinese cabbage（Brassica rapaL.ssp.pekinensis）,originating from China,is one of the largestvegetablecrops in China,and has graduallybecome a worldwidevegetable crop.According to the statistics of ministry of agriculture.Chinese cabbage production area is about 2.67 million hectares,account for about 15%of the total vegetables in China.It is important in vegetable supply and increasing farmers’income in our country.However,tipburn has recently become one of the most irreversible diseases that causing large economic losses in Chinese cabbage cultivation.The disease has spreaded all over the country and the incidence of tipburn increase higher and higher year by year.Therefore,breeding varieties with tipburn resistance has become one of the main objectives in Chinese cabbage breeding.The causes of tipburn are a bit of complex and controversial,however,the most accepted factor is a lack of available(Ca²⁺),which is not only an essential nutrient,but an important intracellular second messenger in signal transduction events.In the study,to further study the role of Ca²⁺ in tipburn resistance,expressions of Ca²⁺transporter genes,ECAndACA,and Ca²⁺ response gene.CAS,under tipburn-inducing artificial and natural conditions were studied.The main results are as follows:①Plants were planted in modified Hoagland solution which contained different grades of Ca²⁺ concentration.The results showed that the incidence and the severity of tipburn decreased with the increase of the Ca²⁺ concentration.The negative correlation b etween the Ca²⁺ concentration and the tipburn symptoms suggested that the lack of Ca²⁺ should be an important incentive to induce the disease.② To further study the correlation between Ca²⁺ and tipburn,total Ca²⁺concentrationin leaves of 100 DH lineswere measured under disease-inflammatory conditions.However,the DI of tipburn and total Ca²⁺ concentration in leaves were completely not correlated with each other（correlation coefficient（r）=0.06,P<0.0001）.These results suggested that the absolute amount of Ca²⁺ in leaves was not the mainfactor that caused the happening of tipburn,and Ca²⁺ should play the role in cytological and cellular level.③ A total of 7 ECA and 4 CAS genes were identifid in Chinese cabbage by protein sequence alignment.The expression of ECA and CAS genes was detected in tipburn-susceptive and resistant lines after Ca²⁺ deficiency treatment.The results showed that ECA genes were up-regulated in both lines,and expressed at a higher level in resistant plant than in sensitive plant.However,the expression pattern ofdifferent CAS genes was not consistent,which might be caused by functional division of different CAS genes.Our study suggested theexpression of ECA and CAS was affected by calcium deficiency,and associated with tipburn occurrence inseedlings ofChinese cabbage,which provided helpful information for further study the molecular mechanism oftipburn resistance in Chinese cabbage.④ Expressions of the genes mentioned above were further proved in 3 Chinese cabbage inbred lines with different tipburn resistance under natural conditions.And in addition,the lower transcriptional level of ECA、ACAand CAS in inner leaves suggested thatthe expression of calcium transport genes and CASin new developing tissues is important for plant tipburn resistance.