Influences of CaCl_2 Pre-spray on Ecophysiology of Nicotiana tabacum L.Seedlings Under Chilling Stress

Temperature is one of the important factors which affect the growth,development,yield and quality of flue-cured tobacco.In southern tobacco-cultivating area of China,lower temperature weather frequerntly occurs in early spring,which limits the culture of healthy and vigorous tobacco seedlings.In an experiment reported in this paper,the young seedlings of tobacco varieties YunYan87(YY87) and Msk326 were pre-sprayed with CaCl2solutions at 0.5%,1.0%,1.5% and 2.0% before exposing them to 8 ℃ and 25 ℃ for 72 h,and then photosynthetic indexes,antioxidant enzyme activities and contents of soluble sugars,free proline and malondialdehyde(MDA)were measured so as to study the ecophysiological adaptation of the seedlings under chilling stress.The results showed that net photosynthesis(Pn),conductance(Gs),transpiration rate(Tr),activities of catalase(CAT)and peroxidase(POD) and soluble sugar contents for YY87 and K326 seedlings under chilling stress were reduced significantly compared with normal temperature(25 ℃) control seedlings,but intercellular CO2 concentration(Ci) showed no significant difference for YY87 under chilling stress.Pre-spraying CaCl2 solutions helped to alleviate the chilling damage to a certain extent,and a CaCl2 concentration of 1.0% effectively increased CAT and POD activities,enhanced the contents of soluble sugars and free proline and decreased malondialdehyde(MDA) content of of the seedlings under chilling stress,thus improving cold resistance of flue-cured tobacco seedlings and maintaining their normal photosynthetic metabolism.