Effect of NaCl stress on physiological characteristics in leaf and cell nuclear morphology in root-tip of Raphanus sativus seedlings

The chlorophyll content,net photosynthetic rate,MDA content and relative electric conductivity in leaf of Raphanus sativus L.seedlings treated by 0.00(CK)-0.50 mol·L-1 NaCl for 48 h were determined,and morphological change of cell nuclear in root-tip and recovery state of seedling growth after NaCl stress were observed.The determination results show that chlorophyll content and net photosynthetic rate in leaf treated by 0.05 mol·L-1 NaCl are all higher than those in the control.While,with 0.10-0.50 mol·L-1 NaCl stressed,chlorophyll content and net photosynthetic rate decrease gradually with rising of NaCl concentration and have the significant difference with the control,in which net photosynthetic rate decreases to 0.00 μmol·m-2·s-1 after treated by 0.35-0.50 mol·L-1 NaCl.With rising of NaCl concentration,MDA content and relative electric conductivity appear the trend of rapidly increasing firstly and then gradually decreasing,and all have the significant difference with those of the control.In which,MDA content is the highest after treated by 0.30 mol·L-1 NaCl and relative electric conductivity is the highest after treated by 0.40 mol·L-1 NaCl.The observation result shows that after treated by 0.05-0.25 mol·L-1 NaCl,cell nuclear morphology in root-tip changes from circle to irregular shapes,and chromatin condenses at different degrees,appearing characteristics of programmed cell death(PCD) at different degrees.But treated by 0.30-0.50 mol·L-1 NaCl,there is coexistence phenomenon of empty cells and normal cells in root-tip.After treated by 0.05 and 0.10 mol·L-1 NaCl,the seedlings can resume to normal growth,and seedling height without obvious difference with that of the control.But seedlings after treated by 0.25-0.50 mol·L-1 NaCl can not resume to normal growth and appear to wither and rot phenomenon with rising of NaCl concentration.It is suggested that NaCl treatment with lower concentration not only has no obvious injury but also has a certain promotion impact on growth,physiological metabolism and cell nuclear morphological structure of R.sativus seedlings.While,NaCl treatment with higher concentration can cause irreversible damage to R.sativus seedlings.