Effect of Low Temperature Stress on Ultrastructure of Mesophyll Cells in Cotton Seedling Stage

The ultrastructural changes of mesophyll cell in six cotton varieties,including two early-maturing varietiesZhong 50 ,two medium-maturing varieties N177 and N181 ,and two late-maturing varietiesN203andK-1,were observed under 4 ℃ low temperature stress for 3 days. The results showed that various organelles of six cotton varieties maintained morphological integrity before low temperature stress. After 3 days of 4℃ stress,the chloroplast of four varieties(N177,N181,N203 and K-1) began deformed and thylakoids were blurred. The ambiguous membrane was observed in the mitochondria and lost integrity. Much of karyotheca disappeared,chromatin condensed,osmiophilic particles increased,and the starch granule became much more and bigger. After 3 days of 4℃stress,the chloroplast and mitochondria of the early-maturing varieties(Zhong 50 and N52) were morphologically integrated. The above results indicated that Zhong50 and N52 have anatomic adaptation to the low temperature stress.