Changes in cell ultra-structure, membrane permeability and protective enzyme activity in Eriobotrya japonica Lindl. leaves under cold stress

Using a pot cultured Eriobotrya japonica Lindl. grafted in “Jiefangzhong” as an experimental material, changes in E. japonica leaf cell ultra-structure, membrane permeability and protective enzyme activity were determined. The results show that under controlled temperature of 7 ℃ and 2 ℃, most leaf cell organelles of E. japonica are not injured and orderly arrange. PMP and MDA content initially raises and then falls, so also is the protective enzyme activity. This suggests that E. japonica can adapt to chilling temperatures of 7 ℃ and 2 ℃. Under -2 ℃, leaf cell chloroplasts are destroyed. Thylakoid is not packed to its normal grana and therefore fails to form typical structures. Though the mitochondrion membrane structure can still be visible, its cristae number drops. Because of increasing content of PMP and MDA, protective enzyme activity is inhibited. Hence the leaf of E. japonica suffers severe frostbite. Under a temperature stress of -7 ℃, plasma membranes break up and protoplasts become greatly concentrated. In fact chloroplasts entirely decompose. Grana lamellace twists, disfigures and even fuses. Mitochondrion membrane system is completely destroyed and cristae can not be found. PMP and MDA content raises drastically, hence protective enzyme activity is greatly inhibited. The vegetation growth of E. japonica are badly distorted. In summary,E. japonica leaf severely freezes when temperatures fall below zero, which inhibits the vegetation growth of the plant.