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Effects of Low Temperature on Mesophyll Cell Ultrastructure of Osmanthus fragrans ‘Zhangyuan Hong’
You Yang1,2, Wang Xianrong1*, Zhang Xiaoyun2
1College of Biology and Environment, Nanjing Forestry University, Nanjing 210037, China; 2School of Horticulture Landscape Architecture, Henan Institute of Science and Technology, Xinxiang 453003, China
Abstract: To investigate the ultrastructural changes in the mesophyll cells of Osmanthus fragrans， which was introduced from southern to northern China， and to investigate the diversified regulation of cytological structures under low-temperature stress， 3-year-old trees of O. fragrans ‘Zhuangyuan Hong’ were exposed to a series of low temperatures. After sample preparation and sectioning， the ultrastructural changes in mesophyll cells of mature leaves were observed by transmission electron microscopy. The ultrastructure of every organelle was normal at the normal outside temperature (20~25 °C). At 5 °C， chloroplasts underwent a slight swelling， while mitochondrial structures were normal. At 0 °C， the osmiophilic granules in chloroplasts increased， chloroplast swelled， and the total number of mitochondria increased， while the starches appeared annulated between bright and dark interphase. At −10 °C， the organelles collapsed and degraded. Therefore， the chloroplasts of different cells exposed to low temperature showed different degrees of sensitivity to low-temperature. These resusts provided cytological basis for the recovery and growth of the plants. The stabilization of chloroplasts， mitochondria and nuclei in the mesophyll cells can be used as important reference indices for the response of O. fragrans to low temperature.
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