Abstract: 【Objective】 The content dynamics of three types of osmoregulation substances in fresh leaves of two cultivars of tea plants and their correlations with air temperatures during winter and early spring were investigated, to evaluate the differences in their responsiveness to the low temperature between the two tea cultivars. 【Method】 Two early bud tea cultivars, ‘Pingyangtezao’ and ‘Zhongcha 102’, were chosen, and air temperatures around their tea shoots were recorded every day from Oct. 21 to April 5 for two consecutive years. The temperature of the dry and wet bulb thermometer at 8:00, 14:00 and 20:00 was daily recorded, and the average of the three dry bulb thermometers set in the experimental tea plantations three times per day standard for the temperature of tea shoot habitat. During these two testing periods adult tea leaves of each cultivar were sampled on the fifth, fifteenth and twenty-fifth days of each month. The soluble sugar contents in the tea fresh leaves were measured by anthrone colorimetric method, the remaining clean fresh leaves were processed into the steamed green tea samples, whereas the contents of proline and free amino acids were determined by SDE-HPLC method. 【Result】The test phase was divided into two stages, the overwintering period (2013/10/21-2014/3/52014/10/21-2015/3/5) and early spring period (2014/3/6-2014/4/52015/3/6-2015/4/5) according to the developmental threshold temperature and the dormancy temperature of the tea plant. Accompanied with initial gradual drops and then maintaining at low air temperatures during the two winters (2013/10/21-2014/3/5, 2014/10/21-2015/3/5), the soluble sugar contents in fresh tea leaves of the two cultivars increased continuingly, negatively correlated with the 10-day average air temperatures. The proline contents increased first and then kept at a high level, also negatively correlated with the 10-day average air temperatures. The free amino acid contents dropped first and then stayed at a low level, which was positively correlated with the 10-day average air temperatures. When the temperature appeared the lowest value, the content of soluble sugars and the content of proline also correspondingly appeared the highest values subsequently, then the content of free amino acids also correspondingly appeared the lowest value. When the temperature was the highest value, the content of soluble sugar and the content of proline also correspondingly appeared the lowest value later, the content of the free amino acids also correspondingly appeared the highest value soon afterwards. During the two spring seasons (2014/3/6-2014/4/5, 2015/3/6-2015/4/5), as air temperatures increased gradually, the soluble sugar contents decreased, while the proline and the free amino acid contents appeared to increase. The frost-resistance of tea plant closely related with air temperature, and soluble sugar, the contents of proline and free amino acids in tea leaves closely related with the frost-resistance of tea plants. During the two winter seasons, compared with ‘Zhongcha 102’, when suffered from the low temperature stress in winter, the content of each of three kinds of osmoregulation substances of ‘pingyangtezao’ more sensitively response to low temperature than ‘Zhongcha 102’, and the contents of the three kinds of substances in cultivar ‘pingyangtezao’ were slightly high. 【Conclusion】 Tea plants are vulnerable to frost, freeze and the late spring coldness from late autumn to Qingming Festival. As important cold-resisting indices of tea plants, the contents of soluble sugars, proline and the free amino acids varied sensitively in responses to the low temperatures, and showed significant correlations with the 10-day average air temperatures during the winter and early spring seasons. The responsiveness of cultivar ‘Pingyangtezao’ to the low temperatures was greater than that of cultivar ‘Zhongcha 102’.

Key words: low temperature, Camellia sinensis L., cold damage, soluble sugar, proline, free amino acids