The present experiment was conducted to study the physiological and biochemical parameters related to low-temperature resistance in the leaves of two longan cultivars,viz.,Shixia and Chuliang.The plants were treated with 10,6,3 and 0℃.The results showed that,compared with the normal temperature 25℃(control),the activities of SOD in longan seedlings with low-temperature treatments increased initially,then decreased followed by an increase at last,while a reverse trend was observed in case of POD activity.The content of MDA in longan seedlings with low-temperature treatments decreased initially and then increased,and relative conductivity and soluble protein content increased slightly and then decreased with decreasing temperatures.Soluble sugar content did not vary much.It was concluded that the cold resistance of variety Chuliang was higher than that of variety Shixia,which showed consistent with external injuries of two varieties’ leaves under low-temperature stress.

[Objective] The research aimed to study the prevention of pollution and browning in tissue culture of Myrica rubra Sieb et Zucc..[Method] Taking the stem segment of Dongkui Myrica rubra Sieb et Zucc.species as the in vitro material,the effects of different disinfection and sterilization,different stem parts,different prevent browning measures to external plants in vitro culture were studied.[Result] The results showed that the sterilizing effect of 75 % alcohol 1 min + 0.1% HgCl2 7 min on the external implant was the best,and the pollution rate was 30.00%,browning and withered rate was 30.00%,stem induction success rate was 40.00%.In the three parts stems,the semi-lignified stem segments was the best,contamination rate was 30.00%,browning and withered rate was 33.33%,success rate was 36.67%.Adding the activated carbon 1.5 g/L + polyvinylpyrrolidone(PVP)2.5 g/L in the medium had the best effect to the external plant anti-browning,and the browning rate from control 60.93% dropped to 21.88%.[Conclusion] The study can lay good basis for extending of good Myrica rubra Sieb et Zucc.species and establishing its effective genetic transformation system.