Repression Of Browing During Tissue Culture Of Phalaenopsis By Heat Shock Treatment

Phalaenopsis sp. is one of the most popular and widely cultivated orchid genus in the horticultural industry with a high additional values. Phalaenopsis is a monopodial epiphytic orchid, which is difficult to propagate vegetatively. Tissue culture has been desired for mass propagation of Phalaenopsis. However, explant browning occurred during micropropagation process is a vital problem conditioned mass production, which could put to death of explant severely. Many measures had been applied to solve this problem, but they were restricted in quantity production due to inefficiency of repressing browning, low differentiative rate and increased production cost caused by complication on operation. Thus, it is necessary to find a new method for mass production.More recently, it had been shown that heat shock treatment remarkably inhibit the progress of the browning by different researchers, but there were no reports on control browning in Phalaenopsis by heat shock treatment several authors. The objective of this study is to find a convenient new way to repress explant browing safely and effectively during tissue culture of Phalaenopsis by heat shock treatment.We analysed the browning of explant from Phalaenopsis during tissue culture, and the effect of heat shock treatment on browning index, total phenolic content, PAL, PPO and POD activaty of explant. This study was to investigate the optimum condition for repressing browning by heat shock treatment, including temperature, lasting time and restoration time of heat shock treatment during the tissue culture of Phalaenopsis. Furthermore, we studied the effect of heat shock treatment on explant browning in different color species of Phalaenopsis.It was shown that the explant browning of Phalaenopsis was repressed significantly after heat shock treatment at 45℃for 6min and restoration for 48h. Compared with the day when inoculation, browning index after heat-shock treatment decreased by 4 fold at 15 days'culture under above condition of heat shock treatment. And the increment of total phenolic content at 9th days after heat-shock treatment decreased by 3 fold than that at same days of non-heat shock treatment explant. The activity of the enzymes related to explant browning decreased after heat shock treatment significantly. PAL activity in control rose by 5 fold while only 2 fold less activity rising in the explant after heat shock treatment at 9th days after inoculation. After 3 days'culture, POD activity in explant of control rose 3 fold compared with the initial value when inoculation, but there was no any noticeable changes in that after heat shock treatment. Even though not significant as in POD activity, PPO activity decreased obviously compared with the control. It is suggested that explant browning of Phalaenopsis (B3) could be repressed effectively and the rise of total phenolic content, the activity of PAL, PPO and POD during tissue culture decreased after heat shock treatment.It was also shown that browning index correlated with the increment of total phenolic content, but not that of the inherent total phenolic content according the results from 20 species with different colours. In other words, the bigger the total phenolic content increases, the bigger the browning index is.The obvious decrease of total phenolic content and the activities of PAL, PPO, POD in explant from 15 and B3 species of Phalaenopsis with much more serious browning while explant culture than F5 species, led to repression of the browning in explant after heat shock treatment. It suggested a potential and extensive value of application on repressing browning of the species with more serious browning by heat shock treatment.Till now, no evidence about heat shock treatment applied on repression browning of Phalaenopsis has ever been reported. We wish this study could lead us to a new pathway to repress browning of explant during tissue culture. The objective of this study is to promote the study on finding a way to control browning safely and effectively, which is practically significant on mass production of high quality seedling of Phalaenopsis.