Comparative study of vegetative and reproductive growth of different tea varieties response to different fluoride...

The amount of fluoride accumulation in tea leaves was gradually increase as the matures of tea plants, and the excessive fluoride intake can threaten people's health. Based on years of field investigations, a low level of fluoride variety Xiangbo Lǜ (XBL) and a high level of fluoride variety Zhenong 139 (ZN139) were selected.

In this study, the root, 1st and the 5th leaf of the two-year-old tea trees were used for morphological, physiological and comparative transcriptomics analysis to understand the different features of "XBL" and "ZN139" under fluoride stress conditions. The color of the 1st and 5th leaves of XBL were yellower, the activity of peroxidase, catalase and antioxidant enzyme were lower than ZN139 under the high-fluoride stress. Transcriptomics analysis indicated that core genes involved in photosynthesis rates regulation showed no significantly exchanged expression, the co-downregulation of magnesium ions transportation, while the ROS scavenging, vegetative growth and self-compatibility between the two varieties were different. Crucial genes' expression were also identified by the real-time RT-PCR.

The tea tree is one of the few plants that has a high-fluoride content, but the different varieties respond differently to fluoride stress. High-fluoride tea tree varieties, such as ZN139, have stronger ROS scavenging abilities through the use of both their non-enzymatic and enzymatic antioxidant systems which act by increasing the expression levels of inositol-1-monophosphatases and peroxidases, among others. ZN139 can also compensate for the decrease in photosynthetic rate that is associated with the ionic imbalance caused by the reduced consumption of light energy during long-periods of high fluoride stress. Reproductive development was protected in ZN139 by the up-regulated expression of S-locus glycoprotein, Mildew resistance locus o and Phospholipase D under fluoride stress, while the vegetative development of low-fluoride varieties such as XBL was retarded. More starch and cellulose were redistributed to glucose by increasing the expression levels of glycosyl transferases and hydrolases to provide more energy for processes involved in the response and tolerance towards fluoride stress.