Effect Of Selenium-Zinc Interaction On The Subcellular Distribution Of Selenium, Zinc And The Change Of Polyphenol Oxidase Activity In Tea Leaves

Tea is a healthy drink and it is rich in zinc, selenium and other trace elements. Developing the tea of "Se-rich and zinc-rich" which contains two mineral nutrition about selenium and zinc is conducive to complement Se, Zn safely and efficiently, and keeping human health. The distribution about selenium and zinc in the tea, especially their distribution in the subcellular not only impact on immersion in the process of tea production directly, but also influenced by the growth and development of tea. The enzymes of Polyphenol oxidase (PPO) is the body's physiological activity of tea, and it plays an important role during the metabolic process in tea .The activity of PPO is closely related to the distribution of selenium and zinc in tea leaves.The status quo about selenium, zinc and their interaction on changes in PPO activity, and the distribution of selenium and zinc in subcellular are not reported. This study through spraying selenium, zinc, and reached the distribution of Se, Zn and the change of PPO activity in tea with different concentration of selenium, zinc and their ratio, as well as different seasons and under different plucking time. The main findings are as follows:(1) The PPO activity of tea leaves was highest in spring, and the summer was lower than spring, but in the autumn the PPO activity was minimum. The PPO activity of tea leaves in spring, summer and autumn was higher when spraying apply Se at 100～200μg/mL and Zn was 0.4%～0.8% compared to other treatments after 8, 16, 24days of spraying. Applying high-concentration of Se (>400μg/mL) or Zn(>1.2%) alone did not significantly improve PPO activity after different plucking time. Combined applying middle-concentration of Se (100～200μg/mL) and Zn (0.4%～0.8%) increased PPO activity after 8, 16, 24days of spraying, but combine applying high-concentration of Se and Zn (08%～1.2%) had no significant effects on PPO activity. The PPO activity was increased with the picking time in different concentration of Se, Zn or Se-Zn interaction and higher PPO activity was observed at 16 day.(2) The Se content in different subcellular component of tea leaves was highest in spring, and the Se content was higher in summer than autumn.The cumulative effect of Se was significantly at 200～400μg/mL of Se in the cell wall (F₁),cell membrane and organelles(F₂), soluble section(F₃) in tea leaves of spring, summer and autumn. The Se content of F₂ in spring tea leaves was higher than F₁, and the content of F₁ was higher than F3 after 8 days of spraying. After 16 days of spraying and 24d, the rule about distribution of Se showed that F₁>F₂>F₃, but the Se absolute content in F₃ remains increased with the spraying of the concentration increasing, which indicates that was used for constructing cell membrane and organelles in the initial period after spraying, and the Se in cell wall (F₁)transfer to the soluble section (F₃) gradually with time expanding. The rule about distribution of Se in different plucking time in summer and autumn showed characteristic as below: F₁>F₂>F₃. The Se content in different subcellular component was lower than overall content levels, also its content was reduced with the Zn concentration increasing, but the content was higher than the control. The trend about distribution of Se in different subcellular component of spring, summer, autumn showed characteristic as below:F₁ >F₂>F₃ at the Zn (0.2～0.4%), and the distribution characteristics was resembled ultimately with the concentration treatment in different plucking time. The Se content in different subcellular component of different seasons was reduced gradually with the plucking time extending. The time effect on Se content has good effect when spraying apply Se at 200～400μg/mL and Zn was 0.2%～0.4% after spraying 8 days and 16 days. Combined applying concentration of Se (100～400μg/mL) and Zn (0.4%～0.8%) increased the Se content in different subcellular component of different seasons after 8,16 ,24days of spraying, but combine applying high-concentration of Zn and different Se concentrations had no significant effects on the Se accumulation.And the distribution of Se trend was similary with the Se alone.The Se content in different seasons presented different lowered range in different plucking time as the same concentration, and especially that the Se content was higher relatively after 8,16 days of spraying.(3) The Zn content in different subcellular component of tea leaves was highest in spring, and the Zn content was higher in summer than autumn similar with Se. The Zn content in different subcellular component of tea leaves in spring, summer, autumn increased with the spraying of the Zn concentration increasing, but the increase amplitude was reduced. When spraying apply Zn at 0.8%～1.2%, the Zn content was higher relatively. The rule about distribution of Zn after spraying 8,16days in spring and summer showed characteristic as below:F₃>F₁>F₂. However, the distribution of Zn after spraying 24 days showed this trend: F₁ >F₃>F₂.These result indicated that the Zn in the soluble section (F3) transfer to cell wall (F₁) gradually in later stage after spraying, and Maybe Zn involved in plant defense response, intercellular signaling and identification of reaction, also it played an important role in the absorption of nutrient, exchange, fixed and so on. The rule about distribution of Zn after different plucking time in autumn showed trend as below: F₁>F₃>F₂, but the distribution proportion of F₁ was decreased with the concentration of Zn increasing which indicated the accumulation of Zn has been transfered as the concentration of Zn increasing, and Zn was cumulatived in F₃ gradually. The Zn content in different subcellular component after different plucking time was lower than overall content levels, also its content was reduced with the Se concentration increasing, but the content was higher than the control which showed that the accumulation of Zn has not significantly effect at high-concentration Se. The Zn content in different subcellular component of different seasons was reduced gradually with the plucking time extending. The time effect on Zn content has good effect when spraying apply Se at 50～100μg/mL and Zn was 0.8%～1.2% after spraying 8 days and 16 days. Combined applying concentration of Zn (0.4%～1.2%) and Se (100～200μg/mL) increased the Zn content in different subcellular component of spring, summer, autumn after 8,16 ,24days of spraying, but combine applying high-concentration of Se and different Zn concentrations had no significant effects on the Zn accumulation. And the distribution of Zn trend was similary with the Zn alone. The Zn content in different seasons presented different lowered range in different plucking time as the same concentration, and especially that the Zn content was higher relatively at combined applying concentration of Zn (0.4%～1.2%) and Se (100～200μg/mL) after 8,16 days of spraying.