Fluoride Uptake By Tea Plant And Effects Of Fluoride On The Metabolism Of Quality-related Component

Tea plants are fluorine-accumulator. In this paper, the fluoride absorption kinetics by tea plants was further studied. Soil experiment was conducted to investigate the impact of fluorine on yield and chemical ingredients related with tea quality of young shoots.1. Kinetics study: modified depletion method was adopted to study the absorption kinetics of fluoride by tea plants. The starting fluoride concentrations in uptake solutions were 5.25, 10.53, 21.05, 31.58, 42.11, 52.63,105.26, 210.53, and 421.10μmol L-1. After uptake of 12, 24, 36, 48, 60, 72 h, an aliquot of 2 ml of uptake solutions was taken for analysis of F concentrations by ion chromatograph and the total and net uptake of F by plants were calculated by depletion method taking into account the water loss by transpiration and evaporation. The results showed that the absorption rate of F increased with the increasing F concentrations in the external solutions. Below 200μmol L-1, the kinetics of fluoride absorption followed Michalis-Menten model. The kinetical parameters Vmax and Km were 0.25μmol g-1 root h-1and 25.3μmol L-1, respecitively (r2 = 0.76). 2. Effects of fluoride on the metabolism of quality-related component. Soil experiment was conducted to investigate the impact of fluoride on yield of young shoots and chemical ingredients related with tea quality. Five-year-old tea plants raised from rooted cuttings in pots filled with 11 kg soil were imposed to different F levels by adding known amounts of fluoride (0, 50, 100, 250, 500, 1000 mg/kg soil, hereafter referred to as F0, F1, F2, F3, F4, F5, respectively) Samples of soil, young shoots of one bud with two leaves and mature leaves were regularly collected and prepared for the analysis of F concentrations and/or quality-related components.2.1 Fluoride concentrations and young shoots yield production. Water-soluble F concentrations in soil and plants increased with amounts of F added to the soil. Yield of young shoots increased slightly at F1 level but decreased significantly at F2 and higher levels as compared to those without F application (F0).2.2. Enzyme activity. The activity of phenylalanine ammonia-lyase (PAL) was increased by F application at F1 levels but decreased by F2 and higher levels. The activity of glutamine-a-ketoglutaric acid transferase (GOGAT) was significantly by the highest application of 2.3 Free amino acids and tea polyphenols. The concentrations of total free amino acid and theanine were increasing from F0 to F3 and then decreased significantly by the highest F application both in the young shoots and mature leaves. Some major components such as glutamate and so on had not a changing-trend with F application,but they all were high in low F content in soil.The total free amino acids and major components(theanine,glutamate et al.)in roots gradually decreased with F increasing The concentrations of total polyphenols, caffeine and catechins (EGCG, etc) in young shoots were reduced by fluoride application. With time, the effects of total free amino acids and tea polyphenols were more obvious.2.4 Carbon, nitrogen contents and the ratio of C/N. Total N of young shoots, mature leaves increased gradually when F amounts increased from F0 to F3 while decreased beyond F3. Total N in stem significantly decreased at F5. Total N of lateral roots decreased by addition of F. Total N in main roots increased in F1 and then significantly decreased in F5.Shoots, mature leaves stem and lateral roots carbon content had not obviously chaged, main roots carnon content increased with F applied. The ratio of C/N in new shoots and mature leaves increased from F0 to F3 and then decreased from F3 to F5,in stem, main roots and lateral roots the ratio of C / N decreased with increasing of Fapplied.2.5 Soluble sugar content. The concentrations of sucrose of main roots, stem and mature leaves incresed at F1 and then deceased when F addition further increased,decreased from F0 to F4 in lateral roots .Glucose and fructose concentrations in mature leaves decreased with increasing F addition in soil.The above results showed that the uptake of F by tea plants followed Michalis-Menten kinetic model within certain range of F concentrations in the uptake solution and can be an active process. The results of soil experiment indicated that, effects of fluoride on the growth and quality of tea related with the content of F applied , although the low concentration of fluoride promote the growth and some components(amino acide et al.)of tea plants,but high concentrations of fluoride inhibited ,and with time the impact of fluoride become more pronounced. Study shows that the impact of fluoride on tea plants through impact photosynthesis and the activity of key enzymes.