Quality-Related Constituents In Tea[Camellia Sinensis (L.) O. Kuntze]Leaves As Affected By Nitrogen

Tea [Camellia sinensis (L.) O. Kuntze] is an economically important perennial crop species that contains abundant secondary metabolites. Nitrogen (N) is a key element in the life-histories of tea plants. The biosynthesis and accmulation of the quality-related metabolites in young shoots of tea plants are largely affected by N supply. The objectives of this study were to investigate the functional relationship between N nutrition and accumulation of primary and secondary metabolites in tea plants. The results are as follows:1. Evaluation of methods for extraction of quality-related constituents in tea leavesA simple and quick method was developed and optimised for the analysis of polyphenols and free amino acids in tea fresh shoots (leaves) in this study. The use of70%Ethanol and grinded by ball mill for5min has been proved to be the most suitable method. In addition, we compared the effect of different dried methods of tea shoots (leaves) on the quality-related constituents and evaluate it to compare the metabolites in tea plant leaves of different positions.2. Motabolic profiling reveals the effects of different nitrogen application rate and light/dark treatment on quality of fresh tea leavesThe different cultivation methods affect tea quality by altering the basic metabolite profiles. In this study, the metabolome changes were investigated in fresh tea shoots by HPLC and1H-NMR coupled with a multivariate data set. The effect of light/dark treatment was observed through the metabolomics method but there were no difference among N application rates. However, the HPLC results showed both variation.3. Response of foliar nitrogen and SPAD readings of tea plants to nitrogen fertilizationMaximization of benefit while offsetting deteriorating effects on quality and environmental problems of N fertilization requires reliable N recommendation in tea plantations. Determination of N concentrations of tissues is an important diagnostic means for N status of plants. Pot and field experiments were carried out to investigate the response of yield and total N of mature leaves of clone Longjing43to N and to evaluate the feasibility using SPAD-502as a diagnostic tool. The yield, total N and total free amino acids showed similar patterns with an initial linear increase followed by a platform to increasing N fertilization. A significant positive linear relationship was observed between the SPAD reading and chlorophyll contents and total N. Furthermore the SPAD reading responded to N fertilization same as for the yield, increasing with increasing N fertilization until a platform observed. The SPAD reading was likely an indicator of N status and a potentially useful and quick diagnostic tool for N fertilization recommendation especially in the range of N deficiency. Those factors which may influence the precision of SPAD measurement, such as the point of test within a leaf, selection of leaves from twig (position), weather condition, in situ or in vitro analysis, surface cleaning and the number of leaves for a composite sample were also investigated.4. Characterization and regulation of ammonium and nitrate uptake and metabolism in roots of tea plantsIt has been pointed out that tea prefers ammonium (NH4+-N) over nitrate (NO3--N) as an inorganic N source.15N studies were conducted using hydroponically grown tea plants to clarify the characteristics of uptake and assimilation of NH4+and NO3-by tea roots. The total15N was detected and kinetic parameters were calculated after feeding15NH4+or15NO3-to tea plants. The process of N assimilation was studied by monitoring the dynamic15N abundance in the free amino acids of tea plant roots by Gas Chromatography-Mass spectrometry (GC-MS). Tea plants supplied with15NH4+absorbed significantly more15N than those supplied with15NO3-. The kinetics of15NH4+and15NO3-influx in tea plants followed a classic biphasic pattern, demonstrating the action of a high affinity transport system (HATS) and a low affinity transport system (LATS). The Maximum rate of uptake (Vmax) value for NH4+uptake was54.5nmol/g DW/min, which was higher than that observed for NO3-(39.3nmol/g DW/min). Apparent michaelis constant (Km) estimates were approximately0.06mmol/L for NH4+and0.16mmol/L for NO3-, indicating a higher rate of NH4+absorption in tea plant roots. Tea plants fed with15NH4+accumulated larger amounts of assimilated N, especially glutamine (Gln), compared with those fed with15NO3-. Gln, glutamic acid (Glu), theanine (Thea), serine (Ser) and aspartic acid (Asp) were the main free amino acids that were labeled with15N under both conditions. The rate of N assimilation into Thea in the roots of NO3--supplied tea plants was quicker than in NH4+-supplied tea plants. NO3-uptake in roots, rather than reduction or transport within the plant, seems to be the main factor limiting the growth of tea plants supplied with NO3-as the sole N source. The NH4+absorbed by tea plants directly, as well as that produced by NO3-reduction, were assimilated through the glutamine synthetase-glutamine oxoglutarate aminotransferase (GS-GOGAT) pathway in tea plant roots. The15N labeling experiments show that there is no direct relationship between the Thea synthesis and the preference of tea plants for NH4+.The inhibitory effects exerted by the pretreatment of tea plants by different level of N or two N source upon N uptake and assimilation by the roots of tea plants have been showed in this study. The regulation of NO3-uptake by Thea and NO3-were showed in our study, and the uptake of NH4+was affected mainly by the NH4+and NO3-.