Physiological And Biochemical Response And Adaptability Of Tea Plants To Phosphorus Deficiency

Tea is an evergreen shrub native to China and is cultivated in humid and sub-humid of tropical, subtropical, and temperate regions of the world mainly on acid soils. Phosphorus (P) deficiency is frequently observed in tea plantations. For this reason, P fertilizers are being used annually in tea plantations in order to raise tea productivity and improve tea quality. Vegetative propagated 10-month-old tea [Camellia sinensis (L.) O. Kuntze cv. Huangguanyin] seedlings grown in pots containing sand were fertilized three times weekly for 17 weeks with nutrient solution at a P concentration of 0, 40, 80, 160, 400 or 1000μM. Thereafter, effects of P deficiency on nutrient absorption of tea seedlings, effects of P deficiency on leaf photosynthesis, effects of P deficiency on leaf reactive oxygne metabolism, effects of P deficiency on quality of green tea, effects of P deficiency on root exudation of OA anions, root and leaf OA metabolism, and effects of P deficiency on root V-ATPase subunit A, V-PPase, ATP-PFK and PPi-PFK gene expression were investigated.1 Effects of P deficiency on nutrient absorption of tea seedlingAs P supply increased, root P content increased linearly, while stem and leaf P content increased in a curve shape. Over the range of P supply, the sequence of P content in the three organs is root P content > leaf P content > stem P content, especially in high P-treated plants. P deficiency decreased the P content of roots, stems and leaves, but had little effects on the Ca content of roots, stems and leaves. P deficiency decreased root Mg content and increased stem Mg content, but had little effects on leaf Mg content. Leaves from 0μM P-treated plants had slightly higher C content, lower N content and higher C/N ratio, whereas P supply had little effects on the contents of C and N and the ratio of C to N in roots and stems. In conclusion, P deficiency not only affects contents of nutrient elements in tea roots, stems and leaves, but also altered the distribution of nutrient elements among roots, stems and leaves.2 Effects of P deficiency on leaf CO2 assimilation, Rubisco and photosynthetic electron transportP-deficient leaves showed decreased CO2 assimilation and stomatal conductance, but increased intercellular CO2 concentration. Both initial and total Rubisco activity, contents of Chl and total soluble protein in P-deficient leaves decreased to a lesser extent than CO2 assimilation. Contents of sucrose and starch were decreased in P-deficient leaves, whereas contents of glucose and fructose did not change significantly except for a significant increase in the lowest P leaves. OJIP transients of P-deficient leaves displayed a rise at the O-step and a depression at the P-step, accompanied by two new steps at about 150μs (L-step) and at about 300μs (K-step). RC/CSo, TRo/ABS (or Fv/Fm), ETo/ABS, REo/ABS, maximum amplitude of IP phase, PIabs and PItot,abs were decreased in P-deficient leaves, while VJ, VI and dissipated energy were increased. In conclusion, P deficiency decreased photosynthetic electron transport capacity by impairing the whole electron transport chain from PSII donor side up to the PSI, thus decreasing ATP content which limits RuBP regeneration, and hence, the rate of CO2 assimilation. Energy dissipation is enhanced to protect P-deficient leaves from photo-oxidative damage in high.3 Effects of P deficiency on leaf reactive oxidative metabolismWhen expressed on a leaf area basis, P-deficient leaves had decreased activities of antioxidant enzymes and contents of antioxidants, but similar or higher activities of antioxidant enzymes and contents of antioxidants on a leaf protein basis. P deficiency did not increase lea MDA content, indicating that the antioxidant systems in P-deficient leaves can provide sufficient protection to them against oxidative damage.4 Effects of P deficiency on quality of green teaP deficiency decreased the contents of total polyphenols, total free amino acids, flavone, water extract and the ratio of total polyphenols to total free amino acids. P deficiency decreased the contents of Thea, Asp+Glu and Thr, but increased the contents of GABA, Pro, Val, Cys, Ile, Ala and Gly. P deficiency increased the content of C (catechin), and decreased the contents of ECG, EC, GC and GCG. P supply did not significantly affect the contents of EGCG, EGC, CG and total catechin except for a slight decrease in EGC content at 400μM P treatment.5 Effects of P deficiency on root exudation of OA anions, root and leaf OA metabolismRoot malate exudation and accumulation were induced by both 0 and 40μM P, while root citrate exudation and accumulation were induced only by 0μM P. P deficiency-induced malate and citrate exudation coincided with enhanced concentrations of root malate and citrate. The enhanced concentrations of malate and citrate were accompanied by increased activities of PEPC, PEPP, CS and NAD-ME and decreased activities of PK, NADP-ME and NADP-IDH in roots. Unlike roots, leaf malate accumulation was induced only by 0μM P, while P deficiency did not increase leaf citrate concentration. P deficiency-induced leaf malate accumulation coincided with increased NADP-ME, NAD-ME and PK activities. To conclude, P deficiency-induced changes in OA metabolism differed between roots and leaves.6 Effects of P deficiency on root V-ATPase subunit A, V-PPase, PPi-PFK and ATP-PFK gene expressionV-ATPase subunit A, V-PPase, PPi-PFK and ATP-PFK gene fragments were cloned from tea roots and the changes in gene expression of the four genes in response to P supply were investigated by using semi-quantitative RT-PCR. P deficiency decreased the expressions of V- ATPase subunit A and ATP-PFK genes, but did not affect or slightly increased the expressions of V-PPase and PPi-PFK genes. This may be a tolerant mechanism of tea seedlings to P deficiency.