| Pruning is a common practice in tea farming speculated to contribute to plant growth and development.However,little information is available on its mechanism in shoots growth.It is;therefore,important to explore the possibility and mechanism involved in auxin signaling and accumulation in plants in response to pruning,leading to shoot growth.It is worth noting that plant growth and development depends on the ability of plants to absorb nutrients from soil.Mineral nutrient uptake involves active transport of ions,a factor of energy expenditure from metabolism.It is unclear how pruning affects nutrient uptake and its role in metabolic processes in plant root.Owing to this,the present study employed metabolomic analysis to explore the mechanism by which prxming improves plant growth and development in tea plants and the molecular link between shoot growth and nutrient uptake.1.In order to investigate the mechanism involved in shoot growth in pruned plants^new shoots were harvested from tea plants forty-five days after pruning,and measured on growth parameter indices.Generally,pruning significantly increased number and weight of new shoots,with half pruned samples showing the highest number and weight of shoots.Interestingly,full prune resulted in least number of shoots but higher shoot weight.Number of shoots was in the order half prune > shallow prune > control > flill prune,while weight of new shoots followed the order half prune > full prune > shallow prune > control.The results,therefore,revealed significant increase in shoots number and weight in shoots of pruned tea plant.Leaf samples were assayed for concentration of indole-3-acetic acid to ascertain its involvement in shoots growth of pruned tea plants.The results revealed that pruning significantly increases the production of indole-3-acetic acid in shoots.Relative to the control ,full pruning resulted in highest synthesis of indole-3-acetic acid(23 ^ mol/L),followed by half pruning(20 \x mol/L)and then shallow pruning(17 \x mol/L),Metabolomic analysis identified 80 differential metabolites in shoots of pruned plants.The metabolites involved a wide range of classes of metabolites such as amino acid derivatives(13 %),nucleotide and its derivatives(11 %)5 organic acids(11 %),flavone C-glycosides(7 %)and vitamins(7 %).Interestingly,indole-3-acetonitrile and menaquinone were the common metabolites identified in all levels of pruning.Protein-protein interaction analysis was performed using indole-3-acetonitrile and menaquinone to study their role in plant growth and development.The results revealed that indole-3-acetonitrile and menaquinone are involved in auxin biosynthesis.KEGG pathway analysis showed that major metabolic pathways such as tryptophan metabolism,vitamin digestion and absorption,biosynthesis of ubiquinone and other terpenoid-quinone,and biosynthesis of amino acids were enriched for metabolites in pruned plants.Gene expression study was conducted using genes related to metabolites in pruned plants.The results revealed higher expression of genes involved in auxin signaling and menaquinone synthesis.According to literature this study reports,for the first time in nature,the synthesis of menaquinone in tea plants.The aforementioned results clearly depicts that pruning enhances shoot growth and development through the modulation of indole-3-acetic acid via synthesis of indole-3-acetonitrile and menaquinone in shoots,a combined effect of tryptophan metabolism and other metabolic pathways.2.Due to stress associated with cutting of apical buds during pruning process,it is imperative to determine the antioxidant level in shoots of pruned plants.In response to environmental stimuli,plants produce antioxidants to protect their cells from oxidative damages.Glutathione is a significant antioxidant and redox buffer that occur naturally in many plants including tea.This study;therefore,investigate the production of glutathione in shoots of pruned plants.Tea plants were pruned at various levels designated as shallow,half and full pruning.One month after pruning,new shoots were harvested and assayed for glutathione level.Metabolic profiling identified metabolites in glutathione metabolism including amino acids and fatty acids associated with glutathione metabolism.Metabolic pathway classification and enrichment analysis revealed that the metabolites identified in new shoots of pruned plants enrich for metabolic pathways including 2-oxocarboxylic acid metabolism,’alanine,aspartate and glutamate metabolism% biosynthesis of axnino acids,Dalanine metabolism,D-glutamine and D-glutamate metabolism,glutathione metabolism,and glyoxylate and dicarboxylate metabolism.These pathways produce intermediate metabolites in the glutathione metabolism pathway.The results revealed that most of the intermediate metabolites in the glutathione metabolism pathway were significantly upregulated in response to pruning.In addition,N-acetylated metabolites in glutathione metabolism pathway including N-y-acetyl-N-2-formyl-5-methoxykynurenamine5 Naacetyl-L-glutamine,N-acetylaspartate and N-acetyl tryptophan.These results indicate that pruning results in significant up-regulation of metabolites in the glutathione metabolism pathway,thereby,leading to the production of glutathione in shoots in response to pruning.3.Based on the molecular and physiological changes in shoots of pruned plants,the mechanism in lateral roots of pruned plant and their role in mineral nutrient uptake were also investigated to reveal the holistic contribution of pruning to plant growth.Lateral roots were harvest from pruned plants analysed for the concentration of macro-(nitrogen,phosphorus and potassium)and micro-nutrients(aluminium,cobalt,iron,manganese,molybdenum,sodium,nickel,silicon and zinc)using ICP-MS technology.Accumulation of mineral nutrient varied with intensity of pruning.Pruning significantly increased the accumulation of mineral nutrients in lateral roots.Accumulation of N in lateral roots was significantly higher in shallow and half prune plants.Relative to the control,concentrations of P and K were highest half prune,while flill pruned samples accumulated the least.The amounts of macro nutrients in lateral roots followed the trend HP > SP > FP > CK.Generally,concentration of micro nutrients was significantly higher in lateral roots of pruned samples.Interestingly,the accumulation of Zn was lower in lateral roots of shallow prune tea plants,relative to the control.Accumulation of Mn? Al5 Zn5 Ni,Mo and Co increased significantly in half prune;Fe was higher in shallow prune;while Na,Fe and Mn increased in lateral roots of full prune tea plants.Metabolomic profiling identified 197 differential metabolites,mainly constituted by phenylpropanoids,nucleotide and its derivatives,organic acids,amino acids and lipids.This indicates a significant metabolic variation in lateral roots of pruned tea.KEGG pathway analysis revealed significant mechanisms in lateral roots of pruned plants.Flavonoid biosynthesis,phenylpropanoid biosynthesis and amino acid metabolism were differentially regulated by pruning.Interestingly,intermediates in caffeine metabolism pathway were significantly hindered,while metabolites in ethylene signaling and production were significantly induced in lateral roots.Metabolites were also analysed on the tricarboxylic acid cycle(TCA)pathway.The results revealed an up-regulation of intermediates in the TCA cycle,indicating high rates of TCA cycle in lateral roots of pruned plant,respectively.Therefore,the accumulation of mineral nutrients in lateral roots of pruned plant is a combined effect of biosynthesis of flavonoid and phenylpropanoid,caffeine metabolism,tricarboxylic acid cycle,etiiylene signaling and metabolism of amino acids. |
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