Histochemical evaluation of catechins in PEG stressed transgenic tea plants using catechin-specific-diazotized sulfanilamide reagent

Molecular Evidence for Catechin Synthesis and Accumulation in Tea Buds (Camellia sinensis)

Early spring buds of the Camellia sinensis variety Shuchazao were separated into two parts, including the shoot tip (ST) and non-expanded young leaves (YL), in which the synthesis and accumulation of catechins in the two parts were assessed by high-performance liquid chromatography (HPLC), p-dimethylaminocinnamaldehyde (DMACA) staining, quantitative real-time polymerase chain reaction (qRT-PCR), and in situ hybridization. HPLC showed that (-)-epigallocatechin-3-gallate (EGCG) and (-)-epicatechin-3-gallate (ECG) amounts in YL were increased significantly by 74.0 and 71.8%, respectively. The results of DMACA staining indicated that catechins in buds accumulated mainly in mesophyll cells and the bud shaft of YL. Meanwhile, qRT-PCR demonstrated that the relative expression levels of genes related to flavonoid metabolism, including CsPAL1, CsC4H1, CsC4H2, CsCHS2, CsF3'5'H1, CsDFR1, CsDFR2, and CsANR1, were significantly higher in YL than in the ST. In situ hybridization revealed that CsDFR1, CsDFR2, CsLAR, and CsANR1 were expressed in leaf primordia and YL but not in the apical meristem. These findings highlight the synthesis and accumulation patterns of catechins in different parts of the ST in C. sinensis, providing a theoretical basis for the assessment of synthesis, accumulation, and transfer patterns of catechins in tea plants.

Transcriptomic Analysis Reveals the Molecular Mechanisms of Drought-Stress-Induced Decreases in Camellia sinensis Leaf Quality

The tea plant [Camellia sinensis (L.) O. Kuntze] is an important commercial crop rich in bioactive ingredients, especially catechins, caffeine, theanine and other free amino acids, which the quality of tea leaves depends on. Drought is the most important environmental stress affecting the yield and quality of this plant. In this study, the effects of drought stress on the phenotype, physiological characteristics and major bioactive ingredients accumulation of C. sinensis leaves were examined, and the results indicated that drought stress resulted in dehydration and wilt of the leaves, and significant decrease in the total polyphenols and free amino acids and increase in the total flavonoids. In addition, HPLC analysis showed that the catechins, caffeine, theanine and some free amino acids in C. sinensis leaves were significantly reduced in response to drought stress, implying that drought stress severely decreased the quality of C. sinensis leaves. Furthermore, differentially expressed genes (DEGs) related to amino acid metabolism and secondary metabolism were identified and quantified in C. sinensis leaves under drought stress using high-throughput Illumina RNA-Seq technology, especially the key regulatory genes of the catechins, caffeine, and theanine biosynthesis pathways. The expression levels of key regulatory genes were consistent with the results from the HPLC analysis, which indicate a potential molecular mechanism for the above results. Taken together, these data provide further insights into the mechanisms underlying the change in the quality of C. sinensis leaves under environmental stress, which involve changes in the accumulation of major bioactive ingredients, especially catechins, caffeine, theanine and other free amino acids.

Subcellular Localization of Galloylated Catechins in Tea Plants [Camellia sinensis (L.) O. Kuntze] Assessed via Immunohistochemistry

Galloylated catechins, as the main secondary metabolites in the tea plant, including (-)-epigallocatechin-3-gallate and (-)-epicatechin-3-gallate, comprise approximately three-quarters of all the tea plant catechins and have stronger effects than non-galloylated catechins, both on the product quality in tea processing and the pharmacological efficacy to human beings. The subcellular localization of galloylated catechins has been the primary focus of studies that assess biosynthesis and physiological functions. Classical histochemical localization staining reagents can not specifically detect galloylated catechins; thus, their subcellular localization remains controversial. In the present study, we generated a monoclonal antibody (mAb) against galloylated catechins, which can be used for the subcellular localization of galloylated catechins in the tea plant by immunohistochemistry. Direct ELISA and ForteBio Octet Red 96 System assay indicated the mAb could recognize the galloylated catechins with high specificities and affinities. In addition, tea bud was ascertained as the optimal tissue for freezing microtomic sections for immunohistochemistry. What's more, the high quality mAbs which exhibited excellent binding capability to galloylated catechins were utilized for the visualization of them via immunohistochemistry. Our findings demonstrated that vacuoles were the primary sites of localization of galloylated catechins at the subcellular level.