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As a plant hormone, salicylic acid (SA) has diverse regulatory roles in plant growth and stress resistance. Although SA is widely found in plants, there is substantial variation in basal SA among species. Tea plant is an economically important crop containing high contents of SA whose synthesis pathway remains unidentified. The phenylalanine ammonia-lyase (PAL) pathway is responsible for basal SA synthesis in plants. In this study, isotopic tracing and enzymatic assay experiments were used to verify the SA synthesis pathway in tea plants and evaluate the variation in phenylalanine-derived SA formation among 11 plant species with different levels of SA. The results indicated that SA could be synthesized via PAL in tea plants and conversion efficiency from benzoic acid to SA might account for variation in basal SA among plant species. This research lays the foundation for an improved understanding of the molecular regulatory mechanism for SA biosynthesis.

Tea ( Camellia sinensis ) is the most popular nonalcoholic beverage worldwide. During cultivation, tea plants are susceptible to herbivores and pathogens, which can seriously affect tea yield and quality. A previous report showed that ( Z )-3-hexenol is a potentially efficient defensive substance. However, the molecular mechanism mediating ( Z )-3-hexenol signaling in tea plants and the resulting effects on plant defenses remain uncharacterized. To clarify the signaling mechanisms in which ( Z )-3-hexenol and light are involved, the gene transcription and metabolite levels were assessed, respectively. This study demonstrated that tea plants rapidly and continuously release ( Z )-3-hexen-1-ol in response to an insect infestation. ( Z )-3-Hexen-1-ol absorbed by adjacent healthy plants would be converted into three insect defensive compounds: ( Z )-3-hexenyl-glucoside, ( Z )-3-hexenyl-primeveroside, and ( Z )-3-hexenyl-vicianoside identified with laboratory-synthesized standards. Moreover, ( Z )-3-hexen-1-ol also activates the synthesis of jasmonic acid to enhance the insect resistance of tea plants. Additionally, a continuous light treatment induces the accumulation of ( Z )-3-hexenyl-glycosides. Hence, ( Z )-3-hexenol serves as a light-regulated signaling molecule that activates the systemic defenses of adjacent plants. Our study reveals the molecular mechanisms by which biotic and abiotic factors synergistically regulate the signaling functions of herbivore-induced plant volatiles in plants, providing valuable information for future comprehensive analyses of the systemic defense mechanisms in plants.

Herbivore-induced plant volatiles (HIPVs) play an important role in insect resistance. As a common HIPV in tea plants ( Camellia sinensis ), β-ocimene has shown anti-insect function in other plants. However, whether β-ocimene in tea plants also provides insect resistance, and its mechanism of synthesis and emission are unknown. In this study, β-ocimene was confirmed to interfere with tea geometrid growth via signaling. Light was identified as the key factor controlling regular emission of β-ocimene induced by the wounding from tea geometrids. β-Ocimene synthase (CsBOS1) was located in plastids and catalyzed β-ocimene formation in overexpressed tobacco. CsBOS1 expression in tea leaves attacked by tea geometrids showed a day-low and night-high variation pattern, while CsABCG expression involved in volatile emission showed the opposite pattern. These two genes might regulate the regular β-ocimene emission from tea plants induced by tea geometrid attack. This study advances the understanding on HIPV emission and signaling in tea plants.

The enzymatic hydrolysis of glycosidically bound volatiles (GBVs) plays an important role in tea aroma formation during the tea manufacturing process. However, during the enzyme-active manufacturing process of oolong tea, most GBVs showed no reduction, while ( Z)-3-hexenyl-β-glucopyranoside significantly enhanced at the turnover stage. This study aimed to determine the reason for this increase in ( Z)-3-hexenyl-β-glucopyranoside. Continuous wounding stress in the turnover stage did not enhance the expression level of glycosyltransferase 1 ( CsGT1), while it induced a significant increase in the ( Z)-3-hexenol content ( p ≤ 0.05). Furthermore, observing the cell structures of tea leaves exposed to continuous wounding and subcellular localizations of CsGTs suggested that the interaction of ( Z)-3-hexenol (substrate) and CsGT1 (enzyme) was available. In conclusion, both continuous wounding and subcellular localizations led to a ( Z)-3-hexenyl-β-glucopyranoside enhancement mechanism during the oolong tea's turnover stage. These results advance our understanding of GBV formation during the tea manufacturing process and their relationship with the stress from the tea manufacturing process. In addition, the information will help us further evaluate contribution of GBVs to enzymatic formation of oolong tea aroma compounds.

Jasmine lactone has a potent odor that contributes to the fruity, sweet floral aroma of tea ( Camellia sinensis). Our previous study demonstrated that jasmine lactone was mostly accumulated at the turnover stage of the oolong tea manufacturing process. This study investigates the previously unknown mechanism of formation of jasmine lactone in tea leaves exposed to multiple stresses occurring during the growth and manufacturing processes. Both continuous mechanical damage and the dual stress of low temperature and mechanical damage enhanced jasmine lactone accumulation in tea leaves. In addition, only one pathway, via hydroperoxy fatty acids from unsaturated fatty acid, including linoleic acid and α-linolenic acid, under the action of lipoxygenases (LOXs), especially CsLOX1, was significantly affected by these stresses. This is the first evidence of the mechanism of jasmine lactone formation in tea leaves and is a characteristic example of plant volatile formation in response to dual stress.

Longan is a delicious subtropical fruit with great health-beneficial effects. It has been utilized for disease prevention and health care since ancient age. To explore the chemicals responsible for the health benefits, water-soluble polysaccharides were extracted from longan flesh in this work. A pure polysaccharide (LPS1) was obtained through column purification. Analysis by gas chromatography showed LPS1 was a homopolysaccharide of glucose with glycosidic linkage of →6)-d-Glc-(1→. Nuclear magnetic resonance (NMR) spectra indicated that the configuration of anomeric carbon in glucose residual was α-form. The polysaccharide structure was further confirmed to be (1→6)-α-d-glucan by chemcial shift of C6. The molecular weight of LPS1 was calculated to be 108 kDa, which had 661 glucose residuals. Anticancer assay showed that LPS1 had anticancer activity against the growth of HepG2 cells to a certain extent. However, it did not show any cytotoxicity against MCF-7 breast cancer cells.

The effects of nitric oxide (NO) on ethylene synthesis and softening of ripening-initiated banana slice were investigated. Fruit firmness, color, and contents of starch and acid-soluble pectin (ASP) were measured. In addition, ethylene production, 1-aminocyclopropane-1-carboxylic acid (ACC) content, expression and activities of ACC synthase (ACS) and ACC oxidase (ACO), and activities of cell-wall-modifying enzymes, polygalacturonase (PG), pectin methylesterase (PME), and endo-beta-1,4-glucanase, were analyzed. Application of NO reduced ethylene production, inhibited degreening of the peel and delayed softening of the pulp. The decrease of ethylene production was associated with the reduction in the activity of ACO and the expression of the MA-ACO1 gene. Moreover, the NO-treated fruit showed a lower expression of the MA-ACS1 gene but higher ACS activity and ACC content. In addition, NO treatment decreased the activities of PG, PME, and endo-beta-1,4-glucanase and maintained higher contents of ASP and starch, which may account for the delay of softening. We proposed that the inhibition of ACO activity and transcription of gene MA-ACO1 by NO resulted in decreased ethylene synthesis and the delay of ripening of banana slice.