Recent Progress Regarding Jasmonates in Tea Plants: Biosynthesis, Signaling, and Function in Stress Responses

Tea plants have to adapt to frequently challenging environments due to their sessile lifestyle and perennial evergreen nature. Jasmonates regulate not only tea plants' responses to biotic stresses, including herbivore attack and pathogen infection, but also tolerance to abiotic stresses, such as extreme weather conditions and osmotic stress. In this review, we summarize recent progress about jasmonaic acid (JA) biosynthesis and signaling pathways, as well as the underlying mechanisms mediated by jasmontes in tea plants in responses to biotic stresses and abiotic stresses. This review provides a reference for future research on the JA signaling pathway in terms of its regulation against various stresses of tea plants. Due to the lack of a genetic transformation system, the JA pathway of tea plants is still in the preliminary stages. It is necessary to perform further efforts to identify new components involved in the JA regulatory pathway through the combination of genetic and biochemical methods.

Endogenously Produced Jasmonates Affect Leaf Growth and Improve Osmotic Stress Tolerance in Emmer Wheat

In light of recent climate change, with its rising temperatures and precipitation changes, we are facing the need to increase the valuable crop's tolerance against unfavorable environmental conditions. Emmer wheat is a cereal crop with high nutritional value. We investigated the possibility of improving the stress tolerance of emmer wheat by activating the synthesis of the stress hormone jasmonate by overexpressing two genes of the jasmonate biosynthetic pathway from Arabidopsis thaliana, ALLENE OXIDE SYNTHASE (AtAOS) and OXOPHYTODIENOATE REDUCTASE 3 (AtOPR3). Analyses of jasmonates in intact and mechanically wounded leaves of non-transgenic and transgenic plants showed that the overexpression of each of the two genes resulted in increased wounding-induced levels of jasmonic acid and jasmonate-isoleucine. Against all expectations, the overexpression of AtAOS, encoding a chloroplast-localized enzyme, does not lead to an increased level of the chloroplast-formed 12-oxo-phytodienoic acid (OPDA), suggesting an effective conversion of OPDA to downstream products in wounded emmer wheat leaves. Transgenic plants overexpressing AtAOS or AtOPR3 with increased jasmonate levels show a similar phenotype, manifested by shortening of the first and second leaves and elongation of the fourth leaf, as well as increased tolerance to osmotic stress induced by the presence of the polyethylene glycol (PEG) 6000.

Effect of Methyl Jasmonate on the Gene Expression, Encoding Non-Protein Thiol Enzymes in Wheat under Cadmium

The effect of the phytohormone methyl jasmonate (MJ) on the expression of the TaGS1 and TaPCS1 genes encoding glutathione synthetase and phytochelatin synthase, respectively, which are key enzymes in the synthesis of glutathione and phytochelatins in wheat (cv. Moskovskaya 39), was studied. It was shown for the first time that pretreatment of plants by exogenous MJ (1 μM) leads to an increase in the accumulation of transcripts of the TaGS1 and TaPCS1 genes in leaves without cadmium effect. When cadmium (CdSO₄, 100 μM) was added into the nutrient solution, the transcript level of the TaGS1 gene in the plants pretreated by MJ increased (compared to the untreated plants), whereas the transcript level of TaPCS1 remained unaffected. The pretreatment of plants with MJ leads to a lower accumulation of cadmium in the roots and leaves of wheat. At the same time, MJ had no effect on the linear growth parameters of plants, but had a positive effect on the accumulation of biomass under cadmium. It was assumed that MJ is involved in plant tolerance to cadmium by increasing the expression of the TaGS1 and TaPCS1 genes and, as a result, enhancing the synthesis of chelating compounds, as well as by reducing the supply of metal ions to plants.

Interactive effects of salicylic acid and jasmonic acid on secondary metabolite production in Echinacea purpurea

Secondary metabolites are highly beneficial to human health and have commercial and industrial values. So, this research aimed to study the effects of exogenous salicylic acid (SA) and jasmonic acid (JA) on some secondary metabolites in purple coneflower. A field experiment as a randomized complete block design with three replications was conducted in Shahrood, Iran. Treatments were the factorial arrangement of 3 SA (0, 0.5, and 1 millimole) and 4 JA concentrations (0, 5, 20, and 50 micromole). The non-linear regression procedure was employed to quantify the relation of these materials with each other. The results indicated that the SA effect on all ten measured secondary metabolites changed with changing the JA levels as there was the interaction between these elicitors. On average, most (7 out of 11) of the combined SA_JA levels up-regulated the production of secondary metabolites as compared to the plants not sprayed with SA and JA. In terms of average response to elicitation with 11 combined SA_JA levels, they ranked from higher to lower as the guaiacol peroxidase, hydrogen proxide (H2O2), polyphenol oxidase, glutathione S-transferase, superoxide dismutase, NADPH oxidase, total phenolic content, phenylalanine ammonia-lyase, anthocyanin, and flavonoid. A few secondary metabolites appeared to have a biphasic relationship with each other. For instance, over lower and medium values of NADPH oxidase activity, anthocyanin content increased linearly with increasing NADPH oxidase activity; over higher values of NADPH oxidase activity, it showed a plateau state.

Role of oxylipin on Luffa seedlings exposed to NaCl and UV-B stresses: An insight into mechanism

Nowadays, among several abiotic stresses, salt, especially NaCl and UV-B are of major concern. They lead to deleterious effects on plant growth and ultimately affect crop productivity. The present study was planned to find out some ameliorative solution against these stresses. Here, the modulatory action of two oxylipins, namely, methyl jasmonate (MeJA) and 12-Oxo-phytodienoic acid (OPDA) on growth, photosynthetic performance, nitrate/ammonia assimilating enzymes, and nutritive values of Luffa Mill. seedlings grown under NaCl (20 and 40 mM) and/or enhanced UV-B stresses (ambient: 8.2 kJ m^-2 d^-1 + additional: 2.2 kJ m^-2 s^-1) were analyzed. Both the stresses when given alone, negatively affected the fresh mass, root/shoot ratio, leaf area, photosynthetic pigments content, photosynthetic oxygen yield and, chlorophyll a fluorescence kinetic parameter. This decline was further aggravated upon combined exposure to the stressors. However, supplementation of MeJA/OPDA effectively counteracted the negative impact on important growth-regulating processes. The activities of nitrate reductase (NR), nitrite reductase (NiR), glutamine synthetase (GS), and glutamate synthase (GOGAT) enzymes, as well as the contents of inorganic nitrogen, protein, and carbohydrate, were increased with the supplementation of MeJA/OPDA. The increase in the Na⁺ and Cl^‾ contents due to NaCl or/and UV-B was depreciated by MeJA or OPDA. Ameliorating behaviour of MeJA or OPDA is correlated with improved photosynthetic activity and nitrogen metabolism. These findings, point out that supplementation of MeJA/OPDA, particularly OPDA more favourably regulated the growth-promoting activities, which can be linked with the mitigation of NaCl and UV-B stress.