Ethylene is a gaseous plant growth hormone that regulates various plant developmental processes, ranging from seed germination to senescence. The mechanisms underlying ethylene biosynthesis and signaling involve multistep mechanisms representing different control levels to regulate its production and response. Ethylene is an established phytohormone that displays various signaling processes under environmental stress in plants. Such environmental stresses trigger ethylene biosynthesis/action, which influences the growth and development of plants and opens new windows for future crop improvement. This review summarizes the current understanding of how environmental stress influences plants’ ethylene biosynthesis, signaling, and response. The review focuses on (a) ethylene biosynthesis and signaling in plants, (b) the influence of environmental stress on ethylene biosynthesis, (c) regulation of ethylene signaling for stress acclimation, (d) potential mechanisms underlying the ethylene-mediated stress tolerance in plants, and (e) summarizing ethylene formation under stress and its mechanism of action.

Salt stress significantly contributes to major losses in agricultural productivity worldwide. The sustainable approach for salinity-accrued toxicity has been explored. The use of plant growth regulators/phytohormones, mineral nutrients and other signaling molecules is one of the major approaches for reversing salt-induced toxicity in plants. Application of the signaling molecules such as nitric oxide (NO) and ethylene (ETH) and major mineral nutrient such as nitrogen (N) and sulfur (S) play significant roles in combatting the major consequences of salt stress impacts in plants. However, the literature available on gaseous signaling molecules (NO/ETH) or/and mineral nutrients (N/S) stands alone, and major insights into the role of NO or/and ETH along with N and S in plant-tolerance to salt remained unclear. Thus, this review aimed to (a) briefly overview salt stress and highlight salt-induced toxicity, (b) appraise the literature reporting potential mechanisms underlying the role of gaseous signaling molecules and mineral nutrient in salt stress tolerance, and (c) discuss NO and ETH along with N and S in relation to salt stress tolerance. In addition, significant issues that have still to be investigated in this context have been mentioned.

Phytohormones have a role in stress adaptation. The major mechanism underlying the role of exogenously-sourced nitric oxide (NO; as sodium nitroprusside, SNP: 50.0 µM) and salicylic acid (SA; 0.5 mM) in the presence of 2.0 mM SO₄⁻² was assessed in heat stress (HS; 40 °C for 6 h daily for 15 days) tolerance in wheat (Triticum aestivum L. cv. HD-3226). The cultivar HD-3226 possessed high photosynthetic sulfur use efficiency (p-SUE) among the six cultivars screened. Plants grown under HS exhibited an increased content of reactive oxygen species (ROS; including superoxide radical and hydrogen peroxide) and extent of lipid peroxidation with a consequent reduction in photosynthesis and growth. However, both NO and SA were found to be protective against HS via enhanced S assimilation. Their application reduced oxidative stress and increased the activity of antioxidant enzymes. NO or SA supplementation along with S under HS recovered the losses and improved photosynthesis and growth. The use of SA inhibitor (2-aminoindane-2-phosphonic acid; AIP) and NO scavenger (cPTIO) confirmed that the mitigating effects of SA and NO involved induction in S assimilation.

Periwinkle (Catharanthus roseus L.) G. Don contains about 130 indole terpenoid alkaloids including vincristine and vinblastine, which are antineoplastic drugs produced in a very minute quantity in periwinkle leaves. Researchers have been finding ways to enhance the production of these valuable alkaloids. A pot experiment was conducted on periwinkle to explore the effect of single and combined application of irradiated sodium alginate (ISA) and methyl jasmonate (MeJA) on growth, physiological attributes and alkaloids production (vincristine and vinblastine) at 6 and 9 month after plantation (MAP). Foliar application of ISA at 80 mg L⁻¹ improved the growth and other physiological parameters, whereas MeJA at 40 mg L⁻¹ enhanced the content and yield of anticancer alkaloids (vincristine and vinblastine). As compared with the control, their combined application (80 mg L⁻¹ of ISA and 40 mg L⁻¹ of MeJA) increased the total alkaloids content by 33.8 and 36.6% and the total alkaloids yield by 47.7 and 58.0% at 6 and 9 MAP, respectively. Combined application increased the vincristine content by 46.7 and 42.8% and vincristine yield by 59.8 and 66.0% at 6 and 9 MAP, respectively. Similarly, it increased the vinblastine content by 24.6 and 21.0% and the vinblastine yield by 35.3 and 40% at 6 and 9 MAP, respectively. Conclusively, combined application of ISA and MeJA could be considered recommendable to enhance the anticancer alkaloids of periwinkle.