Melatonin Induced Cold Tolerance in Plants: Physiological and Molecular Responses.

Cold stress is one of the most limiting factors for plant growth and development. Cold stress adversely affects plant physiology, molecular and biochemical processes by determining oxidative stress, poor nutrient and water uptake, disorganization of cellular membranes and reduced photosynthetic efficiency. Therefore, to recover impaired plant functions under cold stress, the application of bio-stimulants can be considered a suitable approach. Melatonin (MT) is a critical bio-stimulant that has often shown to enhance plant performance under cold stress. Melatonin application improved plant growth and tolerance to cold stress by maintaining membrane integrity, plant water content, stomatal opening, photosynthetic efficiency, nutrient and water uptake, redox homeostasis, accumulation of osmolytes, hormones and secondary metabolites, and the scavenging of reactive oxygen species (ROS) through improved antioxidant activities and increase in expression of stress-responsive genes. Thus, it is essential to understand the mechanisms of MT induced cold tolerance and identify the diverse research gaps necessitating to be addressed in future research programs. This review discusses MT involvement in the control of various physiological and molecular responses for inducing cold tolerance. We also shed light on engineering MT biosynthesis for improving the cold tolerance in plants. Moreover, we highlighted areas where future research is needed to make MT a vital antioxidant conferring cold tolerance to plants.

Physiological, Biochemical, and Yield Responses of Linseed (Linum usitatissimum L.) in α-Tocopherol-Mediated Alleviation of Salinity Stress.

Exogenous application of antioxidants can be helpful for plants to resist salinity, which can be a potentially simple, economical, and culturally feasible approach, compared with introgression and genetic engineering. Foliar spraying of alpha-tocopherol (α-tocopherol) is an approach to improve plant growth under salinity stress. Alpha-tocopherol acts as an antioxidant preventing salinity-induced cellular oxidation. This study was designed to investigate the negative effects of salinity (0 and 120mM NaCl) on linseed (Linum usitatissimum L.) and their alleviation by foliar spraying of α-tocopherol (0, 100, and 200mg L-1). Seeds of varieties "Chandni and Roshni" were grown in sand-filled plastic pots, laid in a completely randomized design in a factorial arrangement, and each treatment was replicated three times. Salinity significantly affected linseed morphology and yield by reducing shoot and root dry weights, photosynthetic pigment (Chl. a, Chl. b, total Chl., and carotenoids) contents, mineral ion (Ca2+, K+) uptake, and 100-seed weight. Concomitantly, salinity increased Na+, proline, soluble protein, peroxidase, catalase, and superoxide dismutase activities in both varieties. Conversely, the growth and yield of linseed varieties were significantly restored by foliar spraying of α-tocopherol under saline conditions, improving shoot and root dry matter accumulation, photosynthetic pigment, mineral ion, proline, soluble protein contents, peroxidase, catalase, superoxide dismutase activities, and 100-seed weight. Moreover, foliar spray of α-tocopherol alleviated the effects of salinity stress by reducing the Na+ concentration and enhancing K+ and Ca2+ uptake. The Chandni variety performed better than the Roshni, for all growth and physiological parameters studied. Foliar spray of α-tocopherol (200mg L-1) alleviated salinity effects by improving the antioxidant potential of linseed varieties, which ultimately restored growth and yield. Therefore, the use of α-tocopherol may enhance the productivity of linseed and other crops under saline soils.

Influence of environmental factors on seed germination and seedling characteristics of perennial ryegrass (Lolium perenne L.).

Information regarding the germination and seedling growth behavior of a potential weed species is an important tool to manage weeds without the use of agricultural chemicals that cause harmful effects on human health and the environment. A series of experiments were directed to investigate the influence of different environmental factors (temperature, pH, NaCl, moisture stress, and seed burial depth) on germination and seedling emergence of perennial ryegrass (Lolium perenne L.) under controlled conditions. Results suggested that 25 °C is the optimum temperature for maximum germination (95%) and seedling growth of perennial ryegrass, however, a quick decline was observed at 35 °C. Seed germination was unaffected by pH levels ranging from 5 to 10. The 92% seed germination was recorded where no salt stress was applied and germination was reduced by 87% at 250 mMNaCl concentration. Seed germination was unaffected by osmotic potential ranges from 0 to - 0.4 MPa thereafter declined and completely inhibited at - 0.8 or - 1.0 MPa. No seed emerged at the soil surface or a soil depth of 6 or 7 cm and 90% emergence occurred at 1 cmsoil depth. The germination and seedlings parameters like time to initial germination, mean germination time, time taken to 50% germination and germination index, root and shoot length, and fresh and dry weight of root and shoot are significantly affected with the environmental factors. The information obtained in this study will be helpful to develop better management strategies for germination and the emergence of perennial ryegrass in areas where it has the ability to rapidly colonize.

Alpha Tocopherol-Induced Modulations in the Morphophysiological Attributes of Okra Under Saline Conditions.

Foliar spray of antioxidants is a pragmatic approach to combat various effects of salinity stress in agricultural crops. A pot trial was conducted to examine the effect of exogenously applied α-tocopherol (α-Toc) as foliar spray to induce morpho-physiological modulations in two varieties (Noori and Sabzpari) of okra grown under salt stress conditions (0 mM and 100 mM NaCl). After 36 days of salinity treatments, four levels (0, 100, 200 and 300 mg L-1) of α-tocopherol were sprayed. Salt stress significantly reduced root and shoot fresh and dry biomass, photosynthesis rate (A), transpiration rate (E), water use efficiency (A/E), stomatal conductance, internal CO2 concentration (C i )and C i /C a ), and photosynthetic pigments. Foliar spray of α-tocopherol proved effective in improving the growth of okra by significantly enhancing root dry weight, root length, shoot fresh weight, shoot length, Chl. a, Chl. b, Total chl., ß-Car., Total Car., A, E, A/E, C i, and C i /C a , leaf and root Ca2+ and K+ ion content, total soluble sugars, non-reducing sugars and total soluble protein content by significantly reducing root Na+ ion content. The Okra variety Noori performed better than Sabzpari in the examined attributes, and 300 mg L-1 application of α-tocopherol was more pronounced in improving the growth of okra by alleviating salinity effects. Therefore, the use of α-tocopherol (300 mg L-1) as a foliar spray is recommended to improve okra production in saline soils.

Foliar Spray of Alpha-Tocopherol Modulates Antioxidant Potential of Okra Fruit under Salt Stress.

As an antioxidant, alpha-tocopherol (α-Toc) protects plants from salinity-induced oxidative bursts. This study was conducted twice to determine the effect of α-Toc as a foliar spray (at 0 (no spray), 100, 200, and 300 mg L-1) to improve the yield and biochemical constituents of fresh green capsules of okra (Abelmoschus esculentus L. Moench) under salt stress (0 and 100 mM). Salt stress significantly reduced K+ and Ca2+ ion concentration and yield, whereas it increased H2O2, malondialdehyde (MDA), Na+, glycine betaine (GB), total free proline, total phenolics, and the activities of catalase (CAT), guaiacol peroxidase (GPX), and protease in both okra varieties (Noori and Sabzpari). Foliar application of α-Toc significantly improved the yield in tested okra varieties by increasing the activity of antioxidants (CAT, GPX, SOD, and ascorbic acid), accumulation of GB, and total free proline in fruit tissues under saline and non-saline conditions. Moreover, α-Toc application as a foliar spray alleviated the adverse effects of salt stress by reducing Na+ concentration, MDA, and H2O2 levels and improving the uptake of K+ and Ca2+. Among the tested okra varieties, Noori performed better than Sabzpari across all physio-biochemical attributes. Of all the foliar-applied α-Toc levels, 200 mg L-1 and 300 mg L-1 were more effective in the amelioration of salinity-induced adverse effects in okra. Thus, we concluded that higher levels of α-Toc (200 mg L-1 and 300 mg L-1) combat salinity stress more effectively by boosting the antioxidant potential of okra plants.