The effect of melatonin (MT) on potato plants under drought stress is still unclear in the available literature. Here, we studied the effect of MT as a foliar application at 0, 0.05, 0.1, and 0.2 mM on potato plants grown under well-watered and drought stressed conditions during the most critical period of early tuberization stage. The results indicated that under drought stress conditions, exogenous MT significantly (p ≤ 0.05) improved shoot fresh weight, shoot dry weight, chlorophyll (Chl; a, b and a + b), leaf relative water content (RWC), free amino acids (FAA), non-reducing sugars, total soluble sugars, cell membrane stability index, superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (G-POX), and ascorbate peroxidase (APX) compared to the untreated plants. Meanwhile, carotenoids, proline, methylglyoxal (MG), H₂O₂, lipid peroxidation (malondialdehyde; MDA) and abscisic acid (ABA) were significantly decreased compared to the untreated plants. These responses may reveal the protective role of MT against drought induced carbonyl/oxidative stress and enhancing the antioxidative defense systems. Furthermore, tuber yield was differentially responded to MT treatments under well-watered and drought stressed conditions. Since, applied-MT led to an obvious decrease in tuber yield under well-watered conditions. In contrast, under drought conditions, tuber yield was substantially increased by MT-treatments up to 0.1 mM. These results may imply that under water deficiency, MT can regulate the tuberization process in potato plants by hindering ABA transport from the root to shoot system, on the one hand, and by increasing the non-reducing sugars on the other hand.

Currently, the world is facing many troubles in crop production and the irrigation water deficit is the most harmful among them. Saving irrigation water is the main target for all countries of the world, especially in arid areas. Field trial was executed aiming to assess the influence of irrigation regimes (100, 80 and 60% of irrigation requirements, IR (IR₁₀₀, IR₈₀ and IR₆₀, respectively), water-absorbent substances (control, hydrogel polymer and zeolite as soil addition) and foliar application of glutathione (GSH) [with GSH or without] on the performance of common bean plants. Findings clarified that plant fresh weight obtained with the combination of IR₈₀ × zeolite × GSH had no significant differences with the superior combination of IR₁₀₀ × hydrogel polymer or zeolite × GSH. Hydrogel polymer plus GSH supply showed distinctive enhancements for N, P and K accumulation in common bean leaves. Application of zeolite plus GSH reduced the accumulation of POX and CAT by 21.8 and 15.5% under IR₈₀ and 16.1 and 7.6% under IR₆₀, respectively. Spraying of GSH × hydrogel polymer under IR_100, IR₈₀ and IR₆₀ significantly increased the value of pods yield by 26.5%, 25.23% and 32.80, respectively, as compared to corresponding control treatment. the interaction of IR₁₀₀ and hydrogel polymer whether with or without GSH showed the highest significant values of N, P, protein, fiber, carbohydrates percentages and TDS. Briefly, it can be concluded that water holding amendments i.e., polymer and zeolite as well as low-molecular-weight antioxidants i.e., glutathione can mitigate the hazard impacts of elevated reactive oxygen species production under drought. Practically, common bean growers are advised to treat the soil with available soil amendment (hydrogel polymer, 0.24 t ha⁻¹ or zeolite, 1.20 t ha⁻¹) and spraying common bean plants by glutathione, 1.0 mM to sustain the crop productivity and quality under shortage water conditions

Salinization, as a serious climate change phenomenon, continues to cause critical issues for soils and crops. Abundance of genetic diversity of plants could contribute in solving the impacts of salinity. However, the relations between physiological and molecular traits of plant species need deep investigation and interpretation. Pot experiments were conducted in the greenhouse to investigate the difference in behavior between two amaranth species when they were beforehand subjected to salinity-stress conditions, specifically on some specific physiological and molecular characteristics. After 45 days from transplanting, salt stress was induced using a 150 mM sodium chloride solution. Treatments were arranged in randomized complete block design using three replications. After 0, 2, 6, 10, and 24 h, samples were collected to evaluate physiological data as well as diversity of gene expression. The samples were immediately frozen in liquid nitrogen and stored in -80⁰ C ultralow temperature refrigerators. Findings revealed that the red amaranth species (Amaranthus cruentus) was more tolerant to saline stress than the green amaranth species (Amaranthus hypochondriacus). Result data revealed that malondialdehyde (MDA) content in the red amaranth increased after 2 h then decreased (after 6 and 10 h) before rising again after 24 h. In the green amaranth, MDA content initially decreased after 2 h before increasing and later decreasing in a zigzag pattern ending in an increase after 24 h. There was an initial steep rise in proline content of green amaranth after 2 h which continued to still rise moderately till 24 h. In the red amaranth the initial rise in proline continued after 2, 6 and 10 h before it stopped. Results also showed that red amaranth gave higher value of superoxide dismutase (SOD) activity as compared with green amaranth in all tested salinity exposure times. The investigation on the expression of four genes assessed through quantitative PCR indicated the efficiency of red amaranth in increasing the expression of SOS1, HKT1, NHX1, and DGR2 genes, which encode adaptation-related proteins under salinity stress. In summary, the current work demonstrated that red amaranth could be an efficient genetic resource in improving salt-tolerant genotypes belonging to Amaranthus genus.

The mechanism by which folic acid (FA) or its derivatives (folates) mediates plant tolerance to sodic-alkaline stress has not been clarified in previous literature. To apply sodic-alkaline stress, maize seedlings were irrigated with 50 mM of a combined solution (1:1) of sodic-alkaline salts (NaHCO₃ and Na₂CO₃; pH 9.7). Maize seedlings under stressed and non-stressed conditions were sprayed with folic acid (FA) at 0 (distilled water as control), 0.05, 0.1, and 0.2 mM. Under sodic-alkaline stress, FA applied at 0.2 mM significantly improved shoot fresh weight (95%), chlorophyll (Chl a (41%), Chl b (57%), and total Chl (42%)), and carotenoids (27%) compared to the untreated plants, while root fresh weight was not affected compared to the untreated plants. This improvement was associated with a significant enhancement in the cell-membrane stability index (CMSI), relative water content (RWC), free amino acids (FAA), proline, soluble sugars, K, and Ca. In contrast, Na, Na/K ratio, H₂O₂, malondialdehyde (MDA), and methylglycoxal (MG) were significantly decreased. Moreover, seedlings treated with FA demonstrated significantly higher activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POX), catalase (CAT), and ascorbate peroxidase (APX) compared to the untreated plants. The molecular studies using RT-qPCR demonstrated that FA treatments, specifically at 0.2 mM, enhanced the K⁺/Na⁺ selectivity and the performance of photosynthesis under alkaline-stress conditions. These responses were observed through up-regulation of the expression of the high-affinity potassium-transporter protein (ZmHKT1), the major core protein of photosystem II (D2-Protein), and the activity of the first enzyme of carbon fixation cycle in C4 plants (PEP-case) by 74, 248, and 225% over the untreated plants, respectively. Conversely, there was a significant down-regulation in the expression ZmSOS1 and ZmNHX1 by 48.2 and 27.8%, respectively, compared to the untreated plants.