Phytohormones (PHs) play crucial role in regulation of various physiological and biochemical processes that govern plant growth and yield under optimal and stress conditions. The interaction of these PHs is crucial for plant survival under stressful environments as they trigger signaling pathways. Hormonal cross regulation initiate a cascade of reactions which finely tune the physiological processes in plant architecture that help plant to grow under suboptimal growth conditions. Recently, various studies have highlighted the role of PHs such as abscisic acid, salicylic acid, ethylene, and jasmonates in the plant responses toward environmental stresses. The involvement of cytokinins, gibberellins, auxin, and relatively novel PHs such as strigolactones and brassinosteroids in plant growth and development has been documented under normal and stress conditions. The recent identification of the first plant melatonin receptor opened the door to this regulatory molecule being considered a new plant hormone. However, polyamines, which are not considered PHs, have been included in this chapter. Various microbes produce and secrete hormones which helped the plants in nutrient uptake such as N, P, and Fe. Exogenous use of such microbes help plants in correcting nutrient deficiency under abiotic stresses. This chapter focused on the recent developments in the knowledge related to PHs and their involvement in abiotic stresses of anticipation, signaling, cross-talk, and activation of response mechanisms. In view of role of hormones and capability of microbes in producing hormones, we propose the use of hormones and microbes as potential strategy for crop stress management.

Melatonin (MT) is a pleiotropic molecule with diverse and numerous actions both in plants and animals. In plants, MT acts as an excellent promotor of tolerance against abiotic stress situations such as drought, cold, heat, salinity, and chemical pollutants. In all these situations, MT has a stimulating effect on plants, fomenting many changes in biochemical processes and stress-related gene expression. Melatonin plays vital roles as an antioxidant and can work as a free radical scavenger to protect plants from oxidative stress by stabilization cell redox status; however, MT can alleviate the toxic oxygen and nitrogen species. Beyond this, MT stimulates the antioxidant enzymes and augments antioxidants, as well as activates the ascorbate–glutathione (AsA–GSH) cycle to scavenge excess reactive oxygen species (ROS). In this review, we examine the recent data on the capacity of MT to alleviate the effects of common abiotic soil stressors, such as salinity, alkalinity, acidity, and the presence of heavy metals, reinforcing the general metabolism of plants and counteracting harmful agents. An exhaustive analysis of the latest advances in this regard is presented, and possible future applications of MT are discussed.

The depletion of fresh water resources leads to the utilisation of various alternative sources of water, such as seawater. In this regard, the foliar application of proline is one of the alternative shotgun approaches to increase plant stress tolerance. A pot experiment was conducted in the wire house of the National Research Centre, Dokki, Cairo, Egypt, during the winter season of 2010–2011. The experiment consisted of three concentrations of proline (0, 25 and 50mM) and two concentrations of diluted seawater (3.13 and 6.25dSm−1), whereas control plants were irrigated with tap water (0.23dSm−1). Diluted seawater caused significant reductions in growth parameters, photosynthetic pigments, some mineral contents (P, K, Ca+2), the K+:Na+ ratio and the level of total carbohydrates. In contrast, N, Na+, and Cl− contents, osmoprotectants (soluble carbohydrates, total phenolic concentrations, free amino acids, proline), and activities of antioxidant enzymes (peroxidase and polyphenol oxidase) significantly increased with an increasing salinity level compared with control plants. The foliar application of 25mM proline caused significant increases in growth parameters, photosynthetic pigments, N, P, K+, and Ca+2 %, the K+:Na+ ratio, total carbohydrates, and soluble carbohydrates, accompanied by significant decreases in Na+, Cl−, phenolic contents, free amino acids, proline, and the activities of antioxidant enzymes compared with the control. In addition, 25mM proline minimised the deleterious effect of salinity on the anatomical structure of the faba bean stem and leaf. The proline treatment at 50mM was as essentially toxic to faba bean plants as to that of salinity stress. This toxicity was apparent by the reduction of growth parameters, photosynthetic pigments, N, P, K+, and Ca+2, K+:Na+ ratio and significant increases in Na+ and Cl− concentrations. Therefore, the exogenous application of proline at a concentration of 25mM partially alleviated the toxicity of diluted seawater on faba bean plants, whereas the 50mM proline treatment was toxic

The effect of a novel organo-mineral fertilizer (OMF) compost, as a partial alternative to mineral fertilizers, on soil characteristics, growth, physio-biochemical attributes, Cd²⁺ and NO₃⁻ concentrations, and yields of Phaseolus vulgaris L. plants grown under salt stress was investigated. Six organic and mineral materials were well mixed with water and composted in a polyvinyl house in a concrete trench of size 4 × 5 × 2 m (W × L × D), respectively. The moisture content was maintained at 50–60% throughout the active composting period by frequent checking. The mixture was turned at 7-day intervals for about 2 months to maintain porosity. This OMF compost was applied for the tested saline soil at 10, 20 and 30 ton ha⁻¹ while reducing the recommended NPK to 50%. In addition,100% NPK was applied as a control to achieve the purpose of this study. Growth characteristics, quantitative and qualitative yield, Cd²⁺ and NO₃⁻ concentrations, and physio-biochemical attributes in common bean plants were assessed. Addition of OMF compost improved the soil chemical and physical properties. Application of OMF compost at a rate of 20 ton h⁻¹, as an alternative to 50% of the recommended dose of mineral-NPK fertilizers, significantly decreased the concentrations of Cd²⁺ and NO₃⁻ in plant leaves, pods and seeds, showing the same growth characteristics, and pod and seed yields compared to the control (100% of mineral-NPK fertilizers). This treatment also improved all determined physio-biochemical attributes and tested soil characteristics compared to the control. The benefit of this OMF compost, as a partial alternative to chemical fertilizers, demonstrated the validity and possibility of sustainable agronomic performance of common bean using locally available recycled organic materials for manufacturing the studied OMF.