The effect of silicon (Si) on physiological attributes and nutritional status of maize (Zea mays cv. DK 647 F1) under water stress was studied in a pot experiment. Treatments were (1) well watered (WW): 100% of FC (soil field capacity), (2) WW + Si1: 100% of FC + 1 mM Si, (3) WW + Si2: 100% of FC + 2 mM Si, (4) water stress (WS): 50% of FC, (5) WS + Si1: 50% of FC + 1 mM Si and (6) WS + Si2: 50% of FC + 2 mM Si. In the control treatment, plants were irrigated to field capacity (100% FC). Water stress was imposed by maintaining a moisture level equivalent to 50% of field capacity, whereas the well-watered pots (control) were maintained at full field capacity. Water stress was found to reduce the total dry matter (DM), chlorophyll content, and relative water content (RWC), but to increase proline accumulation and electrolyte leakage in maize plants. Both Si treatments largely improved the above physiological parameters, but levels remained significantly lower than the control (WW) values except for electrolyte leakage and root:shoot ratios, which were higher. Only root DM appeared to show very little variation in any of the treatments. The concentration of Si in the plants was increased by Si addition into the nutrient solution. Water stress reduced leaf calcium (Ca) and potassium (K) of maize plants, but addition of Si increased these nutrient levels; Ca levels were similar to WW under the high-Si treatment, but K was lower. Root Ca and K were both increased by WS; root Ca was further increased by high Si (WS + Si2 treatment). Addition of Si to the WS treatments did not change root K. Results indicate that while application of Si may be one approach to improve growth of this crop and increase its production in arid or semi-arid areas where water is at a premium, this technique would not fully substitute for an adequate water supply.

Accumulation of arsenic (As) in soils is increasing consistently day-by-day, which has resulted in increased toxicity of this element in various crop plants. Arsenic interferes with several plant metabolic processes at molecular, biochemical and physiological levels, which result in reduced plant productivity. Hence, the introduction of novel ameliorating agents to combat this situation is the need of the hour. The present study was designed to examine the effect of zinc oxide nanoparticles (ZnO–NPs) in As-stressed soybean plants. Various plant growth factors and enzymes were studied at varying concentrations of As and ZnO–NPs. Our results showed that with the application of ZnO–NPs, As concentration declined in both root and shoot of soybean plants. The lengths of shoot and root, net photosynthetic rate, transpiration, stomatal conductance, photochemical yield and other factors declined with an increase in external As level. However, the application of ZnO–NPs to the As-stressed soybean plants resulted in a considerable increase in these factors. Moreover, the enzymes involved in the ascorbate–glutathione cycle including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) showed a significant increase in their activity with the application of ZnO–NPs to the As-stressed plants. Hence, our study confirms the significance of ZnO–NPs in alleviating the toxicity of As in soybean plants.

Abiotic stresses, such as temperature extremes, drought, salinity, and heavy metals are major factors limiting crop productivity and sustainability worldwide. Abiotic stresses disturb plant growth and yield formation. Several chemical compounds, known as plant growth regulators (PGRs), modulate plant responses to biotic and abiotic stresses at the cellular, tissue, and organ levels. Thiourea (TU) is an important synthetic PGR containing nitrogen (36%) and sulfur (42%) that has gained wide attention for its role in plant stress tolerance. Tolerance against abiotic stresses is a complex phenomenon involving an array of mechanisms, and TU may modulate several of these. An understanding of TU-induced tolerance mechanisms may help improve crop yield under stress conditions. However, the potential mechanisms involved in TU-induced plant stress tolerance are still elusive. In this review, we discuss the essential role of TU-induced tolerance in improving performance of plants growing under abiotic stresses and potential mechanisms underlying TU-induced stress tolerance. We also highlight exploitation of new avenues critical in TU-induced stress tolerance.