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Maize is a C4 plant species with higher temperature optima than C3 plant species. Growth and productivity of maize are severely constrained by chilling stress. Here, we review the effects of chilling stress on growth, phenology, water and nutrient relations, anatomy, and photosynthesis in maize. Several management strategies to cope with chilling stress are also proposed. In maize, chilling stress is known to reduce leaf size, stem extension and root proliferation, disturb plant water relations, and impede nutrient uptake. Chilling stress in maize is a complex phenomenon with physiological and biochemical responses at both cellular and whole-organ level. CO2 assimilation by leaves is reduced mainly due to membrane damage, photoinhibition, and disturbed activity of various enzymes. Enhanced metabolite flux through the photorespiratory pathway increases the oxidative load on tissues as both processes generate reactive oxygen species (ROS). Injury caused by ROS to macromolecules under chilling stress is one of the major deterrents to growth. Low-molecular-weight osmolytes, including glycinebetaine, proline, and organic acids, are crucial in sustaining cellular function under chilling stress. Plant growth substances such as salicylic acid, gibberellic acid, and abscisic acid modulate the response of maize to chilling stress. Polyamines and several enzymes act as antioxidants and reduce the adverse effects of chilling stress. Chilling tolerance in maize can be managed through the development and selection of chilling-tolerant genotypes by breeding and genomic approaches. Agronomic approaches such as exogenous application of growth hormones and osmoprotectants to seeds or plants, and early vigour, can also aid in chilling tolerance.

The optimum temperature for maize germination is between 25 and 28 °C. Poor and erratic germination at suboptimal temperature is the most important hindrance in its early sowing. This study was conducted to induce chilling tolerance in hybrid maize (Zea mays L.) by seed priming with salicylic acid (SA) and to unravel the background biochemical basis. For seed priming, maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 ppm (mg l−1) aerated solutions of SA for 24 h and were dried back. Treated and untreated seeds were sown at 27 °C (optimal temperature) and at 15 °C (chilling stress) under controlled conditions. Performance of maize seedlings was hampered under chilling stress. But seed priming with SA improved the seedling emergence, root and shoot length, seedling fresh and dry weights, and leaf and root score considerably compared with control both at optimal and chilling temperatures. However, priming in 50 mg l−1 SA solution was more effective, followed by priming in 100 mg l−1 SA solution. Seed priming with SA improved the chilling tolerance in hybrid maize mainly by the activation of antioxidants (including catalase, superoxide dismutase and ascorbate peroxidase). Moreover, maintenance of high tissue water contents and reduced membrane permeability also contributed towards chilling tolerance.

The study, consisting of two independent experiments, was conducted to evaluate the role of seed priming with ascorbic acid (AsA) in drought resistance of wheat. In the first experiment, seeds of wheat cultivars Mairaj‐2008 and Lasani‐2008 were either soaked in aerated water (hydropriming) for 10 h or not soaked (control). In the second experiment, seeds of same wheat cultivars were soaked in aerated (2 mm) AsA solution (osmopriming) or water (hydropriming) for 10 h. In both experiments, seeds were sown in plastic pots (10 kg) maintained at 70 % and 35 % of water‐holding capacity designated as well watered and drought stressed, respectively. Both experiments were laid out in a completely randomized design with six replications. Drought caused delayed and erratic emergence and disturbed the plant water relations, chlorophyll contents and membranes because of oxidative damage; however, root length in cultivar Lasani‐2008 was increased under drought. Hydropriming significantly improved the seedling emergence and early growth under drought and well‐watered conditions; however, improvement was substantially higher from osmopriming with AsA. Similarly, osmopriming with AsA significantly improved the leaf emergence and elongation, leaf area, specific leaf area, chlorophyll contents, root length and seedling dry weight. Owing to increase in proline accumulation, phenolics and AsA, by seed priming with AsA, plant water status was improved with simultaneous decrease in oxidative damages. These improved the leaf emergence and elongation, and shoot and root growth under drought. However, there was no difference between the cultivars in this regard. In conclusion, osmopriming with AsA improved the drought resistance of wheat owing to proline accumulation and antioxidant action of AsA and phenolics, leading to tissue water maintenance, membrane stability, and better and uniform seedling stand and growth.

Abiotic stresses, including chilling, impede the plant growth and development mainly by oxidative damage. In this study, seed priming with CaCl2 was employed to reduce the damage caused by chilling stress in hybrid maize. Maize hybrid (Hycorn 8288) seeds were soaked in 50, 100 and 150 mg l−1 (ppm) aerated solution of CaCl2 for 24 h and dried. Treated and untreated seeds were sown at 27 °C (optimal temperature) and 15 °C (chilling stress) under controlled conditions. Seed priming with CaCl2 significantly reduced the chilling damage and improved the germination rate, root and shoot length, and seedling fresh and dry weights. Activities of antioxidants, including catalase, superoxide dismutase and ascorbate peroxidase, were also improved. Soluble sugars and α‐amylase concentrations determined as general metabolic indicators of stress were also increased by seed priming with CaCl2. Priming also improved the performance of maize at optimal temperature. Maintenance of tissue water contents, reduction in membrane leakage and increase in antioxidant activities, and carbohydrate metabolism seemed to induce chilling tolerance by CaCl2. Seed priming with 100 mg l−1 CaCl2 was the optimal concentration in improving the performance of hybrid maize both under optimal and stress conditions.

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This study was conducted to investigate the benefits associated with re-drying after seed priming with polyamines. Wheat (cv. AS-2002) seeds were soaked in 10 and 20 mg L -1 aerated solutions of spermidine (Spd), putrescine (Put) and spermine (Spm), and distilled water (CK2) for 12 h at 28 ± 2°C. Untreated seeds (CK1) and priming in distilled water (CK2) were taken as control treatments. Seeds were primed in two sets: In one set, after each treatment, seeds were given three surface washings with distilled water and dried closer to original moisture; in the other, seeds were only surface dried and used immediately. Use of surface-dried seeds after priming was more effective since it reduced emergence time and synchronized the emergence. Moreover, final emergence, shoot and root length, seedling fresh and dry weight were also improved. Improved starch metabolism was considered possible reason of seed invigoration. All the seed treatments resulted in a lower electrical conductivity of seed leachates compared with control; however, there was more decrease in seeds re-dried after priming than the seeds surface dried after priming. Although the effect of all the polyamines was stimulatory, Spd was the more effective for most of the attributes studied. Nonetheless, Put was more effective for seedling fresh and dry weights. All the polyamines were more effective at lower concentrations except Spm, which improved the coefficient of uniformity of emergence at high concentration. To conclude, if immediate sowing is possible, use of surface-dried seeds after priming may be more effective; seed priming with 10 mg L -1 Spd was the most effective technique when surface dried.

Phosphorus (P) defi ciency is a common nutritional factor limiting agricultural production around the globe. Application of phosphatic fertilizers is generally recommended to cope with P defi ciency; however, low use efficiency of available P fertilizers both in calcareous and acid soils limits its viability and also had serious environmental concerns. Higher plants have adapted a number of mechanism to live with low available P in soil such as changes in root morphology and architecture, decreased growth rate, improved P uptake and utilization effi ciency, and exudation of organic acids and enzymes to solubilize external inorganic and organic P compounds in the rhizosphere. Plant species and even cultivars widely differ in P effi ciency because of differences in one or more of these mechanisms. Exploitation of these genetic variations among crop plants can sustain agricultural production. Understanding the mechanism involved in sensing P defi ciency could facilitate selection, breeding, and genetic engineering approaches to improve crop production in P-stressed environments and could reduce dependence on nonrenewable inorganic P resources. In this chapter, we briefl y reviewed the responses of P defi ciency in higher plants, their adaptive mechanisms, and signaling pathways.