Consequences and Mitigation Strategies of Heat Stress for Sustainability of Soybean (<em>Glycine max</em> L. Merr.) Production under the Changing Climate

Increasing ambient temperature is a major climatic factor that negatively affects plant growth and development, and causes significant losses in soybean crop yield worldwide. Thus, high temperatures (HT) result in less seed germination, which leads to pathogenic infection, and decreases the economic yield of soybean. In addition, the efficiency of photosynthesis and transpiration of plants are affected by high temperatures, which have negative impact on the physio-biochemical process in the plant system, finally deteriorate the yield and quality of the affected crop. However, plants have several mechanisms of specific cellular detection of HT stress that help in the transduction of signals, producing the activation of transcription factors and genes to counteract the harmful effects caused by the stressful condition. Among the contributors to help the plant in re-establishing cellular homeostasis are the applications of organic stimulants (antioxidants, osmoprotectants, and hormones), which enhance the productivity and quality of soybean against HT stress. In this chapter, we summarized the physiological and biochemical mechanisms of soybean plants at various growth stages under HT. Furthermore, it also depicts the mitigation strategies to overcome the adverse effects of HT on soybean using exogenous applications of bioregulators. These studies intend to increase the understanding of exogenous biochemical compounds that could reduce the adverse effects of HT on the growth, yield, and quality of soybean

Elevated CO₂ Concentration Improves Heat-Tolerant Ability in Crops

The rising concentration of atmospheric carbon dioxide (aCO2) and increasing temperature are the main reasons for climate change, which are significantly affecting crop production systems in this world. However, the elevated carbon dioxide (CO2) concentration can improve the growth and development of crop plants by increasing photosynthetic rate (higher availability of photoassimilates). The combined effects of elevated CO2 (eCO2) and temperature on crop growth and carbon metabolism are not adequately recognized, while both eCO2 and temperature triggered noteworthy changes in crop production. Therefore, to increase crop yields, it is important to identify the physiological mechanisms and genetic traits of crop plants which play a vital role in stress tolerance under the prevailing conditions. The eCO2 and temperature stress effects on physiological aspects as well as biochemical profile to characterize genotypes that differ in their response to stress conditions. The aim of this review is directed the open-top cavities to regulate the properties like physiological, biochemical, and yield of crops under increasing aCO2, and temperature. Overall, the extent of the effect of eCO2 and temperature response to biochemical components and antioxidants remains unclear, and therefore further studies are required to promote an unperturbed production system

Soybean and Sustainable Agriculture for Food Security

Global food security is under-challenged due to over increasing human population, limited cropland, and risk of climate change. Therefore, an appropriate agricultural policy framework needs to be developed for food security that should be sustainable economically and ecologically. Nitrogen (N) is a crucial element that controls the growth productivity of crop plants. N accounts for around 78 volume per cent of the atmosphere but all crop plants cannot use it directly. Agricultural land is mostly dominated by cereals (e.g. rice, wheat, maize) which have specifically high N demand as compared to food legumes. Soybean exemplifies the most significant and cultivated food legume, presently cultivated worldwide under varying climatic conditions. It plays a significant role in global food security as well as agricultural sustainability due to a high seed protein and oil concentration, and low reliance on N fertilization. Soybean enriches soil health by fixing atmospheric N through biological nitrogen fixation (BNF), the most productive and economical system for N fixation and crop production, associated with more intensive production systems. However, the efficiency of BNF depends on several factors. This study is focused to develop more reliable guidelines for managing BNF by using the potential of natural agro-ecosystems

Maize Adaptability to Heat Stress under Changing Climate

The rapidly increasing human population is an alarming issue and would need more food production under changing climate. Abiotic stresses like heat stress and temperature fluctuation are becoming key issues to be addressed for boosting crop production. Maize growth and productivity are sensitive to temperature fluctuations. Grain yield losses in maize from heat stress are expected to increase owing to higher temperatures during the growing season. This situation demands the development of maize hybrids tolerant to heat and drought stresses without compromising grain yield under stress conditions. The chapter aimed to assess the updates on the influence of high-temperature stress (HTS) on the physio-biochemical processes in plants and to draw an association between yield components and heat stress on maize. Moreover, exogenous applications of protectants, antioxidants, and signaling molecules induce HTS tolerance in maize plants and could help the plants cope with HTS by scavenging reactive oxygen species, upregulation of antioxidant enzymes, and protection of cellular membranes by the accrual of compatible osmolytes. It is expected that a better thought of the physiological basis of HTS tolerance in maize plants will help to develop HTS maize cultivars. Developing HTS-tolerant maize varieties may ensure crops production sustainability along with promoting food and feed security under changing climate

Effects of NaHCO3 Acclimation on Rye (Secale Cereale) Growth Under Sodic-Alkaline Stress

Sodic-alkalinity is a serious limiting factor in agricultural productivity. This study was conducted to examine the contribution of acclimation to the adaptation of rye (Secale cereale) to sodic-alkalinity. Effects of acclimation were determined in two sets of experiments: One experiment for mineral accumulation, antioxidative capacity, and other physiological parameters; and a vivo experiment for root Evan&rsquo;s Blue and Na+ influx from medium to root. Being exposed to sodic-alkalinity, acclimation did not affect plant dry weight. However, acclimation significantly reduced Na+ concentration and maintained a lower Na+/K+ ratio in all the tissues, increased the Ca2+ and Mg2+ concentrations in the root tissues, and increased the water uptake ability in comparison to the non-acclimated plants. Acclimation increased the antioxidant capacity represented by the increased activities of the enzymes SOD, GR, CAT, and GPOX in the leaf tissues of acclimated plants in comparison to the non-acclimated plants. Moreover, acclimation increased the root cell viability inhibited the Na+ influx to the root tissues in comparison to the non-acclimated plants. Together, these results suggest that rye can acclimate to sodic-alkalinity by increasing root cell viability, and therefore limited Na+ influx to root tissues and increased water uptake and antioxidant capacities without any change in the plant growth

Characterization of myo-inositol-1-phosphate synthase (MIPS) gene expression and phytic acid accumulation in oat (Avena sativa) during seed development

Phytic acid (myo-inositol 1,2,3,4,5,6-hexakisphosphate; InsP6) is the main storage form of phosphorus in plant seeds, and it decreases the bioavailability of minerals in the feed of monogastric animals. The enzyme myo-inositol-1-phosphate synthase (MIPS, EC 5.1.1.4) catalyzes the conversion of D-glucose-6-phosphate to myo-inositol-1-phosphate, which is the initial step of phytic acid biosynthesis. To date, there is no information about the relationship between the expression of MIPS and the accumulation of phytic acid in developing oat seeds. In the present study, MIPS was isolated by rapid amplification of cDNA ends (RACE)-PCR method from the early developing oat seeds by using three consensus primers which were designed from highly conserved regions in the MIPS sequence from other plants. We examined the changes in the expression of MIPS and accumulation of phytic acid in different seed development stages, as well as the changes in total P (TP), Ca, and Mg concentrations during seed maturation. The results of RACE-PCR and northern blot showed that the maximal MIPS transcription level was observed at 5 days after flowering (DAF), and it was not detected in stems and leaves. Phytic acid was first detected at 25 DAF, when the inorganic P (Pi) level was 8.4-fold lower and the phytic acid P (Phy-P) level was 7.3-fold higher than those after 30 DAF. The TP, Ca, and Mg concentrations increased with the progress of seed maturation. These results indicate that MIPS was only expressed in seeds at the early stage of seed development, after which the seeds started to accumulate phytic acid. In addition, TP, Ca, and Mg are accumulated during seeds maturation

Seedling growth, physiological characteristics, nitrogen fixation, and root and nodule phytase and phosphatase activity of a low-phytate soybean line

Understanding the influence of the valuable “low-phytate” trait on soybean seedling growth, physiology, and biochemistry will facilitate its future exploitation. The aim was to elucidate the physiological and biochemical characteristics of low-phytate (LP) soybean at the seedling stage. To this end, seed P and mineral content and seedling dry weight, carbon (C) and nitrogen (N) accumulation, nitrogen fixation, and root and nodule phytase and phosphatase activity levels were measured at 21 d after sowing LP and normal-phytate (NP) soybean lines. Seedling dry weight, and C and N accumulation were 31%, 38% and 54% higher, respectively, in the LP line than the NP line. The total and specific nitrogen fixation levels in the LP nodules were 46% and 78% higher, respectively, than those in the NP nodules. The phytase, phosphatase, and specific phytase levels were 1.4-folds, 1.3-folds, and 1.3-folds higher, respectively, in the LP roots than the NP roots. The phosphatase and specific phosphatase levels in LP nodules were 1.5-folds and 1.3-folds higher, respectively, than those in the NP nodules. The mineral levels were substantially higher in the LP seeds and seedings than in those of the NP line. The HCl extractabilities of P, S, Fe, Cu and Mn were higher in the LP seeds than the NP seeds. These results indicate that the LP line presented with superior seedling growth and nitrogen fixation relative to the NP line. The LP line had relatively higher root phytase and root and nodule phosphatase activity levels than the NP line and could, therefore, be better suited and more readily adapt to low P conditions.This study was funded by Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research (KAKENHI), Japan: Grant Number 15K14678 and 18K05948 to Saneoka H., and the financial supported by China Scholarship Council(CSC), China to Mr. Qin Dong

Differences in Physiological Responses of Two Oat (Avena nuda L.) Lines to Sodic-Alkalinity in the Vegetative Stage

Sodic-alkalinity is a more seriously limiting factor in agricultural productivity than salinity. Oat (Avena nuda) is a salt-tolerant crop species and is therefore useful in studying the physiological responses of cereals to alkalinity. We evaluated the differential effects of sodic-alkalinity on two naked oat lines, Caoyou1 and Yanke1. Seedlings of the two lines were exposed to 50 mM alkaline salt mixture of NaHCO3 and Na2CO3 (18:1 molar ratio; pH 8.5) for 2 weeks in a soil environment. Sodic-alkalinity exposure led the assimilation of abundant Na+ at similar concentrations in the organs of both lines. However, Caoyou1 showed much stronger growth than Yanke1, exhibiting a higher dry weight, total leaf area, and shoot height under sodic-alkalinity. Further analysis showed that Caoyou1 was more sodic-alkalinity tolerance than Yanke1. This was firstly because of differences in the oxidative stress defense mechanisms in leaves of the two lines. Antioxidant enzyme activities were either slightly elevated (catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (GP), glutathione reductase (GR)) or unaltered (superoxide dismutase (SOD)) in Caoyou1 leaves, but some enzyme (SOD, GPOX, GR) activities were significantly reduced in Yanke1. AnAPX1 transcript levels significantly increased in Caoyou1 under sodic-alkalinity conditions compared with Yanke1, indicating its better antioxidant capacity. Secondly, the related parameters of Mg2+ concentration, phosphoenolpyruvate carboxylase (PEPC) activity, and AnPEPC transcript levels in the leaves showed significantly higher values in Caoyou1 compared with Yanke1. This demonstrated the effective utilization by Caoyou1 of accumulated HCO3&minus; in the irreversible reaction from phosphoenolpyruvate to oxaloacetate to produce inorganic phosphorus, which was elevated in Caoyou1 leaves under alkalinity stress. Overall, the results demonstrated that the greater sodic-alkalinity tolerance of Caoyou1 is the result of: (1) maintained antioxidant enzyme activities; and (2) a higher capacity for the phosphoenolpyruvate to oxaloacetate reactions, as shown by the higher PEPC activity, Mg2+ concentration, and total phosphorus concentration in its leaves, despite the lower soil pH

Tuzluluk Stresi Altındaki Soya Çeşitlerinin Fizyolojik Olarak Karşılaştırılması

Soya (Glycine max L.), dünyada geniş alanlarda tarımı yapılan tarla bitkilerinden biridir. Mısır, sınırlı tatlı su kaynakları ile yarı kurak bir ülkedir. Sulama suyu ihtiyacını karşılamak için, geleneksel olmayan tuzlu ya da atık suların da sulamada kullanılması gerekmektedir. Bu amaçla, Mısır kökenli üç soya çeşidinde (Giza-35, Giza-82, and Giza-111), tuzlu olmayan (kontrol) ve tuzlu (10 mM NaCl) sulama suyunun etkileri, 2010 yılında Japonya'nın Hiroşima Üniversitesi, bitki besleme fizyolojisi laboratuarında yürütülen saksı çalışmaları ile araştırılmıştır. Tuzluluğun bitki üzerindeki etkileri, bitki büyüme parametreleri (BBP) ile belirlenmiştir. Su ilişkiler ise oransal su içeriği ve elektrolit sızıntısı ile saptanmıştır. Tuzluluk stresine tepkiler, bitki dokularındaki klorofil, azot, K, Na ve prolin içeriğinin analizi ile saptanmıştır. Sonuçlar, tuz stresi ile BBP arasındaki ilişkilerin negatif olduğunu göstermiştir. Buna karşın, Prolin, Na+ ve elektrolit sızıntısı, tuzluluk ile birlikte artmıştır. Bu çalışmadaki sonuçlar, Giza-111 çeşidinin incelenen tüm özelliklerinin diğer çeşitlere göre üstün olduğunu göstermiştir. Bitkideki kuru ağırlık, oransal su içeriği ile N, K+ ve prolin biriminin en yüksek değerlerin, çeşitler karşılaştırıldığında Giza-111 çeşidinde olduğu saptanmıştır. Diğer yandan, tuzluluk, tüm çeşitlerin saplarında elektrolit sızıntısı ve Na+ iyonu birikimini artırmıştır. Bununla birlikte en düşük Na+ birikimine Giza-111 çeşidinde rastlanılmıştır. Benzer şekilde, Giza-111 çeşidinin sızıntıya karşı membranlarının daha kararlı olduğu bulunmuştur. Sonuç olarak, çeşitlerin, tüm özellikleri karşılaştırıldığında Giza-111 çeşidinin tuzlu koşullarda yaşama uyum kabiliyetinin diğer çeşitlere göre daha iyi olduğu görülmüştür.Soybean (Glycine max L.) is one of the main crops and is widely cultivated in the world. Egypt has a semi-arid country with limited fresh water resources. In order to supply to irrigation water demand, it needs to use of non-conventional water resources such as saline or brackish water for irrigation. With this in mind, an pot experiments was conducted at plant nutritional physiology laboratory, Hiroshima University, Japan in 2010 to investigate the effect of irrigation with saline water on three Egyptian soybean cultivars (Giza-35, Giza-82, and Giza-111) under a non-saline (control) and saline (10 mM NaCl) conditions. The effects of salinity on crop was studied by measuring plant growth parameters. The water relations were estimated by studying the relative water contents and electrolyte leakage. The response to salinity stress was analysed by estimating the chlorophyll content, nitrogen, K+, Na+, proline content of plant tissue. The results showed a negative relationship between salinity stress and most of the measured plant growth parameters. In contrast, proline, Na+ and electrolyte leakage increased with irrigation water salinity. Results indicated that Giza-111 cultivar surpassed other cultivars in all characters under study. The highest value of crop dry weight, relative water content and accumulation of N, K+ and proline observed in Giza-111 with the compare to another cultivars. On the other hand, electrolyte leakage and Na+ ions accumulations were increased in the shoot under salinity in all cultivars. However, the lowest accumulation of Na+ ions was occured in Giza-111. Similarly, Giza-111 was more stabilited membrane to leakage. As a result, Giza-111 cultivar showed more capability and appropriate to survive under salinity condition compared with another cultivars regarding of almost all plant traits