Molecular and Physiological Insights into Plant Stress Tolerance and Applications in Agriculture

Rice is a short-day plant, and its heading date (Hd)/flowering time is one of the important agronomic traits for realizing the maximum yield with high nutrition. Theoretically, flowering initiates with the transition from the vegetative stage to shoot apical meristems (SAMs), and it is regulated by endogenous and environmental signals. Under favorable environmental conditions, flowering is triggered with the synthesis of mobile signal florigen in leaves and then translocated to the shoot for activation of cell differentiation-associated genes. In rice, the genetic pathway of flowering comprises OsGI–Hd1–Hd3a, which is an ortholog of the Arabidopsis GI–CO–FT pathway, and the Ehd1-Hd3a pathway. Climate change could affect photoperiod and temperature, which in turn influences heading date and crop yield. In low temperatures and long-day conditions, the expression of the HD3a gene analogous to FT in Arabidopsis deceased, which delays flowering. Similarly, during drought, expression of the Ehd1 gene is suppressed, resulting in a late-flowering phenotype in rice. Drought affects pollen fertility and reduction in grain yield by reducing male fertility, which affects male meiosis during reproduction, microspore development, and anther dehiscence. In this research field, substantial progress has been made to manipulate flowering-related genes to combat abiotic stresses. Here, we summarize the roles of a few genes in improving the flowering traits of rice.

Salt stress is one of the main environmental stresses occurring all over the globe. Soil salinity is a serious issue in arid and semi-arid areas, causing significant ecological disruption. Excess salts in the soil have an impact on plant nutrient intake and osmotic equilibrium, causing osmotic and ionic stress. Complex physiological features, metabolic pathways, enzyme synthesis, suitable solutes, metabolites, and molecular or genetic networks all play a role in plant adaptation or tolerance to salinity stress. Sugar beet is a well-known crop in terms of salt tolerance and for reclaiming such soils, even for the growth of other crops. Natural endowments, accumulation of organic solutes, sodium potassium ions accumulation in vacuoles, and osmotic tolerance potential are some of the key mechanisms involved in providing tolerance to sugar beet. A greater understanding of sugar beet tolerance and response to salt stress will open up new avenues for increasing crop performance in these conditions. The mechanisms involved in sugar beet adaptation to salt stress conditions, as well as the response to such conditions, are discussed in this chapter. 

Plant quality, growth, yield and productivity are repeatedly affected by different abiotic stresses. It sometimes becomes a major upcoming threat to food security when the stress is on some staple crops. Stress-associated gene expression or no expression leads to abiotic stress tolerance, which is an outcome of complex signal transduction networks. Different plants have evolved with diverse, complex signaling networks concerning abiotic stresses. With the advancement of bioinformatics and functional genomics, in particular, many researchers have identified many genes related to abiotic stress tolerance in different crops, which are being used as a promising improvement in abiotic stresses. Different techniques of genome editing also play an important role in combating abiotic stresses. This chapter represents the knowledge regarding stress-tolerant mechanisms using technologies related to the field of functional genomics and may benefit the researchers in designing more efficient breeding programs and eventually for the farmers to acquire stress-tolerant and high-yielding crops to raise their income in the future.

Rice is the major and dominant cereal food crop in the world. Salinity stress is the second most abiotic stress next to drought, limiting rice yield. Approximately 953 Mha area of the world is affected by salinity. Genetic improvement of salt tolerance is an efficient approach to achieving yield gain in salt-affected areas. Although high-yielding salt-tolerant rice varieties are developed, it is difficult to generate tailor-made adapted varieties through traditional breeding. Hence various crop improvement approaches are followed, including marker-assisted selection and transgenic technology apart from classical breeding. Numerous QTLs were identified through the molecular marker approach, and specifically, Saltol QTL was introgressed into elite lines through marker-assisted back cross-breeding, and improved salt-tolerant varieties were bred. Genetic engineering tools are also amply employed whereby the genes underlying various biochemical/physiological processes such as ion and osmotic homeostasis, antioxidation, signaling, and transcription-associated with increased tolerance were characterized, validated, and used to develop salt-tolerant lines of rice. Yet, a clear relationship between expected gains in salt tolerance in vitro has often not been observed in the field in terms of grain yield. Hence, an integrated approach involving molecular breeding and conventional breeding would certainly pave the way to enhance salt tolerance in rice. 

During evolution, plants are exposed to a wide range of beneficial and detrimental environmental conditions. Among these, temperature stress could retard plant growth and development, and even threaten survival. In agriculture, due to temperature stress, crop yield might be reduced remarkably and consequently damage food security. Fortunately, to mitigate these losses, plants have evolved various mechanisms for adaptation, avoidance and acclimatization to overcome temperature stress. For example, chilling or freezing injury can lead to the disruption of many physiological processes in plants, e.g., water status, photosynthesis, respiration, and even most of the metabolism, and thus, various adaptative mechanisms could be activated in plants to avoid damage by the ice crystal formation or other chilling damages. These temperature-stress-tolerant mechanisms for high-temperature stress, cold stress, chilling injury, and freezing injury have been intensively revealed by researchers, and this present chapter attempts to summarize them systematically.

Agricultural productivity across the world is affected by varied abiotic stresses, which require the development of crops tolerant to unfavorable conditions without considerable yield loss. In recent times, considerable importance has been given to phytohormones because of their versatile functions in plant responses to environmental constraints and for their role in the regulation and coordination of the growth and development of plants. Research on phytohormones has shed light on the role of classical and new members of phytohormones in alleviating the harmful effects of abiotic stresses on crop plants, so understanding phytohormone metabolism and its engineering could be a potent and novel approach for developing climate-resilient crops. The present chapter presents a short description of classical and new members of phytohormones and their role in alleviating varied abiotic stresses. Furthermore, molecular and genetic engineering efforts undertaken for the development of crops tolerant to abiotic stresses are also presented along with research gaps and challenges for the utilization of phytohormones for the development of abiotic stress-tolerant plants. 

Mitigating the negative impacts of abiotic stress is an important approach, especially if climate change scenarios are realized. It is important to develop modern applications to deliver adequate and safe food for human consumption, particularly in arid and semi-arid regions that suffer from environmental and economic stressors. The progress made by scientific research in the field of plant tolerance to stress conditions during the last decade is considerable, but it needs to supply technical support for the application. The development strategy is based on combining more than one technique to achieve the integrated management of plants under different abiotic stresses, as will be described in this chapter. 

The change in global climate patterns raised issues related to soil salinization, desertification, unseasonal rains, and droughts which directly or indirectly influence agricultural produce. Plants have some level of tolerance towards various stresses, and this tolerance capacity varies among plant species based on their genetic constitution and evolutionary adaptability. Abiotic stress sensing and responses in plants involve complex pathways containing multiple steps and genes. To survive in stressful conditions, plants need to adjust their physiological and metabolic processes. Adjustments in these processes involve complex changes at the molecular level resulting in a plant’s adaptation at a morphological and developmental level, which in turn impacts agriculture yields (biomass). Here in this chapter, we are emphasizing molecular dissection of the physiological responses towards salt and drought stress. The study of salt and drought stress responses in plants is also important from an agricultural perspective. We aim to provide up-to-date advancements in the molecular biology field to explain ‘stress sensing to stress response’ in plants which involves multifaceted pathways and networks. We will be covering the process starting from sensing, transfer of signals, regulation of gene expressions, synthesis of osmolytes-metabolites, ROS scavenging pathways, etc.., involved in the survival of plants. This chapter will specifically address information regarding salt and drought stress effects and responses in plants. 

In agriculture, salinity has been a major limiting factor in food security. Soil salinity has been shown to limit land utilization and crop productivity. It is especially crucial to avoid such losses as the ever-increasing global population imposes a tremendous amount of pressure on human populations to produce more food and feed. Salt stress has a negative effect on the whole plant and can be seen at all phases of growth, including germination, seedling and vegetative stages. Tolerance to salt stress, on the other hand, varies with plant developmental processes and even from species and cultivars. Salinity in the agricultural system can be managed by adopting various mitigation strategies. To maintain higher productivity in salt-affected environments, salt-tolerant genotypes must be introduced, as well as precise site-specific production systems. Recent advances in genetics and biotechnology, along with traditional breeding methods, provide the potential to create transgenic cultivars that perform well under stress. Exogenous treatment of certain osmoprotectants and growth regulators, as well as nutrient management and seed rejuvenation strategies, may be beneficial for cost-effective agricultural production in saline soils

Various stages of plant growth and development could greatly be affected by abiotic stresses. Among them, two significant abiotic stressors, including drought and heat, hinder crops’ vegetative or reproductive growth stages, which in turn affect sustainable agriculture worldwide. The incidence of drought coupled with heat stress is increasing mainly due to global climate change. It was proved that the effect of drought coupled with heat stress is additive when compared to individual stresses. This chapter focuses on the influence of common dual-stress heat coupled with drought stress on plants. A critical understanding of how different plants respond to heat coupled with drought stress would pave the way to developing suitable agronomic management practices for better crop genotypes with improved productivity.