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Biochemical Responses of Plants to Individual and Combined Abiotic Stresses

Kanchan Sharma1, Kritika Jalota1, Chiti Agarwal2, Puja Pal1 and Suruchi Jindal1*

1Division of Molecular Biology and Genetic Engineering, School of Bioengineering and Biosciences, Lovely Professional University, Phagwara, Punjab, India

2Washington State University, Pullman, Washington, USA

Abstract

The natural environmental conditions constantly subject the plants to different kinds of abiotic stress conditions, and multiple abiotic stress conditions at once are also common. Understanding the plant’s biochemical reactions to individual as well as combined abiotic stresses is essential to know the plant adaptation processes and develop strategies to increase stress tolerance. The main molecular pathways and biochemical processes in response to individual and combined abiotic stress situations were examined. Plants activate numerous biochemical defense mechanisms when specific stress conditions occur including high temperature, cold, drought, flood, salt stress, and heavy-metal contamination, which includes metal chelation procedures, compatible solute synthesis, the buildup of heat-shock proteins, and antioxidant defense mechanisms activation, among others. Plants, when subjected to combined abiotic stressors, can have distinctive responses dissimilar from those seen in single stress conditions. The stress factors that interact with one another can have positive or negative outcomes on physiology and metabolism of the plants. Furthermore, regulation of hormones and signaling pathways has an important part in the modulation of physiological responses to abiotic stressors through coordinated biochemical reactions.

Keywords: Abiotic stress, metabolites, signaling pathways, biochemical response

1.1 Introduction

Abiotic stress has been the subject of major recent advancements in flora. However, the majority of investigations depict the reaction of plants to environmental changes and have concentrated on a particular stress condition that is delivered to plants under laboratory conditions. In the natural environment, plants face a constant array of abiotic stresses, which can significantly impede their growth, development, and productivity. These stresses can manifest individually or in combination, posing significant challenges to plant survival and performance. The impact of these conditions on plant metabolism may exhibit unique characteristics that differ from the effects induced by individual stress conditions. Therefore, their response to abiotic challenges under the field settings can vary significantly from these responses observed in controlled laboratory conditions [1–3]. To fully understand the underlying processes of stress tolerance and to create methods to increase plant tolerance against changing environments, it is essential to know plant’s biochemical reactions against individual and combined abiotic stressors (Figure 1.1).

Figure 1.1 Different abiotic stress conditions leading to plant stress tolerance and adaptation.

1.2 Biochemical Responses to Individual Abiotic Stresses

1.2.1 Heat Stress

A primary abiotic stressor that adversely affects the growth, development, and agricultural productivity of plants is high temperature. Investigation of the plant’s biochemical responses to high-temperature stress becomes important in creating techniques to improve crop heat tolerance when global temperatures rise because of climatic changes. Protein denaturation and oxidative damage occur from stress due to high temperature, which disturbs cellular homeostasis. Different biochemical defense systems are triggered in response by plants. Heat-shock protein (HSP) buildup is one of these. These aid with protein folding and prevent aggregation and molecular chaperones [4]. To counteract ROS accumulation (reactive oxygen species) and mitigate oxidative stress, plants enhance their antioxidant defense mechanisms [5]. The primary impact of high-temperature stress is protein denaturation, which disrupts cellular homeostasis and impairs normal metabolic functions. The plants trigger particular metabolic reactions to combat protein denaturation. Under high-temperature stress circumstances, for protein folding and refolding, HSPs and molecular chaperones are essential. The physiological, biochemical, and molecular factors underlying a plant’s capacity to withstand heat stress were investigated, which emphasized the significance of HSPs in preserving protein integrity and avoiding aggregation under heat stress, especially small HSPs (sHSPs) and HSP70. As molecular chaperones, these proteins help denatured proteins fold correctly and stop them from irreversibly aggregating. Plant’s main metabolic reactions to heat stress are the synthesis and accumulation of these chaperones [4, 6].

Plant cells frequently produce ROS during high heat conditions. ROS includes superoxide radicals (O2–), hydrogen peroxide (H2O2), and hydroxyl radicals (OH). These can harm cellular constituents like lipids, proteins, and DNA through oxidative stress. Plants activate their antioxidant defensive mechanisms to combat ROS buildup and oxidative stress. The activation of antioxidant enzymes occurs as a biological response to high-temperature stress, including SOD (superoxide dismutase), CAT (catalase), and POX (peroxidases). These enzymes are essential for neutralizing ROS and preserving cellular redox balance. Superoxide radicals are changed into H2O2 by SOD, which is then detoxified by the enzymes CAT and POX. Additionally, plants are shielded from oxidative damage by the production and buildup of non-enzymatic antioxidants like ascorbate (vitamin C), glutathione (GSH), and tocopherols (vitamin E) [4, 7]. Under high-temperature stress, for combatting deleterious effects of heat, they undergo metabolic modifications[8]. These modifications entail changes to metabolic pathways, particularly those involved in osmolyte accumulation, energy metabolism, and the creation of secondary metabolites. To sustain cellular hydration and osmotic equilibrium while under the stress of high temperatures, plants acquire suitable solutes or osmolytes, like proline, glycine betaine, and carbohydrates. During heat stress, particularly proline is crucial for stabilizing proteins, preserving membrane integrity, and turgor pressure of cells. Furthermore, the ability of plants to use energy can be impacted by severe temperature stress. When cells are under stress, it frequently results in increased respiration rates and an increase in the need for ATP. To meet the energy requirements of heat-stressed cells, plants may boost glycolysis, respiration, and photosynthetic rates [4, 9].

Phytohormones are also essential for controlling the physiological reactions to stress caused by high temperatures. The hormone ABA (abscisic acid) is associated with plant stress reactions, especially high-temperature stress. For the reduction of the effects of high-temperature plant water status, ABA buildup under heat stress circumstances regulates stomatal closure, limiting water loss through transpiration [4, 10]. Additionally, ABA regulates the antioxidant enzyme and protein production genes in stress response, which helps plants adapt to high temperatures in general. Other hormones involved in the reaction to extreme temperature stress include ethylene and Jasmonic acid (JA). Under stressful circumstances, ethylene is known to control several physiological and biochemical mechanisms. These include aging, ripening of fruits, and defensive responses [8]. High-temperature stress activates both stress-related genes and generates ethylene. HSFs are genetic expression–controlling transcription factors that mediate heat genes that activate during stress to orchestrate high-temperature stress response [11]. Heat-shock domain, a conserved DNA-binding domain, is what distinguishes HSFs from other proteins (HSD). HSFs can attach to particular DNA sequences termed heat-shock elements (HSEs). These are located at the promoter regions of target genes because of the HSD. HSFs interact with chaperones to remain in an inactive monomeric state under typical circumstances. HSFs, however, experience conformational variations undergoing heat stress, which results in trimerization and activation [6]. Numerous high-temperature stress-responsive genes are upregulated when HSFs bind to HSEs in the target gene’s promoter. These genes produce heat stress proteins, also known as HSPs. HSPs play a role as molecular chaperones in high-temperature stress situations to aid protein folding, inhibit protein aggregation, and support protein stability [12].

Excessive heat stress causes osmotic equilibrium disruption within cells, which causes the cells to become dehydrated and get damaged. Plants accumulate osmoprotectants and suitable solutes including proline, glycine betaine, and carbohydrates to prevent these effects. These substances prevent damage to cellular structures, stabilize proteins, scavenge ROS, and preserve cellular osmotic potential. Under heat stress, proline in particular accumulates quickly and functions as a suitable solute to prevent the denaturation of proteins and membranes [13]. The fluidity and stability of cellular membranes can also be negatively impacted by heat stress, which can result in membrane lipid peroxidation and malfunction. In order to improve membrane stability and integrity in response to heat stress,...