Citric Acid-Mediated Abiotic Stress Tolerance in Plants

Several recent studies have shown that citric acid/citrate (CA) can confer abiotic stress tolerance to plants. Exogenous CA application leads to improved growth and yield in crop plants under various abiotic stress conditions. Improved physiological outcomes are associated with higher photosynthetic rates, reduced reactive oxygen species, and better osmoregulation. Application of CA also induces antioxidant defense systems, promotes increased chlorophyll content, and affects secondary metabolism to limit plant growth restrictions under stress. In particular, CA has a major impact on relieving heavy metal stress by promoting precipitation, chelation, and sequestration of metal ions. This review summarizes the mechanisms that mediate CA-regulated changes in plants, primarily CA's involvement in the control of physiological and molecular processes in plants under abiotic stress conditions. We also review genetic engineering strategies for CA-mediated abiotic stress tolerance. Finally, we propose a model to explain how CA's position in complex metabolic networks involving the biosynthesis of phytohormones, amino acids, signaling molecules, and other secondary metabolites could explain some of its abiotic stress-ameliorating properties. This review summarizes our current understanding of CA-mediated abiotic stress tolerance and highlights areas where additional research is needed

A review on regulatory control of chromium stress in plants

Chromium (Cr) is a non-biodegradable heavy metal that persists long in aquatic and terrestrial ecosystems and enters the food chain. It is cytotoxic even at low concentrations and reduces the yield of plants. Plants also have cellular mechanisms to manage the accumulation of metal ions inside the cell to diminish the possible injury from non-essential metal ions. This paper reviews current information on plant response to Cr, a key environmental pollutant. The harmful effects together with absorption, transfer, and aggregation of Cr are discussed. The roles of the cell wall, plasma membrane, and plant microbes as the primary hindrances for Cr ingression into the cell, along with sequestration and compartmentalization process, have also been discussed. Cr-generated oxidative injury is also regarded as the main deliberated effect of Cr toxicity.  It interferes with NADPH oxidases (plasma membrane) and the electron transport chains, which develop electron leakage. Some genes related to Cr stress in plants get expressed, and suppression produces protective effects by activating the signal transduction pathways. The expression of genes like BnaCnng69940D and BnaC08g49360D is increased, which is involved in protein kinase activity, signal transduction, and oxidoreductase activity. The increased mRNA levels of Cr stress response proteins, including HSP90-1 and MT-1, have been reported in the Brassica napus plant. The stressed environment around the plants may stimulate the biosynthesis of phytochelatins and metal-binding proteins, which have a protective role in plant’s growth and development.

Metabolic Processes During Seed Germination

Seed germination is crucial stage in plant development and can be considered as a determinant for plant productivity. Physiological and biochemical changes followed by morphological changes during germination are strongly related to seedling survival rate and vegetative growth which consequently affect yield and quality. This study is aimed to focus on proceeding of the most vital metabolic processes namely reserve mobilization, phytohormonal regulation, glyoxylate cycle and respiration process under either stressful or non-stressful conditions that may be led to suggest and conduct the more successful experimental improvements. Seed imbibition triggered the activation of various metabolic processes such as synthesis of hydrolytic enzymes which resulted in hydrolysis of reserve food into simple available form for embryo uptake. Abiotic stresses potentially affect seed germination and seedling establishment through various factors, such as a reduction in water availability, changes in the mobilization of stored reserves, hormonal balance alteration and affecting the structural organization of proteins. Recent strategies for improving seed quality involved classical genetic, molecular biology and invigoration treatments known as priming treatments. H2O2 accumulation and associated oxidative damages together with a decline in antioxidant mechanisms can be regarded as a source of stress that may suppress germination. Seed priming was aimed primarily to control seed hydration by lowering external water potential, or shortening the hydration period

Bradyrhizobium inoculation plus foliar application of salicylic acid mitigates water deficit effects on cowpea.

To evaluate the interaction between foliar application of salicylic acid and Bradyrhizobium inoculation on the morphophysiology of cowpea under water stress conditions, four genotypes (BRS Rouxinol, BRS Marataoã, BRS Aracê and BR 17 Gurguéia) were subjected to five combinations of water availability: 100% replacement of crop evapotranspiration (control); 50% replacement of crop evapotranspiration (water stress); water stress + salicylic acid; water stress + Bradyrhizobium inoculation; and water stress + salicylic acid + Bradyrhizobium inoculation. The experiment was set up in a 4 × 5 factorial randomized block design, with four replicates and four plants per plot. Water stress negatively affected the leaf water potential, growth, proline contents and antioxidant activity of the cowpea genotypes, and BRS Marataoã was the most sensitive. Under water stress conditions, Bradyrhizobium inoculation was efficient for BRS Rouxinol, but was only efficient for BRS Marataoã, BRS Aracê and BR 17 Gurguéia when associated with foliar application of salicylic acid, maintaining their values of leaf water potential, growth, proline content and activities of superoxide dismutase, ascorbate peroxidase, and catalase similar to those of the control treatment

Absence of phosphoenolpyruvate carboxylase AtPPC3 increases sensitivity of Arabidopsis thaliana to cadmium

Phosphoenolpyruvate carboxylase (PEPC) and PEPC kinase (PPCK) catalyze a reaction feeding into the tricarboxylic acid (TCA) cycle, increasing the production of metal-chelating organic acids. Little research has been conducted on PEPC isoenzymes in Cd-stressed plants. Arabidopsis (Arabidopsis thaliana) wild-type and AtPPC1 – AtPPC3 mutants, each lacking one of three PEPC isoenzymes, grown in 0, 1, or 5 µM CdCl2 were smaller and had increased AtPPC1 – AtPPC3 and AtPPCK1 – AtPPCK2 transcript abundance, relative phosphorylation, and PEPC activity, more so in roots than shoots. Concentrations of oxaloacetate, citrate and total organic acids increased with greater CdCl2 concentrations. The absence of AtPPC3, and to a lesser extent AtPPC2, resulted in greater oxaloacetate concentrations and smaller plants in comparison with wild-type. My results indicate that AtPPC3 plays an integral role in Arabidopsis’ ability to cope with Cd. This information can be used to better understand Cd tolerance and stress in other plants, including crops

6-Benzylaminopurine Alleviates the Impact of Cu2+ Toxicity on Photosynthetic Performance of Ricinus communis L. Seedlings

Copper (Cu) is an essential element involved in various metabolic processes in plants, but at concentrations above the threshold level, it becomes a potential stress factor. The effects of two different cytokinins, kinetin (KIN) and 6-benzylaminopurine (BAP), on chlorophyll a fluorescence parameters, stomatal responses and antioxidation mechanisms in castor (Ricinus communis L.) under Cu2+ toxicity was investigated. Ricinus communis plants were exposed to 80 and 160 MCuSO4 added to the growth medium. Foliar spraying of 15 M KIN and BAP was carried out on these seedlings. The application of these cytokinins enhanced the tissue water status, chlorophyll contents, stomatal opening and photosynthetic efficiency in the castor plants subjected to Cu2+ stress. The fluorescence parameters, such as Fm, Fv/Fo, Sm, photochemical and non-photochemical quantum yields, energy absorbed, energy trapped and electron transport per cross-sections, were more efficiently modulated by BAP application than KIN under Cu2+ toxicity. There was also effective alleviation of reactive oxygen species by enzymatic and non-enzymatic antioxidation systems, reducing the membrane lipid peroxidation, which brought about a relative enhancement in the membrane stability index. Of the various treatments, 80 M CuSO4 + BAP recorded the highest increase in photosynthetic efficiency compared to other cytokinin treatments. Therefore, it can be concluded that BAP could effectively alleviate the detrimental effects of Cu2+toxicity in cotyledonary leaves of R. communis by effectively modulating stomatal responses and antioxidation mechanisms, thereby enhancing the photosynthetic apparatus’ functioning

Microbial-assisted alleviation of chromium toxicity in plants: a critical review

Soil contamination with chromium (Cr) is a serious and burgeoning environmental problem. The infiltration of excess Cr into the food chain causes a number of human health issues, including respiratory disorders, cardiovascular diseases, renal failure, and several types of cancer. The Cr pollution can be contained by different physical, chemical, and biological remediation approaches. Physical and chemical methods are costly and hazardous to the environment as they cause secondary pollution. Biological approaches such as bioremediation that employ plants (phytoremediation) and microbes are eco-friendly, efficient, and cost-effective. Nonetheless, conventional phytoremediation encounters limitations in large-scale applications due to a restricted pool of hyperaccumulator plant species, slow growth rate, limited biomass production, plant-contaminant specificity, and contaminant-mediated oxidative stress in plants. Interestingly, microbes such as bacteria and fungi have the potential to survive and thrive under extreme environmental conditions. Plant growth-promoting bacteria (PGPB) utilize siderophores, organic acids, biosurfactants, redox mechanisms, and biomethylation to convert metals into soluble and bioavailable forms. Further, these bacteria are involved in synthesizing phytohormones and 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase, acquisition of iron, nitrogen fixation, and phosphorus solubilization, which improve plant growth and strengthening eco-physiological resilience, thereby aiding in phytoremediation. This literature review encompasses a breadth of research conducted over the preceding decade, underscoring the contemporary remedial approaches with a primary focus on the crucial role of microbes in facilitating the phytoremediation of Cr. Moreover, this article revealed the underlying and plausible mechanisms involved in the microbe-assisted phytoremediation potential of plants grown under Cr-contaminated soils

Achieving abiotic stress tolerance in plants through antioxidative defense mechanisms

Climate change has increased the overall impact of abiotic stress conditions such as drought, salinity, and extreme temperatures on plants. Abiotic stress adversely affects the growth, development, crop yield, and productivity of plants. When plants are subjected to various environmental stress conditions, the balance between the production of reactive oxygen species and its detoxification through antioxidant mechanisms is disturbed. The extent of disturbance depends on the severity, intensity, and duration of abiotic stress. The equilibrium between the production and elimination of reactive oxygen species is maintained due to both enzymatic and non-enzymatic antioxidative defense mechanisms. Non-enzymatic antioxidants include both lipid-soluble (α-tocopherol and β-carotene) and water-soluble (glutathione, ascorbate, etc.) antioxidants. Ascorbate peroxidase (APX), superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) are major enzymatic antioxidants that are essential for ROS homeostasis. In this review, we intend to discuss various antioxidative defense approaches used to improve abiotic stress tolerance in plants and the mechanism of action of the genes or enzymes involved

The Role of Metal Ions in Biology, Biochemistry and Medicine

Metal ions are fundamental elements for the maintenance of the lifespan of plants, animals and humans. Their substantial role in biological systems was recognized a long time ago. They are essential for the maintenance of life and their absence can cause growth disorders, severe malfunction, carcinogenesis or death. They are protagonists as macro- or microelements in several structural and functional roles, participating in many bio-chemical reactions, and arise in several forms. They participate in intra- and intercellular communications, in maintaining electrical charges and osmotic pressure, in photosynthesis and electron transfer processes, in the maintenance of pairing, stacking and the stability of nucleotide bases and also in the regulation of DNA transcription. They contribute to the proper functioning of nerve cells, muscle cells, the brain and the heart, the transport of oxygen and to many other biological processes up to the point that we cannot even imagine a life without metals. In this book, the papers published in the Special Issue “The Role of Metal Ions in Biology, Biochemistry and Medicine” are summarized, providing a picture of metal ion uses in biology, biochemistry and medicine, but also pointing out the toxicity impacts on plants, animals, humans and the environment

Plant Signaling Molecule: Role and Regulation under Stressful Environments

Plant Signaling Molecule: Role and Regulation under Stressful Environments explores tolerance mechanisms mediated by signaling molecules in plants for achieving sustainability under changing environmental conditions. Including a wide range of potential molecules, from primary to secondary metabolites, the book presents the status and future prospects of the role and regulation of signaling molecules at physiological, biochemical, molecular and structural level under abiotic stress tolerance. This book is designed to enhance the mechanistic understanding of signaling molecules and will be an important resource for plant biologists in developing stress tolerant crops to achieve sustainability under changing environmental conditions