Citrus Physiological and Molecular Response to Boron Stresses

Since the essentiality of boron (B) to plant growth was reported nearly one century ago, the implication of B in physiological performance, productivity and quality of agricultural products, and the morphogenesis of apical meristem in plants has widely been studied. B stresses (B deficiency and toxicity), which lead to atrophy of canopy and deterioration of Citrus fruits, have long been discovered in citrus orchards. This paper reviews the research progress of B stresses on Citrus growth, photosynthesis, light use efficiency, nutrient absorption, organic acid metabolism, sugar metabolism and relocation, and antioxidant system. Moreover, the beneficial effects of B on plant stress tolerance and further research in this area were also discussed.

PHYTHORMONES AND ABIOTIC STRESS (REVIEW)

Plants experience a variety of biotic and abiotic stresses that cause crop losses worldwide. Preventing crop losses due to these factors is of particular importance. For this, it is important to understand the mechanisms of both suppressing and stimulating seed germination and to develop technologies for controlling seed dormancy and development in order to avoid unwanted germination in the ears. Gene switching technologies can be used to address this and similar problems in seed development. Recent studies have shown that classical phytohormones - auxins, cytokinins, abscisic acid, ethylene, gibberellins - control all stages of plant ontogenesis. In addition to the classic phytohormones, there are relatively new ones - brassinosteroids, jasmonates, strigolactones, salicylates, which deserve consideration in a separate review. Together, these compounds are important metabolic engineering targets for the production of stress-resistant crops. In this review, we have summarized the role of phytohormones in plant development and resistance to abiotic stresses. Experimental data were presented on the transport of phytohormones, the interaction between them, as a result of which the activity of a certain hormone can be either enhanced or suppressed. We have identified the main links of phytohormones with an emphasis on the response of plants to abiotic stresses and have shown that the effect of an individual hormone depends on the ratio with other phytohormones and metabolites. Additional research along these lines will help explain different stress responses and provide tools to improve plant stress tolerance.

Initiation and Execution of Programmed Cell Death and Regulation of Reactive Oxygen Species in Plants

Programmed cell death (PCD) plays crucial roles in plant development and defence response. Reactive oxygen species (ROS) are produced during normal plant growth, and high ROS concentrations can change the antioxidant status of cells, leading to spontaneous cell death. In addition, ROS function as signalling molecules to improve plant stress tolerance, and they induce PCD under different conditions. This review describes the mechanisms underlying plant PCD, the key functions of mitochondria and chloroplasts in PCD, and the relationship between mitochondria and chloroplasts during PCD. Additionally, the review discusses the factors that regulate PCD. Most importantly, in this review, we summarise the sites of production of ROS and discuss the roles of ROS that not only trigger multiple signalling pathways leading to PCD but also participate in the execution of PCD, highlighting the importance of ROS in PCD.

Insights into Metabolic Engineering of the Biosynthesis of Glycine Betaine and Melatonin to Improve Plant Abiotic Stress Tolerance

Metabolic engineering in plant can be describe as a tool using molecular biological technologies which promotes enzymatic reactions that can enhance the biosynthesis of existing compounds such as glycine betaine (GB) in plant species that are able to accumulate GB, or produce news compounds like GB in non-accumulators plants. Moreover we can include to these definition, the mediation in the degradation of diverse compounds in plant organism. For decades, one of the most popular ideas in metabolic engineering literature is the idea that the improvement of gly betaine or melatonin accumulation in plant under environmental stress can be the main window to ameliorate stress tolerance in diverse plant species. A challenging problem in this domain is the integration of different molecular technologies like transgenesis, enzyme kinetics, promoter analysis, biochemistry and genetics, protein sorting, cloning or comparative physiology to reach that objective. A large number of approaches have been developed over the last few decades in metabolic engineering to overcome this problem. Therefore, we examine some previous work and propose some understanding about the use of metabolic engineering in plant stress tolerance. Moreover, this chapter will focus on melatonin (Hormone) and gly betaine (Osmolyte) biosynthesis pathways in engineering stress resistance.

Emerging Roles of γ Aminobutyric Acid (GABA) Gated Channels in Plant Stress Tolerance

The signaling role for γ-Aminobutyric acid (GABA) has been documented in animals for over seven decades. However, a signaling role for GABA in plants is just beginning to emerge with the discovery of putative GABA binding site/s and GABA regulation of anion channels. In this review, we explore the role of GABA in plant growth and development under abiotic stress, its interactions with other signaling molecules and the probability that there are other anion channels with important roles in stress tolerance that are gated by GABA.

Nanoceria seed priming enhanced salt tolerance in rapeseed through modulating ROS homeostasis and α-amylase activities

Background Salinity is a big threat to agriculture by limiting crop production. Nanopriming (seed priming with nanomaterials) is an emerged approach to improve plant stress tolerance; however, our knowledge about the underlying mechanisms is limited. Results Herein, we used cerium oxide nanoparticles (nanoceria) to prime rapeseeds and investigated the possible mechanisms behind nanoceria improved rapeseed salt tolerance. We synthesized and characterized polyacrylic acid coated nanoceria (PNC, 8.5 ± 0.2 nm, −43.3 ± 6.3 mV) and monitored its distribution in different tissues of the seed during the imbibition period (1, 3, 8 h priming). Our results showed that compared with the no nanoparticle control, PNC nanopriming improved germination rate (12%) and biomass (41%) in rapeseeds (Brassica napus) under salt stress (200 mM NaCl). During the priming hours, PNC were located mostly in the seed coat, nevertheless the intensity of PNC in cotyledon and radicle was increased alongside with the increase of priming hours. During the priming hours, the amount of the absorbed water (52%, 14%, 12% increase at 1, 3, 8 h priming, respectively) and the activities of α-amylase were significantly higher (175%, 309%, 295% increase at 1, 3, 8 h priming, respectively) in PNC treatment than the control. PNC primed rapeseeds showed significantly lower content of MDA, H2O2, and •O2− in both shoot and root than the control under salt stress. Also, under salt stress, PNC nanopriming enabled significantly higher K+ retention (29%) and significantly lower Na+ accumulation (18.5%) and Na+/K+ ratio (37%) than the control. Conclusions Our results suggested that besides the more absorbed water and higher α-amylase activities, PNC nanopriming improves salt tolerance in rapeseeds through alleviating oxidative damage and maintaining Na+/K+ ratio. It adds more knowledge regarding the mechanisms underlying nanopriming improved plant salt tolerance. Graphical abstract

Genome-Wide Study of the ABI3 Gene Family and Identification of Putative miRNA Targeting ABI3 Gene in Oryza Sativa ssp. Indica

Rice is one of the important cereal crops mainly cultivated in Asia and its productivity is severely affected by drought stress. In response to drought stress, several genes are reported to be up-regulated or down-regulated in plants. Gene expression is negatively regulated by non-coding endogenous microRNAs post-transcriptionally either by mRNA degrading or translational silencing. In the past, single or multiple stress-responsive genes were over-expressed in order to generate drought-tolerant transgenic rice but with very little success. Recently, the development of transgenic plants by over-expressing transcription factors have received much attention because of their ability to regulate several genes. Abscisic Acid Insensitive 3 (ABI3) is a transcription factor, which is known to play a crucial role in mediating plant stress tolerance. Using the Ensembl plants database, we identified 83 putative OsABI3 genes in Oryza sativa Indica. Through in silico approach, five potential miRNAs i.e., ath-miR5021, csi-miR3948, osa-miRf11773-akr, osa-miRf12029-akr and ptc-miRf10053-akr that target OsABI3 genes were identified. Further, the expression of the selected ABI3 genes were analyzed in rice seedlings exposed to 15% PEG, using the RT-qPCR. In comparison to control, OsABI3 genes showed relatively enhanced expression when exposed to drought stress treatment. This indicates that OsABI3 genes may play important role in development and drought stress in rice seedlings.

Nanoceria Seed Priming Improves Salt Tolerance in Rapeseed Through Modulating ROS Homeostasis and α-Amylase Activities

Background: Salinity is a big threat to agriculture by limiting crop production. Nanopriming (seed priming with nanomaterials) is an emerged approach to improve plant stress tolerance; however, our knowledge about the underlying mechanisms is limited. Results: We used cerium oxide nanoparticles (nanoceria) to prime rapeseeds and investigated the possible mechanisms behind nanoceria improved rapeseed salt tolerance. We synthesized and characterized polyacrylic acid coated nanoceria (PNC, 8.5 ± 0.2 nm, -43.3 ± 6.3 mV) and monitored its distribution in different tissues of the seed during the imbibition period (1, 3, 8h priming). Our results showed that compared with the no nanoparticle control, PNC nanopriming improved germination rate (12%) and biomass (41%) in rapeseeds under salt stress (200 mM NaCl). During the priming hours, PNC were located mostly in the seed coat, nevertheless the intensity of PNC in cotyledon and radicle was increased alongside with the increase of priming hours. During the priming hours, the amount of the absorbed water (52%, 14%, 12% increase at 1, 3, 8h priming, respectively) and the activities of α-amylase were significantly higher (175%, 309%, 295% increase at 1, 3, 8h priming, respectively) in PNC treatment than the control. PNC primed rapeseeds showed significantly lower content of MDA, H2O2, and •O2— in both shoot and root than the control under salt stress. Also, under salt stress, PNC nanopriming enabled significantly higher K+ retention (29%) and also significantly lower Na+ accumulation (18.5%) and Na+/K+ ratio (37%) than the control. Conclusions: Our results suggested that besides the more absorbed water and increased α-amylase activities, PNC nanopriming improves salt tolerance in rapeseeds through maintaining ROS homeostasis and Na+/K+ ratio. It adds more knowledge regarding the mechanisms underlying nanopriming improved plant salt tolerance.