Soil salinity is a major environmental stress that restricts the growth and yield of crops. Understanding the physiological, metabolic, and biochemical responses of plants to salt stress and mining the salt tolerance-associated genetic resource in nature will be extremely important for us to cultivate salt-tolerant crops. In this review, we provide a comprehensive summary of the mechanisms of salt stress responses in plants, including salt stress-triggered physiological responses, oxidative stress, salt stress sensing and signaling pathways, organellar stress, ion homeostasis, hormonal and gene expression regulation, metabolic changes, as well as salt tolerance mechanisms in halophytes. Important questions regarding salt tolerance that need to be addressed in the future are discussed.

Mechanisms of Plant Responses and Adaptation to Soil Salinity.

The essentiality of B for growth and development of plants is well-known, but the primary functions of B still remain unknown. Evidence in the literature supports the idea that the major functions of B in growth and development of plants are based on its ability to form complexes with the compounds having cis-diol configurations. In this regard, the formation of B complexes with the constituents of cell walls and plasma membranes as well as with the phenolic compounds seems to be a decisive step affecting the physiological functions of B. Boron seems to be of crucial importance for the maintenance of structural integrity of plasma membranes. This function of B is mainly related to stabilisation of cell membranes by B association with membrane constituents. Possibly, B may also protect plasma membranes against peroxidative damage by toxic O2 species. In B-deficient plants, plasma membranes are highly leaky and lose their functional integrity. Under B-deficient conditions, substantial changes in ion fluxes and proton pumping activity of the plasma membranes were noted. Impairments in phenol metabolism and increases in levels of phenolics and polyphenoloxidase activity are typical indications of B deficiency, particularly in B deficiency-sensitive plant species, such as Helianthus annuus (sunflower). Enhanced oxidation of phenols is responsible for generation of reactive quinones which subsequently produce extremely toxic O2 species, thus resulting in the increased risk of a peroxidative damage to vital cell components such as membrane lipids and proteins. In B-deficient tissues, enhancement in levels of toxic O2 species may also occur as a result of impairments in photosynthesis and antioxidative defence systems. Recent evidence shows that the levels of ascorbic acid, non-protein SH-compounds (mainly glutathione) and glutathione reductase, the major defence systems of cells against toxic O2 species, are reduced in response to B deficiency. There is also increasing evidence that, in the heterocyst cells of cyanobacteria, B is involved in protection of nitrogenase activity against O2 damage.

Boron deficiency-induced impairments of cellular functions in plants: a review

Salinity induced physiological and biochemical changes in plants: An omic approach towards salt stress tolerance

Silicon (Si) is the second most abundant element in soil, where its availability to plants can exhilarate to 10% of total dry weight of the plant. Si accumulation/transport occurs in the upward direction, and has been identified in several crop plants. Si application has been known to ameliorate plant growth and development during normal and stressful conditions over past two-decades. During abiotic (salinity, drought, thermal, and heavy metal etc) stress, one of the immediate responses by plant is the generation of reactive oxygen species (ROS), such as singlet oxygen (1O2), superoxide (O2−), hydrogen peroxide (H2O2), and hydroxyl radicals (OH), which cause severe damage to the cell structure, organelles, and functions. To alleviate and repair this damage, plants have developed a complex antioxidant system to maintain homeostasis through non-enzymatic (carotenoids, tocopherols, ascorbate, and glutathione) and enzymatic antioxidants [superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)]. To this end, the exogenous application of Si has been found to induce stress tolerance by regulating the generation of ROS, reducing electrolytic leakage and malondialdehyde (MDA) contents, and immobilizing and reducing the uptake of toxic ions like Na, under stressful conditions. However, the interaction of Si and plant antioxidant enzyme system remains poorly understood, and further in-depth analyses at the transcriptomic level are needed to understand the mechanisms responsible for the Si-mediated regulation of stress responses.

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Silicon Regulates Antioxidant Activities of Crop Plants under Abiotic-Induced Oxidative Stress: A Review

Toxicity of aluminium on various levels of plant cells and organism: A review

The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Liviidae), is a key vector of the causal agents of Huanglongbing (HLB), a devastating disease affecting citrus almost worldwide. Nicotiana tabacum L. is an important commercial crop in China. Field observations suggested that D. citri adults die on N. tabacum leaves when grown nearby citrus orchards. In this study, the preference for and survivorship of D. citri adults on N. tabacum and their feeding behavior were investigated. The results showed that D. citri adults were attracted to N. tabacum and to the green leaf volatiles (GLVs) (Z)-3-hexenol and (E)-2-hexenol. The survival of D. citri adults on N. tabacum was less than 30 h, which was shorter than that for adults without food (35 h) and on a suitable host Murraya exotica L. (29 days). Electrical penetration graph (EPG) recordings revealed that the pathway phase of D. citri on N. tabacum leaves consisted of four waveforms—the non-probing phase (NP), the pathway phase (PP, including intercellular probing of activity in the phloem (C) and phloem penetration (D)), phloem salivation (E1), and phloem ingestion (E2). Diaphorina citri only secreted saliva and ingested sap from phloem on N. tabacum leaves and spent the longest duration in phloem sap ingestion (E2). Moreover, L-nicotine, an important defense compound against insects in N. tabacum plants, was highly toxic to D. citri. These results suggested that N. tabacum plants could help to sustainably control the spread of D. citri and HLB when growing in and around citrus orchards.

https://www.frontiersin.org/articles/10.3389/fpls.2022.1081663/pdf

Nicotiana tabacum as a dead-end trap for adult Diaphorina citri: A potential biological tactic for protecting citrus orchards

Boron (B) supply alleviates toxic effects of aluminum (Al) on root growth; however, the mechanistic basis of this process remains elusive. This study filled this knowledge gap showing that boron modifies auxin distribution and transport in Al-exposed Arabidopsis roots. In B-deprived roots, Al treatment induced an increase in auxin content in the root apical meristem (MZ) and transition zone (TZ) while in the elongation zone (EZ) auxin content was decreased beyond the level required for adequate growth. These distribution patterns are explained by the fact that basipetal auxin transport from the TZ to EZ was disrupted by Al-inhibited PIN2 endocytosis. Experiments involving modulation of protein biosynthesis by cycloheximide (CHX) and transcriptional regulation by cordycepin (COR) demonstrated that Al-induced increase of PIN2 membrane proteins was depended on the inhibition of PIN2 endocytosis rather than on the transcriptional regulation of PIN2 gene. Experiments reporting profiling of Al3+ and PIN2 proteins revealed that the inhibition of endocytosis of PIN2 proteins was due to Al-induced limitation of the fluidity of the plasma membrane. B supply mediated the turnover of PIN2 endosomes conjugated with IAA and thus restored Al-induced inhibition of IAA transport through the TZ to EZ. Overall, reported results demonstrate that boron supply mediates PIN2 endosome-based auxin transport to alleviate Al toxicity in plant roots.

Boron Supply Restores Aluminum-Blocked Auxin Transport by Modulation PIN2 Trafficking in the Root Apical Transition Zone.

Winter wheat cultivars differing in Mo efficiency (highly efficient cv. 97003 and inefficient cv. 97014) were grown on an acid yellow brown earth which was severely deficient of Mo. Mo application increased the activity of nitrate reductase (NR), accumulation of total nitrogen, content of chlorophyll and protein, stimulated the growth, and decreased the content of total nitrogen. The activity of glutamine synthetase (GS) and the content of glutamate, however, were surprisingly higher under Mo deficiency than after Mo application, glutamate being increased up to tenfold. Cv. 97003 showed higher efficiency than cultivar 97014 under Mo deficient stress in the activities of NR and GS, especially the isoenzyme GS2, content of glutamate, soluble protein and chlorophyll, accumulation of total nitrogen and distribution of nitrogen to the seeds. Cv. 97003 is thus more efficient for uptake, allocation, assimilation and use of nitrogen under Mo deficiency compared to cv. 97014.

Influence of Mo on the metabolism of nitrogen in winter wheat cultivars with different Mo efficiency

Background Development of an evaluation tool to determine genotypic variation in phosphorus (P) utilization efficiency is essential to ensure crop productivity and farmers’ income under low P environments. Aims This study aimed to develop an evaluation tool to determine genotypic variation in low-P tolerance and P use efficiency under low P environments. Methods Root response and P efficiency traits in 20 maize genotypes with contrasting root systems were assessed 32 days after transplanting into the semi-hydroponic root phenotyping system under low P (10 μM) or optimal P (200 μM) supply. Results Compared to optimal P, low P supply increased root-to-shoot biomass ratio by 48.7% (shoot dry weight decreased by 20.0% and root dry weight increased by 20.6%). Low P supply increased total root length by 17.8% but decreased primary root depth, with no significant change in lateral root number across all genotypes. Low P stress enhanced P utilization efficiency. Based on genotypic variation and correlations among the 17 measured plant traits in response to low P stress, nine traits were converted to low-P tolerance coefficients (LPTC), compressed by principal component analysis. The three principal component scores were extracted for hierarchical cluster analysis and classified the 20 genotypes into three groups with different P efficiency, including two P-efficient genotypes and nine P-inefficient genotypes. Conclusions The study demonstrated genotypic variation in response to low P stress. The P-efficient genotypes with higher LPTC values better adapted to low P environments by adjusting root architecture and re-distributing P and biomass in plant organs. The systematic cluster analysis using selected traits and their LPTC values can be used as an evaluation tool in assessing P efficiency among the genotypes. 

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/jpln.202200196

Assessing phosphorus efficiency and tolerance in maize genotypes with contrasting root systems at the early growth stage using the semi‐hydroponic phenotyping system

Min Yu

Papers

Nicotiana tabacum as a dead-end trap for adult Diaphorina citri: A potential biological tactic for protecting citrus orchards

Boron Supply Restores Aluminum-Blocked Auxin Transport by Modulation PIN2 Trafficking in the Root Apical Transition Zone.

Influence of Mo on the metabolism of nitrogen in winter wheat cultivars with different Mo efficiency

Assessing phosphorus efficiency and tolerance in maize genotypes with contrasting root systems at the early growth stage using the semi‐hydroponic phenotyping system

The wall-associated kinase gene family in pea (Pisum sativum) and its function in response to B deficiency and Al toxicity.