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The calcium (Ca2+) signaling is a crucial event during plant-herbivore interaction, which involves a transient change in cytosolic Ca2+ concentration, which is sensed by Ca2+-sensors, and the received message is transduced to downstream target proteins leading to appropriate defense response. Calmodulin-like proteins (CMLs) are calcium-sensing plant-specific proteins. Although CMLs have been identified in a few plants, they remained uncharacterized in leguminous crop plants. Therefore, a wide-range analysis of CMLs of soybean was performed, which identified 41 true CMLs with greater than 50% similarity with Arabidopsis CMLs. The phylogenetic study revealed their evolutionary relatedness with known CMLs. Further, the identification of conserved motifs, gene structure analysis, and identification of cis -acting elements strongly supported their identity as members of this family and their involvement in stress responses. Only a few Glycine max CMLs (GmCMLs) exhibited differential expression in different tissue types, and rest of them had minimal expression. Additionally, differential expression patterns of GmCMLs were observed during Spodoptera litura -feeding, wounding, and signaling compound treatments, indicating their role in plant defense. The three-dimensional structure prediction, identification of interactive domains, and docking with Ca2+ ions of S. litura -inducible GmCMLs, indicated their identity as calcium sensors. This study on the characterization of GmCMLs provided insights into their roles in calcium signaling and plant defense during herbivory. [ABSTRACT FROM AUTHOR]

Stomatal guard cells are specialized epidermal cells regulating gas exchange. The ability to open or close in response to external and internal cues makes stomata a dynamic and fascinating system. Stomatal closure upon infection ensures restriction of pathogen entry into the plant and forms an essential component of innate immunity. The opening or closure of stomata is dependent on the turgidity or flaccidity of guard cells, respectively, facilitated by several signaling components, including reactive oxygen species, nitric oxide (NO) and Ca2+. Among these, NO is the most extensively studied gasotransmitter. Its pivotal role in stomatal closure by modulating various downstream components as well as regulation of crucial proteins by post-translational modifications makes NO an essential factor. Two more gasotransmitters, carbon monoxide and hydrogen sulfide, also trigger stomatal closure. Other gaseous molecules, like ethylene, methane, sulfur dioxide, ozone, and CO2, can modulate stomatal closure, but they are not considered strictly as gasotransmitters due to specific criteria. We review the signaling events in guard cells triggered by these gasotransmitters leading to stomatal closure. We point out the dual role of NO to promote stomatal closure and stomatal opening. Both NO and H2S help in reinforcing the innate immunity against pathogen attack. Although there is extensive information on the mechanism of NO action on stomata, the enzymatic source of NO or CO is still ambiguous. Similarly, research is warranted to establish the relative importance of and interactions among the three main gasotransmitters. Further studies on gasotransmitters would answer the ambiguity about their functions and confirm if they can act independently.

The calcium (Ca2+) signaling is a crucial event during plant-herbivore interaction, which involves a transient change in cytosolic Ca2+ concentration, which is sensed by Ca2+-sensors, and the received message is transduced to downstream target proteins leading to appropriate defense response. Calmodulin-like proteins (CMLs) are calcium-sensing plant-specific proteins. Although CMLs have been identified in a few plants, they remained uncharacterized in leguminous crop plants. Therefore, a wide-range analysis of CMLs of soybean was performed, which identified 41 true CMLs with greater than 50% similarity with Arabidopsis CMLs. The phylogenetic study revealed their evolutionary relatedness with known CMLs. Further, the identification of conserved motifs, gene structure analysis, and identification of cis-acting elements strongly supported their identity as members of this family and their involvement in stress responses. Only a few Glycine max CMLs (GmCMLs) exhibited differential expression in different tissue types, and rest of them had minimal expression. Additionally, differential expression patterns of GmCMLs were observed during Spodoptera litura-feeding, wounding, and signaling compound treatments, indicating their role in plant defense. The three-dimensional structure prediction, identification of interactive domains, and docking with Ca2+ ions of S. litura-inducible GmCMLs, indicated their identity as calcium sensors. This study on the characterization of GmCMLs provided insights into their roles in calcium signaling and plant defense during herbivory.

Stomatal guard cells are specialized epidermal cells regulating gas exchange. The ability to open or close in response to external and internal cues makes stomata a dynamic and fascinating system. Stomatal closure upon infection ensures restriction of pathogen entry into the plant and forms an essential component of innate immunity. The opening or closure of stomata is dependent on the turgidity or flaccidity of guard cells, respectively, facilitated by several signaling components, including reactive oxygen species, nitric oxide (NO) and Ca2+. Among these, NO is the most extensively studied gasotransmitter. Its pivotal role in stomatal closure by modulating various downstream components as well as regulation of crucial proteins by post-translational modifications makes NO an essential factor. Two more gasotransmitters, carbon monoxide and hydrogen sulfide, also trigger stomatal closure. Other gaseous molecules, like ethylene, methane, sulfur dioxide, ozone, and CO2, can modulate stomatal closure, but they are not considered strictly as gasotransmitters due to specific criteria. We review the signaling events in guard cells triggered by these gasotransmitters leading to stomatal closure. We point out the dual role of NO to promote stomatal closure and stomatal opening. Both NO and H2S help in reinforcing the innate immunity against pathogen attack. Although there is extensive information on the mechanism of NO action on stomata, the enzymatic source of NO or CO is still ambiguous. Similarly, research is warranted to establish the relative importance of and interactions among the three main gasotransmitters. Further studies on gasotransmitters would answer the ambiguity about their functions and confirm if they can act independently. [ABSTRACT FROM AUTHOR]

Highlights • Traditional and new topics of plant abiotic stress are covered. • New information and other emerging topics of oxidative stress are discussed. • Characterization of ROS types, production processes and sources. • Detailed description of both enzymatic and non-enzymatic antioxidants. • Special focus attributed to transgenerational effects and QTLs. Abstract A large number of reviews have discussed many aspects of oxidative burst due to plant exposure to biotic and abiotic stresses, including the dual role of reactive oxygen species (ROS) as both signaling and toxic compounds, and the strategies developed by plants to cope with this oxidative imbalance. In this review, we have concentrated on fresh new information and other promising and emerging topics of oxidative stress and antioxidant mechanisms in plants, giving particular attention to genotoxicity, transgenerational alterations and quantitative trait loci (QTL) associated with enhancements in the plant tolerance to stresses. Furthermore, besides the discussion of the "classical" enzymatic and non-enzymatic components of plant defense, novel aspects about the components of the antioxidant machinery, which now includes sugars, annexins and dehydrins, are also presented, along with a final section on future directions in this field. [ABSTRACT FROM AUTHOR]

The Mitogen-activated Protein Kinase (MAPK) Cascades play a crucial role in the regulation of defense responses in plants. Herbivory- or wounding-related MAPKs, SA-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK) have been identified to be associated with insect attack. However, function of MAPKs in crop plants in response to herbivory largely remains unknown. Here, we evaluated the expression patterns of fifteen MAPK genes from chickpea in response to infestation by a major pest, Helicoverpa armigera via quantitative real-time PCR (qPCR). Subsequently, we compared the expression patterns of CaMAPKs in response to two related but different processes i.e. insect attack and mechanical wounding. Signaling compounds such as Jasmonates, Salicylic acid and Ethylene also play crucial function in defense response. Therefore, we have also examined the expression profiles of H. armigera -inducible MAPK genes in response to these signaling compounds. Our results revealed that out of fifteen CaMAPKs, seven of the CaMAPKs are upregulated in response to H. armigera and two are downregulated. Additionally, they show differential expression on comparing Helicoverpa -infestation and wounding. Jasmonates and Ethylene mainly regulate CaMAPK genes that may play a role in defense against Helicoverpa -infestation. This study provides insights into the participation of MAPKs in defense against insects. [ABSTRACT FROM AUTHOR]

Little is known about the enantioselectivity of the processes that determine the efficacy and environmental fate of natural compounds with potential to be used as environmentally-friendly agrochemicals. We conducted incubation and column leaching experiments to examine the extent and enantioselectivity of the sorption, persistence, and leaching of ( RS )-abscisic acid (ABA) in three agricultural soils. Sorption of ABA enantiomers was a non-enantioselective process that occurred only in the soil with pH close to the p K a (4.8) of ABA enantiomers, but not in the two other (alkaline) soils. The degradation of ( RS )-ABA was enantioselective for the three soils tested. ( S )-ABA, the naturally-occurring enantiomer, was always degraded faster (DT 50 < 4 days), compared to ( R )-ABA (DT 50 > 8 days). The movement of ABA enantiomers through the soil profile was enantioselective with column leachates being enriched in ( R )-ABA enantiomer. Leaching was delayed in the soil that displayed sorption for both enantiomers. The results showed that the behavior of ABA enantiomers in soil was enantioselective and that the final fate of ( R )-ABA and ( S )-ABA depended on the soil type and appeared to be affected by their sorption on soil. The longer persistence of ( R )-ABA should be considered when assessing the possibility of using this enantiomer or formulations containing enantiomer mixtures of ABA for crop management. [ABSTRACT FROM AUTHOR]

Abstract: Lipoxygenases (LOXs) have attracted a great deal of attention as potential starting biocatalysts for synthesizing signaling compounds. Significant advances during the past decade include the discovery of regiospecific LOXs and structural investigation for their diverse regiospecificity. Eight regiospecific (5-, 8-, 9-, 10-, 11-, 12-, 13-, and 15-) LOXs catalyze positional-specific dioxygenation of polyunsaturated fatty acids, forming positional-specific hydroperoxy fatty acids that are further metabolized into signaling compounds. The LOX-derived signaling compounds can be applied not only for clinical uses but also for industrial uses. For example, animal lipoxin LXA4, plant jasmonic acids, plant green leaf volatiles, and bacterial lactones have been used as anti-inflammatory agents, anti-pest agents, flavors, and food additives, respectively. Prostaglandins, as controllers of hormone regulation and cell growth, are also suggested as LOX-derived compounds in corals. [Copyright &y& Elsevier]

Abstract: Effects of methyl jasmonate (MeJA), salicylic acid (SA) or 2-aminoindane-2-phosphonic acid (AIP) pre-treatments on the sensitivity of Xanthoria parietina exposed to UV-A were studied. UV decreased chlorophylls and stimulated increase in hydrogen peroxide and superoxide level. Accumulation of soluble phenols and flavonoids increased in response to UV treatment. Metabolic modulators had negligible impact on these UV-induced changes. Within free amino acids, AIP (−UV variant) and SA and MeJA (+UV variants) altered their accumulation. AIP had no effect on the amount of phenylalanine. Benzoic and cinnamic acids were elevated by UV and mainly MeJA influenced their accumulations. Among lichen specific metabolites, vulpinic acid and ergosterol increased while usnic acid and atranorin decreased after exposure to UV; accumulation of parietin was not affected. Applied modulators showed a different effect on these lichen metabolites but biosynthetic pathway-specific trend of alteration was visible. Overall, MeJA showed the most pronounced effect among studied parameters. Accumulation of selected phenolics in response to UV-A seems to be an important feature of Xanthoria tolerance. Present finding in the context of phenolic metabolism in non-vascular plants and with respect to limited data about effect of studied modulators on non-vascular plants are discussed. [Copyright &y& Elsevier]

The potential use of allelopathic and signaling compounds as environmentally friendly agrochemicals is a subject of increasing interest, but the fate of these compounds once they reach the soil environment is poorly understood. This work studied how the sorption, persistence, and leaching of the two enantiomers of the phytohormone abscisic acid (ABA) in agricultural soil was affected by the amendments of two organoclays (SA-HDTMA and Cloi10) and a biochar derived from apple wood (BC). In conventional 24-h batch sorption experiments, higher affinity toward ABA enantiomers was displayed by SA-HDTMA followed by Cloi10 and then BC. Desorption could be ascertained only in BC, where ABA enantiomers presented difficulties to be desorbed. Dissipation of ABA in the soil was enantioselective with S-ABA being degraded more quickly than R-ABA, and followed the order unamended > Cloi10-amended > BC-amended > SA-HDTMA-amended soil for both enantiomers. Sorption determined during the incubation experiment indicated some loss of sorption capacity with time in organoclay-amended soil and increasing sorption in BC-amended soil, suggesting surface sorption mechanisms for organoclays and slow (potentially pore filling) kinetics in BC-amended soil. The leaching of ABA enantiomers was delayed after amendment of soil to an extent that depended on the amendment sorption capacity, and it was almost completely suppressed by addition of BC due to its irreversible sorption. Organoclays and BC affected differently the final behavior and enantioselectivity of ABA in soil as a consequence of dissimilar sorption capacities and alterations in sorption with time, which will affect the plant and microbial availability of endogenous and exogenous ABA in the rhizosphere.