Molecular insights into the functional role of nitric oxide (NO) as a signal for plant responses in chickpea

Nitric oxide and selenium nanoparticles confer changes in growth, metabolism, antioxidant machinery, gene expression, and flowering in chicory (Cichorium intybus L.): potential benefits and risk assessment

This experiment was conducted to provide a better insight into the plant responses to nitric oxide (NO) and selenium nanoparticle (nSe). Chicory seedlings were sprayed with nSe (0, 4, and 40 mg l-1), and/or NO (0 and 25 μM). NO and/or nSe4 improved shoot and root biomass by an average of 32%. The nSe40 adversely influenced shoot and root biomass (mean = 26%), exhibiting moderate toxicity partly relieved by NO. The nSe and NO treatments transcriptionally stimulated the dehydration response element B1A (DREB1A) gene (mean = 29.6-fold). At the transcriptional level, nSe4 or NO moderately upregulated phenylalanine ammonia-lyase (PAL) and hydroxycinnamoyl-CoA quinate transferase (HCT1) genes (mean = sevenfold). The nSe4 + NO, nSe40, and nSe40 + NO groups drastically induced the expression of PAL and HCT1 genes (mean = 30-fold). With a similar trend, hydroxycinnamoyl-CoA Quinate/shikimate hydroxycinnamoyl transferase (HQT1) gene was also upregulated in response to nSe and/or NO (mean = 25-fold). The activities of nitrate reductase and catalase enzymes were also induced in the nSe- and/or NO-treated seedlings. Likewise, the application of these supplements associated with an increase in ascorbate concentration (mean = 31.5%) reduced glutathione (mean = 35%). NO and/or nSe enhanced the PAL activity (mean = 36.4%) and soluble phenols (mean = 40%). The flowering was also influenced by the supplements in dose and compound dependent manner exhibiting the long-time responses. It appears that the nSe-triggered signaling can associate with a plethora of developmental, physiological, and molecular responses at least in part via the fundamental regulatory roles of transcription factors, like DREB1A as one the most significant genes for conferring tolerance in crops.

Cytokinin alleviates cypermethrin toxicity in Nostoc muscorum by involving nitric oxide: Regulation of exopolysaccharides secretion, PS II photochemistry and reactive oxygen species homeostasis

Growth of the most important nitrogen fixing cyanobacterium Nostoc muscorum is reported to be badly affected by the application of insecticides. To overcome their damaging effects, several strategies are being used. Out of these, some works on kinetin (KN, a synthetic cytokinin) has been recognized that it can overcome toxicity of insecticides in cyanobacteria. Besides this, it is now known that every hormone needs certain second messengers such as nitric oxide (NO) for its action. But implication of NO in KN-mediated regulation of insecticide toxicity is yet to be investigated. Hence in the current study, we have investigated the possible involvement of NO in KN-mediated regulation of cypermethrin toxicity in the cyanobacterium Nostoc muscorum. Cypermethrin decreased growth of Nostoc muscorum which was accompanied by decreased pigment contents and altered photosystem II (PS II) photochemistry that resulted in inhibition of photosynthetic process but KN significantly ameliorated cypermethrin toxicity. Cypermethrin induced production of free radicals (in-vivo and in-vitro) and weakened defensive mechanism (enzymatic and non-enzymatic defense system) which was restored by KN. Further, the results revealed that NG-nitro-l-arginine methyl ester (l-NAME, an inhibitor of nitric oxide synthase) worsened the effect of cypermethrin toxicity even in the presence of KN while 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (c-PTIO, a scavenger of NO) reversed KN-mediated amelioration even in the presence of sodium nitroprusside (SNP, an NO donor), suggesting that endogenous NO is required for mitigation of cypermethrin toxicity. Overall, our results first time show that endogenous NO is essential for KN-mediated mitigation of cypermethrin toxicity in the Nostoc muscorum.

Comparative Physiological Analysis Reveals the Role of NR-Derived Nitric Oxide in the Cold Tolerance of Forage Legumes

The role of nitric oxide (NO) signaling in the cold acclimation of forage legumes was investigated in this study. Medicago sativa subsp. falcata (L.) Arcang. (hereafter M. falcata) is a forage legume with a higher cold tolerance than Medicago truncatula, a model legume. Cold acclimation treatment resulted in increased cold tolerance in both M. falcata and M. truncatula, which was suppressed by pretreatment with tungstate, an inhibitor of nitrate reductase (NR), and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO), a scavenger of NO. Likely, NITRATE REDUCTASE 1 (NIA1), but not NIA2 transcript, NR activity, and NO production were increased after cold treatment. Treatments with exogenous NO donors resulted in increased cold tolerance in both species. Superoxide dismutase (SOD), catalase (CAT), and ascorbate-peroxidase (APX) activities and Cu,Zn-SOD2, Cu,Zn-SOD3, cytosolic APX1 (cAPX1), cAPX3 and chloroplastic APX1 (cpAPX1) transcript levels were induced in both species after cold treatment, which was suppressed by tungstate and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). Treatment with exogenous NO resulted in enhanced activities of SOD, CAT, and APX. Moreover, higher levels of NIA1 transcript, NR activity, NO production, and antioxidant enzyme activities and transcripts were observed in M. falcata as compared with M. truncatula after cold treatment. The results suggest that NR-derived NO production and upregulated antioxidant defense are involved in cold acclimation in both species, while the higher levels of NO production and its derived antioxidant enzymes are associated with the higher cold tolerance in M. falcata as compared with M. truncatula.

Nitric Oxide (NO) in Plant Heat Stress Tolerance: Current Knowledge and Perspectives

High temperature is one of the biggest abiotic stress challenges for agriculture. While, Nitric oxide (NO) is gaining increasing attention from plant science community due to its involvement in resistance to various plant stress conditions, its implications on heat stress tolerance is still unclear. Several lines of evidence indicate NO as a key signaling molecule in mediating various plant responses such as photosynthesis, oxidative defense, osmolyte accumulation, gene expression, and protein modifications under heat stress. Furthermore, the interactions of NO with other signaling molecules and phytohormones to attain heat tolerance have also been building up in recent years. Nevertheless, deep insights into the functional intermediaries or signal transduction components associated with NO-mediated heat stress signaling are imperative to uncover their involvement in plant hormone induced feed-back regulations, ROS/NO balance, and stress induced gene transcription. Although, progress is underway, much work remains to define the functional relevance of this molecule in plant heat tolerance. This review provides an overview on current status and discuss knowledge gaps in exploiting NO, thereby enhancing our understanding of the role of NO in plant heat tolerance.