NO to drought-multifunctional role of nitric oxide in plant drought: Do we have all the answers?

The role of plant growth promoting rhizobacteria (PGPR) in inducing the tolerance of crop plants to drought is vital in regulation of physiological reactions that eventually adapts to a stressed environment, however, how PGPR strain induces better drought resistance by accumulation of choline and glycinebetaine (GB) in maize under drought stress (DS) is still poorly understood. A pot experiment was carried out to evaluate the induced role in maize by the three PGPR strains i.e. Klebsiella variicola F2 (KJ465989), Raoultella planticola YL2 (KJ465991) and Pseudomonas fluorescens YX2 (KJ465990) in view of plant growth, water relations and accumulation of choline and GB in leaves. Seedlings of cultivar Zhengdan 958 were inoculated with strains F2, YL2 and YX2 under different DS degrees induced by different PEG-6000 concentrations of 0, 10%, 15% and 20%. The soil microbe strains F2, YL2 and YX2 substantially enhanced the accumulation of choline and GB, and in turn improved leaf relative water content (RWC) and dry mater weight (DMW) under varying DS regimes. The best responses induced by PGPR were obtained by strain YX2 regardless of DS degree and all three strains under moderate DS stimulated by 10-15% concentrations of PEG-6000. The PGPR strains were involved in the regulation of osmotic adjustment via accumulations of choline and subsequent GB, resulting in improvement of water relations and plant growth in maize plants under DS. The effects of PGPR strains on improvement of plant drought resistance might be dependent on microbial species and degree of DS.

/pdf/accumulation-of-choline-and-glycinebetaine-and-drought-391muczhth.pdf

Accumulation of choline and glycinebetaine and drought stress tolerance induced in maize (zea mays) by three plant growth promoting rhizobacteria (pgpr) strains

The influence of drought induced by polyethylene glycol (PEG) and the alleviatory effect of nitric oxide (50 µM) and sulphur (S, 1 mM K2SO4) were studied in Vigna radiata. Drought stress reduced plant height, dry weight, total chlorophylls, carotenoids and the content of nitrogen, phosphorous, potassium and sulphur. The foliar applications of NO and sulphur each individually alleviated the decline, with a greater alleviation observed in seedlings treated with both NO and sulphur. The reduction in intermediates of chlorophyll synthesis pathways and photosynthesis were alleviated by NO and sulphur. Oxidative stress was evident through the increased hydrogen peroxide, superoxide and activity of lipoxygenase and protease which were significantly assuaged by NO, sulphur and NO + sulphur treatments. A reduction in the activity of nitrate reductase, glutamine synthetase and glutamate synthase was mitigated due to the application of NO and the supplementation of sulphur. The endogenous concentration of NO and hydrogen sulphide (HS) was increased due to PEG; however, the PEG-induced increase in NO and HS was lowered due to NO and sulphur. Furthermore, NO and sulphur treatments to PEG-stressed seedlings further enhanced the functioning of the antioxidant system, osmolytes and secondary metabolite accumulation. Activities of γ-glutamyl kinase and phenylalanine ammonia lyase were up-regulated due to NO and S treatments. The treatment of NO and S regulated the expression of the Cu/ZnSOD, POD, CAT, RLP, HSP70 and LEA genes significantly under normal and drought stress. The present study advocates for the beneficial use of NO and sulphur in the mitigation of drought-induced alterations in the metabolism of Vigna radiata.

Alleviation of Adverse Effects of Drought Stress on Growth and Nitrogen Metabolism in Mungbean (Vigna radiata) by Sulphur and Nitric Oxide Involves Up-Regulation of Antioxidant and Osmolyte Metabolism and Gene Expression.

Hydroponic experiments were conducted to investigate the effects of nitrogen forms on nitric oxide accumulation and glycinebetaine (GB) metabolism under osmotic stress (OS) simulated by the addition of polyethylene glycol (PEG-6000) to two maize (Zea mays L.) cultivars Zhengdan 958 (ZD958; drought-tolerant) and Jundan 20 (JD20; drought-sensitive). OS led to the accumulation of NO, GB, and choline, as well as to an increase of betaine aldehyde dehydrogenase (BADH) activity in both the cultivars. The responses of both the maize cultivars to OS were significantly higher under nitrate nutrition than under the mixed supply of ammonium and NO3
 − or sole NH4
 +. Cultivar ZD958 was superior to JD20 under the osmotic stress. Furthermore, compared with sole NH4
 +, sole NO3
 − and the mixed supply of NH4
 + and NO3
 − increased all the parameters in cv. ZD958 but only the GB and choline content in JD20. Therefore, it is concluded that ZD958 showed a higher accumulation of NO and enhanced GB metabolism under OS than JD20 regardless of N form.

Nitric oxide accumulation and glycinebetaine metabolism in two osmotically stressed maize cultivars supplied with different nitrogen forms

The continuously changing environment has led to devastating effects on the normal growth and development of plants. This necessitates the understanding of different components that can be involved in alleviating these effects. In the last two decades, nitric oxide (NO) has been largely focused on as a molecule whose endogenous production and exogenous supply lead to several molecular and physiological changes in plants under stressed conditions. Although its role as a signaling molecule in endogenous production has been largely discussed, its function in dealing with contemporary abiotic stress conditions on exogenous supply remains comparatively less explored. There is growing evidence that NO plays a critical role in many physiological processes; however, there is debate about the exact mechanism(s) through which NO lessens abiotic stress on external supply. In this review, we discuss the studies that were focused on observing the effect of exogenous NO on different abiotic stresses including heavy metal stress, element deficiency or toxicity stress, salt stress, drought stress, ultraviolet radiation stress, waterlogging stress, and chilling stress. Though the positive effects of endogenous NO have been discussed in brief in different sections, the focus of the review is to discuss the effects of exogenous NO on plant grown under abiotic stresses. Deciphering the underlying mechanism of exogenous NO treatment may open up new ideas that can suggest the successful application of NO in agricultural regions to reduce the damaging influences of different abiotic stresses.

/pdf/role-of-exogenous-nitric-oxide-in-protecting-plants-against-uzdaegn9.pdf

Role of Exogenous Nitric Oxide in Protecting Plants against Abiotic Stresses

In this study, we investigated the effects of exogenously applied nitric acid (NO) source i.e., sodium nitroprusside (SNP), NO scavenger i.e., 2-(4-carboxypheny-4,4,5,5-tetramethylimidazoline-1-1oxyl-3-oxide, potassium salt (cPTIO), NO inhibitor i.e., NaN3, and NOS inhibitor i.e., Nω-nitro-larginine methyl ester hydrochloride (L-NAME) on eglycinbetaine (GB) metabolism in root tips and leaves of maize seedlings under drought stress (DS). The accumulation of NO peaked earlier than that of GB in shoot tips and leaves. The maximum NO content in root tips was attained earlier than that in leaves, while the reverse was observed with respect to GB content. The concentrations of NO, GB and choline in root tips and leaves of maize seedlings under DS were greater in the plants which received exogenous SNP application as compared to those in plants without SNP application. Exogenous SNP application also increased betaine aldehyde dehydrogenase (BADH) activity in leaves. The GB metabolism was negatively influenced by exogenous applications of either PTIO, NaN3 or L-NAME. The combined application of NaN3 and L-NAME had the most serious negative effects. These results demonstrate that GB metabolism in drought stressed maize plants was significantly enhanced by exogenous NO application. The accumulation of greater level of NO in maize seedlings contributed to increase GB accumulation by regulating BADH activity and choline content. This study provides a direct evidence of regulation of GB metabolism in maize plants under drought stress by exogenous application of NO.

Effects of exogenous nitric oxide on glycinebetaine metabolism in maize (zea mays l.) seedlings under drought stress

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Effects of exogenous nitric oxide on glycinebetaine metabolism in maize (zea mays l.) seedlings under drought stress