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Sodium nitroprusside (SNP) represents one of the most common uses nitric oxide (NO) donors. It was classified as a phytohormone that might function as a gaseous endogenous plant growth regulator as well as non-traditional plant growth regulator. They are naturally produced within plants and used to regulate the plant growth and developments. NO acts as a signal molecule in plants responsible for the regulation of the expression of many defense-related enzymes. NO has gained increasing interest as important intermediate and intracellular signaling molecule implant systems which mediates various physiological, biochemical and developmental processes in plants, including seed dormancy, seed germination, primary lateral root growth,floral transition, flowering, stomatal movement, photosynthesis, mitochondrial functionality, senescence, plant metabolism and cell death as well as stress response (Paraiz Ahmad et al., 2016). In the past few years, a growing amount of research has provided evidence for the multiple physiological roles of this gaseous free radical in plants (Delledonne, 2001; Wendehenne et al., 2004). The objective of the present study was to investigate whether sodium nitroprusside (SNP), a donor, plays an important role in plant growth and development on the selected crop seedlings.
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Healthy and uniform seeds of Zea mays L. Lablab purpureus (L.) Sweets were purchased from Agricultural Research Centre, Kovilpatti. The percentage of seed germination was found to be 80-85%. The seeds were sown in pots containing a mixture of red soil, black soil, and sand mixed in the ratio of 2: 2: 1. Soon after the emergence of the cotyledons, the seedlings were shifted to daylight conditions. Since the ambient climate was too hot for the seedlings, a 40% cut off mesh filter was used to surround the pots for an initial period of 2-3 days.
Sodium nitroprusside (SNP) treatment
Sodium nitroprusside was obtained from Sigma Chemical Co. (St. Louis, U.S.A). SNP was initially dissolved in water and made up to 1µM, 10µM, 100µM, 1mM and 10 containing 0.02% Tween-20 (Polyoxyethylene sorbitan monolaurate). Each seedling required about 10ml of spray solution. The foliar spray was given for two days early in the morning and growth analyses were done after 10 days of seedling growth. The seedlings were sprayed with solutions until dropping with an atomicsprayer. Plants sprayed with 0.02% Tween-20 served as the control.
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After two days of the treatment, the seedlings of Zea mays L. Lablab purpureus (L.)Sweet was used for measuring the growth parameters such as such as root length, shoot length, leaf area, fresh weight and dry weight were measured. The biochemical and enzymatic characters were analyzed by the following methods:chlorophyll and carotenoids (Wellburn and Lichtenthalar, 1984), Anthocyanin andFlavonoid Mirecki and Teramura (1984), Total soluble sugar (Jayaraman, 1981),Protein content (Lowry et al., 1951), in vivo nitrate reductase activity (Jaworski, 1971), Catalase activity (Kar and Mishra, 1976) and Peroxidase activity (Addyand Goodman, 1972).
Formerly, the plant hormone ethylene was the only gaseous signaling molecule in the living world known to science(Ferreira and Cataneo – ?2010[DNS1] ). However, work on nitric oxide fetched the Nobel Prize for Medicine in 1998(Wojtaszek, 2000), and considered as a signalling molecule.NO has been initially identified as an endothelium-derived relaxation factor and later implicated in signal transduction pathways controlling neurotransmission, cell proliferation, programmed cell death, and host responses to infection (Wink and Mitchell, 1998). Although the history of studies on NO in animals is considerably much more advanced, renewed attention has been given to the mechanism of NO synthesis and its functions in plants in the last decades.
Effect of SNP on growth characteristics
The exogenous application of SNP increased the level of shoot length, root length, shoot fresh weight, root fresh weight, and dry weights. There are several reports that suggest the growth promoting activity of SNP. Huang and She (2003) reported that SNP induced adventitious root formation in mung bean hypocotyl cuttings. Correa-Aragunde et al. (2004) demonstrated that NO and its precursor SNP playing a key role in determining lateral root development in tomato. In addition, NO and SNP promoted root elongation in maize (Gouvea et al., 1997).
The root growth increased by about 30% in seedlings pre-treated with 0.4 mM SNP(followed by10 µM Al treatment) as compared to control (10 µM Al alone). In order to confirm the role of SNP in reducing Al-inhibited root growth, a root growth recovery experiment was carried out. Roots pre-treated with 0.4 mM SNP for 12 h followed by the 20 µM Al treatment for another 12 h were found to be less inhibited and recovered more rapidly than the roots without SNP-treatment. After a 72 h period of recovery, the SNP-pre-treated root elongation reached 60% of the control (–Al treatment), whereas the root elongation without SNP pre-treatment was only 22% of the control. In the present study, all the concentrations of SNP increase the shoot fresh weight and dry weight. The changes in shoot dry weight are a clear representation of the vegetative growth.
Effect of SNP on biochemical constituents
The chlorophyll a and chlorophyll b were found to increase with an increase in the concentration of SNP in Zea and Lablab purpureus. The level of chlorophyll b which was high under SNP treatment indicates changes in stoichiometry of PS II and PS I. As Chl b is associated more with PS II, any significant change in Chl b levels,would indirectly affect the efficiency of PS II rather than PS I. Our results indicated that application of SNP significantly increased Chl content in leaves which might be due to the impairment of Chl biosynthesis. There are many processes in which hormones and phytochrome interact or act separately to give the same response. NO also triggers several of these responses. These overlapping roles raise the question of whether light and hormones share common components in signal transduction pathways to elicit the same response and whether NO role play in the signaling cascade (Lamattina et al., 2003).
Treatment with SNP increased anthocyanin and flavonoids content. The anthocyanin and flavonoids are non-photosynthetic pigments taking part in plant defense mechanisms. The effect of these non-photosynthetic pigments depends on the environmental factors like light temperature, drought, radiation stress etc. Have suggested that the concentration of surface flavonoids decrease with leaf age in all plants. Both anthocyanin and flavonoids tend to accumulate more in foliar tissues at times of abiotic stresses. High concentrations of the phytohormones lead to the development of these pigments in order to protect the seedlings against the action of SNP oxidase.
Foliar application of SNP caused marked increase in the total soluble proteins in the exogenous application of SNPs subjected samples of Zea mays and Lablab purpureus. This result was supported by Nasrin et al. (2012). It may be substantiated by the active participation of an enzyme activity nitrate reductase (reduction of nitrate to nitrite and then to amino acids) and increase in the polyribosome and protein synthesis. The changes in leaf nitrate content and in vivo nitrate reductase activity reveal the high concentration of SNP favored the accumulation of may be due to the enhancement of nitrogen or nitrate uptake by plants.
A key step in nitrate assimilation is the reduction of this anion to nitrite in the reaction catalyzed by NR, an enzyme that is highly regulated at the transcriptional and post-transcriptional levels (Kaiser, 2001). NR has been studied extensively as a key enzyme of nitrogen metabolism. NR activity was significantly enhanced by the addition of SNP. NR activity was significantly stimulated by SNP at 100µM and 10mM. The reason behind is that NO stimulates the post-translational regulatory pathway of NR. All these results indicate the foliar application of SNP is important for enhancing NR activity.
SNP-treated plants in our study showed increases in peroxidase activity at all the concentration of SNP. The higher level of endogenous auxins could also lead to early sprouting of leaves. The high rate of peroxidase activity may be due to enhanced auxin catabolism triggering the root initiation process (Kochhar et al., 2005). While SNP oxidase seems to be involved only in triggering and initiating the root/shoot primordiaperoxidase is involved in both root initiation and elongation processes and oxidation products of auxin catabolism may be involved in the initiation of roots. [DNS1]Don’tcopy any of the sentences./ otherwise, give proper citations.
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