Effect of salicylic acid, zinc Nano-oxide and sodium nitroprusside on pigments and fluorescence amount of sweet violet under water-deficit stress conditions

Introduction: Sweet violet (Viola odorata) is a perennial herbaceous plant with ornamental and medicinal properties. Water scarcity is one of the most effective environmental limiting factors for plants. The use of anti-stress compounds, such as a variety of secondary metabolites, is some way to reduce the harmful effects of water-deficit. Salicylic acid (SA) is a plant growth regulator from the phenol group and is effective as a signal molecule in regulating many physiological processes (Idress et al., 2013; Harrison et al., 2014). Sodium nitroprusside is involved in the action of plant growth regulators and is involved in the transmission of messages and responses to biological and non-biological stresses (Fan et al., 2012). Zinc oxide nanoparticles are among the nanoparticles used in agricultural research that have a very high specific surface area (Idress et al., 2013). The aim of the present study was to investigate the effect of different levels of water-deficit stress and foliar application of anti-stress compounds (SA, sodium nitroprusside and nano zinc oxide) on some pigments and the fluorescence of sweet violet.
Materials and methods: A factorial experiment in completely randomized design was performed with two factors; water-deficit stress at three levels (55, 65 and 85% of field capacity (FC) and foliar spraying including SA (200 and 300 mg/l), zinc nano-oxide (1000 and 1500 mg/l) and sodium nitroprusside (200 and 300 μM) in three replications. In two weeks after establishing the plantlets in the cultivation bed, two weeks apart, foliar applications were made and distilled water was applied as control treatment. The application of water-deficit stress started one week after the second stage of foliar application based on substrate FC by weighting method and continued until the end of the experiment, which coincided with the yellowing of the leaves. Leaf and petal pigments and chlorophyll fluorescence were measured. Data analysis was performed using SAS9.2 statistical software and graphs were drawn using Excel software. LSD test at 5% probability level was used to compare the mean of the data.
Results and discussion: The results showed that the highest chlorophyll a (9.72 mg/g F.W.) and b (4.15 mg/g F.W.) concentrations were related to the treatment of 1000 mg/l Nano-zinc oxide and 200 μM sodium nitroprusside both at water-deficit stress of 55% of field capacity, respectively. The highest leaf carotenoid concentrations in leaf (14 μg/g F.W.) and petal (8.36 μg/g F.W.) were obtained at levels of 200 μM sodium nitroprusside and 300 mg/l SA, respectively, under water-deficit stress of 55% FC, The highest maximum (5.31) and variable (4.27) fluorescence was related to the treatment of 1000 mg/l zinc nano-oxide at water-deficit stress of 85% FC. The highest photofoliar spraying efficiency of photosystem II (4.4) and quantum yield of photosystem 2 (0.81) were obtained at water-deficit stress of 85% of field capacity together with 300 mg/l salicylic acid treatment. The highest effective photofoliar spraying quantum efficiency of the photosystem 2 (0.56) was related to water-deficit stress treatment of 65% FC and 300 μM sodium nitroprusside treatment. The effect of treatment with these substances on the change of biofoliar spraying and physiological processes, especially during the response to various biological and non-biological stresses such as drought in plants (Ricinus communis and sunflower hybrids) was shown (Balabanova et al., 2016; Esparham et al., 2017).
Conclusions: With increasing water-deficit, the concentration of chlorophyll and carotenoid pigments in leaves and petals increased. Zinc nanoparticles increased the maximum and variable fluorescence and salicylic acid also increased the fluorescence ratio, non-photofoliar spraying quicent and regulated and unregulated quantum efficiency of photosystem II. Sodium nitroprusside showed a positive effect on changing the minimum fluorescence and the effective quantum efficiency of photosystem II.