Earlier investigations have exhibited that N metabolism was suppressed in plants exposed to Cd toxicity ( Balestrasse et al., 2003 Gill et al., 2012 Wani et al., 2017 Shahid et al., 2019).Ĭonsequently, a plausible action is indispensable to allay the harmful effects of Cd on plant metabolic events. Thus, it is critically important to maintain optimal the activities of the N metabolism–related enzymes, i.e., NR, NiR, GS, and GOGAT, for maintaining optimum growth of plants ( Liang et al., 2018). The conversion of NH 4 + to glutamate and glutamine takes place through glutamate synthase (GOGAT) and glutamine synthetase (GS) ( Lea and Miflin, 2018). Nitrate reductase (NR) carries out the reduction of NO 3 – to NO 2 – (nitrite), and then nitrite reductase (NiR) converts NO 2 – to ammonium (NH 4 +) ( Kaiser et al., 2018). Plants absorb N basically in the form of nitrate (NO 3 –) by roots and transfer it to leaves for its assimilation therein ( Xuan et al., 2017).
Nitrogen (N) metabolism is a key physiological event that substantially affects growth, yield, and quality of most plants ( Singh et al., 2016 Rajwade et al., 2018). However, such a protective strategy does not constantly work in most plant species including wheat under Cd stress, because of being the crop highly sensitive to this metal stress ( Rizwan et al., 2016). For example, one such promising mechanism is the modulation of the ascorbic acid (AsA)–glutathione (GSH) cycle enzymes ( Khan et al., 2019). Plants possess a well-developed antioxidant defense system to counteract multiple stresses including Cd stress ( Zaid et al., 2019). Overaccumulation of ROS can considerably damage the key membrane biomolecules, thereby causing leakage of all biological membranes ( Jia et al., 2020). Moreover, Cd stress causes overproduction of reactive oxygen species (ROS) in plants ( Gallego and Benavides, 2019). Compared with individual application of MeJA or SNP, the combined application of both showed better effect in terms of improving plant growth and key metabolic processes and reducing tissue Cd content, suggesting a putative interactive role of both compounds in alleviating Cd toxicity in wheat plants.Ĭadmium (Cd) is not required by plants for their optimum growth, so a slight increase in its levels in a growth medium causes considerable damages to several metabolic processes ( Shanmugaraj et al., 2019), such as limitation of assimilation rate ( Anwar et al., 2019 Zhou et al., 2020) and disturbance in plant water balance ( Naeem et al., 2019). Exogenously applied MeJA and SNP jointly or singly also improved nitrogen metabolism by activating the activities of glutamine synthetase, glutamate synthase, and nitrate and nitrite reductases. MeJA and SNP applied jointly or singly improved the concentrations of key antioxidant biomolecules, e.g., reduced glutathione and ascorbic acid and the activities of the key oxidative defense system enzymes such as catalase, superoxide dismutase, dehydroascorbate reductase, glutathione S-transferase, and glutathione reductase. Cd stress suppressed plant growth, chlorophylls ( Chl), and PSII maximum efficiency ( F v/ F m), but it elevated leaf and root Cd, and contents of leaf proline, phytochelatins, malondialdehyde, and hydrogen peroxide, as well as the activity of lipoxygenase. The principal intent of the investigation was to examine the influence of joint application of methyl jasmonate (MeJA, 10 μM) and a nitric oxide–donor sodium nitroprusside (SNP, 100 μM) to wheat plants grown under cadmium (Cd as CdCl 2, 100 μM) stress.
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