Unexpected Behavior of Some Nitric Oxide Modulators under Cadmium Excess in Plant Tissue

Abstract

Various nitric oxide modulators (NO donors - SNP, GSNO, DEA NONOate and scavengers – PTIO, cPTIO) were tested to highlight the role of NO under Cd excess in various ontogenetic stages of chamomile (Matricaria chamomilla). Surprisingly, compared to Cd alone, SNP and PTIO elevated Cd uptake (confirmed also by PhenGreen staining) but depleted glutathione (partially ascorbic acid) and phytochelatins PC2 and PC3 in both older plants (cultured hydroponically) and seedlings (cultured in deionised water). Despite these anomalous impacts, fluorescence staining of NO and ROS confirmed predictable assumptions and revealed reciprocal changes (decrease in NO but increase in ROS after PTIO addition and the opposite after SNP application). Subsequent tests using alternative modulators and seedlings confirmed changes to NO and ROS after application of GSNO and DEA NONOate as mentioned above for SNP while cPTIO altered only NO level (depletion). On the contrary to SNP and PTIO, GSNO, DEA NONOate and cPTIO did not elevate Cd content and phytochelatins (PC2, PC3) were rather elevated. These data provide evidence that various NO modulators are useful in terms of NO and ROS manipulation but interactions with intact plants affect metal uptake and must therefore be used with caution. In this view, cPTIO and DEA NONOate revealed the less pronounced side impacts and are recommended as suitable NO scavenger/donor in plant physiological studies under Cd excess.

Effects of exogenous nitric oxide on cadmium toxicity and antioxidative system in perennial ryegrass

“…However, NO elevated Cd uptake in plants while inhibited the root-to-shoot translocation of Cd (Figure 4), thus resulting in lower Cd accumulation in leaves, this may be an important mechanism for NO-increased Cd tolerance. Our data agree with those reported in chamomile where SNP enhanced Cd uptake (Kovacik et al, 2014b).…”

Exogenous NO depletes Cd-induced toxicity by eliminating oxidative damage, re-establishing ATPase activity, and maintaining stress-related hormone equilibrium in white clover plants

“…NO indirectly amplifies root Cd uptake by promoting the upregulation of the expression of Feuptake genes. Exogenous NO enhances Cd accumulation in the shoots and roots of M. chamomilla and Scenedesmus quadricauda plants (Štork et al 2013;Kováčik et al 2014b). Interestingly, in this work, the application of exogenous NO to Cd-treated plants had nearly the opposite effect (Fig.…”

“…Thus, the activity of APX in roots might be due to the lack of Fe (Liu et al 2015) in the biosynthesis of these enzymes, as certain enzymes (CAT and APX) contain Fe in their structures. Moreover, the metal content could affect the activity of this enzyme despite the predicted reaction based on the applied regulators (Kováčik et al 2014b). For instance, Cd increased APX in alfalfa roots, but SNP decreased it in a way that was related to the reduction of the Cd concentration (cf.…”

“…For instance, NO might directly remove ROS as an antioxidant or promote metal accumulation in root cell walls by increasing pectin and hemicellulose levels in the whole plant (Xiong et al 2010). Some authors believe that NO is a stress-inducing agent, whereas others firmly believe that the protective effect of NO depends on the supplied dose, treatment time, and selected species (Kováčik et al 2014b). Additionally, NO is suggested to be involved in ethylene (ET) emission, response to disease resistance, cell death, and stomatal closure in plants (Rodríguez-Serrano et al 2009;Asgher et al 2014).…”

“…It can accumulate large amounts of metal ions, such as Cd 2+ , Pb 2+ , and Zn 2+ , without visible damage and is therefore suitable for the rehabilitation of metal-contaminated fields. To our knowledge, some regulators of NO, such as sodium nitroprusside (SNP), Snitrosoglutathione (GSNO), and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), are widely used for investigating the role of NO in plant studies (Xiong et al 2010;Verma et al 2013;Kováčik et al 2014b). However, other regulators, such as N G -nitro-L -Arg-methyl ester ( L -NAME, an NO inhibitor), 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (cPTIO, an NO scavenger), and its analogues [sodium nitrite/nitrate (SN) and sodium ferrocyanide (SF)] are not widely investigated.…”