Antioxidant gene–enzyme responses in Medicago truncatula genotypes with different degree of sensitivity to salinity

Abstract

Antioxidant responses and nodule function of Medicago truncatula genotypes differing in salt tolerance were studied. Salinity effects on nodules were analysed on key nitrogen fixation proteins such as nitrogenase and leghaemoglobin as well as estimating lipid peroxidation levels, and were found more dramatic in the salt-sensitive genotype. Antioxidant enzyme assays for catalase (CAT, EC 1.11.1.6), superoxide dismutase (EC 1.15.1.1), ascorbate peroxidase (EC 1.11.1.11) and guaiacol peroxidase (EC 1.11.1.7) were analysed in nodules, roots and leaves treated with increasing concentrations of NaCl for 24 and 48 h. Symbiosis tolerance level, depending essentially on plant genotype, was closely correlated with differences of enzyme activities, which increased in response to salt stress in nodules (except CAT) and roots, whereas a complex pattern was observed in leaves. Gene expression responses were generally correlated with enzymatic activities in 24-h treated roots in all genotypes. This correlation was lost after 48 h of treatment for the sensitive and the reference genotypes, but it remained positively significant for the tolerant one that manifested a high induction for all tested genes after 48 h of treatment. Indeed, tolerance behaviour could be related to the induction of antioxidant genes in plant roots, leading to more efficient enzyme stimulation and protection. High induction of CAT gene was also distinct in roots of the tolerant genotype and merits further consideration. Thus, part of the salinity tolerance in M. truncatula is related to induction and sustained expression of highly regulated antioxidant mechanisms.

The Legume Root Nodule: From Symbiotic Nitrogen Fixation to Senescence

“…As mentioned before, Lb has a crucial role in nodule functioning (Ott et al, 2009;Ott et al, 2005). Decrease of Lb content has been shown during drought stress (Gogorcena et al, 1995;Gordon et al, 1997;Guerin et al, 1990), salt stress Mhadhbi et al, 2011) and dark stress (Gogorcena et al, 1997;Matamoros et al, 1999). This diminution of Lb will impact the general metabolism of nodule by decreasing the O 2 availability to bacteroid and by potentially releasing free iron which may be a co-factor of the Fenton reaction to produce reactive oxygen species.…”

“…Superoxide dismutase and catalase, two enzyme families involved in ROS degradation, are down regulated during dark stress (Matamoros et al, 1999;Gogorcena et al, 1997), salt stress (Jebara et al, 2005) and drought stress (Gogorcena et al, 1995;Rubio et al, 2002). Similarly, enzymes of the Asc-GSH cycle are modulated during nodule SIS (Gogorcena et al, 1995;Jebara et al, 2005;Matamoros et al, 1999;Mhadhbi et al, 2011). Nevertheless, whereas the majority of the reports suggest that SIS is associated with a decrease of the antioxidant defence, other articles have shown that some elements of the antioxidant defence are stable or even up regulated during stress.…”

Oxidative and nitrosative signaling in plants

“…7 Today, several parameters regarding ROS generation, scavenging and signaling have been uncovered, but how their role is being controlled is largely unknown. [2][3][4][5][6][7][8][9][10][11][12] Also, it is becoming increasingly apparent that ROS signal molecules can Reactive oxygen species (ROS) and reactive nitrogen species (RNS) constitute key features underpinning the dynamic nature of cell signaling systems in plants. Despite their importance in many aspects of cell biology, our understanding of oxidative and especially of nitrosative signaling and their regulation remains poorly understood.…”

Nitric oxide affects salt-induced changes in free amino acid levels in maize

“…Similarly, the salt-tolerant species Plantago maritima exhibited better tolerance to salt stress than the salt-sensitive Plantago media due to its greater antioxidant activities (APX, glutathione reductase (GR), SOD, catalase) (Sekmen et al, 2007). The salinity tolerance of Medicago trunculata was found to be related to the induction and sustained expression of highly regulated antioxidant mechanisms in the roots and leaves (Mhadhbi et al, 2011). In the induction of antioxidants the osmotic effect of salt may be important, since osmotic stress induced by the water deficit also affected antioxidant levels (Varga et al, 2012).…”