Hydrogen peroxide scavenging mechanisms are components of Medicago truncatula partial resistance to Aphanomyces euteiches

Abstract

The biochemical processes underlying the expression of resistance in the roots of Medicago truncatula against Aphanomyces euteiches infection was investigated, with emphasis on oxidative stress. The levels of H 2 O 2 , superoxide dismutase, peroxidase, ascorbate peroxidase, catalase, soluble phenolics and lignin were measured in the roots of two lines, A17 partially resistant and F83005.5 susceptible to A. euteiches at three infection stages; penetration of the epidermis (1 dpi), colonization of the cortex (3 dpi) and invasion of the root stele (6 dpi). A rapid and large decrease of the H 2 O 2 levels in A17 roots occurred. However, in F83005.5 roots, the decrease in H 2 O 2 levels was delayed until 3 dpi. In A17 roots, the activities of ascorbate peroxidase, peroxidase and catalase were induced as early as 1 dpi, whereas a general decrease in the activity of the four antioxidant enzymes was observed in F83005.5 roots. The levels of soluble phenolics and lignin were increased in A17 roots at 3 and 6 dpi, respectively. The H 2 O 2 levels were negatively correlated to ascorbate peroxidase, catalase and lignin production at 1, 3 and 6 dpi, respectively in A17 roots. Physiological concentrations of H 2 O 2 found in M. truncatula infected roots had no detrimental effect on the in vitro growth of this oomycete. Our data suggest that H 2 O 2 does not have a direct antimicrobial effect on M. truncatula resistance to A. euteiches, but is involved in cell wall strengthening around the root stele, preventing pathogen invasion of the vascular tissues.

MtNF-YA1, A Central Transcriptional Regulator of Symbiotic Nodule Development, Is Also a Determinant of Medicago truncatula Susceptibility toward a Root Pathogen

“…Twenty-one days post inoculation, root tissues were heavily colonized in F83005.5 and numerous oospores were produced inside dead cells, indicating that the pathogen fulfilled its life cycle ( Figure 2C ). In A17, numerous intercellular hyphae invaded the entire cortex but never entered the vascular tissues and only a few oospores were detected, in line with previous studies (Supplementary Figure 3A) (Djébali et al, 2009, 2011). The Mtnf-ya1-1 mutant displayed consistently a reduced hyphal colonization mostly located in the outer root cortex whilst reduced colonization of the inner cortex was observed (Supplementary Figure 3B).…”

Silencing of the Rac1 GTPaseMtROP9inMedicago truncatulaStimulates Early Mycorrhizal and Oomycete Root Colonizations But Negatively Affects Rhizobial Infection

“…For the progressive A. euteiches hyphal colonization, a delay in rapid colonization of approximately 5 d can be estimated in Mtvector roots when compared with MtROP9i. This is consistent with recent studies on the establishment of partial resistance in M. truncatula cultivars toward A. euteiches, which is mediated by initial induction of a high level of antioxidant enzymes accompanied by increased concentrations of soluble phenolics and lignin (Djébali et al, 2011). For AM infection, the infection intensity in mycorrhized MtROP9i root fragments was clearly increased for the first 15 dpi.…”

Changes in antioxidant systems in sunflower partial resistant and susceptible lines as affected by Sclerotinia sclerotiorum

“…Decreased activity of CAT has also been observed in some other environmental stress (Mishra et al 2006). Madoui et al (2007) and Djebali et al (2011) reported the differences in CAT activity and biochemical processes underlying the expression of resistance in the roots of Medicago truncatula against Aphanomyces euteiches infection.…”

“…Previous studies have shown that alteration in the expression/activity of ROS-scavenging enzymes could also be a key step in the activation of plant defence against phytopathogens. It has been reported that the activity of the enzymatic antioxidant system limits the propagation of oxidative processes allowing cells to maintain their viability against the penetration of Aphanomyces euteiches and S. sclerotiorum in plant tissues (Burhenne & Gregersen 2001;Peluffo et al 2010;Djebali et al 2011). Accumulation of free L-proline occurs in response to many abiotic and biotic stresses, such as fungi infection (Hare & Cress 1997;Slama et al 2006).…”