Phenylalanine ammonia lyase activity in chilli CM-334 infected by Phytophthora capsici and Nacobbus aberrans

Abstract

We tested the hypothesis that PAL activity in chilli plants CM-334 inoculated with Nacobbus aberrans (Na) alone or in combination with Phytophthora capsici (Pc), is lower than in those inoculated only with Pc. At 21 days after nematode inoculation, inoculated plants showed a significant (P<0.01) reduction of 48% in PAL activity compared to those non-inoculated in two separate experiments. In two other tests, where plants were inoculated with the oomycete 21 days after inoculation with the nematode, PAL activity at 2, 4, 6, 8 and 24 h after inoculation with Pc was significantly higher (Tukey, P<0.01) in plants inoculated only with Pc than in plants inoculated only with Na or both pathogens (Na+Pc).

Alterations in peroxidase activity and phenylpropanoid metabolism induced by Nacobbus aberrans Thorne and Allen, 1944 in chilli (Capsicum annuum L.) CM334 resistant to Phytophthora capsici Leo.

“…The lower PAL activity in CM334 plants inoculated with Na alone or in combination with Pc was in agreement with the results reported by Godínez-Vidal et al (2008), who suggested that, in a similar way to M. incognita, N. aberrans could alter the patterns of genetic expression in its host, including repressing the expression of PAL, as previously reported in compatible plant-nematode interactions (Goddijn et al 1993;Baldridge et al 1998). Inhibition of the gene PALwhich codes for PAL biosynthesis, a key enzyme in defense mechanisms (Cahill and McComb 1992;Fernández-Pavia 1997;Boudet 2000;Dixon et al 2002;Shadle et al 2003)-would favor infection and reproduction of the nematode.…”

“…The lower contents of chlorogenic acid in resistant (CM334) and susceptible (J. E. Parker) plants inoculated with N. aberrans as compared to the non-inoculated ones, along with the fact that PAL activity was lower in nematode-inoculated plants compared to those noninoculated, further supports the idea that in compatible interactions the nematode interferes with the plant defence mechanisms-most likely those related to the phenylpropanoid pathway- (Edens et al 1995;Wuyts et al 2006a;Godínez-Vidal et al 2008). Our results also reinforce the idea that, in the incompatible interaction M. incognita-CM334, the chlorogenic acid synthesized through the phenylpropanoids route might play an important role in the resistance to this nematode, as previously reported by Pegard et al (2005); such resistance was expressed as a classical hypersensitive response.…”

“…CM334 is resistant to P. capsici and to some species of Meloidogyne, but susceptible to N. aberrans (Vargas et al 1996;Trujillo-Viramontes et al 2005;Godínez-Vidal et al 2008). Pegard et al (2005) found that chlorogenic acid increased significantly in the resistant (CM334) chilli pepper plants after infection by Meloidogyne spp.…”

“…The reduction in the enzymatic activity of peroxidase, PAL, total soluble phenolics and chlorogenic acid by N. aberrans could be in part associated with the breakdown of resistance to P. capsici induced by the nematode. All of these effects probably occur through the repression of the genes in the phenylpropanoid metabolism (Zavaleta-Mejía 2002;Godínez-Vidal et al 2008). However, the reduction in the defence responses of CM334 do not necessarily require the repression of gene expression, and we cannot discard the possibility that N. aberrans represses the defence responses by mechanisms working at the post-transcriptional level, through metabolites produced directly by the nematode or by the host after N aberrans induction that interfere with the synthesis or the activity of the peroxidases and PAL, or with the accumulation and toxicity of phenolic compounds.…”

“…In previous studies we found that the CM334 chili pepper plants showed susceptibility when they were first inoculated with the false root knot nematode N. aberrans (Vargas et al 1996;Trujillo-Viramontes et al 2005;Godínez-Vidal et al 2008). This phenomenon is known as "resistance breaking" (Sasser et al 1955;Hernández et al 1992;Maheshwari et al 1995).…”