The form of nitrogen nutrition affects resistance against Pseudomonas syringae pv. phaseolicola in tobacco

Abstract

Different forms of nitrogen (N) fertilizer affect disease development; however, this study investigated the effects of N forms on the hypersensitivity response (HR)—a pathogen-elicited cell death linked to resistance. HR-eliciting Pseudomonas syringae pv. phaseolicola was infiltrated into leaves of tobacco fed with either or . The speed of cell death was faster in -fed compared with -fed plants, which correlated, respectively, with increased and decreased resistance. Nitric oxide (NO) can be generated by nitrate reductase (NR) to influence the formation of the HR. NO generation was reduced in -fed plants where N assimilation bypassed the NR step. This was similar to that elicited by the disease-forming P. syringae pv. tabaci strain, further suggesting that resistance was compromised with feeding. PR1a is a biomarker for the defence signal salicylic acid (SA), and expression was reduced in -fed compared with fed plants at 24h after inoculation. This pattern correlated with actual SA measurements. Conversely, total amino acid, cytosolic and apoplastic glucose/fructose and sucrose were elevated in - treated plants. Gas chromatography/mass spectroscopy was used to characterize metabolic events following different N treatments. Following nutrition, polyamine biosynthesis was predominant, whilst after nutrition, flux appeared to be shifted towards the production of 4-aminobutyric acid. The mechanisms whereby feeding enhances SA, NO, and polyamine-mediated HR-linked defence whilst these are compromised with , which also increases the availability of nutrients to pathogens, are discussed.

Moving nitrogen to the centre of plant defence against pathogens

“…For instance, symptoms of black root rot (Rhizoctonia solani) of sugar beets (Afanasiev and Carlson, 1942) or Fusarium wilt on tomato (Borrero et al, 2012) were reported to increase following NH þ 4 nutrition. In a recent metabolomic study, we have found that NH þ 4 nutrition enhances the content of apoplastic sugar and amino acids as well as GABA, thereby increasing the availability of nutrients to the invading pathogen; in this case P. syringae (Gupta et al, 2013). Conversely, under NO -3 nutrition, increased resistance to P. syringae was observed.…”

“…One was the increase in polyamine levels, i.e. putrescine, spermidine and spermine production (Gupta et al, 2013). Polyamines are known to increase plant resistance; for example, increasing in barley (Hordeum vulgare) during the hypersensitive response (HR)-associated resistance response against the powdery mildew fungus B. graminis f. sp.…”

“…It is therefore possible that defence-associated NO could influence this homeostatic mechanism to favour N diversion either away from the infection site or towards defensive metabolism. NH þ 4 nutrition is also of importance, as this leads to reduced levels of NO via suppression of NR activity (Planchet et al, 2005;Gupta et al, 2013). The NR NO-generating mechanism has been shown to be central to the HR in response to avirulent Pseudomonas interactions with the host (Melotto et al, 2006;Gupta et al, 2013;Vitor et al, 2013).…”

“…NH þ 4 nutrition is also of importance, as this leads to reduced levels of NO via suppression of NR activity (Planchet et al, 2005;Gupta et al, 2013). The NR NO-generating mechanism has been shown to be central to the HR in response to avirulent Pseudomonas interactions with the host (Melotto et al, 2006;Gupta et al, 2013;Vitor et al, 2013). Gupta and colleagues (2013) also reported that during compatible interaction between tobacco and P. syringie pv.…”

Nitrate Increased Cucumber Tolerance to Fusarium Wilt by Regulating Fungal Toxin Production and Distribution

“…In contrast, compared to the NH 4 + , NO 3 − increased tobacco resistance to Pseudomonas syringae pv. p haseolicola by the accumulation of SA and NO, as well as the increase in polyamine-mediated HR-linked defence [41]. In addition, studies have reported that a high N supply generally increases the susceptibility of plants to obligate parasites but decreases the susceptibility of plants to necrotrophs and facultative parasites [19,35].…”