Infection with virulent and avirulent P. syringae strains differentially affects photosynthesis and sink metabolism in Arabidopsis leaves

Abstract

Infection of plants with pathogens leads not only to the induction of defence reactions but also to changes in carbohydrate metabolism. In this study, the effects of infection by a virulent and an avirulent strain of P. syringae on spatio-temporal changes in photosynthesis were compared using chlorophyll fluorescence imaging. The maximum PSII quantum yield, effective PSII quantum yield and nonphotochemical quenching were decreased in Arabidopsis leaves infected with either strain. At the same time, the quantum yield of nonregulated energy dissipation was increased. These changes could be detected by chlorophyll fluorescence imaging before symptoms were visible by eye. The effects were restricted to the vicinity of the infection site and did not spread to uninfected areas of the leaf. Qualitatively similar changes in photosynthetic parameters were observed in both interactions. Major differences between the responses to both strains were evident in the onset and time course of changes. A decrease in photosynthesis was detectable already at 3 h only after challenge with the avirulent strain while after 48 h the rate of photosynthesis was lower with the virulent strain. In contrast to photosynthesis, the regulation of marker genes for source/sink relations and the activities of invertase isoenzymes showed qualitative differences between both interactions. Inoculation of the virulent but not the avirulent strain resulted in downregulation of photosynthetic genes and upregulation of vacuolar invertases. The activity of vacuolar invertases transiently increased upon infection with the virulent strain but decreased with the avirulent strain while extracellular invertase activity was downregulated in both interactions.

The role of sugar signaling in plant defense responses against fungal pathogens

“…For example, during sunflower cotyledon infection by the necrotrophic fungus Sclerotinia sclerotiorum, sucrose level was reduced by 100 %, fructose by 85 %, whereas for glucose it was only 20 % (Jobic et al 2007). Sugar levels decrease in tomato plants after inoculation with B. cinerea (Berger et al 2004;Bonfig et al 2006). Sugar deficit may lead to sugar starvation in cells, a phenomenon well characterized in terms of metabolism and at the gene expression level (Morkunas et al 2003).…”

Light and Oxygen Are Not Required for Harpin-induced Cell Death

“…Chloroplasts and mitochondria probably have other roles in plant/pathogen interactions in addition to ROS generation, particularly since both organelles are essential contributors to cell metabolism. Roles for metabolic interplay and sugar sensing in particular have been described in both virulent and avirulent plant/pathogen interactions (13). It has been suggested that photosynthesis and assimilatory metabolism are switched off in order to initiate respiration and defense reactions (12).…”

“…Exposure to abiotic stresses, such as drought, frequently causes inhibition of photosynthesis and accelerated ROS production (10). Pathogen attack causes suppression of photosynthetic gene expression (11) and a concomitant inhibition of photosynthesis (12,13), suggesting that light and ROS trigger common signaling pathways in plants exposed to abiotic and biotic stresses (14,15). Although ROS production by the mitochondrial ETC represents less than 1% of chloroplastic ROS generation in photosynthetic tissues (16), mitochondria have been proposed to be as important in the establishment of cell death in plants as they are in animals (17).…”

An Overview of Plant Photosynthesis Modulation by Pathogen Attacks

“…At present, it is not clear if this stimulation of photosynthesis is due to the defence strategy of the plant (Berger et al, 2007). A decrease in photosynthesis has also been reported in incompatible interactions (Bonfig et al, 2006). The decrease in photosynthesis was detectable earlier with the avirulent strain than with the virulent strain.…”

“…Theoretically, the photosynthetic capacity of plants is unlimited when the optimal growing conditions are met. Unfortunately, terrestrial plants are constantly challenged by abiotic (UV, water, salinity, temperature) (Baker et al, 1988, Baldry et al, 1966, Barhoumi et al, 2007, Barrow and Cockburn, 1982, Bassham, 1977, Batista-Santos et al, 2011, Bauerle et al, 2007, Berry, 1975, Bischof et al, 2000, Ripley et al, 2008, Ripley et al, 2007, Roberntz and Stockfors, 1998 and biotic (pathogens, pests, animal and human) stresses that reduce their productivity and even threaten their survival (Bilgin et al, 2010, Bonfig et al, 2006, Erickson and Hawkins, 1980, Garavaglia et al, 2010, Kocal et al, 2008. While the regulation of plant defence responses has been extensively investigated, the effects of pathogen infection on primary metabolism, including photosynthesis, are however less known.…”