Photosynthesis and carbohydrate metabolism in tobacco leaves during an incompatible interaction with Phytophthora nicotianae

Abstract

The metabolic and cellular changes in source leaves of Nicotiana tabacum L. cv SNN during an incompatible interaction with Phytophthora nicotianae van Breda de Haan were investigated and compared with defence reactions. Hypersensitive cell death was preceded by a rapid and highly localized shift to non-assimilatoric metabolism. During the first 6 h post infection (hpi), reactive oxygen species (ROS) accumulated. Callose was deposited at the interface of adjacent mesophyll cells ( ≥ 1 hpi), the export of sucrose collapsed and its content in the apoplast increased. Stomata closed and photosynthetic flux was reallocated from CO 2 assimilation in favour of photorespiration. This was accompanied by an increase in respiration, glucose-6-phosphate dehydrogenase (G6PDH) activity, apoplastic invertase and hexose content. Later ( > 6 hpi) the photosynthetic electron transport chain was interrupted and photosynthesis completely collapsed. This was accompanied by a further increase in apoplastic invertase and carbohydrates, respiration and oxidative pentose phosphate pathway (OPPP) and followed by further burst in ROS release. Hypersensitive cell death did not appear until photosynthesis completely declined. Photosynthesis was visualized by chlorophyll-a fluorescence imaging on a macro-and microscopic scale. Decline in photosynthesis and defence reactions were highly localized processes, which occur in single mesophyll cells. We propose that in photoautotrophic leaves, photosynthesis and assimilatory metabolism must be switched off to initiate respiration and other processes required for defence. An early blockage of intercellular sugar transportation, due to callose deposition, in conjunction with enhanced apoplastic invertase activity could facilitate this metabolic shift.

Isoenzyme replacement of glucose-6-phosphate dehydrogenase in the cytosol improves stress tolerance in plants

“…S3). In summary, these changes effectively alter carbon partitioning in favor of metabolic sourceto-sink transitions within infected leaf areas (5,6). Additional evidence for an altered pathogen response in cP2 plants is the accumulation of transcripts encoding PR-Q (5), which now also occurred in the Xanthi background, comparable with the resistant SNN (Fig.…”

“…Immunoblot analyses with various G6PDH antisera (14,19) demonstrated that these defense-induced rises in G6PDH activity mainly result from up-regulated expression of cytosolic isoforms, encoded by G6PD (Fig. 1B), probably due to sensing elevated soluble sugar levels (7), known to accompany sourceto-sink transitions of infected tobacco source leaves (5,6).…”

“…Nonetheless, photosynthetically active source leaves of resistant plants can exhibit strong defense reactions, including HR. We have previously shown for a resistant tobacco cultivar that metabolic source-to-sink shifts accompany early defense reactions in source leaves (5,6), and that sink situations stimulate de novo synthesis of cytosolic glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49) in leaf discs (7), suggesting a role for this enzyme during plant defense.…”

Cell Wall Invertase Promotes Fruit Set under Heat Stress by Suppressing ROS-Independent Cell Death

“…Conversely, overexpression of CWIN in rice (Oryza sativa) driven by its native promoter enhanced grain filling and yield (Wang et al, 2008). An increase in CWIN transcription or activity is also commonly observed upon pathogen infection in a wide range of plant species (Benhamou et al, 1991;Scharte et al, 2005), indicating a role for CWIN in defense against pathogens, possibly through Glc signaling (Ruan, 2014). For instance, constitutive expression of a yeast (Saccharomyces cerevisiae) INV gene in the apoplasm increased tobacco (Nicotiana tabacum) resistance to potato virus Y (Herbers et al, 1996), whereas RNA interference (RNAi)-mediated repression of CWIN in tobacco compromised its response to infection by the oomycete Phytophthora nicotianae (Essmann et al, 2008).…”

Directed Biosynthesis of Phytotoxic Alkaloids in the Cyanobacterium Nostoc 78–12A

“…Preliminary experiments on the mechanism of photosynthesis inhibition as measured by P700 redox kinetics [23] indicate that the electron transport chain might be restricted upstream of photosystem I (PS I, data not shown). The effect of nostocarboline might be comparable to the non-selective herbicide paraquat (methylviologen, 1,1'-dimethyl-4,4'-bipyridinium), which is a strong autooxidable electron acceptor in PS I; and its presence in light-exposed plants has several drastic consequences, like the production of superoxide.…”