Alterations on rice leaf physiology during infection by Bipolaris oryzae

Abstract

Brown spot, caused by Bipolaris oryzae, is one of the most destructive diseases of rice. This study investigated some physiological and biochemical changes on rice leaves infected by B. oryzae. Rice plants (cv. "Oochikara") were grown for 35 days in hydroponic culture and inoculated with B. oryzae. Leaf samples were assessed for disease severity and also collected to determine lipid peroxidation (equivalents of malondialdehyde acid-MDA), electrolyte leakage (EL), and pigment concentrations. Gas exchange parameters were also evaluated. Brown spot severity increased over time, which was associated with increased MDA concentration and high EL. Chlorophyll (Chl) concentrations were significantly lower at 144 h after inoculation (hai) as compared to leaves from non-inoculated plants. At 144 hai, the concentration of total carotenoids (Car) was less than on 72 hai, and the Chl a+b/Car ratio was significantly lower on inoculated plants as compared to their noninoculated counterparts. Overall, chlorophylls were more affected by fungal infection than were carotenoids. The net carbon assimilation rate, stomatal conductance, and transpiration rate were reduced by about 65% in plants at 144 hai as compared to non-inoculated plants, but the internal CO 2 concentration was unresponsive to infection. Changes in photosynthesis were largely related to both impaired light capture ability and decreased mesophyll capacity to fix CO 2 . It can be concluded that the infectious process of B. oryzae on rice affects the leaf physiology mainly through the damage to the cells, basically at membrane level.

Magnesium-induced alterations in the photosynthetic performance and resistance of rice plants infected with Bipolaris oryzae

“…When corroborating the reported potential and empirical effects of Mg in reducing BS severity, we also found that there was a pronounced decrease in gas exchange parameters (especially A and g s ) in inoculated plants regardless of the Mg rate. This fact, along with the negative correlations between disease severity and gas exchange parameters substantially supports the negative effects of BS on rice physiology as already reported by Dallagnol et al (2011).…”

“…Increased antioxidant activity in rice plants inoculated with B. oryzae has already been reported (Dallagnol et al, 2011;Hermans and Verbruggen, 2005). Cakmak and Kirkby (2008) reported chlorophyll breakdown and the generation of highly reactive oxygen species in plants under Mg deprivation.…”

“…Stomatal closure is a primary innate immunity response to pathogen-associated molecular patterns (PAMPs) for bacterial and fungal pathogens (Melotto et al, 2006;Gudesblat et al, 2009). Furthermore, being a necrotro- phic pathogen, non-host selective toxins (ophiobolins A and B) produced by B. oryzae may cause tissue necrosis to damage the leaf blade structure and also favor a reduction in g s (Tullis, 1935;Dallagnol et al, 2011). Subsequent limitation in diffusion may have reduced the CO 2 uptake from the atmosphere, reducing C i as a consequence.…”

Capacidade fotossintética de plantas de algodoeiro infectadas por ramulose e supridas com silício

“…Na maioria das doenças foliares, a A é reduzida a partir do início da infecção (Berger et al, 2007), sendo uma menor g s uma das principais restrições para a fotossíntese nas plantas doentes. A redução na g s limita o influxo de CO 2 às folhas (Dallagnol et al, 2011). Nas folhas de plantas infectadas por diferentes patógenos, observa-se que, geralmente, ocorre uma redução no transporte de elétrons da cadeia fotossintética, indicando decréscimo na eficiência do uso da luz e, consequentemente, um aumento no excesso de energia de excitação.…”

“…No patossistema arroz-B. oryzae, a colonização dos tecidos foliares pelo patógeno em estágios mais avançados da infecção reduziu as concentrações de cl a e de cl b , porém os carotenoides foram menos prejudicados (Dallagnol et al, 2011). No patossistema milho-Exserohilum turcicum, a cl a foi mais afetada do que a cl b pelas toxinas secretadas pelo fungo (Chauhan et al, 1997).…”