RESUMO
Infection with ectomycorrhizal fungi can increase the ability of plants to resist drought stress through morphophysiological and biochemical mechanisms. However, the metabolism of antioxidative enzyme activities in the ectomycorrhizal symbiosis remains poorly understood. This study investigated biomass production, reactive oxygen metabolism (hydrogen peroxide and malondialdehyde concentration) and antioxidant enzyme activity (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) in pure cultures of the ectomycorrhizal fungi Descolea antartica Sing. and Pisolithus tinctorius (Pers.) Coker & Couch, and non-mycorrhizal and mycorrhizal roots of Nothofagus dombeyi (Mirb.) roots under well-watered conditions and drought conditions (DC). The studied ectomycorrhizal fungi regulated their antioxidative enzyme metabolism differentially in response to drought, resulting in cellular damage in D. antartica but not in P. tinctorius. Ectomycorrhizal inoculation and water treatment had a significant effect on all parameters studied, including relative water content of the plant. As such, N. dombeyi plants in symbiosis experienced a lower oxidative stress effect than non-mycorrhizal plants under DC. Additionally, ectomycorrhizal N. dombeyi roots showed a greater antioxidant enzyme activity relative to non-mycorrhizal roots, an effect which was further expressed under DC. The association between the non-specific P. tinctorius and N. dombeyi had a more effective reactive oxygen species (ROS) metabolism than the specific D. antartica-N. dombeyi symbiosis. We conclude that the combination of effective ROS prevention and ROS detoxification by ectomycorrhizal plants resulted in reduced cellular damage and increased plant growth relative to non-mycorrhizal plants under drought.
Assuntos
Basidiomycota/crescimento & desenvolvimento , Secas , Fagaceae/metabolismo , Fagaceae/microbiologia , Micorrizas/crescimento & desenvolvimento , Espécies Reativas de Oxigênio/metabolismo , Biomassa , Contagem de Colônia Microbiana , Peróxido de Hidrogênio/metabolismo , Malondialdeído/metabolismo , Micélio/enzimologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia , Brotos de Planta/crescimento & desenvolvimento , Brotos de Planta/microbiologia , Solo/análise , ÁguaRESUMO
Drought stress conditions (DC) reduce plant growth and nutrition, restraining the sustainable reestablishment of Nothofagus dombeyi in temperate south Chilean forest ecosystems. Ectomycorrhizal symbioses have been documented to enhance plant nitrogen (N) and phosphorus (P) uptake under drought, but the regulation of involved assimilative enzymes remains unclear. We studied 1-year-old N. dombeyi (Mirb.) Oerst. plants in association with the ectomycorrhizal fungi Pisolithus tinctorius (Pers.) Coker & Couch. and Descolea antartica Sing. In greenhouse experiments, shoot and root dry weights, mycorrhizal colonization, foliar N and P concentrations, and root enzyme activities [glutamate synthase (glutamine oxoglutarate aminotransferase (GOGAT), EC 1.4.1.13-14), glutamine synthetase (GS, EC 6.3.1.2), glutamate dehydrogenase (GDH, EC 1.4.1.2-4), nitrate reductase (NR, EC 1.6.6.1), and acid phosphomonoesterase (PME, EC 3.1.3.1-2)] were determined as a function of soil-water content. Inoculation of N. dombeyi with P. tinctorius and D. antartica significantly stimulated plant growth and increased plant foliar N and P concentrations, especially under DC. Ectomycorrhizal inoculation increased the activity of all studied enzymes relative to non-mycorrhizal plants under drought. We speculate that GDH is a key enzyme involved in the enhancement of ectomycorrhizal carbon (C) availability by fuelling the tricarboxylic acid (TCA) cycle under conditions of drought-induced carbon deficit. All studied assimilative enzymes of the ectomycorrhizal associations, involved in C, N, and P transfers, are closely interlinked and interdependent. The up-regulation of assimilative enzyme activities by ectomycorrhizal fungal root colonizers acts as a functional mechanism to increase seedling endurance to drought. We insist upon incorporating ectomycorrhizal inoculation in existing Chilean afforestation programs.
Assuntos
Desidratação/metabolismo , Magnoliopsida/microbiologia , Micorrizas/fisiologia , Nitrogênio/metabolismo , Fósforo/metabolismo , Secas , Magnoliopsida/crescimento & desenvolvimento , Magnoliopsida/metabolismo , Nodulação , Raízes de Plantas/enzimologia , Raízes de Plantas/crescimento & desenvolvimento , Raízes de Plantas/microbiologia , Plântula/enzimologia , Plântula/crescimento & desenvolvimento , Plântula/microbiologia , SimbioseRESUMO
At present, reforestation has focused on native forests with anthropogenic intervention and eroded soils. There is interest in producing Nothofagus seedlings which can overcome adverse conditions encountered on reforestation sites. It is necessary to find new fungi that can be utilized as mycorrhizal inoculants and that enable the seedlings to increase their tolerance to adverse conditions. Two ectomycorrhizal strains of the fungus Descolea antarctica (D1 and D2) were cultured at different temperatures, pH levels and the activities of amylases, cellulases, and phosphatases were determined. In greenhouse and nursery trials, the growth responses of inoculated Nothofagus obliqua seedlings were evaluated. D1 and D2 exhibited the highest growth rates at 23ºC. Both strains grew at pH levels from 4 to 11. The highest enzymatic activities were registered for amylase (57.2 mg glucose/ml g of mycelium hr) and acid phosphatases (58.1 mg p-nitrophenol/ml g of mycelium hr) at 37ºC, and acid phospatases (1.720 mg p-nitrophenol/ml of mycelium hr) and alkaline phosphatases (1.360 mg p-nitrophenol/ml g of mycelium hr) at pH 4 and pH 11, respectively. We conclude that suitable N. obliqua seedlings for use in reforestation were obtained using D2 as inoculant.