Fermentative metabolism in soybean roots and nodules under hypoxia and post-hypoxia conditions

O metabolismo das plantas reage sensivelmente ??s mudan??as de disponibilidade de oxig??nio impostas pelo alagamento. Uma das consequ??ncias imediatas da deple????o do oxig??nio ?? a ativa????o do metabolismo anaer??bico e uma redu????o significativa na produ????o de energia. Este trabalho teve por objetivo avaliar o metabolismo fermentativo em ra??zes e n??dulos de soja [Glycine max (L.) Merril] sob condi????es de hipoxia e p??s-hipoxia. Para isso dois experimentos foram conduzidos em casa de vegeta????o com os gen??tipos Fundacep 53 RR e BRS Macota, cultivados em vasos de 3L contendo vermiculita como substrato, em associa????o com Bradyrhizobium elkanii. Os tratamentos foram aplicados quando as plantas atingiram o est??dio R2 (reprodutivo). Experimento I - o sistema radicular da soja foi submetido ?? hipoxia pelo encaixe de um segundo vaso sem perfura????es e inundado com solu????o nutritiva dilu??da a 1/3 da concentra????o original, de forma a se manter uma l??mina de 20 mm sobre a superf??cie do substrato. A inunda????o das plantas foi conduzida por 8 dias, ap??s este per??odo foi retirado os vasos sem perfura????es para avalia????o da recupera????o. O material vegetal foi coletado no 2??, 4??, 6?? e 8?? dia ap??s a inunda????o (DAI) ou recupera????o (DAR), juntamente com seus respectivos controles (mantidos em normoxia) para a dosagem da atividade das enzimas fermentativas, ??lcool desidrogenase (ADH), piruvato descarboxilase (PDC) e lactato desidrogenase (LDH) em ra??zes e n??dulos. Experimento II - as plantas foram transferidas para um sistema hidrop??nico e submetidas ?? hipoxia do sistema radicular pelo borbulhamento de N2 gasoso por 24 e 72 h ou mantidas em vermiculita (controle). Posteriormente retornaram para vermiculita sob condi????es de normoxia por 24 e 72 h. Foram avaliadas a atividade das enzimas ADH, PDC e LDH , metab??litos anaer??bicos (etanol, lactato e piruvato) e conte??do de carboidratos (sacarose, a????cares sol??veis totais, amido e polissacar??deos sol??veis em ??gua) em ra??zes e n??dulos. O delineamento foi inteiramente casualizado com quatro repeti????es. Os dados foram submetidos ?? ANOVA e as m??dias comparadas pelo teste de Tukey a 5% de probabilidade. No experimento I a inunda????o promoveu aumento significativo da atividade da ADH, PDC e LDH, bem como a diminui????o da atividade com a recupera????o em ra??zes e n??dulos. Fundacep 53 RR respondeu de forma mais efetiva aos tratamentos. No experimento II, a atividade das enzimas ADH, PDC e LDH, bem como os teores de etanol e lactato, aumentaram com a hipoxia em ra??zes e n??dulos e retornaram aos n??veis pr??-hip??xicos com a recupera????o em ambos os gen??tipos. O teor de piruvato aumentou nos n??dulos e diminuiu nas ra??zes e os teores de a????cares e sacarose aumentaram nas ra??zes e diminu??ram nos n??dulos em hipoxia para ambos os gen??tipos. Fundacep 53 RR foi mais responsiva aos efeitos provocados pela hipoxia e p??s-hipoxia que BRS Macota. Os efeitos foram mais pronunciados nas plantas submetidas ?? hipoxia pelo sistema hidrop??nico em fun????o da r??pida deple????o do oxig??nio na solu????o.Plant metabolism is sensitively to changes in oxygen availability by waterlogging. The immediate consequences of oxygen depletion are the activation of anaerobic metabolism and a reduction in energy production. This study aimed to evaluate the fermentative metabolism in soybean [Glycine max (L.) Merrill] roots and nodules under hypoxia and post-hypoxia conditions. Two experiments were conducted in greenhouse conditions with soybean genotypes Fundacep 53 RR and BRS Macota grown in 3L pots containing vermiculite as substrate, in association with Bradyrhizobium elkanii. The treatments were applied when the plants reached the R2 stage (reproductive). Experiment I - the root system of plants was subjected to hypoxia by fitting a second pot without holes and flooded with nutrient solution diluted to one-third of the original, in order to keep a blade of 20 mm on the surface of the substrate. Plants were maintained flooded for eight days, and so the pot without drilling holes was removed for recovery assessment. Non-waterlogging plants were maintained as control (normoxic condition). The activities of fermentation enzymes, alcohol dehydrogenase (ADH), pyruvate decarboxylase (PDC) and lactate dehydrogenase (LDH) were quantified in roots and nodules collected at 2, 4, 6 and 8 days after flooding or recovery . Experiment II - soybean plants were transferred to a hydroponic system and roots were subjected to hypoxia by flowing N2 gas during 24 and 72 h. For recovery, plants returned to vermiculite for 24 and 72 h. A control group of plants was maintained in vermiculite.The enzymatic activities of ADH, PDC and LDH, levels of anaerobic metabolites (ethanol, lactate and pyruvate) and carbohydrate content (sucrose, soluble sugars, starch and water soluble polysaccharides) were quantified in roots and nodules. The experiments were completely randomized with four replications and data were analyzed by ANOVA and compared by the Tukey test (P 0.05). Experiment I - activities of ADH, PDC and LDH increased significantly in roots and nodules of flooded plants and decreased during recovery. Fundacep 53 RR responded more effectively to treatments effects. Experiment II - the activity of ADH, PDC and LDH enzymes, as well as the content of ethanol and lactate, increased with hypoxia in roots and nodules, and returned to pre-hypoxic levels with the recovery in both genotypes. The pyruvate content increased in nodules and decreased in roots, sugars and sucrose levels increased in roots and decreased in nodules under hypoxia for both genotypes. Fundacep RR 53 was more responsive to the effects caused by hypoxia and post-hypoxia than BRS Macota. The effects were more pronounced in plants subjected to hypoxia by hydroponic system due to the rapid depletion of oxygen in the solution