Glutamine and antioxidant metabolism during adventitious organogenesis of Ananas comosus leaves / Glutamina e metabolismo antioxidante durante a organogênese adventícia em folhas de Ananas comosus

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

A positive influence of glutamine on organogenesis of in vitro cultured plant tissues has been demonstrated by several studies. It is well known that the endogenous synthesis of phytohormones can be influenced by nitrogen sources, although it is not completely established in which way glutamine acts in this process. The addition of this amino acid to the culture medium has enhanced the organogenesis rate and resulted in a better vigor of the shoots that were originated from the leaf bases of Ananas comosus (L.) Merr. cultured in in vitro conditions. It is also suggested that the tissue excision may result in a stressful condition by increasing the production of reactive oxygen species and changing the endogenous redox state, which might be involved in the induction of organogenic process. However, this stress should be beneficial only if restricted. The aim of this work was to comprehend the positive influence of glutamine on the in vitro adventitious organogenesis of pineapple leaf bases. It was also attempted to determine whether the glutamine would be involved on a possible oxidative stress decrease during the organogenesis induction. In order to answer these questions, we tried to correlate the presence of glutamine in the culture medium and the endogenous hydrogen peroxide, glutathione, ascorbate levels. The redox state of these antioxidants is also analyzed during the induction of adventitious shoot organogenesis. Moreover, two antioxidants enzymes activities are quantified in the leaf explants: catalase and superoxide dismutase. The glutathione influence on the process was also investigated, considering the glutamine presence or not. It was done in order to establish the effect of this antioxidant in the organogenic process. The results showed that glutathione could replace, but not enhance, the positive effect of glutamine on the organogenesis rate of pineapple leaf bases. This antioxidant did not substitute the positive effect presented by the glutamine on the acquisition of fresh and dry masses by the new shoots. On the other hand, glutathione enhanced the number of adventitious buds per explant. Apparently, the excision of the leaf bases and its subsequent cultivation in the induction culture medium resulted in the tissue oxidative stress early in the first 24 hours of incubation. This could be inferred by the high H2O2 concentrations detected during this period. However, this possible stressful condition was controlled during the culture period, leading to the return of the homeostasis of the tissue and allowing the cells to become determined to shoot organogenesis. During the probable period of oxidative stress, glutamine seemed to maintain the reduced redox state on both ASC and GSH. The results of the antioxidant enzymes activities suggested that CAT may have been responsible for the regulation of the endogenous H2O2 levels, while SOD did not showed significant changes during the induction of organogenesis of leaf bases cultivated either in SIM or SIMGln. Taken together, the results obtained in this work suggest that the oxidative stress caused by the excision of the leaf tissues and its in vitro cultivation may be an important signal to the induction of the leaf organogenesis. Furthermore, the glutamine may have a role in the maintenance of the reduced redox state when higher levels of endogenous H2O2 are present in the tissues.

ASSUNTO(S)

organogenesis bromeliaceae glutamina organogênese glutamine metabolismo antioxidante bromeliaceae antioxidant metabolism

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