versão ISSN 0258-5936
FREIXAS, J.A; TORRES, W; REYNALDO, Inés M e NAPOLES, María C. Ureides LEVELS IN SOYBEAN PLANTS WITH DIFFERENT INOCULANTS AND SUBMITTED TO WATER DEFICIT. cultrop [online]. 2011, vol.32, n.2, pp. 122-135. ISSN 0258-5936.
Soybean [Glycine max (L.) Merr.] establishes symbiosis with N2 fixing bacteria from Rhizobia group, such as Bradyrhizobium sp. Nitrogen fixed in nodules is transferred to leaves as ureides, these molecules are able to increase its levels in soybean leaves under drought stress. Indeed, biological nitrogen fixation in soybean is especially sensitive to drought and ureides seem to be involved through a negative feedback from leaves to nodules. In addition, induction of nodulation genes in Bradyrhizobium sp. has positive effects in soybean growth under moderate drought stress. The goal of this work is to study ureides level in soybean with different inoculants in response to water deficit. Soybean plants (cv. INCAsoy27) were firstly grown in nutrient solution during 15 days. Afterwards, they were drought stressed for a 20 days period adding 10% PEG 6000. Bradyrhizobium elkanii ICA 8001 was the strain cultivated with the purpose of inoculating soybean plants. This strain was separately grown in three culture media, two of them induced in nodulation factor production and the other one without induction. A statistically significant increase of ureides level in leaves and nodules was observed in plants with water deficit and inoculants without nodulation factor induction (NFI). However, this increase was not observed in plants drought stressed and inoculated with the strain previously induced in nodulation factor production. It might suggest an important role of NFI in soybean ureides level regulation under drought conditions. At the end of the stress period, the activity of the enzyme glutamine synthetase in soybean nodules was measured, but there were no statistically significant differences among each treatment with NFI, although differences were reported between non-stressed and stressed soybean plants inoculated with B. elkanii ICA 8001 without NFI.
Palavras-chave : soybean; Bradyrhizobium; water deficit; ureides; nodulation factors.