Dwarfism reversion of dx rice seedlins and hidrolisis of glucosil conjugates of GA20 by Acetobacter diazotrophicus

COHEN A.; LUNA V.; PICCOLI P; BOTTINI R

Rio de Janeiro. Brasil

Simposio; II Mini-Simpósio sobre Agrobiologia. Reunião da Academia Brasileira de Ciências; 1998

EMBRAPA, Itajaí, RJ. Brasil

dwarfism ReversiOn OF dx rice seedlings and hydrolysis of glucosyl conjugates of gA20 by Acetobacter diazotrophicus Cohen A, PICCOLI P, Luna V, Bottini R. Laboratorio de Fisiología Vegetal, Facultad de Ciencias Exactas, Físico-Químicas y Naturales, Universidad Nacional de Río Cuarto, 5800 Río Cuarto, Argentina. The plant growth-promoting effect of rhizobacteria is adjudicated to phytohormones, mainly gibberellins (GA) and IAA. Azospirillum spp. promoted root growth in corn and reversed dwarfism in rice, and these effects were associated with GA production and hydrolysis of GA-glucosydes. Acetobacter diazotrophicus, endophytic of sugar cane, produces GA1, GA3 and IAA in cultured-defined medium (Bastián et al., 1998, Plant Growth Regulation 24: 7-11). This work studied reversion in expression of the dx dwarf gene in cv. Tan-ginbozu rice seedlings and hydrolysis of GA20-glucosydes, by A. diazotrophicus. A. diazotrophicus PAL 5, ATCC 49037, was cultured in LB medium (32°C, 80 r.p.m.) until stationary phase. Disinfected seeds of dwarf rice cv. Tan-ginbozu were germinated on Uniconazol 80 mM, and incubated 72 h at 32°C and continuous fluorescent light. The seedlings were grown in Fähraeus medium at 28°C and 16 h of continuous fluorescent light and submitted to: inoculation (106 and 107 CFU.ml-1); GA3 (1 and 10 mg.lt-1); AIA (1 and 10 mg.lt-1); GA3 + AIA (1 and 10 mg.lt-1). Eight days later root volume, root and shoot DW, root and first internode length, root number, and number of bacteria in roots and shoots were measured. Also A. diazotrophicus cultures were centrifuged, the pellets suspended en saline medium, sonicated, centrifuged again and 100 ml supernatant + 1 mg [2H2]GA20-GE or [2H2]GA20-G incubated for enzymatic activity at 32°C. The substrate was prepared by organic synthesis from [2H2]GA20 and a-ceto-Br-glucose. The reaction was stopped with H3PO4, and free [2H2]GA20 extracted with ethyl acetate. The presence of the aglycone was assessed by GC-MS. Results showed that plant infection was 107 UFC.root-1. Inoculation partially reversed the expression of dx gene. Volume, number and length of roots in plants inoculated were higher than in controls. Shoot DW in plants inoculated with 107 UFC.ml-1 was similar to 10 ppm GA3 and both duplicated controls. Crude enzymatic extracts of A. diazotrophicus were effective in hydrolyzing [2H2]GA20-GE/G. Our results demonstrate that the growth-promoting effect of A. diazotrophicus in plants, might be in part induced by GA, either throughout their synthesis or enzymatic hydrolysis of GA-glucosydes.