Effect of Scytonema hofmanni (Cyanobacteria) extracellular products on the metabolism of salinity stressed rice seedlings

GLORIA ZULPA; MONICA STORNI; MARIA CRISTINA ZACCARO; ANDRES RODRIGUEZ; ANA MARIA STELLA

Villa Carlos Paz, Córdoba, Argentina

Workshop; Fifth International PGPR (Plant Growth Promoting Rhizobacteria) Workshop; 2000

Although Cyanobacteria usually cohabitate with rice, strains selected on the basis of their nitrogen fixing capacity, have been inoculated into paddy fields in order to enhance soil nitrogen content. However, the beneficial effect of this biofertilization is not limited to the soil fertility, but it also influences plant growth and development by producing bioactive substances such as plant growth regulators (auxins, gibberellins), aminoacids, vitamins. The aim of this work was to study the effect of exometabolites from cyanobacterial strains isolated from Argentine paddy fields and of gibberellic acid, on rice seedlings growth. Extracellular products (EP) were obtained from mass cultures of Scytonema hofmanni, Microchaete tenera, Nostoc muscorum and Tolypothrix tenuis. Oryza sativa L. seedlings were grown in hydroponics: Hoagland culture medium added with different cyanobacterial EP and gibberellic acid (0.5 mg/L). Shoot length, shoot fresh and dry weight, root length and root dry weight were measured after 7 and 14 days of growth. The shoot/root ratio of length and dry weight were calculated. S. hofmanni EP were studied with a spectrophotometer comparing with indol acetic acid, gibberellic acid and kinetin. EP effect differs according to the cyanobacterial strain used, and the exposure time of the rice roots to these products. Gibberellic acid increased the shoot length (64%) and inhibited the growth of the root (37%), probably due to a better utilization of the photosyntates by the shoot as its dry weight also increased (29%). S. hofmanni exometabolites induced the increment of both shoot length and fresh weight by 17 y 42%, respectively after 7 days of treatment. This kind of effect has been already observed in plants treated with gibberellic acid. The S. hofmanni EP absorbance spectra do not coincide with those obtained with auxin, kinetin and gibberellic acid. The observed growth promoting effects are probably due to a combination of plant growth regulators and other growth promoting substances liberated by Cyanobacteria into the culture medium.