Rice seedling growth promotion by Cyanobacteria

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

Villa Carlos Paz, Córdoba, Argentina

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

High salinity is one of the most important environmental factors that produce osmotic stress and limit plant growth and crop productivity. In accordance with FAO, aproximately 7% of the land is affected by salt. 12% of this land is localized in the south and south east of Asia, where rice is the principal crop. Plant growth reduction is the consecuense of the effect of salt on the dry biomass distribution, ionic and water relation or the combination of these factors. Cyanobacteria are photosynthetic procariotic microorganisms. They excrete a great number of substances that enhance the fertility and structure of soil and influence plant growth and development. The effects of Cyanobacteria on salinity stressed rice plants are unknown. The aim of the present work was the study the influence of Scytonema hofmanni extracellular products (EP), on the growth and porphyrin metabolism in rice seedlings stressed by NaCl. Rice seedlings were grown in hydroponics with the addition of S. hofmanni EP (strain isolated from Argentine paddy fields) and/or NaCl (5 g/L). After 14 days shoot length, fresh and dry weight; root length and dry weight, and the root/shoot ratio for length and dry weight were determined. The biochemical parameters studied in the shoot were: total free porphyrin, chlorophylls a and b and carotenoids contents, a/b chlorophyll relation and ALA-D activity. Sodium Chloride (5 g/L) inhibited the morphological and biochemical parameters except for the content of chlorophylls a and b that increased by 45 and 49% respectively, probably due to an adaptation to the salinity stress, maintaining the seedlings their photosynthetic capacity. The combined treatment (EP + NaCl) showed that EP reversed by 16% the shoot length inhibition produced by NaCl, increased by 35% and 43% the content of chlorophyll a and b, respectively, increased ALA-D activity by 34%, produced partial reversion (18%) of the total free porphyrin content reduced by NaCl, as well as cause the total reversion inhibition produced by the salt in carotenoids level. So Scytonema hofmanni exametabolites counteract part of NaCl detrimental effects on the shoot length probably due to the reactivation of the salt inhibited porphyrin biosynthesis.