Association of non-heterocystous cyanobacteria with crop plants

Cyanobacteria have the ability to form associations with organisms from all domains of life, notably with plants, which they provide with fixed nitrogen, among other substances. This study was aimed at developing artificial associations between nonheterocystous cyanobacteria and selected crop plants. We isolated several non-heterocystous cyanobacteria from various rice fields. The cultures were tested for their capacity to produce the plant hormone indole-3- acetic acid (IAA), and the possible role of IAA in the association of cyanobacteria with seedling roots was evaluated. Axenic cultures were co-inoculated with 10-day-old plant seedlings of Triticum aestivum, Vigna radiata and Pisum sativum and incubated for 1 week. Cyanobacterial association with the roots of these seedlings was quantified by measuring chlorophyll-a. Cyanobacterial associ by light microscopy as well as by confocal laser scanning microscopy (CLSM). Based on sequence analysis of the 16S rRNA gene, the isolates were identified as Synechocystis sp., Chroococcidiopsis sp., Leptolyngbya sp., and Phormidium sp. CLSM observations revealed the intimate association of cyanobacteria with the seedling roots as well as invasion of the roots and root cells. Strains producing IAA were more efficient in the colonization of the roots than those that lacked this ability. IAA-produ a tryptophan-dependent pathway, and these cyanobacteria showed IAA synthesis activity in the presence of roots in media lacking tryptophan. Based on the results of this study, we conclude that nonheterocystous cyanobacteria also have the potential for use in agriculture to improve the growth and yield of crop plants that do not naturally form associations with cyanobacteri