Int.J.Curr.Microbiol.App.Sci (2015) 4(6): 1010-1024 1010 Original Research Article Potential impact of cyanobacterial exudates on seed germination and antioxidant enzymes of crop plant seedlings Ashraf M. M. Essa*, Wael M. Ibrahim, Rania M. Mahmud and Nabil Abo ElKassim Botany Department, Faculty of Science, Fayoum University, Fayoum, Egypt *Corresponding author ABSTRACT Introduction Cyanobacteria are oxygenic, photosynthetic prokaryotic organisms that are distributed worldwide and can inhabit a wide range of habitats including freshwater, marine and terrestrial environments (Pankratova 2006; Tripathi et al., 2007; Nagarajan et al., 2012; Whitton 2012). In agricultural soils, they potentially contribute towards biological nitrogen fixation that improve soil fertility and crop productivity. Although, the great majority of cyanobacteria that fix nitrogen are heterocystous (Granhall & Henriksson 1969), non-heterocystous cyanobacteria can fix nitrogen as well (Kallas et al., 1983). The fixed nitrogen is then released as available form of ammonia that is required for the growth of higher plants. International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 4 Number 6 (2015) pp. 1010-1024 http://www.ijcmas.com Cyanobacteria are a diverse group of prokaryotes that are spread worldwide. They improve the growth and development of the plants they share their vicinity via releasing various biologically active substances. The effect of the exudates of the cyanobacterial strains; Anabaena oryzae, Nostoc ellipsosporum and Synechococcus sp. on the percent of seed germination and the seedling growth criteria of Sorghum durra and Helianthus annuus was investigated in this study. A marked promotion in the seed germination of Sorghum durra was recorded with Anabaena oryzae and Synechococcus sp. while the three culture filtrates demonstrated a negative consequence with Helianthus annuus. At the same time, the seedling growth criteria of the treated plants were highly significantly enhanced especially with Anabaena oryzae. Also, A clear augmentation in the activity of the antioxidant enzymes; catalase, peroxidase and polyphenol oxidase was recorded in the treated plants. Analysis of Anabaena oryzae exudates by Gas Chromatography Mass Spectrometry (GC-MS) demonstrated the occurrence of gibberellins, n-acetyl-D- glucosamine, linalool, dihydroxyphenyl glycol in addition to niacinamide. The presence of these bioactive compounds in the exudates of Anabaena oryzae might be directly or indirectly involved in root initiation, cell division and cell enlargement in addition to their role in the activation of the antioxidative defense enzymes of the treated plants. Keywords Cyanobacteria, crops, germination, growth, antioxidant enzymes, metabolites.