Physicochemical confirmatory evidences for cyanobacterial released plant growth hormones governing escalation of rice (Oryza sativa L.) and wheat (Triticum sp.) crop

Abstract

Numerous plant-associated bacteria produce auxin and related indolic compounds. These indolic compounds were assessed based on their biological effects upon plants, such as shoot elongation and root hair deformation (Avena curvature test) or coleoptile elongation. Thus, precise identification of auxin and related molecules obtained following extraction of bacterial culture supernatants, concentration of the extracts, and separation and identification of the compounds by using thin layer chromatography (2D-TLC), high-performance liquid chromatography (HPLC) or gas chromatography-mass spectrometry. The present study includes in-vitro screening of 31 cyanobacterial isolates from 11 different genera along with one reference culture having history of 5 to 6 years rice-wheat crop organic practices. The cyanobacterial isolates were tested for their physiological role in rice-wheat growth promotion with reference to seed germination, seedling root-shoot elongation and secretion of growth promoting substances followed by detection and chemical identification of growth related substances like Indole-3-acetic acid and Indole-3-butyric acid. Among these test isolates, the highest germination 94.67 (±00.52) per cent with vigor index 76.69 (±02.85) was observed in rice seeds treated with 21 days old intracellular exudates of Westillopsis sp. (CCC-554) and the rice seedling plumule length 12.63 (±01.050) cm was observed in rice seed treated with 21 days old intracellular exudates of isolate Nostoc sp. (CCC546) while the longest radical length 09.18 (±00.17) cm was observed in rice seed treated with 14 days old cellular exudates. The highest wheat seed germination 99.00 (±00.57) per cent with vigor index 2533(±96) was observed in case of Chroococcus minutus (CCC582) and the wheat seedling plumule length 16.13 (±00.52) cm was observed in seeds treated with 21 days old cellular exudates of isolate Microcystis robusta (CCC568), while the longest radical length 23.270 (±0.173) cm was observed in wheat seed treated with 21 days old cellular exudates of Anabaena spp. (CCC573). Cyanobacterial isolate Cylindrospermum sp. (CCC547) exhibited highest 27.53 (±01.332) μg per ml Indole-3-acetic acid (IAA) production during dark incubation period. Along with their growth promoting and regulatory effects the seletected isolates were subjected for chromatographic analysis using 2D TLC and HPLC for the presence of indolic substances in the different algal extracts which were under study. The separated spots of different cyanobacterial culture extracts of Westelopsis sp. (CCC559), Nostoc sp. (CCC560), Chroococcus minutus (CCC582) and the reference culture Nostoc muscurum (UTEX387) on thin layer chromatography (2D TLC) have comparable rate of flow to authentic Indole compounds like Indole-3-acetic acid and Indole butyric acid (IBA) where the retention time was similar to those of the authentic IAA and IBA