[Effect of blue light on conidiation development and glucoamylase enhancement in Aspergillus niger]

Pure blue (BL) or red light (RL) were obtained by filtering blue or red fluorescent lamp light through plastic filters. With the dark condition as control, the effect of BL and RL on the Aspergillus niger were studied including soluble protein content of mycelium, glucoamylase activity, the biomass as well as sporangiophore photomorphogenesis and vegetative spore development. Irradiation with BL and RL wholly promoted glucoamylase activity together with the rise of the soluble protein content and the mycelium growth. The glucoamylase activity of mycelia culture under blue light was enhanced 2.54 times than that of control. In the phases of developmental growth (young mycelia and sporangiophores), glucoamylase activity and relative conductivity ratio of mycelium were higher under blue light than under dark, the enhanced glucoamylase activity likely stemmed from development of macrosporangiophores of Aspergillus niger promoted by blue light. In addition, the increase of glucoamylase activity under blue light was highest at the stage of macrosporangiophores forming and conidiation, then declined owing to spores aging. As to young microsporangiophores under darkness the glucoamylase activity just relatively increased and declined rapidly with age. Different from control, irradiation with blue light at the time of 72 h after inoculation was able to stimulate development of macrosporangiophore and conidium along with the rise of glucoamylase activity of Aspergillus niger.