Ascorbic Acid In Relation To Sclerotial Differentiation And Carotenoid Production By Penicillium Sp.PT95

A strain of Penicillium sp. PT95 was isolated from soil sample collected close to Fenyang, Shanxi Province. The strain can form abundant orange, sand-shaped sclerotia in which carotenoid is accumulated. By morphological observation and RAPD typing, PT95 strain had been identified to P. thomii series. The aim of this study was the effect of oxidative stress and ascorbic acid on sclerotial differentiation and carotenoid yield of PT95 strain.By comparing growth period, sclerotial biomass and content of carotenoid of PT95 strain in Czapek Agar(CA) and Joham's nutrient agar medium, it was found that the high-oxidative stress growth condition (light exposure plus iron in the growth medium) was favourable to formation of sclerotia and carotenoid biosynthesis of this fungus. Joham's nutrient agar medium could shorten the growth period and enhance carotenoid yield of PT95 strain.Exogenous ascorbic acid did not support PT95 strain growth at the tested concentrations. Therefore it could not affect indirectly sclerotial differentiation by acting as sole carbon source. The effect of various concentrations of exogenous ascorbic acid in the growth medium on sclerotial differentiation of PT95 strain was studied. The result showed that a concentration-dependent inhibition of sclerotial differentiation. The higher the concentration of exogenous ascorbic acid was, the lower sclerotial biomass. The carotenoid production of PT95 strain was obviously reduced by exogenous ascorbic acid under different oxidative stress. It suggested that exogenous ascorbic acid could inhibit carotenoid accumulation via its antioxidant action.The change of concentration of endogenous ascorbic acid was quantified in exudates, sclerotia, differentiated mycelia and whole colonies of PT95 strain. The result showed that PT95 strain in culture produced ascorbic in levels dependent on oxidative growth conditions and developmental stages. The transition of PT95 strain from the undifferentiated to the differentiated stage was accompanied by a sharp shift in the ratio of reduced/oxidized ascorbicacid. It suggested that high oxidative stress might cause more accumulation of oxidized ascorbic acid and depress reduced ascorbic acid during differentiation, thus more sclerotia were produced in the survival of PT95 for long periods in poor conditions.The reduced and oxidized ascorbic acid patterns between high- and low-oxidative stress and between undifferentiated and differentiated colonies, suggest that ascorbic acid was produced by PT95 strain in concentration gradients and ratios characteristic to its response to oxidative stress caused by reactive oxygen species during growth.Ascorbic acid profiles were different between the sclerotial PT95 strain grown under high- and low-oxidative stress conditions, as well as between a nonsclerotial PT9 strain grown under high-oxidative stress conditions. Ascorbic acid might be produced by the sclerotial strain to reduce oxidative stress, although less efficiently than the nonsclerotial strain. In addition, the ratio of the reduced/oxidized ascorbic acid in the nonsclerotial strain remained unchanged throughout growth.The relationship between lipid peroxidation and sclerotial differentiation of PT95 strain was studied. The data showed that the time of sclerotial initiation on the colony was related to a high increase of lipid peroxidation levels in mycelia. The results suggested that lipid peroxidation is a very important physiological phenomenon that is closely associated with the initiation of sclerotia in PT95. A positive correlation between the levels of mycelial lipid peroxides and the number of sclerotia formed in the corresponding mycelia.The influence of illumination and Fe2+ on the level of lipid peroxidation was studied. The results showed that the effect of illumination and Fe2+ isolated and the synergistic effect of illumination and Fe2+ could increase the level of lipid peroxidation.The data showed that exogenous ascorbic acid can reduce the levels of lipid peroxides obviously, which were equivalent to the percentage of sclerotial differentiation decrease of this fungus caused by the corresponding ascorbic acid. The data also strongly suggested that the lipid peroxidation...