Investigations of some intertidal green macroalgae to hyposaline stress: Detrimental role of putrescine under extreme hyposaline conditions

Abstract

We found recently that putrescine and spermidine accumulated in a marine green macroalga Ulva fasciata Delile exposed to hyposaline stress (5‰) (T.M. Lee, M.H. Chen, Hyosaline effect on polyamine accumulation in Ulva fasciata (Uvales, Chlorpphyta). Bot. Bull. Acad. Sci. (1998) in press). Changes of polyamine levels in relation to hyposaline (5‰) tolerance were determined in some marine green macroalgae including Chaetomorpha crassa, Chlorodesmis caespitosa L. Agardh, Ulva fasciata Delile, Ulva reticulata Foreek., Ulva lactuca L., Boodlea composita (Harv.) Brand and Valoniopsis pachynema (Mart.) Boergs, which as evaluated by specific growth rate and chlorophyll levels C. crassa and C. caespitosa were highly tolerant and V. pachynema was less tolerant. On exposure to 5‰, free putrescine accumulated in algae except C. caespitosa and C. crassa, soluble conjugated putrescine in C. crassa, C. caespitosa and U. lactuca, and insoluble conjugated putrescine in algae except B. composita. Free spermidine accumulated in algae except C. caespitosa, U. lactuca and B. composita, soluble conjugated spermidine in V. pachynema and C. caespitosa, and insoluble conjugated spermidine in V. pachynema, C. caespitosa, B. composita and U. lactuca. Spermine only accumulated in B. composita as the free form. The relative changes in 5‰-induced free putrescine accumulation are negatively correlated with specific growth rate ( r 2=0.90) and chlorophyll levels ( r 2=0.70). The 5‰-induced free putrescine accumulation, chlorophyll loss and growth reduction in axenically cultured U. fasciata were inhibited by both α-difluoromethylarginine (0.2 mM) and α-difluoromethylornithine (0.2 mM), the specific inhibitor of arginine decarboxylase and ornithine decarboxylase, respectively, and their effects were reversed by 0.5 mM putrescine. Application of 0.5 mM putrescine decreased both chlorophyll levels and growth rate in U. fasciata axenically cultured at 30‰, but 0.5 mM spermidine and 0.5 mM spermine had less effect. Overall, polyamines, especially putrescine and spermidine, accumulated in some marine green macroalgae under extreme hyposaline conditions, and free putrescine synthesized from ADC or ODC may be a causal factor of hyposaline injury.