Induction of acid phosphatase activity by phosphorus deficiency in Gracilaria coronopifolia (Gigartinales, Rhodophyta)

Abstract

The effects of phosphorus (P) deficiency on acid phosphatase [ACP; enzyme classification(EC) 3.1.3.2] activity were studied in Gracilaria coronopifolia by exposure to 0 μM NaH2P04 as a P-deficient treatment or 20 μM NaH2P04 as a P-sufficient treatment. After 8 d of exposure to P-deficient treatment, growth rate and tissue P content decreased but tissue C:P and N:P molar ratios increased. Tissue soluble nonreactive P and total soluble P contents decreased 4 d after the switch to P deficiency while tissue soluble reactive P contents remained unchanged. On exposure to P deficiency, intracellular ACP activity increased immediately whereas activity of extracellular alkaline phosphatase (EC 3.1.3.1) increased after 8 d. After 8 d of treatment, the apparent Km, and Vonmax values for partially purifiedACP of P-sufficient thalli were 3.87 mM p-nitrophenol phosphate (P-NPP) and 31.08 μmol mg−1 protein h−1, respectively, and those for P-deficient thalli were 2.40 mM p-NPP and 82.17 μmol mg−1 protein h−1, respectively. Activity staining on native-polyacrylamide gels showed that one isozyme (ACP I) was enhanced by P-deficient treatment, but depressed by the P-sufficient treatment, whereas another isozyme (ACP3) was induced after 8 d of P deficiency. Another isozyme (ACP2) appeared in P-sufficient thalli after 8 d of incubation. Phosphate (NaH2P04) inhibited ACP activities of both P-deficient and P-sufficient thalli but the inhibition was more profound for P-deficient thalli. NaF, ZnCi2 and CuCi2 inhibited the ACP activities of both P-deficient and P-sufficient thalli, whereas the ACP activity of P-deficient thalli was inhibited by CaCi2 and MnCl2 and slightly inhibited by MgCl2 and NaCI. In conclusion, the degradation of stored P in C. coronopifolia under P-deficientconditions to meet P requirement is due to increased ACP activity via a change in kinetic properties, isozyme expression and cation levels.