Copper and zinc ions induce both stylar RNase inhibition and fruit set in Japanese pear

Abstract When inhibitory effects on stylar RNase activity were investigated in the Japanese pear ( Pyrus pyrifolia Nakai), CuSO 4 and ZnSO 4 were significantly effective, and the inhibition was dose-dependent. Since MgSO 4 and CaCl 2 did not show any inhibition, the active ions would be Cu 2+ and Zn 2+ . Because Cu 2+ separated clearly from the stylar proteins when protein–CuSO 4 mixture was loaded on Sephadex G-10 column chromatography, the cation may not be combined strongly with the protein. The RNase activity of the protein, furthermore, was almost completely recovered when the proteins were isolated from the mixture by (NH 4 ) 2 SO 4 precipitation. Copper ions strongly reduced the RNase A activity, moderately RNase S and weakly RNase T 1 at 1 mM, while it did not affect the RNase B. The CuSO 4 application at 2 mM induced more than 30% fruit set following self-pollination but Na 2 SO 4 and K 2 SO 4 did not, suggests that Cu 2+ causes fruit set through reducing stylar RNase activity.