Heat shock pretreatment suppresses cadmium-induced ammonium ion accumulation and phenylalanine ammonia-lyase activity in rice seedling leaves.

摘要

We investigated the effects of heat shock (HS) on the subsequent cadmium (Cd)-induced ammonium ion (HN₄+) accumulation and the phenylalanine ammonia-lyase (PAL) activity in rice seedling leaves. Increases in PAL activity occurred prior to NH₄+ increases in rice leaves. Both of these Cd-induced increases were significantly deterred by the potent PAL inhibitor alpha -aminooxy- beta -phenylpropionic acid. Exposing rice seedlings to 3 h HS in the dark effectively reduced subsequent Cd-induced increases in PAL activity and NH₄+ content. The HS effect can be mimicked by pretreating rice seedlings with exogenous H₂O₂, glutathione (GSH), ascorbic acid (AsA), or L-galactono-1,4-lactone (GalL, a precursor of AsA biosynthesis) under non-HS conditions. The protection that HS provides however, can be counteracted by imidazole, a NADPH oxidase inhibitor, buthionine sulfoximine (BSO, a GSH synthesis inhibitor), or lycorine (Lyc, an AsA synthesis inhibitor). Furthermore, the effects of BSO and Lyc can be reversed by the addition of GSH and AsA, respectively. The mechanisms of the protective effect of HS against subsequent Cd effects are discussed.