High spermidine levels are implicated in enhanced heavy metal tolerance in a spermidine synthase-overexpressing transgenic European pear by exerting an antioxidant system

Abstract

A transgenic European pear (#32) overexpressing apple spermidine synthase (SPDS) and wild type were subjected to the stress for CdCl₂, PbCl₂, ZnCl₂ or their combination. Based on the shoot growth, #32 was much better than wild type. SPDS expression and Spd titer in #32 were higher than those in wild type. Glutathione was significantly depleted in line #32 with stress, but not so much in wild type. Activities of glutathione reductase/superoxide dismutase and malondialdehyde content were changed under stress toward a more favorable direction for survival in #32: these changes were closely related to the Spd titer. Accumulation of heavy metals tended to be less in #32 than that in wild type except for ZnCl₂ stress, while calcium content showed the reverse trend. Therefore, Spd levels are implicated in enhanced heavy metal tolerance possibly via the antioxidant property of Spd per se as well as by exerting an antioxidant system.