Tomato Jasmonic Acid-Deficient Mutant <Emphasis Type="Italic">spr2</Emphasis> Seedling Response to Cadmium Stress

The involvement of jasmonic acid (JA) in the plant response to cadmium (Cd) stress has been addressed in some publications by application experiments or analysis of endogenous contents of JA. In this study, we comparatively investigated the response of tomato wild type (WT) and its JA-deficient mutant spr2 to Cd stress aimed at clarifying the role of JA. One-month-old potted plants were exposed to CdCl₂ at final concentrations of 5, 25, and 50 mg kg^?1 in soil, respectively, for 15 days. The root and leaf Cd contents were dramatically increased, especially in the spr2 plants, in a CdCl₂ dose-effect manner. In the Cd dose-dependent inhibitory effect on plant growth, spr2 plants were more obvious than WT plants. This was also reflected by certain physiological and biochemical metabolisms. We analyzed photosynthesis-related parameters including total chlorophyll, actual efficiency of PS2, ratio of variable to maximum chlorophyll fluorescence, and net photosynthetic rate; relative water content, soluble sugar and proline contents, and starch accumulation; oxidative stress and antioxidative defense including malondialdehyde production, electrolyte leakage, H₂O₂ levels, activities of superoxide dismutase, peroxidase, and catalase, and their isoform expression profiles. The Cd-induced changes in all these parameters supported the conclusion that endogenous JA deficiency enhanced tomato seedling sensitivity to Cd. This implies that JA positively regulates the tomato plant response to Cd stress.