Copper toxicity and sulfur metabolism in Chinese cabbage

PhD ceremony: Mr. M. Shahbaz, 12.45 uur, Aula Academiegebouw, Broerstraat 5, Groningen

Dissertation: Copper toxicity and sulfur metabolism in Chinese cabbage

Promotor(s): prof. J.T.M. Elzenga

Faculty: Mathematics and Natural Sciences

Copper is an essential nutrient for plants, however, at enhanced concentrations in the root environment it may rapidly become phytotoxic. Muhammad Shahbaz has investigated the physiological basis of the phytotoxicity of Cu and significance of sulfur metabolism in its detoxification in Chinese cabbage. From his research it was evident that enhanced Cu²⁺ concentrations (> 2 μM) in the root environment are toxic for Chinese cabbage. The presence of UV radiation strongly enhanced Cu toxicity. Enhanced Cu²⁺ concentrations resulted in sulfate accumulation in the shoot and an enhanced synthesis of other sulfur-rich compounds (viz. phytochelatins and glutathione) in the root. Enhanced Cu²⁺ concentrations interfered with the regulation of the uptake and assimilation of sulfur in Chinese cabbage, but there was no direct relation between the plant sulfur status and Cu toxicity. It is generally presumed that sulfate itself or metabolic products of the sulfate assimilation, viz. thiols (glutathione), would act as signals in the regulation of the expression and activity of the sulfate transporters. This presumed signal transduction pathway in regulation of expression and activity of the sulfate transporters (sulfate and thiols) were by-passed or overruled, if Chinese cabbage was exposed to enhanced Cu²⁺ concentrations. It is proposed that undissociated H₂S may function as an endogenous gaseous transmitter in the cross-talk between the sulfate reduction pathway in chloroplast/plastid and the transcription of sulfate transporters in the nucleus. A Cu-induced decrease in subcellular H₂S concentration might be responsible for the observed upregulation of the expression and activity of the sulfate transporters.