Copper toxicity and sulfur metabolism in Chinese cabbage are affected by UV radiation

• Published in: Environmental and experimental botany 2013-04, Vol.88, p.60-70
• Main Authors: Shahbaz, Muhammad, Parmar, Saroj, Stuiver, C. Elisabeth E., Hawkesford, Malcolm J., De Kok, Luit J.
• Format: Article
• Language: English
• Subjects: APS reductase; Biological and medical sciences; biomass production; Brassica; Chinese cabbage; Chlorophyll fluorescence; Copper toxicity; crop production; dry matter content; Fundamental and applied biological sciences. Psychology; leaf area; leaves; photosystem II; pigments; roots; shoots; Sulfate transporters; sulfates; sulfur; Sulfur metabolism; toxicity; transporters; ultraviolet radiation; UV irradiation
• ISSN: 0098-8472; 1873-7307
• DOI: 10.1016/j.envexpbot.2012.04.007

► UV radiation enhances the phytotoxicity of copper. ► UV radiation enhances the copper levels in Chinese cabbage. ► Enhanced copper levels and UV radiation enhance the expression and activity of sulfate transporters in Chinese cabbage. ► Elevated copper contents in the roots interferes/reacts with signal compounds involved in regulation of sulfate transporters. Biomass production, dry matter content, specific leaf area and pigment content of Chinese cabbage were all quite similar, when plants were grown in the absence or presence of UV-A+B (2.2mWcm−2). Elevated Cu2+ concentrations (2–10μM) in the root environment and UV radiation had negative synergistic effects for Chinese cabbage and resulted in a more rapid and stronger decrease in plant biomass production and pigment content. The quantum yield of photosystem II photochemistry (Fv/Fm) was only decreased at ≥5μM Cu2+ in the presence of UV radiation, when leaf tissue started to become necrotic. The enhanced Cu toxicity in the presence of UV was largely due to a UV-induced enhanced accumulation of Cu in both roots and shoots. An enhanced Cu content strongly affected the uptake and assimilation of sulfur in plants. The total sulfur content of the root increased at ≥2μM Cu2+ in presence of UV and at 10μM Cu2+ in absence of UV and that of the shoot increased at ≥2μM Cu2+ in presence of UV and at ≥5μM Cu2+ in absence of UV. In the shoot it could be attributed mainly to an increase in sulfate content. Moreover, there was a strong increase in the water-soluble non-protein thiol content upon Cu2+ exposure in the root and, to a lesser extent in the shoot, both in the presence and absence of UV. The regulation of the uptake of sulfate responded to the occurrence of Cu toxicity directly, since it was more rapidly affected in the presence than in the absence of UV radiation. For instance, the expression and activity of the high affinity sulfate transporter, Sultr1;2, were enhanced at ≥2μM in the presence of UV, and at ≥5μM Cu2+ in the absence of UV. In the shoot, the expression of the vacuolar sulfate transporter, Sultr4;1, was upregulated at ≥5μM Cu2+ in the presence and absence of UV whilst the expression of a second vacuolar sulfate transporter, Sultr4;2, was upregulated at 10μM Cu2+ in the presence of UV. It is suggested that high Cu tissue levels may interfere/react with the signal compounds involved in the regulation of expression and activity of sulfate transporters. The expression of adenosine 5′-phosphosulf