Copper microlocalisation and changes in leaf morphology, chloroplast ultrastructure and antioxidative response in white lupin and soybean grown in copper excess

Abstract

The microlocalisation of Cu was examined in the leaves of white lupin and soybean grown hydroponically in the presence of 1.6 (control) or 192μM (excess) Cu, along with its effect on leaf morphology, (ultra)structure and the antioxidative response. The 192μM dose led to a reduction in the total leaf area and leaf thickness in both species, although more strongly so in white lupin. In the latter species it was also associated with smaller spongy parenchyma cells, and smaller spaces between them, while in the soybean it more strongly reduced the size of the palisade parenchyma and epidermal cells. Energy-dispersive X-ray microanalysis showed that under Cu excess the metal was mainly localised inside the spongy parenchyma cells of the white lupin leaves, and in the lower epidermis cell walls in those of the soybean. Cu excess also promoted ultrastructural chloroplast alterations, reducing the photosynthetic capacity index and the green area of the leaves, especially in the soybean. Despite this, soybean appeared to be more tolerant to Cu excess than white lupin, because soybean displayed (1) lower accumulation of Cu in the leaves, (2) enhanced microlocalisation of Cu in the cell walls and (3) greater levels of induced total -SH content and superoxide dismutase and catalase activities that are expected for better antioxidative responses.