Chromium toxicity to pollen, the male gametophyte of higher plants

The ability of both trivalent and hexavalent forms of chromium to interfere with some metabolic pathways in germinating kiwifruit pollen has been investigated. Chromium exposure resulted in a marked increase of ubiquitin-conjugated proteins, suggesting a role for the ubiquitin proteolytic system in the response to chromium stress. A significant rise of lipid peroxide production was also observed, more pronounced under Cr(VI)-treatment. GSH and GSSG content appeared to be affected by the metal, and both of them increased in the presence of each of the two chromium forms. In particular, Cr(III) induced a dose-dependent increase. Finally, dramatic alterations at the cell wall level of germinating kiwifruit pollen were induced by Cr(III). In fact, not only was the wall thickness highly irregular, but also the localization of arabinogalactan proteins, which are known to play an important role in cell wall assembly and expansion, was strongly altered as demonstrated by TEM-immunogold analysis by using JIM8 antibody. Key words: arabinogalactan proteins (AGPs), chromium, GSH/GSSG, kiwifruit, lipid peroxidation, pollen germination, ubiquitin