Early response of wheat seminal roots growing under copper excess

• Cu exposure during wheat imbibition and germination resulted in shorter roots.
• Increased levels of ROS and cell death took place in seminal roots under Cu stress.
• More carbonylated cyclin D and CDKA were found in the roots of Cu-treated seedlings.
• Less Ub-cyclin D and more proline levels were found in roots under 10 μM Cu.
• Expansin genes were upregulated upon Cu; pcna, rdr, and mcm2 become downregulated.

Growth reduction caused by copper excess during plant photoautotrophic metabolism has been widely investigated, but information regarding early responses of root apical meristem (RAM) to toxic concentrations of this metal at the initial heterotrophic stage is certainly scarce. We analysed some determinants of seminal root growth in developing wheat seedlings germinated in the presence of 1, 5 and 10 μM CuCl2, focussing on oxidative damage to cell membrane and to proteins, and investigated the expression patterns of some genes relevant to cell cycle progression and cell expansion. The proliferation zone of the RAM was shorter under 5 and 10 μM CuCl2. Cyclin D and CDKA levels remained unchanged in the root apexes of wheat seedlings grown under these Cu2+ concentrations, but more carbonylated levels of both proteins and less ubiquitinated-cyclin D was detected under 10 μM CuCl2. Increased levels of ROS were revealed by fluorescent probes at this Cu2+ dose, and severe cell membrane damage took place at 5 and 10 μM CuCl2. Several genes related to retinoblastome phosphorylation and therefore involved in the transition from G1 to S cell cycle stage were found to be downregulated at 10 μM CuCl2, while most expansin genes here analysed were upregulated, even at a non-toxic concentration of 1 μM.These results together with previous findings suggest that a “common” signal which involves oxidative posttranslational modifications of specific cell cycle proteins may be necessary to induce root growth arrest under Cd2+ and Cu2+ stress.