Water deficit altered proline and chlorophyll concentrations, and 1–Amino–cyclopropane–1– Carboxylic-Acid Oxydase accumulation in white clover

The effect of water deficit on concentration of proline and chlorophyll, as well as ACC oxydase gene expression and protein accumulation was examined in white clover subjected to water deficit. The water deficit treatment was imposed by acomplete withholding of water and examined until the PER ceased (at -1,4 MPa). The water deficit below 20% caused a decrease in the LWP and PER, but an increase in the total chlorophyll and proline concentrations of the FFE leaves. However, the totalchlorophyll of the SFE leaves did not altered by water deficit imposion. The expression of specific ACO genes and accumulation of ACO protein were examined within the tissues in which each gene is expressed during natural leaf ontogeny. No changes inTR-ACO1 expression and TR-ACO1 protein accumulation were determined in the apex. However, expression of the developing-leaf associated TR-ACO2 and accumulation of TR-ACO2 protein in the FFE leaves was stimulated further by water deficit treatment. This was most marked in an SWC associated with a decrease in PER, but before the significant change of rapid proline accumulation occurred. For the leaf senescence-associated TR-ACO3, no changes in expression were observed over the two stages of leaf development examined, suggesting that the severity and time-frame of exposure to the water deficit was not sufficient to induce this gene. These results show that water deficit does induce changes in the ACC Oxydase particularly the TRACO2 in the FFE leaf, and the changes were associated with an increase in chlorophyll and proline accumulation.