Oligogalacturonide-induced changes in the developmental pattern of Daucus carota L. somatic embryos

Oligogalacturonides (OGs) are pectic fragments released from the plant cell wall. These signalling molecules are well known elicitors of biological responses ranging from defense mechanisms to growth and developmental responses. Using as a model system the carrot somatic embryo development, we have investigated the morphogenetic activity of OG mixtures with different degrees of polymerization (DP). Our results provide evidence that long OGs (DP 9-18) administered at the onset of embryogenesis slow down the temporal sequence of the embryo maturation, induce H2O2 accumulation in the embryogenesis culture medium, and alter the embryo developmental pattern with remarkable modifications of the shoot pole. A globular stage-specific sensitivity to the elicitor is demonstrated, indicating that juvenile stages of embryogenesis are key steps in the induced developmental program. Even short OGs (DP 1-5) were found to affect the embryogenesis. This agrees with the finding that developing embryos were able to modify the applied OG molecules, indicating the participation of gradually generated shorter OGs in the induced morphological changes. The antagonist behaviour of OGs on auxin activity, already reported for other aspects of plant growth and development, is suggested as a possible explanation for the modified pattern of embryogenesis observed.