Fusicoccin-induced cell elongation and endogenous fusicoccin-like ligands in germinating seeds

Abstract As cell elongation is the primary growth process at early seed germination, we studied the influence of fusicoccin A (FC A) on growth initiation in axial organs in parallel with endogenous fusicoccin-like ligands (FLL) in germinating seeds in which initial and subsequent growth of axes occurs only by cell elongation. In quiescent broad beans ( Vicia faba var. minor L.), exogenous 20 μM FC A promoted radicle emergence by inducing earlier initiation of cell elongation first in the hypocotyl, then in the radicle. Prior to initiation of elongation, FLL appeared in the axes and acidification of cell walls sharply increased. In nondormant horse chestnut ( Aesculus hippocastanum L.) seeds, treatment with 100 μM FC A promoted radicle protrusion and further growth of axial organs by cell elongation. FLL were absent from the axes at dormancy, but appeared when the seeds acquired germinability and remained during germination. Their presence was also accompanied by enhanced cell wall acidification which was sensitive to diethylstilbestrol (DES) and attributed to plasmalemma H + -ATPase. Endogenous FCs or FC-like compounds are presumed to participate in the regulation of cell preparation for elongation and then axis elongation. Therefore, the system of cell elongation response comprises not only FC receptors and H + -ATPase, but previously unreported endogenous FC-like compounds as well.