Auxin as an inducer of asymmetrical division generating the subsidiary cells in stomatal complexes ofZea mays

Abstract

The data presented in this work revealed that in Zea mays the exogenously added auxins indole-3-acetic acid (IAA) and 1-napthaleneacetic acid (NAA), promoted the establishment of subsidiary cell mother cell (SMC) polarity and the subsequent subsidiary cell formation, while treatment with auxin transport inhibitors 2,3,5-triiodobenzoic acid (TIBA) and 1-napthoxyacetic acid (NOA) specifically blocked SMC polarization and asymmetrical division. Furthermore, in young guard cell mother cells (GMCs) the PIN1 auxin efflux carriers were mainly localized in the transverse GMC faces, while in the advanced GMCs they appeared both in the transverse and the lateral ones adjacent to SMCs. Considering that phosphatidyl-inositol-3-kinase (PI3K) is an active component of auxin signal transduction and that phospholipid signaling contributes in the establishment of polarity, treatments with the specific inhibitor of the PI3K LY294002 were carried out. The presence of LY294002 suppressed polarization of SMCs and prevented their asymmetrical division, whereas combined treatment with exogenously added NAA and LY294002 restricted the promotional auxin influence on subsidiary cell formation. These findings support the view that auxin is involved in Z. mays subsidiary cell formation, probably functioning as inducer of the asymmetrical SMC division. Collectively, the results obtained from treatments with auxin transport inhibitors and the appearance of PIN1 proteins in the lateral GMC faces indicate a local transfer of auxin from GMCs to SMCs. Moreover, auxin signal transduction seems to be mediated by the catalytic function of PI3K.

Deliberate ROS production and auxin synergistically trigger the asymmetrical division generating the subsidiary cells in Zea mays stomatal complexes

“…Paradermal leaf sections were also visualized with a Zeiss microscope equipped with a micrometric scale. Some sections were incubated with aniline blue, as described previously (Livanos et al 2015).…”

“…In Z. mays seedlings grown in darkness at 25±1°C, the majority of GMCs displaying a ratio of width/length between 0.8 and 1.4 appear capable of inducing polarization and asymmetrical division of SMCs and are called "advanced" GMCs (Fig. 1b, c;Apostolakos et al 2008;Livanos et al 2015). Similarly, the GMCs exhibiting a width/length ratio larger than 1.4 are characterized as "young" GMCs ( Fig.…”

“…To investigate the recent hypothesis that GMCs function as protodermal auxin sources in Z. mays leaves (Livanos et al 2015), IAA-immunolocalization was performed. Surprisingly, among protodermal cell types, IAA was predominantly detected in GMCs and young stomatal complexes (Fig.…”

“…The timely-controlled distribution of PIN1 auxin efflux carriers in the lateral GMC faces and the inhibitory effects of auxin transport inhibitors in subsidiary cell formation indicate a local auxin transfer from GMCs to SMCs. Auxin polar transportation seems to be essential for the establishment of polarity in SMCs and their asymmetrical division (Livanos et al 2015).…”

“…Afterwards, Rho-GTPases of plants (ROPs) are recruited to the polar SMC site (Humphries et al 2011;Sutimantanapi et al 2014;Facette et al 2015). Besides, phospholipases C and D are necessary for the perception or the transduction of the stimulus emitted by the GMCs (Apostolakos et al 2008), whereas auxin stimulation is accomplished by the catalytic activity of phosphatidylinositol-3-kinase (PI3K; Livanos et al 2015).…”