Root Contraction in Hyacinth. I. Effects of IAA on Differential Cell Expansion

Abstract

Contractile roots of Hyacinthus orientalis L. cv 'Pink Pearl' shorten as a result of growth of inner cortical cells which expand radially and contract longitudinally. Brief treatment with IAA (indole-3-acetic acid-0.5 and 1.0 mgll) induces subapical swelling, root cap proliferation and decreased rates of elongation in potentially contractile roots. Growth resumes with removal of IAA from the culture medium and contraction subsequently occurs. The pattern of subsequent contraction is affected by prior IAA treatment; contraction occurs in the normal manner both acropetal and basipetal to the points ofIAA-induced swelling, but does not occur in the swollen region itself. Microscopic examination ofthe swollen region reveals that cells of the middle and outer cortex are radially expanded and longitudinally shortened relative to middle and outer cortical cells of contracted and uncontracted portions of the same root and control roots. In contrast, inner cortical cells in swollen regions of IAA-treated roots show approximately 50% less radial expansion than inner cortical cells of control contracted roots. Middle and outer cortical cells in the swollen region ofIAA-treated roots undergo radial expansion, while middle and outer cortical cells in adjacent contracting zones are compressed by radially expanding inner cortical cells. Average volumes of cortical cells in the IAA-induced swollen region increased approximately two-fold when contraction occurred in adjacent regions. These results suggest that in hyacinth roots, under certain circumstances, inner and outer cortical cells alike possess the ability for growth reorientation and expansion. However, during the usual course of contractile root development, cells of the outer cortex are restricted in this ability, through an as yet unknown mechanism, and are passively compressed by the radially expanding inner cortical cells.

G-fibres in storage roots ofTrifolium pratense(Fabaceae): tensile stress generators for contraction

“…However, Wardrop and Davies (1964) and Funada et al (2008) were able to induce compression and tension wood formation without a gravitational stimulus just by applying auxin (IAA) and gibberelin, respectively. In addition, the growth reorientation and expansion of inner and outer cortical cells of Hyacinths' contractile roots can be enhanced by auxin treatment (Jernstedt, 1984).…”

Contractile roots in succulent monocots: convergence, divergence and adaptation to limited rainfall

“…A relatively high root permeability near the base of the shoot in members of the Agavaceae may be an example of function following form (Woodward 2008) in that improved water uptake may be ancillary to the primary role of CRs, which is to pull plants further down into the soil to protect shoots from unfavourable conditions above-ground. For most species with CRs and for all monocots examined, root contraction is accomplished by the radial expansion and longitudinal shortening of cells in the inner and/or middle cortical layers (Jernstedt 1984;Pütz 2002). Outer cortical cells are crushed as the root contracts, and vascular tissues are compressed.…”

Involvement of naphthalene acetic acid in contractile root formation and the growth of <i>Gladiolus grandiflorus</i> cv. ‘Eurovision’ cormel plants

“…However, higher concentrations of NAA delayed CR elongation (the onset and the development rate), thus delaying also the onset of CZ formation in treated gladiolus plants. Jernstedt (1984) found in hyacinth CR segments, that exogenous IAA inhibited root elongation and induced radial swelling. The ability of auxin, even at low concentrations, to inhibit root elongation and enhance their …”