Cooperation of epidermis and inner tissues in auxin-mediated growth of maize coleoptiles

• Published in: Planta 1987-02, Vol.170 (2), p.168-180
• Main Authors: Kutschera, U. (Freiburg Univ. (Germany, F.R.). Biologisches Inst. 2), Bergfeld, R, Schopfer, P
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Auxin; AUXINAS; AUXINE; AUXINS; Biological and medical sciences; Cell growth; Cell walls; CELLS; CELLULE; CELULAS; Chemical agents; CHEMICOPHYSICAL PROPERTIES; Coleoptiles; Corn; CRECIMIENTO; CROISSANCE; Economic plant physiology; Epidermal cells; EPIDERME; EPIDERMIS; Excretion; Fundamental and applied biological sciences. Psychology; GROWTH; Growth and development; Growth regulators; Insulin antibodies; Koleoptyle; Plant physiology and development; PLANTULAS; PLANTULE; Plastizitaet; PROPIEDADES FISICO-QUIMICAS; PROPRIETE PHYSICO-CHIMIQUE; Saemling; SEEDLINGS; Vegetative apparatus, growth and morphogenesis. Senescence; Wachstum; Wachstumsregulator; Zea; ZEA MAYS; Zelle
• ISSN: 0032-0935; 1432-2048
• DOI: 10.1007/BF00397885

The function of the epidermis in auxin-mediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 μm diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5—5.0 is too low to be compatible with a 'second messenger' function of protons also in the growth response of the inne