Plant Growth Regulation 27: 161–165, 1999. © 1999 Kluwer Academic Publishers. Printed in the Netherlands.
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Gibberellic acid (GA) increases fibre cell differentiation and secondary cell-wall deposition in spring wheat (Triticum aestivum L.) culms S. Lev-Yadun1 , A. Beharav2 , R. Di-nur3 & S. Abbo4∗ 1 Department
of Natural Resources, Agricultural Research Organization, The Volcani Center, PO Box 6 Bet Dagan 50250, Israel; 2 Institute of Evolution, Haifa University, Haifa 31905, Israel; 3 Kibbutz Na’an 76829, Israel; 4 Department of Field Crops, Vegetables and Genetics, Faculty of Agriculture, The Hebrew University of Jerusalem, Rehovot 76100, Israel (∗ author for correspondence; phone: 972-8-9481943; fax: 972-8-9468265; e-mail:
[email protected]) Received 22 October 1998; accepted in revised form 8 January 1999
Key words: cortical fibre cell, gibberellic acid, spring wheat, Triticum aestivum
Abstract The role of gibberellic acid (GA) in differentiation and secondary cell-wall deposition of fibre cells of spring wheat (Triticum aestivum) culms was studied using applications of GA and chlormequat (a GA biosynthesis inhibitor). In certain genotypes, higher GA levels may increase the number of cortical fibre cell files by changing cell fate from parenchyma to fibre, and induce thicker secondary cell-walls.
1. Introduction Fibres form a mechanical tissue characterised by its strength and elasticity. The role of fibres in the mechanical properties of culms is well demonstrated in reeds, bamboo and cereals which are strong and flexible because of their fibre bands. The fibres are long and usually have thick lignified secondary walls [6]. The basic culm structure of wheat and other Gramineae species has been described in detail [5, 8, 13, 17, 18, 19]. Wheat (Triticum aestivum L.) plants have fibres of two origins: (1) fibres that differentiate from the ground promeristem and form a continuous cylinder in the stem; and (2) fibres that partly differentiate from the procambium and the ground promeristem, and form the fibrous sheath of the vascular bundles [5]. Since wheat has no secondary growth, the structure of wheat culms is determined near the apex, very early in its development. Therefore, structural changes of wheat culms, in response to environmental stimuli (such as wind sway), are minor [4]. In dicotyledonous plants, fibre differentiation has been studied by application of hormones and hormone inhibitors, removal of leaves and buds, and stem wounding and was found to be dependent mainly upon
a mixed stimulus of auxin and gibberellin. Further to the auxin and GA effect, cytokinin indirectly influences fibre differentiation since it promotes the development of leaves, which are the source of IAA and GA [1, 20]. The height-reducing alleles (Rht1, Rht2), which confer relative insensitivity to endogenous as well as to exogenous GAs, are of great value in modern wheat breeding [7]. The role of the Rht genes in wheat tissue differentiation has been studied with respect to their effect on cell dimensions during leaf elongation [9, 10, 15, 16, 22]. The dose of Rht1 and Rht2 alleles does not influence the amount of fibre strands in wheat leaves, but does affect their mechanical properties [14]. In recent work, we studied the relationship between the GA-insensitivity locus (Rht1) and fibre differentiation in spring wheat culms [12] and demonstrated that the Rht system affects mainly stem and leaf elongation, whereas the determination of cell fate in producing fibres is controlled by a different genetic system [12]. In this study, we used exogenous application of GA and chlormequat (CCC) [11] to study the role of endogenous and exogenous GA in fibre cell differentiation and secondary cell-wall build-up in the primary tissues of spring wheat culms. Due to the assumed short
162 Table 1. Estimate of the effect of family, treatments and their interaction on the number of fibre cell files of tall and semi-dwarf F12 isolines derived from the cross ‘Mivhor’ × ‘Lakhish’ tall rht1rht1
semi-dwarf Rht1Rht1
Trait
Source of Variation
Degrees of Freedom
Mean Square
P(F)
Degrees of Freedom
Mean Square
P(F)
No. of fibre cell files
Family Treatment Fam. × Treat. Residual
2 2 4 30
5.40 3.54 2.86 0.55
