Effects of plant growth regulator treatments on stem vascular tissue development in linseed (Linum usitatissimum L.)

Linseed (Linum usitatissimum L.) is a widely grown source of industrial and edible oil. Other varieties of the same species (flax) are cultivated for the long, strong bast fibres of their stems. The bast fibres of linseed generally go unused, although there is growing interest in developing linseed into a dual-purpose flax from which both seed and fibre could be utilized. Towards this objective, an improved understanding is required of the role of plant growth regulators in stem and fibre development in linseed. We have tested the effects of applying varying combinations of gibberellic acid (GA3), the auxin indole-3-acetic acid, and a GA biosynthesis inhibitor (paclobutrazol) to an elite linseed variety (CDC Bethune). Results showed that GA stimulated stem elongation, stem expansion and the proliferation, expansion, elongation and cell wall thickening of xylem fibres. The impact of GA on phloem tissues was less apparent, although GA had a positive effect on the number of bast fibres observed in stem transverse section, and GA3 application in combination with IAA increased the thickness of bast fibre secondary walls nearly two-fold. Other than the bast fibre cell walls, IAA treatments (alone or in combination with GA3) did not affect most aspects of linseed stem development, suggesting that the observed effects of GA were not mediated by cross-talk with IAA. The relationships defined here between GA, stem architecture, and bast fibre properties in linseed provide a useful framework for manipulation of fibre properties through breeding, biotechnology, and field treatments.

► Gibberellin stimulates cell wall thickening of bast fibres.
► Effect of gibberellin on cell wall thickness is independent of stem height.
► Gibberellin stimulates and paclobutrazol represses xylogenesis in the stem.
► IAA does not affect xylogenesis, bast/xylem fibre elongation or cell wall thickening.