Effect of exogenous gibberellin A_4/7 on tracheid production, longitudinal growth and the levels of indole‐3‐acetic acid and gibberellins A₄, A₇ and A₉ in the terminal shoot of Pinus sylvestris seedlings

Abstract

Gibberellin A4/7 (GA4/7) was applied twice weekly to 2‐year‐old Pinus sylvestris (L.) seedlings in each of two years, starting close to budbreak and ending after shoot elongation, but before cambial activity ceased. In 1988, the GA4/7 was injected into the 1987 terminal shoot (0, 0.2 or 2 mg seedling−1 application−1), while in 1990 it was applied as a soil drench (0, 10 or 50 mg seedling−1 application−1). In the 1988 experiment, GA4/7 treatment promoted diameter growth, and tended to increase both longitudinal growth and the indole‐3‐acetic acid (IAA) level in the 1988 terminal. In the 1990 experiment, GA4/7 treatment increased tracheid production, longitudinal growth, and the cambial region IAA concentration in the 1990 terminal, but did not affect its pith diameter, needle number, needle dry weight, or needle IAA level. Tracheid production in the previous‐year's terminal was also promoted in both experiments. The 50 mg GA4/7 soil drench markedly elevated the concentrations of GA4, GA7 and GA9 in the needles and cambial region of the 1990 terminal, while the 10 mg treatment raised the GA4 level in the cambial region, providing evidence that GA4 and GA7 applied to the roots reaches the shoot system. The results support the hypothesis that the exogenous GA4/7‐induced stimulation of tracheid production in the terminal shoot of intact plants is mediated through an increase in the IAA level in the cambial region. However, per se activity of GA4, GA7 or their metabolites cannot be ruled out.

Changes in phytohormone contents in chickpea seeds germinating under lead or zinc stress

“…The analysis of gibberellic acid equivalents was performed according to Fujioka et al (1986), Cakmak et al (1989 and Wang et al (1992) with some modifications. The freeze-dried tissue samples (1 g) were ground to powder in liquid nitrogen and homogenized in 3 cm 3 of 100 % methanol.…”

Role of auxin and gibberellin in regenerative differentiation of tracheids in Pinus pinea seedlings

“…1), suggests that the effect of gibberellin on tracheid elongation is a cell-type-specific reaction which does not affect the rest of the tissue. Previous studies have shown a gibberellin effect on stem elongation (Wang et al, 1992 ;Little & Pharis, 1995), but these did not investigate the role of gibberellin on tracheid elongation. This specific effect on regenerated tracheid elongation is, therefore, different from the one reported by Aloni (1979), where gibberellin induced both primary phloem fibre elongation and also promoted maximal internode elongation under a high GA $ : low IAA ratio.…”

“…Little attention has been given to the possible role of gibberellin in tracheid differentiation (Little & Savidge, 1987). Wang et al (1992) reported that gibberellin, applied as a soil drench, caused an increase in tracheid number and stem elongation. However, the possible role of gibberellin in tracheid elongation was not studied by these workers.…”

An Overview of the Biology of Reaction Wood Formation

“…Several GAs have been identified in the cambial region, and both endogenous and applied GAs have been found to be possibly related to stem radial increment (Aloni 1979(Aloni , 1988(Aloni , 1991Little and Savidge 1987;Wang et al 1992Wang et al , 1995Little and Pharis 1995). There has been one study reporting that applied gibberellin A 3 (GA 3 ) induced compression wood formation (Wardrop and Davies 1964).…”