Role of Plant Growth Regulators in Adventitious Populus Tremula Root Development In Vitro

Abstract

Eurasian aspen (Populus tremula L.) is a tree species with recognised ecological and economic importance for both natural and plantation forests. For the fast cloning of selected aspen genotypes, the method of plant propagation through in vitro culture (micropropagation) is often recommended. The efficiency of this method is related to the use of shoot-inducing chemical growth regulators, among which cytokinins, a type of plant hormone, dominate. Although cytokinins can inhibit rooting, this effect is avoided by using cytokinin-free media. This study sought to identify concentrations and combinations of growth regulators that would stimulate one type of P. tremula organogenesis (either shoot or root formation) without inhibiting the other. The investigated growth regulators included cytokinin 6-benzylaminopurine (BAP), auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA), auxins indole-3-acetic acid (IAA) and indole-3-butyric acid (IBA), gibberellin biosynthesis inhibitor paclobutrazol (PBZ), and a gibberellin mixture (GA₄/₇). Both BAP and TIBA increased shoot number per P. tremula explant and decreased the number of adventitious roots, but TIBA, in contrast to BAP, did not inhibit lateral root formation. However, for the maintenance of both adventitious shoot and root formation above the control level, the combination of PBZ and GA_4/7 was shown to be especially promising.

Keywords: aspen; lateral roots; phytohormones; plant tissue culture; shoot-derived roots.

Figure 1

Number of shoots (A) and adventitious roots (AR) (B) per explant (means ± SE), the rate of explants with lateral roots (LR) (C) and main (D) and total (E) adventitious root lengths (means ± SE) of explants, as affected by the presence of different TIBA concentrations (0, 1, 5 and 15 µmol L⁻¹) in the nutrient medium. (A–C) data are from the total number of explants, and (D–F) are from the number when the part of the explants with lateral roots exceeds ½ the total number. Lateral root density (LRD) (F) was calculated as the number of lateral roots per centimetre of cumulative adventitious root length (LRD = N/L). Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05).

Figure 2

Shoots (A,C) and adventitious roots (AR) (B,D) per explant (means ± SE) of explants, as affected by the presence of IAA (A,B) and IBA (B,D) at the concentrations of 0, 1, 3 and 5 µmol L⁻¹ combination without and with TIBA (5 µmol L⁻¹) in the nutrient medium. Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05), n.s. indicates not significant (p > 0.05).

Figure 3

Shoots (A) and adventitious roots (AR) (B) per explant (means ± SE), the rate of explants with lateral roots (LR) (C), main (D) and total (E) adventitious root length (means ± SE) of explants, as affected by the presence of different BAP concentrations (0, 1, 3 and 5 µmol L⁻¹) in the nutrient medium. (A–C) data are from the total number of explants or (D–F) from the number when the part of the explants with lateral roots exceeds ½ the total number. Lateral root density (LRD) (F) was calculated as the number of lateral roots per centimetre of cumulative adventitious root length (LRD = N/L). Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05), n.s. indicates not significant (p > 0.05).

Figure 4

Shoots (A) and adventitious roots (AR) (B) per explant (means ± SE) of explants, as affected by the presence of IAA at the concentrations of 0, 1, 3 and 5 µmol L⁻¹ combination without and with BAP (1 µmol L⁻¹) in the nutrient medium. Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05), n.s. indicates not significant (p > 0.05).

Figure 5

Number of shoots (A) and adventitious roots (AR) (B) per explant (means ± SE), the rate of explants with lateral roots (LR) (C), and the main (D) and total (E) adventitious root lengths (means ± SE) of explants, as affected by the presence of different PBZ concentrations (0, 0.5, 1 and 3 µmol L⁻¹) in the nutrient medium. (A–C) data are from the total number of explants, or (D–F) from the number where the part of the explants with lateral roots exceeds ½ the total number. Lateral root density (LRD) (F) was calculated as the number of lateral roots per centimetre of cumulative adventitious root length (LRD = N/L). Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05), n.s. indicates not significant (p > 0.05).

Figure 6

Shoots (A) and adventitious roots (AR) (B) per explant (means ± SE) of explants, as affected by the presence of GA₄₊₇ at the concentrations of 0, 1, 3 and 5 µmol L⁻¹ combination without and with PBZ (1 µmol L⁻¹) in the nutrient medium. Significantly different means of samples grown under different nutrient media conditions are labelled with different letters (p < 0.05).