Effects of exogenous gibberellin and auxin on shoot elongation and vegetative bud development in seedlings of Pinus sylvestris and Picea glauca

Abstract

The hormonal control of stem unit (foliar appendage and axillary structure, if present, plus subtending internode) number and length was investigated in shoots of Scots pine (Pinus sylvestris L.) and white spruce (Picea glauca (Moench) Voss). Seedlings were treated with six gibberellins (GA1, GA3, GA4, GA5, GA9 and GA20) and two auxins (indole-3-acetic acid (IAA) and naphthaleneacetic acid (NAA)) when either neoformed growth was occurring or the terminal vegetative bud was developing. Hormones were applied by drenching the shoot tip, injecting the stem or spraying the foliage. Combined results for all three application methods indicated that shoot elongation in first-year seedlings (i.e., neoformed growth) was promoted in both species by GA1, GA3, GA4 and, less obviously, by GA9. This promotion was attributable to an increase in length, rather than number, of stem units. However, the number of stem units formed during terminal bud development, as reflected in the number of needles (white spruce) or cataphylls (Scots pine) present on the shoot resulting from the terminal bud, was stimulated by GA1, GA3 and GA4 in both species and by GA9 in Scots pine. The GA-induced increase in the number of preformed stem units was associated with increased bud width in white spruce and increased bud length and resulting shoot length in Scots pine. In contrast, application of IAA or NAA either did not affect or inhibited both neoformed growth and terminal bud stem unit number, depending on the application method and concentration. We conclude that, in the Pinaceae, (1) GA stimulates the activity of both the subapical meristem during neoformed growth and the apical meristem during vegetative bud development, and (2) the early non-hydroxylation pathway, via GA9, is the major route of GA biosynthesis. The role of auxin in the control of stem unit number and length remains to be resolved.

Evolutionarily Conserved DELLA‐mediated Gibberellin Signaling in Plants

“…Gibberellins form a large family of tetracyclic diterpenoids and play important roles in modulation of seed plant growth and development (Little and MacDonald 2003; Waghorn et al 2003). GA was first isolated from Gibberella fujikuroi in the 1930s (Takahashi et al 1991).…”

Micropropagation of Alibertia edulis Rich

“…Hence, BA alone and combined with IBA had similar effects on elongation. It is well documented that auxins, gibberellins and polyamines usually favor shoot elongation (Little and MacDonald, 2003;Nuri, 2004), while cytokinins may act in a different manner and favor shoot sprouting (Perez-Tronero et al, 2000). However, the effects of these classes of plant growth regulator are not always the same and depend on variables such as the plant species, the type and the concentrations of the growth regulators, and growth conditions.…”

Regulating Growth of Betula alnoides Buch. Ham. ex D. Don Seedlings with Combined Application of Paclobutrazol and Gibberellin

“…[13] and Dalbergia odorifera T. Chen [14]; Foliar application of GA 3 could increase height growth, photosynthetic pigment contents of Pogostemon cablin Benth. [15]; Little and Macdonald's [16] study showed that gibberellins (GA 1 , GA 3 and GA 4 ) could accelerate shoot elongation and vegetative bud development of Pinus sylvestris L. and Picea glauca (Moench) Voss seedlings. These findings and experiences will be contributed for regulating seedling growth by combined application of PBZ and gibberellins although there is no case study using comprehensively both regulators.…”