Altered Growth and Wood Characteristics in Transgenic Hybrid Aspen Expressing Agrobacterium tumefaciens T-DNA Indoleacetic Acid-Biosynthetic Genes

Abstract

A key regulator of cambial growth is the plant hormone indoleacetic acid (IAA). Here we report on altered wood characteristics and growth patterns in transgenic hybrid aspen (Populus tremula L. x Populus tremuloides Michx.) expressing Agrobacterium tumefaciens 1-DNA IAA-biosynthetic iaaM and iaaH genes.Eighteen lines simultaneously expressing both genes were regenerated. O f these, four lines, verified to be transgenic by northern blot analysis, were selected and raised under controlled growth conditions. All four lines were affected in their growth patterns, including alterations in height and stem diameter growth, internode elongation, leaf enlargement, and degree of apical dominance. Two transgenic lines, showing the most distinct phenotypic deviation from the wild type, were characterized in more detail for free and conjugated IAA levels and for wood characteristics. 60th lines showed an altered IAA balance, particularly in mature leaves and roots where IAA levels were elevated. They also exhibited changes in wood anatomy, most notably a reduction in vessel size, an increase in vessel density, and changes i n ray development. Thus, the recent development of techniques for gene transfer to forest trees enabled us t o investigate the influence of an altered IAA balance on xylem development i n an intact experimental system. In addition, the results demonstrate the possibility of manipulating wood properties in a forest tree through controlled changes of IAA concentration and distribution.

Somaclonal variations as a mean for obtaining regenerants with different growth rates in poplar (<i>Populus × berolinensis</i> Dipp.)

“…Overexpression of pine glutamine synthetase in transgenic hybrid poplar caused an increase of number of internodes and leaf area [30]. Another example of stem growth regulation by the change of the rate of internodes' production was presented in the work of Tuominen et al [31]: increased IAA content in hybrid aspen due to the inclusion of IAA-synthesizing genes from Agrobacterium tumefaciens led to the slower rate of internodes' production, whereas did not change internode's length. So, different mechanisms of stem growth regulation may exist, one-by the change of internodes' length and other -by the change of internodes' number.…”

The Use of Auxin Quantification for Understanding Clonal Tree Propagation

“…GC-MS was later applied to assess seasonal variation in IAA concentrations in Pinus sylvestris Thunb. seedlings [125] and to investigate the influence of IAA concentration and distribution on xylem development in transgenic Populus tremula × P. tremuloides [113]. GC-MS has also been used to quantify free IAA levels in vascular tissues of Populus × tomentosa Carrière [126], to show that the highest IAA oxidase activity in Ginkgo biloba L. leaves occurs in environments with high CO 2 and C concentrations [127], and to demonstrate that IAA contents are correlated with IAA oxidase activity in Pinus tabuliformis Carrière needles exposed previously to high CO 2 concentrations [128].…”

“…HPLC has been used for extract purification both in herbaceous species [112] and forest species (e.g., Populus tremula × P. tremuloides Michx.) [113]. HPLC with diode-array ultra-violet (UV) detection was used to quantify seasonal variation in IAA and ABA concentrations in Eucommia ulmoides Oliv.…”

Structure and Expression Profile of the Phosphate Pht1 Transporter Gene Family in Mycorrhizal Populus trichocarpa

“…Cuttings of wild-type plants and transformants of P. tremula 3 Populus tremuloides cv T89 containing the pLeExt1.1::GUS construct (Tuominen et al, 1995) were grown in sterile glass jars on half-strength solid MS medium with 10 g L 21 Suc and 0.8% agar-agar (Merck; Hampp et al, 1996). After 1 month, 20 transgenic and wild-type poplar plants were transferred in the greenhouse to aeroponic systems.…”