Effects of drought, transgenic expression of a fructan synthesizing enzyme and of mycorrhizal symbiosis on growth and soluble carbohydrate pools in tobacco plants

Abstract

The effects of three conditions likely to affect soluble carbohydrate pools, namely drought, expression of barley sucrose : fructan 6-fructosyl transferase (6-SFT, EC 2;4;1;10) and the establishment of the arbuscular mycorrhizal symbiosis with Glomus mosseae were studied in a multifactorial experiment using tobacco (Nicotiana tabacum). Tobacco, a plant naturally unable to form fructan, accumulated fructan in leaves, and to a larger extent in the roots, when transformed with 6-SFT. Under drought conditions, growth was considerably reduced, but neither expression of 6-SFT nor mycorrhiza formation had an effect on growth rate. However, in response to drought, carbon partitioning was significantly altered towards accumulation of soluble sugars. In plants exposed to drought, pools of sucrose were greater than those of unstressed plants, particularly in their roots. In the transgenic plants expressing 6-SFT, there were also increased contents of the products of 6-SFT, namely fructan, most probably because of the increased availability of the substrate, sucrose. These effects were the same in the presence or absence of mycorrhiza. Hexoses (glucose and fructose) also increased in response to drought, primarily in the leaves. This effect of drought was little affected by the expression of 6-SFT, except that it slightly enhanced drought-induced glucose accumulation in roots. However, the presence of mycorrhiza led to a considerable reduction in drought-induced accumulation of hexoses in the leaves. The content of the fungal disaccharide trehalose was greatly increased in the roots of all mycorrhizal plants upon exposure to drought, particularly in some of the transgenic plants expressing 6-SFT.

The growth defect of lrt1 , a maize mutant lacking lateral roots, can be complemented by symbiotic fungi or high phosphate nutrition

“…Once per week plants were watered with Hoagland solution, containing either full phosphate (1 mM KH 2 PO 4 ) or reduced phosphate (0.1 mM KH 2 PO 4 ;Fink 1979). This reduced phosphate supply has been shown before not to be limiting for wild-type tobacco plants but to allow high colonization of their roots by mycorrhizal fungi (Schellenbaum et al 1999).…”

“…In order to provide a low-fertility soil substrate, and at the same time to facilitate the assessment of the root systems, germinating seedlings were transferred into a sand mixture containing sterilized coarse sand, ®ne quartz sand and loam (8:1:1, by weight, respectively) in 1-l pots (Schellenbaum et al 1999). The phosphate content of the sand mixture was 39.25 mg P 2 O 5 /kg sand (for comparison: commercially available standard soil had a value of 183.95 mg P 2 O 5 /kg soil) following the standard protocol of the Deutsche Bodenkundliche Gesellschaft (Oldenburg, Germany).…”

Soybean Metabolites Regulated in Root Hairs in Response to the Symbiotic BacteriumBradyrhizobium japonicum

“…Trehalose also accumulated in ectomycorrhized and endomycorrhized roots, particularly during drought stress (Schellenbaum et al, 1999;Pfeffer et al, 2004;Lopez et al, 2007). Genetic engineering of tobacco, potato, and tomato (Solanum lycopersicum) transformed with trehalose biosynthetic genes conferred higher resistance to drought, low and high temperature, salt, and oxidative stresses (Yeo et al, 2000;Almeida et al, 2005;Cortina and Culianez-Macia, 2005).…”

Leaf non-structural carbohydrates regulated by plant functional groups and climate: Evidences from a tropical to cold-temperate forest transect

“…To date, studies on factors influencing leaf NSCs have focused on nutrient elements (Nanamori et al, 2004), temperature (Gaudet et al, 1999;Gough et al, 2010), precipitation (Schellenbaum et al, 1999), and phenology (Gough et al, 2010). Less information is available regarding factors such as light intensity, leaf traits, leaf life forms (e.g., needle-leaf and broad-leaf), and plant functional groups (PFGs, trees, shrubs, and herbs).…”