Impact of Altered Gibberellin Metabolism on Biomass Accumulation, Lignin Biosynthesis, and Photosynthesis in Transgenic Tobacco Plants

Abstract

Gibberellins (GAs) are involved in regulation of many aspects during plant development. To investigate the impact of altered GA levels on plant growth and metabolism, transgenic tobacco (Nicotiana tabacum) plants have been engineered to express either a GA20-oxidase (AtGA20-ox) or a GA2-oxidase (AtGA2-ox) gene from Arabidopsis under control of the cauliflower mosaic virus 35S promoter. Resulting plants were characterized by elongated or stunted shoot growth, respectively, indicating changes in the content of bioactive GAs. In accordance with the effect on plant growth, biomass production was increased or decreased in AtGA20-ox or AtGA2-ox plants, respectively, and was found to be positively correlated with the rate of photosynthesis as determined at the whole plant level. Differences in dry matter accumulation were most likely due to changes in lignin deposition as indicated by histochemical staining and quantitative measurements. Altered lignification of transgenic plants was paralleled by up-or down-regulation of the expression of lignin biosynthetic genes. Short-term GA 3 feeding of excised petioles induced lignin formation in the absence of a transcriptional activation of pathway-specific genes. Thus, shortterm GA treatment mediates lignin deposition most likely by polymerization of preformed monomers, whereas long-term effects on lignification involve elevated production of precursors by transcriptional stimulation of the biosynthetic pathway. Interestingly, analysis of stem cross sections revealed a differential effect of GA on the formation of xylem and pith cells. The number of lignified vessels was increased in AtGA20-ox plants pointing to a stimulation of xylem formation while the number of pith cells declined indicating a negative regulation.

RNA Interference of LIN5 in Tomato Confirms Its Role in Controlling Brix Content, Uncovers the Influence of Sugars on the Levels of Fruit Hormones, and Demonstrates the Importance of Sucrose Cleavage for Normal Fruit Development and Fertility

“…By contrast, the total fruit yield correlates much better with the degree of reduction in invertase expression and, therefore, also the levels of GAs and cytokinins. These links are not without precedence, since invertase has long been associated with sink strength (see introduction), while cytokinins have also been clearly demonstrated to be associated with growth and GAs have previously been documented to play a role in growth (Chaudhury et al, 1993;Werner et al, 2003;Biemelt et al 2004). However, analysis of the pollen vitality and morphology also revealed a defect in pollen growth similar to that previously observed in LeSUT2 antisense tomato plants, which exhibited severely reduced expression of one of the isoforms of the Suc transporter family (Hackel et al, 2006).…”

Green Revolution Trees: Semidwarfism Transgenes Modify Gibberellins, Promote Root Growth, Enhance Morphological Diversity, and Reduce Competitiveness in Hybrid Poplar

“…They had higher chlorophyll content and steeper angles of their branches and leaf petioles, which might result in increased photosynthesis and more efficiency at intercepting light, but only under intense competition. Higher photosynthetic activity in older leaves of GAdeficient transgenics was previously reported and associated with their typical dark green foliage (Biemelt et al, 2004), which should reflect elevated nitrogen as well as the increased chlorophyll (Evans, 1989). The depth of their crowns was much less sensitive to increased competition than it was for the control trees (Fig.…”

Efecto de la sobreexpresión y del silenciamiento de genes del metabolismo de giberelinas sobre el desarrollo de tabaco

“…For instance, the overexpression of genes controlling the early steps of gibberellin biosynthesis in Arabidopsis (AtCPS and AtKS) confers no phenotypic alterations or increase in active gibberellins (Fleet et al 2003), suggesting a critical limiting step later in the pathway. However, overexpression of GA20oxs produces elongated phenotypes associated with gibberellin overproduction in Arabidopsis (Huang et al 1998, Coles et al 1999, potato (Carrera et al 2000), hybrid aspen (Eriksson et al 2000), rice (Oikawa et al 2004) and tobacco plants (Vidal et al 2001, Biemelt et al 2004, indicating the limiting activity of this enzyme in the gibberellin pathway. Overproduction of GA3ox, which catalyzes the last step in gibberellin biosynthesis, has generated conflicting results.…”