Transgenic tobacco (Nicotiana tabacum L. cv. Samsun-NN) plants over-expressing a synthetic HRP-C gene are altered in growth, development and susceptibility to abiotic stress

Abstract

The physiological role of class III peroxidases (EC 1.11.1.7) in controlling plant growth and development has been investigated by overexpression of both native and heterologous peroxidases. However, it has remained an enigma as to why the phenotypes of different peroxidase over-expressing transgenics vary. In order to resolve the conflicting information about the consequences of peroxidase over-expression, we have explored the role of the subcellular targeting of HRP-C in controlling stem growth, root development, axillary branching and abiotic stress tolerance in tobacco (Nicotiana tabacum L.). Altering the sub-cellular targeting of vacuolar HRP-C, such that over-expressed peroxidase accumulates in the cytoplasm and cell wall, induced phenotypic changes that are typically associated with altered auxin homeostasis, and overexpression of cell wall located peroxidases. We conclude that sub-cellular targeting is a determinant of the phenotype of peroxidase over-expressing plants.

Modification of reactive oxygen species scavenging capacity of chloroplasts through plastid transformation

“…Mn transgenic lines had no increased tolerance to Cd in UV-B tolerance in cyanobacteria (Bhargava et al 2004), while H 2 O 2 is an important oxidant in phenolpropanoid metabolism, and can therefore influence the synthesis of UV-screening compounds. Manipulation of cytosolic or apoplastic peroxidases has been shown to influence UVtolerance in tobacco (Jansen et al 2004;Heggie et al 2005), so diffusion into the cytosol of excess H 2 O 2 , a substrate of peroxidase, generated by MnSOD in the chloroplasts, might also affect the plant's response to UV. It should be emphasised that this UV protection would be due to alterations in phenolic metabolism in the absence of UV, and is not due to induction of a defence response by UV-B, which would not be plausible during the short timeframe of high level exposure in these experiments.…”

Role of Reactive Oxygen Species during Cell Expansion in Leaves

“…Early reports on cell growth revealed an inverse correlation between cell growth and POX activity (Fry, 1986;Goldberg et al, 1987). Also, during abiotic stress, POX activity increases and can cause lignification and rigidification of the cell wall, limiting leaf growth (Heggie et al, 2005;Lee et al, 2007). In Arabidopsis, several POX genes have been linked to the regulation of cell expansion during leaf development.…”

Specific functions of individual class III peroxidase genes

“…Although some of these studies provided interesting data (e.g. Ostergaard et al, 2000;Heggie et al, 2005;Bindschedler et al, 2006), many of these approaches have produced disappointing, inconclusive results (e.g. Sherf et al, 1993;McIntyre et al, 1996;Kristensen et al, 1997;Ray et al, 1998;Schlimme et al, 2002), and the in planta role of most peroxidases remains elusive.…”