Increased Resistance to Oxidative Stress in Transgenic Plants by Targeting Mannitol Biosynthesis to Chloroplasts

Abstract

To investigate the potential role of a polyol, mannitol, in oxidative stress protection, a bacterial mannitol-1 -phosphate dehydrogenase gene was targeted to chloroplasts by the addition of an aminoterminal transit peptide. Transgenic tobacco (Nicofiana fabacum) lines accumulate mannitol at concentrations ranging from 2.5 to 7 pmol/g fresh weight. Lhe BSI-31 accumulated approximately 1 O0 mM mannitol in chloroplasts and was identical to the wild type in phenotype and photosynthetic performance. l h e presence of mannitol in chloroplasts resulted in an increased resistance to methyl viologen (MV)-induced oxidative stress, documented by the increased retention of chlorophyll in transgenic leaf tissue following M V treatment. In the presence of MV, isolated mesophyll cells of BS1-31 exhibited higher CO, fixation than the wild type. When the hydroxyl radical probe dimethyl sulfoxide was introduced into cells, the initial formation rate of methane sulfinic acid was significantly lower in cells containing mannitol in the chloroplast compartment than in wild-type cells, indicating an increased hydroxyl radicalscavenging capacity in BS1-31 tobacco. We suggest that the chloroplast location of mannitol can supplement endogenous radicalscavenging mechanisms and reduce oxidative damage of cells by hydroxyl radicals.

Increased Salt and Drought Tolerance by D-Ononitol Production in Transgenic Nicotiana tabacum L

“…The rate constants for reactions with hydroxyl radicals in aqueous solution for mannitol and myo-inositol are similar, suggesting that both are effective scavengers, whereas Pro, for example, is four times slower (Buxton et al, 1988). Mannitol has recently been shown to act in the chloroplast as a scavenger of hydroxyl radicals in vivo (Shen et al, 1997). It has also been shown in vitro that myo-inositol was most effective as a heat protectant in Plant Physiol.…”

“…Other mechanisms by which these metabolites might enhance resistance to stress are, however, still not well understood. Some of these metabolites could act, for example, as scavengers of hydroxyl radicals-extremely toxic, short-lived active oxygen species that have no known enzymatic systems for breakdown (Smirnoff and Cumbes, 1989;Smirnoff, 1993;Asada, 1994;Shen et al, 1997)--or their protective function might be in maintaining the hydration sphere of proteins under water-stress conditions (Galinski, 1993;Papageorgiou and Murata, 1995).…”

“…Other mechanisms by which these metabolites might enhance resistance to stress are, however, still not well understood. Some of these metabolites could act, for example, as scavengers of hydroxyl radicals-extremely toxic, short-lived active oxygen species that have no known enzymatic systems for breakdown (Smirnoff and Cumbes, 1989;Smirnoff, 1993;Asada, 1994;Shen et al, 1997)--or their protective function might be in maintaining the hydration sphere of proteins under water-stress conditions (Galinski, 1993;Papageorgiou and Murata, 1995).We have previously shown that tobacco, transformed to accumulate mannitol, survives high salinity better when stressed at the beginning of the exponential growth phase (Tarczynski et al, 1993). However, the amount of mannitol accumulated was usually not greater than approximately 6 to 8 pmol g-' fresh weight, possibly because of the fact that the Escherickia coli mtlD gene product catalyzed an equilibrium reaction that could also result in a conversion of mannitol-6-P to Fru-6-P, owing to the equal affinity of MtlD for either mannitol-6-P or Fru-6-P (Teschner et al, 1990).…”

Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

“…AIPC (ABA induced promoter complex) has also been used in conferring salt and water stress tolerance by engineering P5CS in rice . Targeted expression has been achieved by using a constitutive promoter along with a transit peptide sequence, consequently targeting the protein specifically to the required organelle (Bowler et al, 1991;van Camp et al, 1996;Shen et al, 1997;Yu et al, 1999;McKersie et al, 2000). Use of DEXinducible promoter (Qin and Zeevaart, 2002) or a TcInducible promoter (Thompson et al, 2000) to regulate the expression of PvNCED1 and LeNCED1, respectively, resulted in elevated ABA levels thereby effecting the seed dormancy and water relations in the plant.…”

Exogenous application of mannitol and thiourea regulates plant growth and oxidative stress responses in salt-stressed maize (Zea maysL.)

“…Its proportion is about 50% of the total translocated photoassimilates (Loester et al 1992). Although mannitol plays an important role in osmotic adjustment, it acts as an antioxidant to scavenge of hydroxyl radicals (OH ) (Shen et al 1997;Srivastava et al 2010). However, there is little information available in the literature on the role of mannitol in stress tolerance in plants of agronomic importance.…”