Salinity and drought tolerance of mannitol‐accumulating transgenic tobacco

Abstract

Tobacco plants (Nicotiana tabacum L.) were transformed with a mannitol-1-phosphate dehydrogenase gene resulting in mannitol accumulation. Experiments were conducted to determine whether mannitol provides salt and/or drought stress protection through osmotic adjustment. Non-stressed transgenic plants were 20-25% smaller than non-stressed, non-transformed (wild-type) plants in both salinity and drought experiments. However, salt stress reduced dry weight in wild-type plants by 44%, but did not reduce the dry weight of transgenic plants. Transgenic plants adjusted osmotically by 0*57 MPa, whereas wild-type plants did not adjust osmotically in response to salt stress. Calculations of solute contribution to osmotic adjustment showed that mannitol contributed only 0-003-0-004 MPa to the 0 2 MPa difference in full turgor osmotic potential {KJ between salt-stressed transgenic and wild-type plants. Assuming a cytoplasmic location for mannitol and that the cytoplasm constituted 5% of the total water volume, mannitol accounted for only 30-40% of the change in K^ of the cytoplasm. Inositol, a naturally occurring polyol in tobacco, accumulated in response to salt stress in both transgenic and wild-type plants, and was 3-fold more abundant than mannitol in transgenic plants.Drought stress reduced the leaf relative water content, leaf expansion, and dry weight of transgenic and wild-type plants. However, Ji^was not significantly reduced by drought stress in transgenic or wild-type plants, despite an increase in non-structural carbohydrates and mannitol in droughted plants. We conclude that (1) mannitol was a relatively minor osmolyte in transgenic tobacco, but may have indirectly enhanced osmotic adjustment and salt tolerance; (2) inositol cannot substitute for mannitol in this role; (3) slower growth of the transgenic plants, and not the presence of mannitol per sc, may have been the cause of greater salt tolerance, and (4) mannitol accumulation was enhanced by drought stress but did not affect 71^ or drought tolerance.

Dissecting the roles of osmolyte accumulation during stress

“…The comparatively recent advances in plant molecular genetics and transformation technologies have opened new 536 P. D. Hare et al © 1998 Blackwell Science Ltd, Plant, Cell and Environment, 21, 535-553 Tarczynski et al (1993); dehydrogenase Karakas et al (1997) …”

Characterization of Sicilian Olive Genotypes by Multivariate Analysis of Leaf and Fruit Chemical and Morphological Properties

“…Furthermore, polyols may function as scavengers of reactive oxygen species and represent a non-enzymatic mechanism to protect cells from oxidative stress (Smirnoff & Cumbes, 1989). In transgenic plants exposed to salt or water stress, mannitol induces better survival and/or performance compared to wild types (Tarczynski, Jensen, & Bohnert, 1993;Abebe, Guenzi, Martin, & Cushman, 2003;Macaluso, Lo Bianco, & Rieger, 2007), and this does not seem to be attributable to osmotic protection by mannitol (Karakas, Ozias-Akins, Stushnoff, Suefferheld, & Rieger, 1997;Abebe et al, 2003) but rather to a more specific radical scavenging mechanisms (Shen, Jensen, & Bohnert, 1997).…”

Effect of exogenous application of sugars on the salt tolerance of perennial ryegrass protoplasts

“…Therefore, it is possible that some of the sugars that accumulate in plant cells under conditions of NaCl stress play a role in increasing salt tolerance by protecting the structures of enzymes and biomembranes. While the mechanism of osmomodulation by sugars has been the focus of several salt tolerance studies (Karakas et al 1997;Garg et al 2002;Taji et al 2002), the involvement of the functional groups of sugars in salt tolerance has received relatively little attention.…”