PLANT PHYSIOLOGY , Vol 106, Issue 2 703-712, Copyright © 1994 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Comparative Analysis of Short- and Long-Term Changes in Gene Expression Caused by Low Water Potential in Potato (Solanum tuberosum) Cell-Suspension Cultures
A. Leone, A. Costa, M. Tucci and S. Grillo
Research Centre for Vegetable Breeding, National Research Council, (A.L., A.C., S.G.), and Department of Agronomy and Plant Genetics (M.T.), University of Naples, 80055 Portici, Italy
To dissect the cellular response to water stress and compare changes
induced as a generalized response with those involved in
tolerance/acclimation mechanisms, we analyzed changes in two-dimensional
electrophoretic patterns of in vivo [35S]methionine-labeled polypeptides of
cultured potato (Solanum tuberosum) cells after gradual and long exposure
to polyethylene glycol (PEG)- mediated low water potential versus those
induced in cells abruptly exposed to the same stress intensity. Protein
synthesis was not inhibited by gradual stress imposition, and the
expression of 17 proteins was induced in adapted cells. Some polypeptides
were inducible under mild stress conditions (5% PEG) and accumulated
further when cells were exposed to a higher stress intensity (10 and 20%
PEG). The synthesis of another set of polypeptides was up-regulated only
when more severe water-stress conditions were applied, suggesting that
plant cells were able to monitor different levels of stress intensity and
modulate gene expression accordingly. In contrast, in potato cells abruptly
exposed to 20% PEG, protein synthesis was strongly inhibited. Nevertheless,
a large set of polypeptides was identified whose expression was increased.
Most of these polypeptides were not induced in adapted cells, but many of
them were common to those observed in abscisic acid (ABA)-treated cells.
These data, along with the finding that cellular ABA content increased in
PEG-shocked cells but not in PEG-adapted cells, suggested that this hormone
is mainly involved in the rapid response to stress rather than long-term
adaptation. A further group of proteins included those induced after long
exposure to both water stress and shock. Western blot analysis revealed
that osmotin was one protein belonging to this common group. This class may
represent induced proteins that accumulate specifically in response to low
water potential and that are putatively involved in the maintenance of
cellular homeostasis under prolonged stress.
