Hypoxia acts as a plant stress factor, particularly in cucumbers plants under hydroponic culture.
Calcium is involved in stress signal transmission and in the growth of plants. To determine the effect of exogenous
calcium on hypoxic-responsive
proteins in cucumber (Cucumis sativus L. cv. Jinchun No.2) roots, proteomic analysis was performed using two-dimensional electrophoresis (2-DE) and mass spectrometry.
RESULTS: Cucumber roots were used to analyze the influence of
hypoxia on plants. The expressions of 38
protein spots corresponding to
enzymes were shown to change in response to
hypoxia. Of these, 30 spots were identified by matrix-assisted
laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF/TOF MS analysis). The
proteins were categorized according to functional groups, including glycolysis, the
tricarboxylic acid (TCA) cycle, fermentative metabolism,
nitrogen metabolism, energy metabolism,
protein synthesis and defense against stress. Exogenous
calcium appeared to alleviate hypoxic stress via these metabolic and physiological systems. Western blotting was used to analyze the accumulation of
alcohol dehydrogenase (ADH) and
pyruvate decarboxylase (PDC);
calcium further increased the expression of ADH and PDC under
hypoxia. In addition, semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to assess the transcript levels of differentially expressed
proteins.
CONCLUSIONS: Exogenous
calcium enhanced the expression of
enzymes involved in glycolysis, the TCA cycle, fermentative metabolism,
nitrogen metabolism, and
reactive oxygen species (ROS) defense in plants under
hypoxia.
Calcium appears to induce hypoxic tolerance of cucumber seedlings. These phenomena have prompted us to further investigate the mechanisms by which cucumbers respond to exogenous
calcium under
hypoxia.