Abstract
BackgroundHypoxia 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.ResultsCucumber 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.ConclusionsExogenous 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.
Highlights
Hypoxia acts as a plant stress factor, in cucumbers plants under hydroponic culture
We found that exogenous calcium could enhance both responsive metabolism and fermentative metabolism of cucumber seedlings, improving their tolerance to hypoxia
Identification and functional classification of proteins by MALDI-TOF/TOF To examine the effect of exogenous calcium on the proteome of cucumber seedlings under hypoxic stress in water culture, 2-DE analysis of total proteins in the roots was performed
Summary
Hypoxia acts as a plant stress factor, in cucumbers plants under hydroponic culture. Calcium is involved in stress signal transmission and in the growth of plants. The first process to be Exogenous calcium can improve the suppression of growth/development of plants and help to maintain cell function by relieving gene repression caused during salt stress [8], anoxia [9], and chilling [10]. The oxygen debt (anoxia) in cells of maize, rice and wheat plants causes a rise in cytoplasmic Ca2+ concentration [11,12]. According to our previous research [14], exogenous calcium enhances the biomass and soluble protein content of cucumber seedlings under hypoxia (Additional file 1: Table S1). The mechanism of calcium’s involvement in resistance to hypoxia remains unclear
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