Abstract
Physiology and nutritional quality of a facultative CAM plant Mesembryanthemum crystallinum under drought stress alone are poorly understood. To induce drought, M. crystallinum was cultured aeroponically with different nutrient spraying intervals such as 5, 30, 60 and 240 min. The long spraying interval such as 240 min resulted in lower mass of root and shoot, shorter total root length with less tips and smaller surface area, compared to short interval of 5 min. Grown under the longest spraying interval of 240 min, M. crystallinumalso had significantly higher leaf dry matter content but lower leaf succulence. However, CAM acidity was undetectable for any plants. Although M. crystallinum grown under extended spraying intervals had higher photosynthetic pigments, they utilized lesser light energy and did not dissipate heat as effectively as those grown under 5 min. Compare to other shorter spraying intervals, photosynthetic gas exchange rates were significantly reduced under 240 min spraying interval, indicating signs of water deficit stress. Shoot nitrate, total reduced nitrogen, total soluble protein and Rubisco concentrations were similar for all plants. For phytochemicals and dietary minerals, plants grown under 240 min spraying interval had significantly higher values than the other plants. Therefore, drought does not result in the induction of CAM but regulates photosynthetic performance and enhances nutritional quality of M. crystallinum.
Highlights
Many studies demonstrated that crassulacean acid metabolism (CAM) was elicited if a drought- and salt-tolerant species Mesembryanthemum crystallinum following drought coupled with salinity [1,2] and salinity stress [3]
The shoot, and root fresh weight (FW) (Fig 2A and 2B) and dry weight (DW) (Fig 2D and 2E) were significantly higher for plants grown under 5 min nutrient spraying interval than under all other spraying intervals
For the plants grown under 5 min nutrient spraying interval, the shoot/root ratio DW had no significant difference from the other groups
Summary
Many studies demonstrated that crassulacean acid metabolism (CAM) was elicited if a drought- and salt-tolerant species Mesembryanthemum crystallinum (the common ice plant) following drought coupled with salinity [1,2] and salinity stress [3]. Apart from M. crystallinum, facultative CAM has been demonstrated in many other drought- and slat-tolerant species [4,5]. Proline accumulation is a well-known response to salt and drought stress [15]. Paul and Cockburn [12] reported that the irrigation of M. crystallinum plants with 400 mM NaCl induced CAM that was accompanied by the accumulation of proline and pinitol that was constituted 71% of the soluble carbohydrate. Other researches reported that proline is accumulated in halophytes under conditions of high salinity [16]. Natural antioxidants that exhibit antioxidant activities are phenolics, carotenoids and vitamins in plants and the synthesis of these antioxidants is stimulated in responses to environment stress [19]
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