Abstract
Soil alkalization severely affects crop growth and agricultural productivity. Alkali salts impose ionic, osmotic, and high pH stresses on plants. The alkali tolerance molecular mechanism in roots from halophyte Puccinellia tenuiflora is still unclear. Here, the changes associated with Na2CO3 tolerance in P. tenuiflora roots were assessed using physiological and iTRAQ-based quantitative proteomic analyses. We set up the first protein dataset in P. tenuiflora roots containing 2,671 non-redundant proteins. Our results showed that Na2CO3 slightly inhibited root growth, caused ROS accumulation, cell membrane damage, and ion imbalance, as well as reduction of transport and protein synthesis/turnover. The Na2CO3-responsive patterns of 72 proteins highlighted specific signaling and metabolic pathways in roots. Ca2+ signaling was activated to transmit alkali stress signals as inferred by the accumulation of calcium-binding proteins. Additionally, the activities of peroxidase and glutathione peroxidase, and the peroxiredoxin abundance were increased for ROS scavenging. Furthermore, ion toxicity was relieved through Na+ influx restriction and compartmentalization, and osmotic homeostasis reestablishment due to glycine betaine accumulation. Importantly, two transcription factors were increased for regulating specific alkali-responsive gene expression. Carbohydrate metabolism-related enzymes were increased for providing energy and carbon skeletons for cellular metabolism. All these provide new insights into alkali-tolerant mechanisms in roots.
Highlights
Amino acid and the enhanced activities of ATPase and proteases in roots suggest that the osmotic homeostasis, energy supply, and protein turnover play crucial roles in alkali tolerance[7]
The NaHCO3-responsive genes in roots of woody halophyte Tamarix hispida under 300 mM NaHCO3 for 12 h, 24 h, and 48 h imply that various specific strategies are employed for surviving from alkaline stress, such as induced biosynthesis of proline and trehalose, enhancement of protein folding and osmotic homeostasis, and diverse transcription regulations[13]
The relative water content (RWC) in roots was decreased by 6%, 10.3%, and 13.9% under 200 mM Na2CO3 for 12 h, 150 mM for 24 h, and 200 mM for 24 h, respectively (Fig. 1B)
Summary
Amino acid and the enhanced activities of ATPase and proteases in roots suggest that the osmotic homeostasis, energy supply, and protein turnover play crucial roles in alkali tolerance[7]. The expression patterns of these alkali-responsive genes reveal that maize roots possess unique biological pathways for adapting to Na2CO3 stress. They include Na2CO3-induced brassinosteroid biosynthesis, and Na2CO3-reduced ascorbate (AsA) and aldarate metabolism, protein processing in endoplasmic reticulum (ER), the biosynthesis of N-glycan and fatty acid, and circadian rhythm[11]. Yeast or transgenic plants over-expressing these genes exhibited greater tolerance to alkali/salt stress, indicating their important roles in alkali/salt tolerance[1,14,15] These results are not adequate for unraveling the molecular basis and dynamic networks underlying alkaline tolerance in plant roots. P. tenuiflora is considered as an outstanding pasture for soil improvement, as well as a good plant model among monocotyledonous plants for understanding alkali tolerance mechanisms
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