Abstract
Biochar is known to have a number of positive effects on plant ecophysiology. However, limited research has been carried out to date on the effects and mechanisms of biochar on plant ecophysiology under abiotic stresses, especially responses to cold. In this study, we report on a series of experiments on rice seedlings treated with different concentrations of biochar leacheates (between 0 and 10% by weight) under cold stress (10°C). Quantitative real-time PCR (qRT-PCR) and cold-resistant physiological indicator analysis at low temperatures revealed that the cold tolerance of rice seedlings increased after treatment with high concentrations of biochar leacheates (between 3 and 10% by weight). Results also show that the organic molecules in biochar leacheates enhance the cold resistance of plants when other interference factors are excluded. We suggest that the positive influence of biochar on plant cold tolerance is because of surface organic molecules which likely function by entering a plant and interacting with stress-related proteins. Thus, to verify these mechanisms, this study used gas chromatography-mass spectrometry (GC-MS) techniques, identifying 20 organic molecules in biochar extracts using the National Institute of Standards and Technology (NIST) library. Further, to illustrate how these organic molecules work, we utilized the molecular docking software Autodock to show that the organic molecule 6-(Methylthio)hexa-1,5-dien-3-ol from biochar extracts can dock with the stress-related protein zinc-dependent activator protein (ZAP1). 6-(Methylthio)hexa-1,5-dien-3-ol has a similar binding mode with the ligand succinic acid of ZAP1. It can be inferred that the organic molecule identified in this study performs the same function as the ZAP1 ligand, stimulating ZAP1 driving cold-resistant functions, and enhancing plant cold tolerance. We conclude that biochar treatment enhances cold tolerance in rice seedlings via interactions between organic molecules and stress related proteins.
Highlights
Low temperature is one of the most significant environmental factors that negatively influences crop yields globally (Masoomi-Aladizgeh et al, 2015)
Total chlorophyll contents were measured in order to explain these symptoms; results show that total chlorophyll contents in 1% concentration treatments had decreased by 14.16% compared with the control (Table 5), while in 3, 5, 7, and 10% concentration treatments, total chlorophyll contents increased by 2.6, 16.31, 28.09, and 35.33% (Table 5)
Increasing biochar leacheate concentrations (i.e., 3, 5, 7, and 10%) led to the up-regulation of all genes (Figure 3), most obviously OsDREB1A and OsDREB1B (Figure 3). These results suggest that the small organic molecules present on the surface of biochar and involved in improving rice cold tolerance may affect the expression of these transcription factors; cold tolerance improved in plants as biochar leacheate concentration increased
Summary
Low temperature is one of the most significant environmental factors that negatively influences crop yields globally (Masoomi-Aladizgeh et al, 2015). Plant cells have a protective system that includes enzymatic antioxidants that combat oxidative stress; three examples, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) are widely distributed in plants and enable the adaption and regulation of ROS in response to abiotic stresses, especially chilling (Li et al, 2015). Plant genomes are known to contain numerous transcription factors which play important roles in a number of processes including responses to abiotic and biotic stress (Udvardi et al, 2007). A variety of genes induced by low temperature have been identified in rice, including kinase and transcription factor regulatory proteins (Seki et al, 2002; Rabbani et al, 2004; Nakashima et al, 2009); Dubouzet et al (2003) separated five complementary DNA (cDNA) regions that are dehydration responsive element binding (DREB) homologs in rice (i.e., OsDREB1A, OsDREB1B, OsDREB1C, OsDREB1D, and OsDREB2A), responsible for low temperature-induced expression of OsDREB1A and OsDREB1B (Dubouzet et al, 2003). Experiments show that when the novel cold-induced genes OsCOIN and OsiSAP8 are over-expressed in transgenic rice lines, salt, drought, and chilling tolerance are all significantly enhanced (Liu et al, 2007; Kanneganti and Gupta, 2008)
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