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Abiotic Stress in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Ashutosh K. Pandey, Annesha Ghosh, Kshama Rai, Adeeb Fatima, Madhoolika Agrawal, S.B. Agrawal
Lower doses of UV-B can be regulatory and provide early adaptation prior to extreme conditions. However, higher doses of UV-B induces the activation of higher synthesis of phenolics, specific flavonol glycosides and anthocyanins to cope with the severe distress of massively produced ROS (Emiliani et al., 2013; Hectors et al.,2014; Hideg et al., 2013). Furthermore, pigments accumulations, increased wax deposition, lignin production, secondary metabolites formations, mutations and genetic material impairment, etc. are some of the common biochemical responses due to increased production of ROS in response to such abiotic stresses. Various antioxidative metabolism (enzymatic or non-enzymatic), gets activated to scavenge ROS. Flavonoid mutants showed highly sensitive behavior towards higher UV-B, proving that flavonoids have a direct role in plant defense mechanisms and pathways. Biosynthetic pathway of flavonoids is mainly regulated by a group of genes encoding biosynthetic enzymes, including chalcone synthase (CHS), chalcone isomerase (CHI), flavanone 3-hydroxylase (F3H), flavonol synthase (FLS), dihydroflavonol 4-reductase (DFR) a nd leucoanthocyanidin dioxygenase (LDOX) (Tilbrook et al., 2013), which also help in scavenging excessively produced ROS under such radiation stress.
Enhanced production of total flavones from Inonotus baumii by multiple strategies
Published in Preparative Biochemistry & Biotechnology, 2018
Hui Li, Xue Jiao, Wanlong Zhou, Yajie Sun, Wei Liu, Weiping Lin, Ao Liu, Aihuan Song, Hu Zhu
In general, flavonoids in plants are derived from the products of shikimate and acetate-malonate pathways. The synthesis is always initiated from transformation of phenylalanine into cinnamic acid catalyzed by phenylalanine ammonia-lyase (PAL), one key enzyme of phenylpropanoid pathway.[23] Two precursors, phenylalanine and cinnamic acid, may play important roles in flavone synthesis of I. baumii. Malonyl-CoA, derived from acetate,[24] is condensed with p-coumaroyl-CoA through a reaction catalyzing by chalcone synthase to form the C15 chalcone intermediate that is further transformed into various flavonoids.[25] Thus, sodium acetate was also chosen to investigate its influence on the flavone production. These precursors had shown positive effects on the flavonoid synthesis and cell growth in cell suspension cultures of Glycyrrhiza inflata Bat.[24] Therefore, their influences on the flavone biosynthesis of I. baumii were also investigated (Figure 3a to f). The results showed that the addition of phenylalanine had little effect on the cell growth. However, the flavone titers changed as expected. When the concentration of phenylalanine was only 0.025 mmol/L, the flavone yield was nearly the same as the control group. As the concentration increased to 0.05 mmol/L, the yield reached 1806.84 mg/L, about 1.2-fold of the control group. When the concentration was 0.1 mmol/L, the yield decreased slightly. Thus, the most favorable concentration of phenylalanine for PTF is 0.05 mmol/L. The addition of cinnamic acid can also result in the change of DMW and PTF. The optimum concentration of cinnamic acid was found to be 0.2 mmol/L and DMW and PTF reached 1.24- and 1.05-fold of the control group. Different from the former two precursors, sodium acetate presented negative effect on cell growth and the maximum inhibition rate was 34% when the concentration of sodium acetate was 0.05 mmol/L. The yield of total flavones exhibited a slight enhancement by 9% at the concentration of 0.10 mmol/L (Figure 3c). As flavones are secondary metabolites, the addition time of precursors was also optimized. The addition time of phenylalanine showed the obvious influence on the PTF and the optimum time was found to be day 4 with an increase by 18.84%. This result was in consistent with the fact that PTF increased sharply from day 4 of culture (Figure 2f). Similarly, the optimum addition time of the other two precursors was day 4.