Cold stress affects antioxidative response and accumulation of medicinally important withanolides in Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal (Indian ginseng) is a high value medicinal plant. It synthesizes a large array of biologically active withanolides. In this study, two month old seedlings of AGB002 (wild genotype) and AGB025 (cultivated genotype) of W. somnifera were subjected to cold stress (4 ◦C) under controlled envi-ronment. Plants were analyzed for three medicinally important secondary metabolites (withanolide A, withanone and withaferin A), lipid peroxidation (MDA), cell injury, superoxide radical (O2 •−) accumula-tion and anti-oxidative enzymes activities such as superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR). Increases in the titers of superoxide anion and MDA were observed from day 1 to day 7 in both genotypes, although the increase on the first day of exposure was significantly higher. Enzymatic activities of SOD, CAT, APX and GR also showed an increasing trend in both genotypes and reached a maximum on day 7 of the cold temperature exposure; however, this increase was higher in AGB002 than AGB025. Withanolide A (WS-1) in the roots of both genotypes sig-nificantly decreased on the first day of cold exposure and then showed a recovery until day 7. WS-1 was not detected in the leaves of either genotype. Withanone (WS-2) content in the leaves also decreased towards the end of the cold period in both genotypes. Cold stress also elicited the accumulation of WS-2 in AGB025, but was not detectable in control seedlings. At maturity, WS-2 was also detected in control plants. Furthermore, a significant increase in the leaf withaferin A (WS-3) content was recorded from day 1 to day 7 of the cold exposure in both the genotypes, suggesting the possible involvement of with-anolides in cold-protection. AGB002 showed comparatively higher accumulation of antioxidant enzymes and selected marker withanolides than AGB025, indicating that AGB002 is better adapted to cold than AGB025. It could be inferred from these observations that cold stress induces bioactive withanolide accu-mulation in W. somnifera as a mechanism for scavenging reactive oxygen species (ROS). These studies also provide an impetus for enhancing the withanolide accumulation in W. somnifera using controlled environment technology.CSIR-Indian Institute of Integrative Medicine (CSIR-IIIM).http://www.elsevier.com/locate/indcrop2016-11-30hb2016BiochemistryChemistryGenetic

Myrosinase: insights on structural, catalytic, regulatory, and environmental interactions

Glucosinolate–myrosinase is a substrate-enzyme defense mechanism present in Brassica crops. This binary system provides the plant with an efficient system against herbivores and pathogens. For humans, it is well known for its anti-carcinogenic, anti-inflammatory, immunomodulatory, anti-bacterial, cardio-protective, and central nervous system protective activities. Glucosinolate and myrosinase are spatially present in different cells that upon tissue disruption come together and result in the formation of a variety of hydrolysis products with diverse physicochemical and biological properties. The myrosinase-catalyzed reaction starts with cleavage of the thioglucosidic linkage resulting in release of a D-glucose and an unstable thiohydroximate-O-sulfate. The outcome of this thiohydroximate-O-sulfate has been shown to depend on the structure of the glucosinolate side chain, the presence of supplementary proteins known as specifier proteins and/or on the physiochemical condition. Myrosinase was first reported in mustard seed during 1939 as a protein responsible for release of essential oil. Until this date, myrosinases have been characterized from more than 20 species of Brassica, cabbage aphid, and many bacteria residing in the human intestine. All the plant myrosinases are reported to be activated by ascorbic acid while aphid and bacterial myrosinases are found to be either neutral or inhibited. Myrosinase catalyzes hydrolysis of the S-glycosyl bond, O-β glycosyl bond, and O-glycosyl bond. This review summarizes information on myrosinase, an essential component of this binary system, including its structural and molecular properties, mechanism of action, and its regulation and will be beneficial for the research going on the understanding and betterment of the glucosinolate–myrosinase system from an ecological and nutraceutical perspective.</p