Abiotic stress responses are of the utmost importance for plants because they cannot survive unless they are able to cope with environmental changes, such as high and low temperatures, drought, flooding, salinity, freezing, change in pH, strong light, UV, and heavy metals. Plants respond to various stresses at different levels, including molecular and cellular levels, as well as by modifying their metabolomes. Hence, studies on plant responses to stresses can be conducted at any of these levels to provide an understanding of the mechanisms involved. The present chapter focuses on the metabolomic approach to understand the responses of plants to different abiotic stresses, which can then be utilized to evolve strategies to combat such stress. Osmoprotectant metabolites, such as proline, glycine betaine, and polyamines, as well as carbohydrates, play important roles in the protection of plants against osmotic disbalances due to abiotic stresses. In addition, oxidative stresses are also overcome by an array of antioxidants, such as phenols, ascorbate, carotenoids, and a-tocopherol, as well as antioxidative enzymes. Signaling cascades activated during abiotic stresses lead to overexpression of protein kinases and stress proteins, and also involve molecules such as jasmonic acid and salicylic acid. Protein kinases and protein phosphatases that are encoded by large gene families often act in tandem to perform the phosphorylation and dephosphorylation leading to their activation and inactivation involved in stress signaling in plants. Analysis of microRNAs and transcriptomes has provided sufficient understanding of the gene expression levels during periods of stress. Hence, taken together, all these results can be utilized for identifying genes and/or metabolites overexpressed in tolerant species during periods of stress, and can be utilized to achieve higher tolerance and survivability during stresses. 727
Maize is one such crop, the production of which is highly challenged due to water shortage and soil water losses. The present study was undertaken on artificially induced water stress of maize in vitro, where stress was applied with PEG-6000 on one week old seedlings of four varieties BN 10, Dhanya. Kaveri-Super 244, and Swarna for 3, 5 and 7 days. The activity of antioxidative enzyme like peroxidase, catalase, ascorbate peroxidase, glutathione reductase and superoxide dismutase was assayed in the stressed and control plants. Peroxidase activity decreased on the 7th day in Dhanya and Swarna but in BN 101 and Super 244 the activity decreased slightly on the 5th day and increased again on the 7th day. Ascorbate peroxidase and superoxide dismutase showed a similar trend where the activity decreased after a certain period of stress. Similar trend was seen for GR activity too in case of Dhanya and Swarna. But in BN 101 and Super 244 there was an increase in the activity with the increase in the period of stress. Catalase activity declined during stress in Dhanya and Swarna while the other two varieties showed an increase during stress. Other than enzymatic activities, various biochemical analyses like proline, ascorbate, chlorophyll was also carried out. With the increase in intensity of drought there was an increase in both proline and ascorbate content in all. A significant increase in the ascorbate content was observed in BN 101 and super 244, H202, accumulation and lipid peroxidation showed an increase during stress in Dhanya and Swarna but no increase was seen in the other two varieties. Chlorophyll content showed a decline during the period of drought when compared to the control plants of all varieties. Enzymatic activity and biochemical tests show that Dhanya and Swarna are susceptible to drought stress than super 244 and BN 101 which are the tolerant varieties.
AIM: The present study was performed to prole some phenolics and explore the antioxidant effect of eight locally available ferns collected from different places of Darjeeling Himalayas, India. Methods: The antioxidant activities of methanol (MeOH) extract was evaluated by DPPH free radical scavenging activity. Qualitative analysis of phenol was done using standard methods. Further, characterization of phenolics was done using High performance liquid chromatography. Result: The content of phenolics ranged from 6.77 to 60.066mg FAE/g dry weight. The DPPH antioxidant activity expressed as IC values 50 revealed Nephrolepis cordifolia and Microsorum punctatum to exhibit highest and lowest antioxidative activity respectively. Moderate correlation 2 (R =0.547) was observed between the total phenolics content and antioxidant activity. HPLC analysis of phenolics from all the investigated plants revealed the presence of caffeic acid, ferulic acid and salicylic acid while the other phenolics such as phloroglucinol, gallic acid, pyrogallol, 3,4- dihy droxybenzoic acid, catechol, catechin, chlorogenic acid, caffeine, vanillic acid and cinnamic acid were not uniformly present in all the plants. The phenolic contents values showed wide variation among themselves, as well as within different plants. These ferns with considerable amount of phenolics can be the potential source of natural antioxidants.
Citrus reticulata grows in warm climatic conditions. Stresses such as water logging, drought, soil acidity, unbalanced nutrition and pathogenic infestation lead to root injury resulting in citrus tree decline and therefore huge economic losses. In order to determine the effect of flooding and drought on mandarin plants, mandarin plants were subjected to water logging condition in the field and in pots for drought condition. Biochemical and morphological changes induced by water logging and drought conditions were determined. The plants showed slight wilting and leaf dropping by the third day of flooding whereas in drought the leaves curled up, became crisp and later dried out. Marked changes in antioxidative enzymes such as peroxidase, catalase and ascorbate peroxidase was observed during stress in comparison to control plants. Antioxidative activity was seen to be more in the leaves than in the roots. Among the antioxidants carotenoid content showed a significant decrease during the flood stress but increased in drought stress. An increase in ascorbate content was observed during stress in comparison to the control. From this study, we can conclude that water stress causes adjustment of antioxidant balance in mandarin plants.
Toddalia asiatica (Rutaceae) a woody liana is used traditionally in the treatment of malaria, sprains, cough, fever, neuralgia, epilepsy, dyspepsia, and other disease conditions. A wide range of chemical constituents are found in leaf extracts such as tannin, alkaloids, flavonoids, terpenoids and phenolic compounds and in fruit extract, phytoconstituents such as tannin, saponin, phenolic compounds, and reducing sugar are reportedly present. In recent years, drug resistance to human pathogenic bacteria has been commonly reported from all over the world. In the present scenario of emergence of multiple drug resistance to human pathogenic organisms, this has necessitated a search for new antimicrobial substances from other sources including plants. It was investigated that the leaf and fruit extract of T. asiatica showed potential antibacterial activity against human pathogens such as Streptococcus mutans, Streptococcus pyogenes, Vibrio cholera, and Shigella flexneri. This study could be helpful to develop antibacterial agent against the tested strains which will help to formulate a new drug effective against these pathogens.
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