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Molecular Approaches for Enhancing Abiotic Stress Tolerance in Plants
Published in Hasanuzzaman Mirza, Nahar Kamrun, Fujita Masayuki, Oku Hirosuke, Tofazzal M. Islam, Approaches for Enhancing Abiotic Stress Tolerance in Plants, 2019
Sushma Mishra, Dipinte Gupta, Rajiv Ranjan
The enzymes involved in synthesizing osmoprotectants have also been targeted to impart stress tolerance to high salt conditions. For example, the levels of polyamines have been increased in transgenic rice plants by expressing arginine decarboxylase, a key enzyme of polyamine biosynthesis pathway under the control of an ABA-inducible promoter (Roy and Wu, 2001). These transgenics exhibited increased biomass than the wild-type plants under salt stress. These plants were found to accumulate higher levels of spermine and spermidine, as a result of enhanced putrescine levels. On the contrary, wild-type plants failed to accumulate significant polyamine levels and hence were stress sensitive. In another report, the levels of glycine betaine have been increased in transgenic potato plants by overexpressing the codA gene of Arthobacter globiformis in chloroplast under the control of an oxidative stress-inducible SWPA2 promoter to impart salt and drought tolerance (Ahmad et al., 2008). The increase in hydrogen peroxide content in these transgenics also contributed to stress tolerance as a ROS scavenger, and also as an important signaling molecule. Similarly, transgenic tobacco plants over-expressing the P5CS gene (proline biosynthetic pathway) produced 10- to 18-fold more proline and exhibited better performance under salt stress (Kishor et al., 1995).
Biochemistry
Published in Ronald Fayer, Lihua Xiao, Cryptosporidium and Cryptosporidiosis, 2007
Polyamines are a group of small molecules essential to all cells. During polyamine synthesis, arginine is first converted to either ornithine by arginase, or agmatine by arginine decarboxylase (ADC). Ornithine or agmatine is further converted to putrescine by ornithine decarboxylase (ODC) or agmatine iminohydrolase (AIH). Longer polyamines, including spermidine and spermine, can be made from putrescine by spermidine or spermine synthase (SpdSyn or SpnSyn). However, spermine can be back-converted to spermidine, and to putrescine by a spermidine:spermine A-acetyltransferase (SSAT). Humans, animals, and fungi use the ODC pathway, whereas plants typically use ADC. Bacteria may have both ODC and ADC to make putrescine. Many protists use the ODC pathways. Among them, Trypanosoma ODC is the target for difluoromethylornithine (DFMO), an effective drug against African trypanosomiasis (Bacchi and Yarlett, 2002).
Impact of exogenous nicotine on the morphological, physio-biochemical, and anatomical characteristics in Capsicum annuum
Published in International Journal of Phytoremediation, 2022
Rami Alkhatib, Batool Alkhatib, Nour Abdo
Nicotine is synthesized from the polyamine putrescine, directly from ornithine, catalyzed by ornithine decarboxylase, or indirectly from arginine catalyzed by arginine decarboxylase. Nicotine is synthesized in the roots and then transported to the shoot by the xylem (Selmar, Engelhardt, et al. 2015). Moreover, Jasmonic acid at the root zone plays a crucial role in regulating the gene expression as well as in stimulating synthesis of the enzymes required for nicotine biosynthesis (Shoji et al.2008; Zhang et al. 2012; Afrin et al. 2015). In addition to nicotine synthesis endogenously, there are generally three nicotine sources for contamination of plant, such as contaminations by smokers (smoke of cigarettes/nicotine residues at the fingers of harvesters) and nicotine which is taken up from the soil (e.g. resulting from butts of cigarettes thrown away).