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Effect of Elevated CO2 Conditions on Medicinal Plants
Published in Azamal Husen, Environmental Pollution and Medicinal Plants, 2022
Anuj Choudhary, Antul Kumar, Harmanjot Kaur, Mandeep Singh, Gurparsad Singh Suri, Gurleen Kaur, Sahil Mehta
This abrupt rise in carbon dioxide stimulates photosynthetic carbon assimilation rates of about 31 per cent across 40 plant species (Dusenge et al. 2019). In Lolium perenne elevated CO2 results in an increased tiller number, root and shoot dry weight, and total plant biomass. It also affects physiological processes such as enhanced photosynthetic activity and reduced stomatal resistance (Jia et al. 2018). In the family Asteraceae, elevated carbon dioxide enhanced photosynthetic rate and leaf area, and reduced water-use efficiency in Aster tripolium (Geissler et al. 2009) (Table 5.1). Elevated carbon dioxide also promotes root elongation and root branching in Pteridium revolutum (Zheng, J. et al. 2008), and enhances plant shoot biomass in Trigonella foenum-graecum and Ocimum basilicum (Jain et al. 2007; Tursun et al. 2020). Under higher CO2 levels, due to increment in carbon supply, more root exudates are accumulated inside plants (Zheng, Y. et al. 2008). According to various reports, carbon accumulation is more in roots than leaves and stem parts (Singh et al. 2018). Studies conducted by Zhu et al. (2002) showed that under elevated conditions there are more relative growth rates and net assimilation rates in Ananas comosus, a plant used in analgesic medicines. Kalanchoe blossfeldiana is an active immunosuppressive plant that responded positively to more leaves and nodes production under a CO2-rich environment (Cho et al. 2020) (Figure 5.4).
GABA/BABA Priming Causes Signaling of Defense Pathways Related to Abiotic Stress Tolerance in Plants
Published in Akula Ramakrishna, Victoria V. Roshchina, Neurotransmitters in Plants, 2018
K.C. Jisha, A.M. Shackira, Jos T. Puthur
On the other hand, BABA, an isomer of naturally occurring GABA, occurs very rarely in nature (Jakab et al. 2005; Mayer et al. 2006). So far BABA has been reported only in root exudates of tomato plants grown in solarized soils, in the xylem/phloem sap of Eucalyptus regnans, Acacia, and in some types of grapevine (Gamliel and Katan 1992; Barrado et al. 2009; Pfautsch et al. 2009). Interestingly, BABA, being similar to GABA in structure and also present naturally in plants, offers a great deal for enhancing the tolerance of plants toward various abiotic stresses. Thus, GABA and BABA trigger the defense system in order to equip the plant for the future exposure to different stress factors and to maintain a basal level of resistance. Figure 13.1 illustrates the chemical structures of GABA and BABA.
Genetics as a Tool to Understand Structure and Function
Published in Peter M. Gresshoff, Molecular Biology of Symbiotic Nitrogen Fixation, 2018
The central theme of this book is the interaction between nitrogen-fixing microorganisms and the plants with which they associate symbiotically. Until very recently virtually nothing was known about the biochemical genetics of these interactions, such as the nature and sequence of the plant products that are presumed to switch on the genes known to be concerned with various aspects of nodulation, several of which have been mapped, for example, on a small region (14 kb) of the Rhizobium trifolii symbiotic plasmid. The main difficulty of such studies has been the tedious and time-consuming in vivo testing of potential inducers for their specific effects on nodulation. This has been enormously simplified by inserting, in turn, in each of the four nod genes on the 14-kb fragment of DNA, a kanamycin-resistant transposon which also carries part of the E. coli lactose operon containing the β-galactosidase Z gene (see above). Each fusion complex was then inserted into a conjugal plasmid and introduced into an R. trifolii strain which has lost its symbiotic plasmid, and exposed to the plant products suspected of being Nod inducers. If effective, the inducer would switch on the operator of the mutant nod gene and mRNA transcription would then proceed along the hybrid DNA to the lactose operon, leading to the production of β-galactosidase, identified by a simple colorimetric assay. Using this method it has recently been shown that only one nod gene (nodD) is actively expressed by free-living Rhizobium in artificial culture, but that the other three genes are also induced when clover plants are grown in the medium.18 Subsequent work using lac gene fusions has identified and characterized various phenolic compounds from clover roots which either stimulate or inhibit the induction of R. trifolii nod genes.19 Similar findings were obtained from root exudates of alfalfa, pea, and soybean (see Chapter 6).
Rhizobacterial biofilm and plant growth promoting trait enhancement by organic acids and sugars
Published in Biofouling, 2020
Jishma Panichikkal, Radhakrishnan Edayileveetil Krishnankutty
Plant root exudates generally contain low molecular weight (amino acids, organic acids, sugars, phenolics, etc.) and high molecular weight (mucilage and proteins) compounds (Kumar et al. 2007; Liu et al. 2014). The factors determining the chemical complexity of root exudates are species or genotype specific and can also be influenced by the plant’s photosynthetic activity and size, and soil conditions (Sasse et al. 2018). The root exudates released by plants have also been reported to generate a nutrient gradient in the rhizosphere which can direct the movement of bacteria towards the plant root. Thus, the chemical composition of root exudates has been suggested to have a direct effect on shaping the rhizosphere microbiome to utilize its functioning for the growth and health of the plant (Schuch et al. 2013; Zhang et al. 2014; Mhlongo et al. 2018). In addition, the compounds present in the exudates including the organic acids and sugars can also be expected to play a key role in determining the functioning of bacteria at the rhizosphere.
Uptake kinetics of silver nanoparticles by plant: relative importance of particles and dissolved ions
Published in Nanotoxicology, 2020
Fei Dang, Qi Wang, Weiping Cai, Dongmei Zhou, Baoshan Xing
Accurate mechanistic insights into particle-specific uptake depend on AgNP dissolution under the experimental conditions. Dissolved oxygen (DO), root exudates and oxidative species at root surface may facilitate AgNP dissolution and thus confound its uptake. Dissolved oxygen (DO) is a key factor responsible for the massive release of ionic Ag from AgNPs in bulk suspension (Liu and Hurt 2010, Zhang, Xiao, and Fang 2018). The released Ag ions, as well as their complexes with different ligands in soil porewater, may be taken up by plants at higher rates and affinities than NPs, which could mask the biological uptake of the latter. The ionic-specific toxicity of AgNPs under anoxic condition has already been demonstrated, for example, in Escherichia coli (Xiu et al. 2012), similar knowledge in plants is still lacking. Further, plants release root exudates to enhance the acquisition of nutrients and to protect themselves against environmental stress, including metal contamination (Jones 1998). The exudates are composed of organic acids, amino acids, and phenolics and may increase the dissolution of AgNPs and/or reduce Ag ions into Ag nanoparticles, thus affecting the particle-specific uptake (Dimkpa et al. 2013, Guo et al. 2019, Stegemeier et al. 2015). In addition, the release of oxygen by aquatic plants (Soda et al. 2007) and reactive oxidative species (ROS) by roots (Erdmann and Wiedenroth 1988, Minibayeva et al. 2001) may increase the dissolution of AgNPs at the root surface. The interfacial dissolution of AgNPs has been reported (Leclerc and Wilkinson 2014, Ma et al. 2012) and the species of Ag at the interface (and thus the bioavailability) were shown to differ from those in bulk solution. Nevertheless, the presence of DO and root exudates in the bulk suspension, as well as ROS at root surface, have complicated mechanistic understanding of particle-specific bioavailability.