Question

give the systematic representation of glycolysis

Answer 1

Plants are autotrophic organisms able to use solar radiation to split water molecules (H 2 O) and reduce the carbon dioxide (CO 2 ) compounds that can finally be stored as insoluble polysaccharides (starch) or used directly in the synthesis of other compounds. In plants glucose is the main substrate for respiration. This process oxidizes carbohydrates through two principal pathways: glycolysis and the tricarboxylic acid (TCA) cycle. The products from these two pathways are CO 2 and the reduced compounds NAD(P)H 2 and FADH 2 , which in turn are used for oxidative phosphorylation (OXPHOS), transferring their electrons to the terminal oxidase where O 2 acts as the final electron acceptor, producing high- energy phosphate bonds (ATP) (Millar et al., 2011; van Dongen et al., 2011). ATP represents the most efficient way to obtain energy for the synthesis of biomolecules and to maintain cellular structures, transport photoassimilates, uptake ions, assimilate N and S, regulate protein turnover and maintain electrochemical potential gradients across membranes in cells (Amthor, 2000). Plant respiration has been widely studied, but despite this effort and the available new technologies, its mechanisms of regulation and control still require further elucidation. For instance, studies on the enzymatic functionality of glycolysis have determined the importance of phosphoglucomutase (PGM) in starch formation processes in both heterotrophic (root and seed) and autotrophic tissues as well as the role of hexokinases (HXK) and other enzymes such as the glucose signaling network (Sheen, 2014). Regarding the TCA cycle, some progress has been made in understanding how alternative pathways involving γ-aminobutyric acid (GABA) and the glyoxylate cycle operate, with special attention given to changes in the optimal conditions, in order to show the high level of plasticity in the response of the TCA cycle to environmental changes (Sweetlove et al., 2010). More details will be given in another section below. On the other hand, research has been directed at finding new non-phosphorylates or alternative pathways for OXPHOS that allow energy to be dissipated. Alternative oxidase (AOX) is a protein associated with the inner mitochondrial membrane, it has been shown to be induced by a series of stress factors such as high and low temperatures, drought, and nutrient deficiency, among others (Moore et al., 2002). Furthermore, alternatives have also been found to the maintenance of the proton gradient in the mitochondrial matrix, which is performed through uncoupled proteins (UCP) that enables flows of protons to enter the matrix independent of ATP synthesis (Arnholdt- Schmitt et al., 2006). In turn, UCP would participate in the reduction of reactive oxygen species (ROS), a function also contributed to by AOX (Smith et al., 2004). Respiration plays an important role in acclimation to different types of abiotic stress (water, temperature, photoinhibition, salinity, nutrient deficiencies, and hypoxia/anoxia, etc.), therefore many studies have focused on understanding the function, organization, and regulation of respiratory metabolism under unfavorable environments. These stresses usually result in changes in the energy requirements of plants, which in turn induce changes in respiratory metabolism as well as in other enzymes, electron transport, and redox gradient formation, among others. One important stress that affects respiration is partial deficiency (hypoxia) or absolute absence (anoxia) of oxygen.