In biochemistry a metabolic pathway is a combination of chemical reactions inside a cell. There are various chemical reactions which occurs in our body as well in the plants to release usable energy. These chemical reactions drive the processes that keep the living organism ‘alive’. There are two types of metabolic pathways found, anabolic and catabolic pathways depending on their ability to either combines the molecules with the use of energy or splitting/breakdown of complex molecules by producing some energy in the process. The reactant, product and the intermediates may or may not be same. Sometimes these compounds act as enzymes to perform the certain reactions. Somewhere the product of one reaction acts as enzyme for other one. Some of the major metabolic networks in our body are glycolysis, citric acid cycle, urea cycle etc. Some metabolic pathways are present in the nature too such as photosynthesis and photorespiration.The food making process by plants is the most basic metabolic pathways found in environment but still have a greater importance. Increase in demand of food especially Carbohydrate rich food in India always encourage researchers to develop strategies to increase in food production. So, we are focusing on the carbohydrate giving plants and that is C3 plants. There are three different type of plants occurs in nature namely C3, C4, and Crassulacean Acid Metabolism (CAM) plants, which named on the number of carbon present in the first stable compound formed during the photosynthesis process. Three photosynthesis pathways exist among terrestrial plants. Different plants have different networks depending on certain conditions [1,2]. Graph theory results are also available in several biological networks and in photosynthetic effect [3, 4]. Several other mathematical models are proposed in order to understand the network of plants photosynthesis and explain the stomatal behavior of leaf-level C3 photosynthesis but they all are analytical model [5,6]. In this paper we propose a Descriptive mathematical model which approaches through graphical representation and draws some better qualitative and quantitative properties of any biological model or any complex system network. In order to understand the dynamic property and behavior of C3- plants Carboxylation process (Photosynthesis) and the Oxygenase process (Photorespiration), we propose a mathematical and graphical approach of modeling and that is Petri Net (PN). Due to its adaptability Petri net is very much efficient to model any biological system and can handle any concurrent and distributed complex system perfectly This model is Petri net (PN) which is a discrete event systemfirst proposed by Carl Adam Petri in early sixties to model the concurrent, asynchronous, distributed system [7,8]. Petri net is also used in several other field of sciences determining binary vectors or can be used as a recommender system in several networks [9,14]. Petri net has also application in biological networks like in Cardiovascular disease or in tuberculosis [15,18]
In this paper we focus on C3 plants metabolic network and will compare the networks with C4 plants using Petri net model. There are several software available to trace Petri net model and validate the system modeled and provide several results to explain the behavior of network considered. In this paper we are using PIPE v4.3.0 to draw the network and uses the results to explain the C3 plant network [19]
Photosynthesis is the most common and most important biochemical reaction occurring in nature. Almost all types of plants undergo photosynthesis under different conditions. C3 plants are the most common plants found in nature. Most of the carbohydrate producers are the C3plants for example Beans, Rice, Wheat, Potatoetc,whichare alsocalled energy giving plants. The process in which these plants produce energy is Photosynthesis. This process has a network explained in Figure 1, as they are efficient at photosynthesis in cool and wet climates. C3 plants do photosynthesis using NORMAL CALVIN CYCLE. Photosynthesis is the process where Reduced Nicotinamide Adenine Diphosphate (NADPH) and Adenosine Diphosphate (ATP) are created in CBB(Calvin Benson Bassham).In the suitable weather CO2 enters through the tiny pores on leaves called stomata.This carbon dioxide then combines with an enzyme called RuBisCO to produce Sugar. This process produces a molecule made up of three carbon atoms, and that is why C3 plants named. For C3 plants, this process takes place in a chloroplast layer, the green cells present in plants which helps in photosynthesis whichmakesany plant green. The cycle continues and with the help of energy in the form of light from the sun, sugar is made as well as RuBp is also produced forthe future use [20]. Sometimes the C3 plant consumes oxygen too, which can slow down the process of photosynthesis.This process is called Photorespiration also called oxidative photosynthetic carbon cycle, or C2 cycle. C2cycleis named so as the first stable compound formed is atwo carbon molecule. In Figure 2, one can observe the network involved in producing energy in C3 plants during Photorespiration. It is the process of taking O2 instead of CO2 in the process of Photosynthesis. Instead of fixing carbon when Rubisco fixes oxygen under certain conditions results in Photorespiration (PR).Sometimes it is also called anti-photosynthesis process. Under hot conditions RuBisCo has more affinity towards oxygen, so under hot weather when stomata closed so CO2 can’t diffuse in and O2 can’t diffuse out. Earlier it was said that this process is harmful for plants but recent researches shows the importance of this process.The process PR converts 2-phosphoglycolate (2PGP) into 3-phosphoglycerate (3PGA) and is escorted by O2 intake and CO2 release. PR plays the role of salvage or metabolic repair process which convert the toxic compound produced i.e., PGP into a useful compound PGA which produced during CBB cycle. PR also leads to the loss of CO2 and NH3. Eventually, PR decreases the rate of photosynthesis by 30% in current atmospheric concentration of CO2 and O2[21].