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Clarification on Hatch and slack pathway

Clarification on Hatch and slack pathway


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The following is a minor clarification that I want to make, since it is rarely addressed directly in most of the texts I have gone through.

In C₄ pathway, the chloroplasts are dimorphic, that is, the bundle sheath chloroplasts contain RuBisCO, but lack grana and can hence perform only the light-independent reactions. The mesophyll chloroplasts lack RuBisCO but contain the granal apparatus to perform light reactions for synthesis of ATP and NADPH. The bundle sheath cells are impervious to gaseous transport (to prevent the entry of O₂), but recieve the required CO₂ by the intake of an organic acid produced by CO₂ fixation by the mesophyll cells.

But, to effect the Calvin cycle in the bundle sheath cells, it requires a high concentration of the light reaction products, i.e., ATP and NADPH. Since they themselves lack grana, they must obtain the required share from elsewhere. Where do they obtain it from?

My guess is that NADPH enters the bundle sheath cell with the organic acid primarily produced in the mesophyll cells where light reaction occurs. ATP is met by a similar uptake plus the utilisation of the ATP produced by respiration. I need to confirm this as it is usually never addressed in texts.


I am not sure about the source of ATP but I can tell you something about NADPH.

The conversion of malate to pyruvate and CO₂ by malic enzyme is carried out in the bundle sheath cell. This process produces NADPH.


See the very 1st thing is bundle sheath cell shows very less concentration of Grana, hence we say Grana is absent, the required amount of ATP & NADPH₂ are also transported from mesophyll cell to bundle sheath cell via plasmodesmata.


C4-Dicarboxylic Acid Pathway (With Diagram) | Photosynthesis

It was worked out by Hatch and Slack (1965, 1967). However, initial discovery was made by Kortschak (1965) who found that labelled carbon dioxide ( 14 CO2) assimilated by Sugarcane leaves first appeared in a 4-carbon compound oxalo-acetic acid (OAA or oxaloacetate).

Because of the initial discovery by Kortschak, this pathway of carbon assimi­lation is also called HSK (Hatch Slack Kortschak) pathway. Hatch and Slack found it a regular mode of CO2-fixation in a number of tropical plants, both monocots and dicots, e.g., Maize, Sugarcane, Sorghum, Panicum, Pennisetum (Pearl Millet), Atriplex, Amaranthus, Salsola, etc.

These plants are called C4 plants because of the first stable photosynthetic product being a 4-carbon compound. Other plants are C3 plants. C4 plants live in hot moist or arid and non-saline or saline habitats. They have Kranz anatomy (Fig. 13.24).

In Kranz anatomy, the mesophyll is undifferentiated and its cells occur in concentric layers around vascular bundles. Vascular bundles are surrounded by large sized bundle sheath cells which are arranged in a wreath-like manner (kranz— wreath) in one to several layers.

The mesophyll and bundle sheath cells are connected by plasmodesmata or cytoplasmic bridges. The chloroplasts of the mesophyll cells are smaller. They have well developed grana and a peripheral reticulum but no starch. Mesophyll cells are specialised to perform light reaction, evolve O2 and produce assimilatory power (ATP and NADPH).

They also possess enzyme PEP Case for initial fixation of CO2. The chloroplasts of the bundle sheath cells are agranal. They possess a peripheral reticulum and starch grains.

Thylakoids occur as stroma lamellae. ATP can be synthesised through cyclic photophospho­rylation. However, photolysis and O2 evolution are absent. Rather, bundle sheath cells are well protected from O2 being released from mesophyll cells. Bundle sheath cells possess Rubisco.

In C4 plants, initial fixation of carbon dioxide occurs in mesophyll cells. The primary acceptor of CO2 is phosphoenol pyruvate or PEP. It combines with carbon dioxide in the presence of PEP carboxylase or PEPcase to form oxalo-acetic acid or oxaloacetate.

Malic acid or aspartic acid is trans-located to bundle sheath cells through plasmodesmata. Inside the bundle sheath cells they are decarboxylated (and deaminated in case of aspartic acid) to form pyruvate and CO2. Since a number of mesophyll cells are feeding bundle sheath cells, the latter come to have a carbon dioxide concentrations several times that of atmosphere.

CO2 released in bundle sheath cells is fixed through Calvin cycle. RuBP of Calvin cycle is called secondary or final acceptor of CO2 in C4 plants.

Pyruvate and PEP formed in bundle sheath cells are sent back to mesophyll cells. Here, pyruvate is changed to phosphoenol pyruvate. Energy is required for this. The same is provided by ATP. The latter is changed into AMP (adenosine monophos­phate).

Conversion of AMP to ATP requires double the energy than energisation of ADP to ATP. Therefore, actual requirement of energy is equal to two molecules of ATP.

This energy is in addition to 3 ATP required for fixation of one molecule of CO2 through Calvin cycle. Therefore, C4 plants consume 5 ATP molecules per molecule of CO2 fixed instead of 3 ATP molecules for C3 plants. For the formation of a glucose molecule, C4 plants require 30 ATP while C3 plants utilize only 18 ATP.

(i) C4 plants have a disadvantage. They consume more energy (2 more ATP molecules per molecule of CO2 fixed). However, sufficient energy is available in the tropics where the plants grow. Further, C4 plants have little photorespiration while in C3 plants, more than half of photosynthetic carbon may be lost in photorespiration. C4 pathway, is therefore, of adaptive advantage,

(ii) C4 plants are more efficient in picking up CO2 even when it is found in low concentration because of the high affinity of PEP.

(iii) Concentric arrangement of mesophyll cells produces a smaller area in relation to volume for better utilization of available water and reduce the intensity of solar radiations,

(iv) They can tolerate excess salts because of the presence of organic acids,

(v) Normal oxygen concentration is not inhibitory for the growth in contrast to C3 plants,

(vi) They are adapted to high temperature and intense radiation of tropics.

Crassulacean Add Metabolism:

It is a mechanism of photosynthesis involving double fixation of CO2 which occurs in succulents belonging to crassulaceae, cacti, euphorbias and some other plants of dry habitats where the stomata remain closed during the daytime and open only at night.

The process of photosynthesis is similar to that of C4 plants but instead of spatial separation of initial PEP case fixation and final Rubisco fixation of CO2, the two steps occur in the same cells but at different times, night and day, e.g., Sedum, Kalanchoe, Opuntia, Pineapple, Agave, Vanilla. The initial fixation of CO2 occurs at night and final fixation occurs during day time. This results in conserving water.

Cardinal Points (Fig. 13.27):

Sachs (1860) found that a factor influencing a physiological process has three principal values called cardinal points— minimum, optimum and maximum.

The minimum of a factor is that value below which the physiological process cannot continue. Maximum of a factor is that value beyond which the process comes to stop. Optimum value of the factor is that point where the physi­ological process can continue indefinitely at its highest velocity.


C4 Plants Pathway And Hatch & Slack Pathway NEET Notes | EduRev

C3 and C4 Pathways

Photosynthesis is the biological process by which all green plants, photosynthetic bacteria and other autotrophs convert light energy into chemical energy. In this process, glucose is synthesised from carbon dioxide and water in the presence of sunlight. Furthermore, oxygen gas is released out into the atmosphere as the by-product of photosynthesis.
The balanced chemical equation for the photosynthesis process is as follows:
6CO2 + 6H2O → C6H12O6 + 6O2
Sunlight is the ultimate source of energy. Plants use this light energy to prepare chemical energy during the process of photosynthesis. The whole process of photosynthesis takes place in two phases - photochemical phase and biosynthetic phase.
The photochemical phase is the initial stage where ATP and NADPH for the biosynthetic phase are prepared. In the biosynthetic phase, the end product – glucose is produced. Let us focus more on pathways in biosynthetic phase.
During the biosynthetic phase, carbon dioxide and water combine to give carbohydrates i.e. sugar molecules. This reaction of carbon dioxide is termed as carbon fixation. Different plants follow different pathways for carbon fixation.
Based on the first product formed during carbon fixation there are two pathways: the C3 pathway and C4 pathway.


Walking the C4 pathway: past, present, and future

The year 2016 marks 50 years since the publication of the seminal paper by Hatch and Slack describing the biochemical pathway we now know as C4 photosynthesis. This review provides insight into the initial discovery of this pathway, the clues which led Hatch and Slack and others to these definitive experiments, some of the intrigue which surrounds the international activities which led up to the discovery, and personal insights into the future of this research field. While the biochemical understanding of the basic pathways came quickly, the role of the bundle sheath intermediate CO2 pool was not understood for a number of years, and the nature of C4 as a biochemical CO2 pump then linked the unique Kranz anatomy of C4 plants to their biochemical specialization. Decades of "grind and find biochemistry" and leaf physiology fleshed out the regulation of the pathway and the differences in physiological response to the environment between C3 and C4 plants. The more recent advent of plant transformation then high-throughput RNA and DNA sequencing and synthetic biology has allowed us both to carry out biochemical experiments and test hypotheses in planta and to better understand the evolution-driven molecular and genetic changes which occurred in the genomes of plants in the transition from C3 to C4 Now we are using this knowledge in attempts to engineer C4 rice and improve the C4 engine itself for enhanced food security and to provide novel biofuel feedstocks. The next 50 years of photosynthesis will no doubt be challenging, stimulating, and a drawcard for the best young minds in plant biology.

Keywords: Bundle sheath C4 decarboxylation C4 photosynthesis Kranz anatomy PEP carboxylase Rubisco..


What is Photorespiration? Explain C2 cycle and C4 cycle (Hatch and Slack pathway)

Photorespiration is a process which involves oxidation of organic compounds in plants by oxygen in the presence of light. Like ordinary respiration, this process also releases carbon from organic compound in the form of carbon dioxide but does not produce ATP. Thus, it seems to be a wasteful process. Photorespiration occurs only in C3 plant during daytime usually when there is high concentration of oxygen. RuBP carboxylase (or RuBisCO), the enzyme that joins carbon dioxide to RuBP now, functions as oxygynase. As a result, oxygen instead of carbon dioxide, gets attached to the binding site of the enzyme and RuBP is oxidised. RuBP releases one molecule of 3 carbon compound phosphoglyceric acid, which enters C3 cycle and one molecule of a 2 carbon compound phosphoglycolate.

Photorespiration was first demonstrated by Dicker and Tio (1959) in tobacco and the term, photorespiration, was given by Krotkov in the year 1963. The process of photorespiration takes place in chloroplast, peroxisome and mitochondria.

The steps involved in photorespiration in C3 plant are as follows:

  1. When carbon dioxide concentration in the atmosphere becomes less and oxygen concentration inside the plant increases ribulose 1-5 diphosphate combines with oxygen to form one molecule each of 3 phosphoglyceric acid and 2 phosphoglycolic acid (2 carbon compound) in the presence of enzyme RuBP oxygenase.
  2. 2 phosphoglycolic acid loses its phosphate group in the presence of enzyme phosphatase and convert it into glycolic acid.
  3. The glycolic acid synthesized in chloroplast is then transported to peroxisome, inside the peroxisome, it reacts with oxysome to form glyoxylic acid and H2O2 in the presence of enzyme, glycolic acid oxidase. H2O2 is converted into water and oxygen in the presence of enzyme, catalase.
  4. Glyoxylic acid is then converted into an amino acid, glycine by transamination reaction with glutamic acid.
  5. Glycine enters into mitochondria where 2 molecules of glycine interacts to form 1 molecule each of serine, carbon dioxide, and ammonia. NH3 is transported to cytoplasm where it is synthesized into glutamic acid.
  6. Serine returns to peroxisome where it is deaminated and reduced to hydroxy pyruvic acid and finally to glyceric acid.
  7. Glyceric acid finally enters into chloroplast where it is phosphorylated to 3 phosphoglyceric acid, which enters into C3 cycle.

C4 PATHWAY (HATCH AND SLACK PATHWAY)

In 1967, M.D. Hatch and C. R. Slack demonstrated an alternate pathway of carbon dioxide fixation, in higher plants found in tropical region. They found that in certain plants, the first product of photosynthesis is a 4 carbon acid, oxaloacetic acid (OAA), instead of 3 carbon compound. This type of carbon dioxide fixation was first demonstrated in some plants of family Poaceae like sorghum, maize, sugarcane (monocots) and in some dicots, Atriplex, Amaranthus, Euphorbia.

The C4 appears to be better equipped to withstand drought and are able to maintain active photosynthesis under condition of water stress. Water stress would lead to stomatal closure in C3 plants and consequent reduction in carbon dioxide uptake, whereas in C4 plants, carbon dioxide concentration is higher resulting in the suppression of photorespiratory carbon dioxide loss.

In C4 plants, initial fixation of carbondioxide occurs in mesophyll cells . The primary acceptor of carbondioxide is phosphoenolpyruvate. It combines with carbondioxide in the presence of phosphoenol pyruvate carboxylase to form oxaloacetic acid. Oxaloacetic acid is reduced to malic acid. Inside the bundle sheath cells malic acid is decarboxylated to form pyruvate and carbondioxide. Carbondioxide is again fixed inside the bundle sheath cells through calvin cycle. RuBP is called secondary or final acceptor of carbondioxide of C4 plants. Therefore, C4 plants have 2 carboxylation reaction.

Another basic feature of C4 plants is the occurrence of Kranz anatomy in the leaves. The chloroplasts present in bundle sheath cells are of abnormal type. They are large in size, centripetally arranged and lack well-organized grana. They contain starch grain. The chloroplast of mesophyll cells are normal. Hence, in C4 plants, chloroplasts are dimorphic in nature.

C4 leaves are also characterized by the presence of tightly packed, thick-walled bundle sheath cells all around the vascular bundle. Because of the wreath-like configuration of these bundle sheath cells, this arrangement is known as Kranz anatomy .Bundle sheath cells are well protected from oxygen being released from mesophyll cells.

The steps involved in Hatch and Slack pathway are as follows:


C4 Pathway : Hatch and Slack Pathway

M.D. Hatch and C. R. Slack in 1967, demonstrated an alternate pathway of carbon dioxide fixation, in higher plants found in tropical region. They termed it as the C4 pathway. They found that in certain plants, the first product of photosynthesis is a 4 carbon acid, i.e., oxaloacetic acid (OAA), instead of 3 carbon compound.

This type of carbon dioxide fixation was first demonstrated in some plants of family poaceae like sorghum, maize, sugarcane (monocots) and in some dicots, for example, Atriplex, Amaranthus, Euphorbia etc. These plants are termed as C4 plants because of the first stable photosynthetic product being a 4 carbon compound.

Characteristics of C4 plants:

Following are the characteristics of C4 plants:

The C4 plants appear to be better equipped to withstand drought and are also able to maintain active photosynthesis under condition of water stress. Water stress would lead to stomatal closure in C3 plants and consequent reduction in carbon dioxide uptake, whereas in C4 plants, carbon dioxide concentration is higher resulting in the suppression of photorespiratory carbon dioxide loss. C4 plants often live in hot, arid and saline habitats. Thus, C4 plants can tolerate halophytic conditions.

Kranz anatomy:

Another basic feature of C4 plants is the occurrence of Kranz anatomy in their leaves. The anatomy of a typical C4 leaf is different from that of C3 leaf. The photosynthetic parenchyma cells in a typical C3 leaf are organized into two distinct tissues-an upper region of tightly packed palisade cells and the more loosely arranged spongy mesophyll cells bordering large intercellular spaces.

C4 leaves are generally thinner than C3 leaves. The vascular bundles of C4 leaves are closer and also have smaller air spaces . Besides, in C4 leaves there are only one type of mesophyll cells which are loosely arranged like those of spongy mesophyll in C3 leaves.

In C4 leaves the chloroplasts present in bundle sheath cells are of abnormal type. They are large in size, centripetally arranged and lack well-organized grana. They also contain starch grain. The chloroplast of mesophyll cells are normal. Hence, in C4 plants, chloroplasts are dimorphic in nature.

C4 leaves are also characterized by the presence of tightly packed, thick-walled bundle sheath cells all around the vascular bundle. Because of the wreath-like configuration of these bundle sheath cells, this arrangement is termed as Kranz anatomy . Bundle sheath cells are well protected from oxygen being released from mesophyll cells.

The bundle sheath cells contain large number of chloroplasts. Thus one can easily recognize C4 plants by their prominent dark green veins.

Fig: Leaf showing Kranz anatomy (C4 pathway)

C4 pathway

In C4 plants, initial fixation of carbondioxide occurs in mesophyll cells . The primary acceptor of carbondioxide is phosphoenolpyruvate. It combines with carbondioxide in the presence of phosphoenol pyruvate carboxylase to form oxaloacetic acid .

Oxaloacetic acid reduces to malic acid. Inside the bundle sheath cells malic acid is decarboxylated to form pyruvate and carbondioxide. Carbondioxide is again fixed inside the bundle sheath cells through calvin cycle. RuBP is termed as secondary or final acceptor of carbondioxide of C4 plants. Therefore, C4 plants have 2 carboxylation reaction.

Following are the steps involved in Hatch and Slack pathway or C4 pathway :

  1. Phosphoenolpyruvic acid accepts carbon dioxide. As a result it forms oxaloacetic acid inside mesophyll cells in the presence of enzyme, phosphoenolpyruvate carboxylase.
  2. Oxaloacetic acid is reduced by NADPH2. Thus it forms malic acid in the presence of enzyme, malate dehydrogenase.
  3. Oxaloacetic acid also produces aspartic acid by a transamination reaction with the help of enzyme, transaminase.
  4. Malic acid is transported to bundle sheath cells, where it is decarboxylated by NADP and specific malic enzyme. As a result pyruvic acid and carbon dioxide is produced. Carbondioxide is again fixed inside the bundle sheath cells through calvin cycle.
  5. Pyruvic acid is sent back to mesophyll cell. There it converts to phosphoenolpyruvate with the help of ATP. This results in the formation of AMP (adenosine monophosphate) instead of ADP (adenosine diphosphate).

Hence, regeneration of ATP from AMP requires 2ATP each or 12 ATP for formation of 6 molecules of phosphoenol pyruvate. Therefore ,C4 pathway requires 12 additional ATP or total 30 ATP(18 ATP in C3 cycle+12 additional ATP).


Walking the C4 pathway: past, present, and future

The year 2016 marks 50 years since the publication of the seminal paper by Hatch and Slack describing the biochemical pathway we now know as C4 photosynthesis. This review provides insight into the initial discovery of this pathway, the clues which led Hatch and Slack and others to these definitive experiments, some of the intrigue which surrounds the international activities which led up to the discovery, and personal insights into the future of this research field. While the biochemical understanding of the basic pathways came quickly, the role of the bundle sheath intermediate CO2 pool was not understood for a number of years, and the nature of C4 as a biochemical CO2 pump then linked the unique Kranz anatomy of C4 plants to their biochemical specialization. Decades of "grind and find biochemistry" and leaf physiology fleshed out the regulation of the pathway and the differences in physiological response to the environment between C3 and C4 plants. The more recent advent of plant transformation then high-throughput RNA and DNA sequencing and synthetic biology has allowed us both to carry out biochemical experiments and test hypotheses in planta and to better understand the evolution-driven molecular and genetic changes which occurred in the genomes of plants in the transition from C3 to C4 Now we are using this knowledge in attempts to engineer C4 rice and improve the C4 engine itself for enhanced food security and to provide novel biofuel feedstocks. The next 50 years of photosynthesis will no doubt be challenging, stimulating, and a drawcard for the best young minds in plant biology.

Keywords: Bundle sheath C4 decarboxylation C4 photosynthesis Kranz anatomy PEP carboxylase Rubisco..


A revolution in genomics and next-generation sequencing

In the past decade, there has been a transformational advance in our capacity to sequence genomes rapidly and cheaply and to carry out sequence-based RNA expression analysis ( Egan et al., 2012). While there has barely been a field of biology left untouched by these new technologies, there has been a major impact on C4 photosynthesis research, both in the study of evolution of C4 plants and in gene discovery. Sequence-based molecular phylogenies have provided new insight into the evolutionary relationships of C3 and C4 plants and provided a number of surprises in terms of the relationships between clades in the grasses ( Grass Phylogeny Working Group II, 2012). Combining these new phylogenies with whole-genome sequencing and RNA expression analysis though RNA-sequencing (RNA-seq, e.g. via the 1KP initiative, www.onekp.com/) has enabled the identification of a suite of genes under selection during the evolution of C4 photosynthesis and related transcription factors which may be responsible for evolution of C4 molecular specialization ( Aubry et al., 2014). This is achieved by comparing sequence information from closely related C3 and C4 species and C3–C4 intermediates. The evolution of C4 photosynthetic traits has recently been reviewed comprehensively ( Brautigam and Gowik, 2016).

A particularly powerful platform for gene discovery, driven in part by the desire to engineer C4 photosynthesis into C3 plants ( von Caemmerer and Furbank, 2012), has been the use of RNA-seq to examine gene expression patterns along a leaf developmental gradient in C4 monocots ( Li et al., 2010). This has now been achieved to compare rice with the C4 plants Setaria, Sorghum, and maize ( Ding et al., 2015), with additional information from C4 dicots such as Gynandropsis and Cleome ( Kulahoglu et al., 2014 Williams et al., 2016). In addition, many data sets are enriched by separation of transcript pools from mesophyll and bundle sheath cells, providing information on the likely importance of a particular transcript in regulating expression of C4 genes and allowing clustering analysis of expression of known C4 transcripts with expression of genes of unknown or dubious function ( Aubry et al., 2014 Williams et al., 2016). Combining these transcriptional data sets with other ‘omics’ measurements on the same tissues and careful microscopy for leaf cellular and subcellular morphology ( Li et al., 2010) provides a powerful research tool for testing hypotheses on regulation of C4 leaf development and searching for new genes important in defining the C4 paradigm. Such data sets have also provided insight into the biochemical complexities of potential crossover between the three C4 decarboxylation types ( Bräutigam et al., 2014) and the plethora of membrane transporters required for metabolites to transverse the plastids of C4 plants (reviewed in Weber and von Caemmerer, 2010).

An example of the utility of such transcriptional approaches in teasing apart the gene regulation required for C4 plants to evolve has been work carried out on the regulatory gene network involved in conferring Kranz anatomy in C4 leaves. For example, of the gross morphological differences between a C3 and C4 monocot leaf, of note is the difference in vein spacing, with the former having 6–9 mesophyll cells between vascular bundles and the latter rarely having more than two. These leaf developmental patterns are determined early in meristematic tissue during leaf development and, until recently, candidate genes determining C4 leaf anatomy have been elusive (see Slewinski, 2013). An opportunity to use RNA-seq to examine this issue is provided by making comparisons of genes expressed in maize husk development, tissues with more C3-like vein spacing, with development of true leaves with C4 vein spacing ( Wang et al., 2013). Comparison of C4 leaf primordial RNA pools with RNA from husk primordia of similar developmental age ( Wang et al., 2013) combined with analysis of maize mutants with disruption of the Scarecrow gene (see Slewinski 2013) have now resulted in at least a partial model of how Kranz anatomy develops. How easily this network can be installed in a C3 plant and whether the bundle sheath cells and chloroplasts of C3 grasses are appropriately equipped to accept C4 biochemistry are currently unanswered questions.

As such large transcriptional and genomic sequence data sets have become available online, in silico mining has become a common practice for the new generation of young researchers interested in testing hypotheses on gene function and designing gene constructs for transgenic engineering. The power of these data sets is massive, and the current limitation to their rapid adoption in C4 photosynthesis research seems to be higher level bioinformatics training required to mine, filter, and interpret such data appropriately.


Photorespiration

Ribulose bisphosphate possess affinity for both carbon-dioxide and oxygen. Though the affinity of RuBisco is high for carbon-dioxide as compared to oxygen, sometimes RuBisco binds oxygen which decreases the carbon-dioxide fixation. Instead of forming 3-phosphoglyceric acid (3-PGA), it forms one molecule of phosphoglycerate and phosphoglycolate. This pathway is known as photorespiration. Three cell organelles are involved in photorespiration- chloroplast, peroxisomes and mitochondria.

Fig.12. Photorespiration

During photorespiration, neither ATP nor sugar are synthesized. It is considered as waste process as it utilizes ATP and releases carbon-dioxide. Photorespiration is feature of C3 plants but not C4 plants. So, productivity and yield in high in case of C4 plants as compared to C3 plants. C4 plants also work efficiently during high temperature.


Clarification on Hatch and slack pathway - Biology

krebs cycle n slck n hatch pthway

Jahirul Mazumder answered this

Krebs&rsquos cycle is also known as citric acid cycle or tricarboxylic acid cycle. It is next step of glycolysis to yield energy. Kreb&rsquos cycle occurs in all aerobic organisms where the acetate derived from carbohydrates, fats and proteins is oxidized to carbon dioxide and yields energy in the form of ATP. The overall reaction of Kreb&rsquos cycle is:
Acetyl CoA + 3NAD + FAD + ADP + HPO42-&rarr 2CO2 + CoA + 3 NADH+ + FADH+ + ATP

Hatch and Slack pathway is a cycle of carbon fixation in plants growing in the regions where temperatures are quite high. When the temperatures are high oxygenase activity of RuBISCO increases and leads to photorespiration which is a futile process. In order to prevent this Hatch and Slack pathway evolved. In Hatch and Slack pathway which is also known as C4 pathway carbon dioxide first adds to phosphoenol pyruvate in a reaction catalyzed by PEP Carboxylase and this reaction produces oxalo acetic acid in mesophyll cells which then later is transported to the bundle sheath cells and carbon dioxide is liberated for later use in Calvin cycle.


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Comments:

  1. Nelabar

    Leave which can I ask?

  2. Kazragar

    I am finite, I apologize, but it all doesn’t come close. Are there other variants?

  3. Mccoy

    strange, I myself came to this, only later, judging by the date of the post. but thanks anyway.



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