Hatch slack

FIGURE 22.30 Essential features of the coinpartinenCation and biochemistry of die Hatch-Slack padiway of carbon dioxide uptake in C4 plants. Carbon dioxide is fixed into organic linkage by PEP carboxylase of meso-phyll cells, forming OAA. Eidier malate (die reduced form of OAA) or aspartate (the ami-iiated form) serves as die carrier transpordiig CO9 to the bundle slieadi cells. Within die bundle slieadi cells, CO9 is liberated by decar-boxyladon of malate or aspartate die C-3 product is returned to die mesophyll cell. 

The Hatch-Slack C4 pathway, alluded to briefly in the song, miglit be dealt with separately in ihe next edition, if there is a demand for it). 

Most plants reduce CO2 to carbohydrate according to the well-known Calvin-Benson or C3 pathway, where the initial product of photosynthesis is the 3C compound phosphoglycerate. Fixation of CO 2 to phosphoglycerate occurs with the assistance of the enzyme ribulose bisphosphate (RuBP) carboxylase, which discriminates heavily against C02 (11). Consequently, plants with C3 photosynthesis have 6 values that average -27.0 (12). Plants with the Hatch-Slack or Ci,... 

The primary focus of isotopic studies on human bone has revolved around the distinction between consumption of C3 plant material and plant material Some years ago, it was discovered that the C3 (or Calvin) and the (or Hatch-Slack) photosynthetic pathways generated plant tissue with quite different abundances, an approximately 15 parts per thousand (0/00) difference in the isotopic ratio ( ) This isotopic difference between two types of plants is the main basis for most studies of human diets that have used stable isotopes of carbon as an analytical tool Most plants in temperate areas are of the C3 type, but corn (maize) is a plant and is of special interest to archaeologists because of the apparent dependence of many cultures on maize agriculture ... 

Some plants employ a photosynthetic pathway creating at first a three-carbon phosphoglyceric acid (C3 or Calvin-Benson photosynthesis). These plants fractionate isotopes more intensely, and so have more negative values (-33%o to —22%o PDB) than plants which use a photosynthetic pathway creating at first a four-carbon malic and aspartic acid (C4 or Hatch-Slack photosynthesis -16%o to -9%o PDB). Crassulacean acid metabolism (CAM) is yet another photosynthetic pathway, which creates organic matter of intermediate isotopic composition (-35%o to -ll%o PDB). Methanogenic microbes are even more extreme in their fractionation of the light isotope (5 C down to -110%o and typically -60%o PDB ... 

Hatch-Slack or four-carbon pathway catalyzed by phosphoenolpyruvate carboxylase. 

The lithoautotrophs have to form cellular materials from carbon dioxide. The process to change carbon dioxide into organic compounds is called fixation of carbon dioxide. On the basis of the knowledge to date, all algae and cyanobacteria, and many of the plants, fix carbon dioxide through the Calvin-Benson cycle (or reductive pentose phosphate cycle) (Bassham et al., 1954), while the plants of 20 families and 1200 species have been known to fix carbon dioxide through the Hatch-Slack pathway (or C4 dicarboxylate pathway) (Hatch et al., 1967). 

As a result, oxaloacetate (OAA, C4-compound) is formed unlike the case of the Calvin-Benson cycle in which 3-phosphoglycerate (C3-compound) is formed. The pathway in the fixation of carbon dioxide by the catalysis of PEP-carboxylase is observed in sugar cane, corn, etc., and is called the Hatch-Slack pathway (Hatch et al., 1967). The plants having the Hatch-Slack pathway have chloroplasts both in mesophyll cells and in vascular bundle sheath cells, and the Hatch-Slack pathway occurs in the mesophyll cells. Oxaloacetate formed by the fixation of carbon dioxide in the mesophyll cells is reduced to malate. Malate thus formed moves to the vascular bundle sheath cells and releases carbon dioxide there. Carbon dioxide released is fixed by the catalysis of Rubisco, and the organic compounds are formed through the Calvin-Benson cycle. (Fig. 6.3). 

The plants producing organic compounds from carbon dioxide through the Calvin-Benson cycle are called C3-plants, while the plants producing organic compounds from carbon dioxide through the Hatch-Slack pathway are called C4-plants. 

C4 plants are found primarily in the tropics. Such plants include sugar cane and maize (com). They have been assigned the name C4 plants because a four-carbon molecule (oxaloacetate) plays a prominent role in a biochemical pathway that avoids photorespiration. This pathway is called the C4 pathway or the Hatch-Slack pathway (after its discoverers). 

Plant leaves e.g. spinach cycle or Hatch-Slack pathway) ... 

In tropical plants, there is a G4 pathway (Figure 22.18), so named because it involves four-carbon compounds. The operation of this pathway (also called the Hatch-Slack pathway) ultimately leads to the Gg (based on 3-phosphoglycerate) pathway of the Galvin cycle. (There are other G pathways, but this one is most... 

C4 plants Plants that employ the Hatch-Slack pathway during photosynthesis. C4 plants are named such because they employ an intermediate compound, oxaloacetic acid that contains four carbon atoms. These plants moderately discriminate (8 to 14% ) against C during carbon incorporation. C4 plants are usually higher land plants that are specially adapted to dry and low-/JCO2 conditions. 

The most significant is the photos5mthetic mechanism. There are two classes of the photosynthetic cycle, the Calvin-Benson photosynthetic cycle and the Hatch-Slack photos5mthetic cycle. 

On the other hand, the Hatch-Slack photosynthetic cycle is important for tropical grasses, com and sugarcane. Phosphenol-pyr-uvate carboxylase is responsible for the primary carboxylation reaction. The first stable carbon compound is a C-4 acid, which is subsequently decarboxylated (101,102). The fundamentals and sys-tematics of the non-statistical distributions of isotopes in natural compounds have been reviewed (103). 

C4-acid cycla see Hatch-Slack-Kortschack cycle. 

Calvin cycle (see), and a lesser amount by the Hatch-Slack-Kortschack cycle (see). C. can also be driven by chemical energy in autotrophic or che-moautotrophic organisms, in particular bacteria. Some of these use a process similar to the Calvin cycle. The methanogenic bacterium, Methanobacterium thermoautotrophicum, however, fbtes CO2 by a series of S major reactions which do not include the Calvin cycle (Fig.). There is also anaplerotic CO2 fixation (see Carboxylation, Biotin enzymes). 

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