Hatch and Slack pathway

Fig. 5.8. The Hatch and Slack pathway of COj fixation. The alternative routes between the primary carboxylation and the Calvin cycle are shown as dotted arrows. OAA, oxalo-acetate PEP, phosphoenolpyruvate PPi, pyrophosphate.

It has been suggested that the Hatch and Slack pathway is a modification of the Calvin cycle of advantage to plants growing in dense stands of tropical vegetation where the carbon dioxide concentration may be reduced to a very low level. The reduction of atmospheric CO2 concentration which has occurred since the evolution of photosynthetic reactions may also have contributed to the selection of this reaction sequence. The discovery of the Hatch and Slack pathway, although it is not yet fully authenticated, has demonstrated the possible existence of photosynthetic reactions other than the conventional Calvin cycle and suggests that other and as yet undiscovered variations on the photosynthetic theme may exist. 

Answer In maize, C02 is fixed by the C4 pathway elucidated by Hatch and Slack. Phospho-enolpyruvate is rapidly carboxylated to oxaloacetate, some of which undergoes transamination to aspartate but most of which is reduced to malate in the mesophyll cells. Only after subsequent decarboxylation of labeled malate does 14C02 enter the Calvin cycle for conversion to glucose. The rate of entry into the cycle is limited by the rate of the rubisco-catalyzed reaction. 

Some pathways lead to glory, like Hatch and Slack and Knoop Utter, Calvin, Cori—a most distinguished group. 

The interpretation of CAM in this sense was stimulated by the discovery of another variant of photosynthesis, the C4-pathway (see Black, 1973 Hatch and Slack, 1970 Hatch, 1976). Because this newly discovered photosynthetic pathway is recognized to be very closely related to the CAM pathway, the work on the latter became intensified during these last years. The increased effort in research on CAM provided a large amount of new data which can now be collected and critically evaluated. We have undertaken this as one of the goals of the present monograph. 

Some plants, such as corn and sugar cane, have evolved an auxiliary C4-dicarboxylic acid cycle< > that cooperates with the reductive pentose cycle in the photosynthetic assimilation of CO2. In plants with this cycle (sometimes referred to as the Hatch and Slack cycle), chloroplasts in the mesophyll cells near the surface on the leaf contain three C4-pathway specific enzymes pyruvate, phosphate-dikinase that directly converts pyruvate into phosphoenolpyruvate (PEP) with ATP, PEP carboxylase that catalyzes the carboxyla-tion of PEP to oxaloacetate, and malate dehydrogenase that finally reduces oxaloacetate to malate with NADPH. The purpose of these steps is apparently to incorporate CO2 and NADPH into malate in order to translocate them to the vascular bundle sheath cells, where they are again released by the action of a NADP-dependent malic enzyme. The malic enzyme is located in the bundle sheath chloroplasts together with the en mes of the Calvin cycle. CO2 is then reduced to carbohydrates while pyruvate is presumably transported back to the mesophyll cells. Besides the malate-type C4-plants, there is a second and larger group of species (aspartate type) that contains little malic enzyme and utilizes aspartate as the COj carrier. 

Until recently it was assumed that the Calvin cycle was the only universally feasible pathway of CO2 fixation, even though the data for maize and sugar cane were not in complete agreement with this view. In 1966, Hatch and Slack demonstrated that, in fact, there is another pathway of CO2 fixation in higher plants. It was first demonstrated in gra-mineae, and then later in other monocotyledons and in dicotyledons too. 

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). 

Hart A, Murrel JC, Poole RK, Norris PR (1991) An acid-stable cytochrome in iron-oxidizing Leptospirillum ferrooxidans. FEMS Microbiol Lett 81 89-94 Hatch MD, Slack CR, Johnson HS (1967) Further studies on a new pathway of photosynthetic carbon dioxide fixation in sugar-cane and its occurrence in other plant species. Biochem J 102 417-422... 

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). 

Hatch, M. D. 8 Slack, C. R. (1966). Photosynthesis by sugarcane leaves. A new carboxylation reaction and the pathway of sugar formation. Biochemical Journal 101, 103-111. 

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. 

Stable isotope ratio analysis (SIRA, GC-IRMS [Gas Chromatography-Isotope Ratio Mass Spectrometry], and Site Specific Isotope Fractionation — Nuclear Magnetic Resonance [SNIF-NMR]) have proven useful in many adulteration situations. In nature, and exist at relative proportions of 1.11 98.89 [27]. The photosynthetic process selectively enriches the plant in dependent upon the type of photosynthetic process used by the plant. Plants using the Hatch-Slack pathway (e.g., com, sugar cane, millet, and lemon grass) give 8 C values the closest to the standard, i.e., 5 C values of ca. -10. The 5 C value is calculated as ... 

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 ... 

C4 (or Hatch-Slack) photosynthetic pathway, such as maize, differ from C3 plants typically by 10%o in their bulk value, and so it is comparatively easy to detect this difference between maize eaters and nonmaize eaters from the analysis of the surviving bone, enabling the history of the adoption of maize in the diet in North America to be followed (Figure 35.7). 

Slack CR and Hatch MD (1967) Comparative studies on the activity of carboxylases and other enzymes in relation to the new pathway of photosynthetic carbon dioxide fixation in tropical grasses. Biochem J 103 660-665... 

Typically, grasses originally native to hot, arid environments follow the C4 (Hatch-Slack) photosynthetic pathway, and will have 6 C values averaging about -12%o trees, shrubs, and grasses from temperate regions, which follow the C3 (Calvin-Benson) photosynthetic pathway, will have 6 C values averaging about -26%o. Metabolic fractionation in their consumers results in bone collagen values of about -7%o and -21%o and bone apatite values of about 0%o and -14%o, respectively, for pure C4 and pure C3 diets. 

Hatch,M.D., Osmond,C.B. Compartmentation and transport in C4 photosynthesis. In Transport in plants III. Enzyclopedia of plant physiology. New series, Vol. 3. Stocking, C.R., Heber,U. (eds.), pp. 144-184. Berlin, Heidelberg, New York Springer 1976 Hatch, M.D., Slack, C.R. Studies on the mechanism of activation and inactivation of pyruvate, phosphate dikinase. A possible regulatory role for the enzyme in the C4 dicarboxylic acid pathway of photosynthesis. Biochem. J. 112,549-558 (1969)... 

Slack, C.R., Hatch, M.D., Goodchild,D.J. Distribution of enzymes in mesophyll and parenchyma-sheath chloroplasts of maize leaves in relation to the C -dicarboxylic acid pathway of photosynthesis. Biochem. 3.114,489-498 (1969)... 

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