Kranz anatomy

Voznesenskaya, E.V., Fraceschi, V.R., Kiirats, O., Artyusheva, E.G., Freitag, H., Edwards, G.E. (2002) Proof of C4 photosynthesis without Kranz anatomy in Bienertia cyclaptera (Chenopodiaceae). Plant J. 31, 649-662. 

Unlike the RPP cycle in which carboxylation and carbon reduction are restricted to the chloroplast, the C4 pathway involves the interaction of two cell types and several different compartments within these cells. C4 plants are characterized by a radial leaf anatomy (Kranz anatomy) in which one cell type, the mesophyll cells, surrounds the other type, bundle sheath cells. This arrangement of the cell types and the division of labor between them is central to the functioning of the C4 pathway. Carbon dioxide is first captured in the outer tissues (mesophyll) and then transported to the inner tissues (bundle sheath) where CO2 and reducing... 

As discussed above, the spatial separation of these processes in C4 plants necessitates a degreee of structural organization in the form of Kranz anatomy. CAM plants do not show such anatomy but have other specializations because the temporal separation of the synthesis and decarboxylation of C4 acids requires storage of large amounts of C4 acids in the vacuole. 

All C4 plants show Kranz anatomy. The bulk of the photosynthetic tissue is concentrated in two layers around the vascular bundles the irmer bundle-sheath layer and the outer mesophyll layer. C4 leaf veins show up as a darker green than the rest of the leaf you can usually spot this just by holding a leaf upto the light. 

CAM plants use the same chemistry but package it differently. Specifically, they lack the Kranz anatomy that is the defining characteristic of the C4 plants. Kranz is the German word for wreath and refers to the appearance—in a cross-sectioned leaf—of the cells which sheath the vascular bundles in C4 plants. CAM stands for Crassulacean Acid Metabolism. There is no such thing as crassulacean acid. The name instead refers to the initial discovery of this pathway of carbon fixation, in which oxaloacetic, malic, and pyruvic acids play key roles, in plants from the family Crassulaceae. cam plants open their stomata, take in CO2, and produce malate at night. Temperatures and, consequently, water losses are lower. During the day, the stomata are closed and the malate is processed as in the bundle-sheath cells of C4 plants. Diffusive losses of CO2 are, however, greater than those in C4 plants. 

Very recently, it has been demonstrated that some unicellular algae utilize the C4 pathway of carbon fixation (Reinfelder 2000). Accordingly, it is necessary to distinguish clearly between C4 plants, which have the Kranz anatomy, and the Qpathway, which is apparently quite widely distributed. 

There has been considerable speculation regarding connection between "Kranz" anatomy and the physiology of C type carbon assimila-tion(l),Plant tissue culture offers an opportunity to study the mechanism of photosynthesis at cellular level. Development of photosynthetic apparatus has been studied in several dicot callus cultures(2). However it has been relatively difficult to induce greening in callus cultures derived from monocot C. plants (3). The present investigations were undertaken with an object to study the chloroplast development in the callus cultures, derived from a monocot C. plant maize, in relation to "Kranz" anatomy and chloroplast dimorphism. 

Most callus cultures excised from higher plants turn green under proper physico-chemical, nutritional and hormonal regimes. Some of these cultures are reported to have mixotrophic and autotrophic mode of nutrition(l-3). Photoautotrophic cell cultures provide a system for studying the physiological and biochemical aspects of photosynthesis at cellular level. There has been considerable speculation about the connection between "Kranz" anatomy and physiology of C. plants. 

There are increasing number of reports which suggest that less of a dependence exists on "Kranz anatomy than has long been believed (4). Present investigations were undertaken with the objective to study the enzyme patterns during different stages of leaf development and callus cultures, by characterising the PEPC and RuBISCO. 

C- plants (9). One of the features of C. plants, is the presence of "Kranz" anatomy. There is compartmentalization of enzymes in "Kranz" anatomy viz PEPC in the cytosol of mesophyll cells and RuBISCO in the chloroplasts of the bundle sheath cells(ll). Accordingly in the present study, predominent activity of PEPC in the partially green maize callus cultures and lowest portion of young leaf lacking well developed chloroplasts can be explained. 

C4 plants green plants in which the primary product of CO2 fixation is not 3-phosphoglycerate (cf. C3 plants) but a C4 acid such as oxaloacetate, malate or aspartate. These plants possess two types of photi>-synthesizing cells. In mesophyll cells near the leaf surface, CO2 is fixed into C4-compounds. This prefixation of CO2 is due to the action of the cytosolic enzyme, phosphoeno/pyruvate carboxylase (EC 4.1.1.31), which carboxylates phosphoenolpyruvate to oxaloacetic acid (see Hatch-Slack-Kortschak cycle). The Calvin cycle (see) operates in the the vascular bundle cells of C4 plants, and CO2 for the Calvin cycle is derived from the decarboxylation C4 compounds rather than directly from the atmosphere. This Kranz anatomy , i.e. photosynthetically active bundle sheath cells with a photosynthetically active layer... 

These two forms possessed anatomical structures of culms clearly differing from each other. The terrestrial forms had an unusual Kranz type of anatomy which is characterized by the presence of colourless mestome sheath cells intervening between the mesophyll cells and the Kranz cells (1,2,3). The chloroplasts with well-developed grana and many large mitochondria were scattered in the Kranz cells, although the terrestrial forms had biochemical features of the NAD-malic enzyme C4 subtype (2,3). The submersed forms possessed large spherical mesophyll cells and reduced vascular bundles, which are characteristic of submersed aquatic plants (2,4). Kranz cells contained relatively smaller chloroplasts than the Kranz cells of the terrestrial forms. 

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