Az Eszterházy Károly Tanárképző Főiskola Tudományos Közleményei. 2004. Sectio Biologiae. (Acta Academiae Paedagogicae Agriensis : Nova series ; Tom. 25)

Mustárdy, L.: Tree-dimensional Organization of Thylakoid System in Granal Chloroplasts and its Functional Role

Acta Acad. Paed. Agriensis, Sectio Biologiae XXV (2004) 99-12

6 Tree-dimensional Organization of Thylakoid System in Granal Chloroplasts and its Functional Role Mustárdy, L. Institute of Plant Biology, Biological Research Center, Hungarian Academy of Sciences, H-6701 Szeged, Hungary Abstract. In the chloroplasts of mesophyll cells of C3 and C

4 plants the thylakoid membranes shows multiple helices of stroma lamellae around the cylindrical grana. Although this spatial relationship has been known for more than two decades, most textbooks and research papers continue to contain erroneous 3D models and simplified schemes. These reviews presents a detailed computer model, based on electron microscopic observations and explain the ontogenetic formation and functional importance of this unique structure. Development of 3-dimenzionaI view The electron microscopic investigations of thin section of chloroplast showed numerous flattened membrane sacs, called thylakoid. Thylakoid membranes are the internal membranes of chloroplasts, which accommodate all light-harvesting and energy-transducing functions. They are embedded in an aqueous matrix, called the stroma, which is surrounded by double envelope membrane (Fig 1). The thylakoids fell into two general size ranges. The smaller sizes around 0.5 |im in diameter are appressed and form grana stacks. The larger sizes, called stroma thylakoids, are continuation of every second or third grana and interconnect the grana stacks. From this view was constructed the first simple model by Menke (1960). Weier et al., constructed a tubular model in 1961, which shows an anastomosing system of membranous channels. This concept was an artifact caused by KMn0

4 instead of glutaraldehyde fixation (Falk and Sitte, 1963). The further detailed studies on the sections revealed, that in some cases the stroma thylakoid is not continued from one granum disc but interconnect