Effects of Mn on anatomy, growth and carbohydrate content of adventitious roots in Citrus maxima (Burm.) Merr. shoot explants IOANNIS E. PAPADAKIS1*, KORTESSA N. DIMASSI1, IOANNIS N. THERIOS1, ARTEMIOS M. BOSABALIDIS2 and THOMAS E. SOTIROPOULOS3 1 Laboratory of Pomology, School of Agriculture, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece 2 Department of Botany, School of Biology, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece 3 Pomology Institute, N.AG.RE.F., P.O. Box 122, 592 00 Naoussa, Greece Abstract Microshoots of Citrus maxima (Burm.) Merr. were cultured in vitro for 75 days in a modified MS rooting medium containing 1.5 mg l–1 NAA (naphthaleneacetic acid) and 0, 1.37, 2.74, 5.48 or 10.96 mg l–1 Mn. Small pieces from two regions, i.e. 5-10 mm and 30-35 mm behind the apex, of adventitious roots were examined by light microscopy. Various root growth parameters and the carbohydrate contents of shoots and roots were also measured. The diameters of root cortex and stele progressively decreased as Mn concentration in the medium increased. Shoot explants grown without Mn (0 mg l–1 Mn) formed shorter and thicker roots when compared to those treated with Mn (1.37-10.96 mg l–1). The diameter of roots in the 10.96 mg l–1 Mn treatment was smaller compared to the other Mn treatments, although the mean length of roots did not differ among the 1.37, 2.74, and 10.96 mg l–1 Mn treatments considerably. The greatest root length was observed in 5.48 mg l–1 Mn. However, the total length of roots formed per microshoot in 0 and 10.96 mg l–1 Mn was significantly smaller than that in 1.37-5.48 mg l–1 Mn. The carbohydrate content (μmol) of the roots was higher in 1.37-5.48 mg l–1 Mn than in 0 and 10.96 mg l–1 Mn.   < back .