ORIGINAL PAPER Leaf anatomy and chloroplast ultrastructure of Mn-deficient orange plants Ioannis E. Papadakis Æ Artemios M. Bosabalidis Æ Thomas E. Sotiropoulos Æ Ioannis N. Therios Received: 27 May 2006 / Revised: 19 December 2006 / Accepted: 20 December 2006 / Published online: 22 February 2007 Ó Franciszek Go ´ rski Institute of Plant Physiology, Polish Academy of Sciences, Krako ´ w 2007 Abstract Leaf samples of Mn-deficient and Mn-suf- ficient (control) ‘Navelate’ orange plants grown in a greenhouse were taken to investigate the effects of Mn deficiency in leaf structure and chloroplast ultrastruc- ture. Total leaf chlorophyll concentration was signifi- cantly lower in Mn-deficient plants than in control ones. Entire lamina thickness was not altered due to Mn deficiency. However, Mn deficiency resulted in disorganization of mesophyll cells, mainly of palisade parenchyma cells. The number of mesophyll chlorop- lasts per cellular area and their length were both affected negatively. The membranous system of chlo- roplasts was also disorganized. The percentages of starch grains and plastoglobuli per chloroplast of Mn- deficient leaves were significantly greater than those of control leaves. Keywords Chloroplast ultrastructure Á Citrus Á Deficiency Á Leaf anatomy Á Plant nutrition Introduction Manganese (Mn) is an essential micronutrient for plant growth, since it affects numerous physiological and biochemical processes. Mn acts as a cofactor, activating at least 35 enzymes. Most of these enzymes catalyze oxidation–reduction, decarboxylation, and hydrolytic reactions affecting the metabolism of proteins, carbo- hydrates, and lipids. Furthermore, two Mn-containing enzymes have been well established up to date, namely the 33 kDa polypeptide of the water-splitting system associated with photosystem II (PSII) and the Mn- containing superoxide dismutase (MnSOD) (Burnell 1988; Marschner 1995). Mn deficiency is a nutritional disorder affecting growth of many plant species in soils with low Mn availability. Most of the studies on this disorder have been limited to evaluations of growth, yield, visual symptoms, and photosynthetic rates. However, little information exists on cytological and ultrastructural effects of Mn deficiency (Possingham et al. 1964; Simpson and Robinson 1984; Henriques 2003), in spite of their importance in physiological and developmental aspects of plant function. The aim of this study was to investigate the effects of Mn deficiency on leaf anatomy and mesophyll cell chloroplast ultrastructure of orange plants, which are very sensitive to Mn deficiency. Materials and methods Plant material and mineral analysis Ten 3.5-year-old ‘Navelate’ orange plants (Citrus sinensis L.) grafted on the C. volkameriana (L.) Communicated by Z. Krupa. I. E. Papadakis (&) Á I. N. Therios Laboratory of Pomology, School of Agriculture, Aristotle University, 541 24 Thessaloniki, Greece e-mail: jpapad2004@yahoo.gr A. M. Bosabalidis Department of Botany, School of Biology, Aristotle University, 541 24 Thessaloniki, Greece T. E. Sotiropoulos Pomology Institute, N.AG.RE.F, P.O. Box 122, 592 00 Naoussa, Greece 123 Acta Physiol Plant (2007) 29:297–301 DOI 10.1007/s11738-007-0038-1