Flora 206 (2011) 360–364 Contents lists available at ScienceDirect Flora journal homepage: www.elsevier.de/flora Dianthus caryophyllus stems and Zantedeschia aethiopica petioles/pedicels show anatomical features indicating efficient photosynthesis Charilaos Yiotis, George K. Psaras ∗ Section of Plant Biology, Department of Biology, University of Patras, GR 265 00 Patras, Greece article info Article history: Received 16 March 2010 Accepted 23 July 2010 Keywords: Dianthus caryophyllus Green stems Palisade parenchyma Stem anatomy Stem photosynthesis Zantedeschia aethiopica abstract The fine structure of the green stem of Dianthus caryophyllus, the leaf petiole and the flower pedicel of Zantedeschia aethiopica were studied using light and scanning electron microscopy. It was revealed that these non-foliar plant parts of both species possess epidermis with numerous stomata. Stomatal density of D. caryophyllus stem was found to be relatively high (79 vs 100 per mm 2 found on leaf surface). Z. aethiopica petioles and pedicels also possess numerous stomata (17 per mm 2 ), yet stomatal density was found to be about half of that of leaves. Anatomical differences observed between petioles and pedicels were only minor. Stems of D. caryophyllus as well as petioles and pedicels of Z. aethiopica have a chlorenchyma- type tissue whose fine structure is quite similar to the leaf palisade chlorenchyma. Yet, the palisade of Z. aethiopica petioles and pedicels shows a peculiar arrangement: palisade cells are arranged with their long axis parallel to the longitudinal organ axis. Palisade tissue found in the aforementioned non-foliar plant organs in both species shows strong red chlorophyll auto-fluorescence under epi-fluorescence optics, consists of cells with abundant chloroplasts, possesses high percentage of intercellular spaces (13 and 20%, respectively) and its cells expose considerable part of their surface to the intercellular air. The fine structure of this stem palisade tissue along with the abundance of functional stomata found on the epidermis may support efficient photosynthesis. © 2010 Elsevier GmbH. All rights reserved. Introduction Photosynthesis takes place in all green plant parts, i.e. plant organs with chloroplasts. The prime sites of photosynthesis are leaves, yet photosynthesis in non-foliar plant parts may contribute a substantial amount to the plant’s net carbon gain under partic- ular conditions. For example, in several desert species stems are the primary photosynthetic organs (Gibson, 1983; Nilsen, 1995). Moreover, green parts of flowers (Aschan and Pfanz, 2006; Aschan et al., 2005; He and Teo, 2007; Weiss et al., 1988), fruits (Blanke and Lenz, 1989), or even roots (Benzing et al., 1983; Hew et al., 1984; Kitaya et al., 2002; Moreira et al., 2009) may be photosynthetically active. Among the alternative photosynthetic plant parts, stems contribute significantly to the whole plant carbon budget. Photo- synthesis in plant stems can be distinguished into four types: (i) crassulacean-acid metabolism (CAM) photosynthesis; (ii) corticular or bark photosynthesis, which takes place in the cor- tex of secondary stems; ∗ Corresponding author. Tel.: +30 2610 996765; fax: +30 2610 997411. E-mail address: g.k.psaras@upatras.gr (G.K. Psaras). (iii) wood photosynthesis, which occurs in ray parenchyma and in pith cells; and (iv) photosynthesis similar to that of leaves occurring in stomata bearing stems, simply called stem photosynthesis. CAM photosynthesis takes place in the stems of succulent species. Corticular photosynthesis, wood photosynthesis and pith photosynthesis which take place in secondary thickened stems seem to be of importance not only for the whole carbon balance of the plant but also for alleviating potential hypoxia since perid- erm impedes gas exchange between internal tissues and external atmosphere (Aschan and Pfanz, 2003). Although all four types of photosynthesis are carried out by stem tissues, the term stem photosynthesis is usually applied to the fourth type of photosynthesis. The case of stem photosynthesis differs from corticular and wood photosynthesis in that the CO 2 is taken up through abundant stomata of the stem epidermis and carbon fixation follows the C 3 pathway (Nilsen, 1995). Gibson (1983) analyzing the structure of mature yet lack- ing periderm photosynthetic stems of non-succulent dicotyledons recognized the following four basic anatomical designs on the basis of relative position of chlorenchyma versus supporting tis- sues: (i) cylindrical stems with continuous chlorenchyma, lacking peripheral supporting tissues; (ii) cylindrical or angular stems hav- 0367-2530/$ – see front matter © 2010 Elsevier GmbH. All rights reserved. doi:10.1016/j.flora.2010.07.004