Spatial organization of mesophyll in leaves of some coniferous (Pinaceae)

Leaves of the coniferous have a variety of shapes of assimilating cells, but it is practically unknown what characteristics of their arrangement in the space of a leaf are, as our ideas of the structure of mesophyll of needles are mainly based on cross-section cuts. The problem of the present work was to give comparative anatomic characteristics of the spatial organisation of mesophyll of needles of Picea obovata, Pinus sylvestris and Larix sibirica, characterised by originality of cellular forms. The structure of mesophyll of coniferous leaves was studied on the example of two-year-old needles of Picea obovata Ledeb. and Pinus sylvestris L., Larix sibirica Ledeb. leaves of the current year shoots were analysed. The anatomic structure of mesophyll was investigated in the middle part of needles at transverse, longitudinal and radial cuts of leaves fixed in mixture Gammalunda. The configuration of cells was also examined in macerated squash preparation (Possingham, Saurer, 1969). The form of projections among mesophyll cells distinguished simple and complex cells, the latter, in their turn, were subdivided into cellular and lobar ones (Berezina, Korchagin, 1987; Ivanova, Pyankov, 2002; Zvereva, 2007, 2009). In mesophyll of Picea obovata needles, there are almost no cells of the complex form; simple cells on radial cuts have projections of the adjoining cylinders stretched from endoderm to epidermis. At cross-section cuts of Pinus sylvestris needles, the so-called folded cells of mesophyll are well exposed, they also have a rectangular shape at radial cuts, a narrower one, which incorporating with each other extend from endoderm to epidermis. According to the terminology we offer, it is possible to say that mesophyll of needles of Pinus sylvestris and Picea obovata consists of practically one type of cells - median, with Pinus sylvestris having the complex form of cells and Picea obovata having the simple one. The structural basis of Larix sibirica mesophyll is formed by three groups of assimilating cells of the complex form, which are located in mutually perpendicular directions of their largest surfaces. Median cells of various shapes - from spongy up to laciniate lobar and laciniate ones at cross-section cuts - represent the first group; they have an extended rod-like shape at radial sections. Cellular cells represent two other groups; by their sections they are located along the leaf, perpendicular to each other. Two structural groups of mesophyll are allocated in the investigated species of coniferous: median and mixed. The structure of mesophyll of Pinus sylvestris and Picea obovata needles refers to the first group, the structure of Larix sibirica to the second one.

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