Microrelief of the leaf epidermis and stomatal polymorphism of Malus orientalis, Pyrus caucasica and Mespilus germanica in mountains and plains

Abstract

The parameters of the stomatal apparatus were widely used for environmental monitoring. Thus, samples of stomata may include the size groups differing both in the time of formation and in the number of cuticular folds. Stomatal polymorphism was found in many dicotyledonous species, in particular, in subtribe Pyrinae (Rosaceae). Sample variability complicates the interpretation of the impact of environmental conditions. This work aimed to study the polymorphism of stomata and altitudinal effects in the model Pyrinae species. Scanning electron microscopy was used to study microrelief of leaf epidermis of Malus orientalis Uglitzk., Pyrus caucasica Fed. and Mespilus germanica L. growing in the mountains and on the plain (370–1750 m above sea level). Large single primary stomata and numerous small secondary stomata were observed. The stomata were surrounded by 2-5 bands of radial cuticular folds. Usually, the stomatal length linearly increased with an increase in the number of folds. The calculation of the mean length of stomata accounting for the stomatal polymorphism did not affect the conclusions, however, was more sensitive for assessing the altitude effect on stomata. The length of secondary stomata correlated inversely with their density. The sizes of epidermal cells on the abaxial and adaxial sides did not depend on the altitude. Pyrus caucasica and Mespilus germanica at an altitude of 600 and 800 m, respectively, had larger stomata comparing plants at higher altitudes. Altitudinal effects on stomatal length in Malus orientalis were less pronounced but had the same direction. In Mespilus germanica, the stomata in the steppe zone were also smaller. The decrease in stomata size is probably due to the sensitivity of plants to nonspecific stress, regardless of the altitude.