بومشناسی جنگلهای ایران (May 2024)
Investigation of the Leaf and Pollen Micromorphology of Maples (Acer L.) of Iran
Abstract
Extended Abstract Background: The genus Acer L. (maples) from the Aceraceae are mostly deciduous trees, almost all of which are distributed in the temperate regions of the Northern Hemisphere. This genus contains 148-150 species around the world, and the presence of 8-10 native species of this genus has been mentioned in different floras of Iran. Some species of maples in Hyrcanian forests have great commercial value, and the height of these trees reaches 40-45 m. Maples are the major vegetation elements in most forest ecosystems of Iran. Hyrcanian forests in the north of Iran contain the highest diversity of this genus. Despite the molecular and morphological studies on the taxa of the genus in the world, no comprehensive studies have been conducted on its micro-morphological characteristics. Therefore, the present research describes the taxonomic value of the anatomical features of the leaf epidermis and pollen morphology of the members of this genus in Iran. Methods: Eleven maple taxa available in Iran (nine native and two introduced taxa), mainly from Hyrcanian and Zagros ecosystems, were collected and analyzed in the current study. The investigated taxa were A. hyrcanum, A. velutinum, A. platanoides, A. mazandaranicum, A. campesstre, A. cappadocicum, A. negundo, A. palmatum, A. monspessulanum subsp. cinerascens, A. monspessulanum subsp. turcomanicum, and A. monspessulanum subsp. ibericum. The leaf samples of each individual were prepared from the branches grown in the sun and dried with the herbarium sample method to prevent mold. Dried leaf samples were placed in boiling water for 3 min to prepare dissections. Then, thin slices were prepared from the dorsal and ventral epidermis from the middle of the leaf and in the vicinity of the midrib using a surgical blade. To remove the color of chlorophyll and make the samples transparent, they were placed in a sodium hypochlorite solution for 5 min. After washing with distilled water, they were photographed and studied under a light microscope. For electron microscopy, the dorsal and ventral epidermises and the pollen samples of the taxa were stabled on aluminum stubs. Then, a very thin gold layer was sprinkled on the surface of all pollen and leaf samples using a gold sputter coater and then photographed using a Philips Scanning Electron Microscope. The voltage intensity was 20 kV, and the image magnification was set to 2500-5100 x. Epicuticular waxes, trichomes, epidermal cell wall shape, stomatal type, pollen type, pollen morphological characteristics, and the stomatal density and index were classified and studied from the prepared microphotographs. Results: The morphology of epicuticular wax was absolutely unique in such taxa as A. velotinum, A. mazandaranicum, A. hyrcanum, A. platanoides, and even some subspecies of A. monspessulanum. The most structured type of epicuticular waxes was observed in A. velotinum, showing circular rosette-like structures formed around some stomata, which could not be seen in the other taxa. The dorsal leaf surface in A. platanoides was also uniquely covered with a completely smooth and uniform layer of wax. Certain wax structures were observed on the surfaces of A. monspessulanum subsp. cinerasens and A. mazandaranicum, making the surface of the epidermal cells appear prominent in the former and indented in the latter taxa. The highest stomatal index and the number of stomata per unit area belonged to two non-native species, namely A. palmatum and A. negundo, and these parameters were lowermost in A. mazandaranicum, A. monspessulanum subsp. turcomanicum, A. velutinum var. velutinum, and A. monspessulanum subsp. cinerascens. Many of the stomata are covered and buried under the thick layers of the epicuticular wax, and there are trichomes and wax crystalloids around other stomata to reduce the rate of evaporation and transpiration. Therefore, it can be acknowledged that the mentioned native taxa have higher drought resistance than others. The epidermal cell wall pattern of the taxa was classified into three different types, the most distinctive of which was seen in A. platanoides, having a completely wavy and puzzle-like wall. Relatively wavy wall was seen only in the epidermis cells of A. negundo. The other taxa showed smooth and straight cell walls. The arrange of subsidiary cells of the stomata was anomocytic in all taxa while the paracytic type was completely distinctive and dominant in A. mazandaranicum. Trichomes in all the owning taxa were simple and branchless, divided into two short- and long-size groups. None of the morphological characteristics of the pollen, such as pollen shape (isopolar prolate to spheroidal), exine ornamentation (striate), the form of pollen colpi, and even the number of pollen pores (Tricolporate), revealed a specific differentiation exclusive to a certain taxon. Conclusion: The results of the current research reveal that the micro-morphological traits of leaves can help remove the taxonomical obstacles of the genus Acer while the pollen type and morphology do not provide such a capability for the genus. In general, the differentiation of epidermal characteristics among the studied maple taxa shows that the leaf dorsal has useful micromorphological characteristics, especially in terms of epicuticular waxes, which can play an important role in classifying, describing, and determining the boundaries of the taxa to be used as a useful tool in plant biosystematics.
