Abstract
Climatic changes observed around the world in recent years are associated with an increase in the solar radiation intensity and temperature and reduction in the humidity. Fluctuations of environmental factors significantly change the conditions for the existence of plants, which dictates the need for adaptive reactions of plant organisms at the different levels of their organization. Such dangerous processes as excessive heating of the surface of plant leaves and water loss can be prevented by the formation of a cuticle, which is a complex composition consisting of cutin and the soluble intracuticular and epicuticular waxes. We suggested that the structure, component composition and properties of the cuticle of trees undergo adaptive changes due to microclimatic conditions in different parts of the tree crown. The study was aimed at the identification and evaluation of light-induced differences in the accumulation and composition of leaf epicuticular waxes of Ulmus trees (native U. minor Mill. and alien U. pumila L.), and was conducted in 2018–2019 in Dnipro city located in the steppe zone of Ukraine. Analysis of the waxes’ chloroform extracts was carried out using GC Shimadzu 2010 PLUS equipped with a flame ionization detector and capillary column SP-2560. The highest amount of epicuticular waxes (12.23 ± 0.39 µg/cm2) was on the sunlit leaves of U. pumila, and wax deposits on the sunned leaves exceeded twice those on the shaded leaves in both U. minor and U. pumila. Long-chain hydrocarbons detected in the epicuticular waxes of both elm species were represented by free fatty acids, aldehydes, alcohols, and n-alkanes in various ratios. In the epicuticular waxes of U. minor, fatty acids dominated both on shaded and sunned leaves, while alkanes together with alcohols were the main components in U. pumila waxes, especially on the sunlit leaves. According to our results, local high illumination of leaves in the crown of both elm species caused increase in share of long-chain alkanes (1.2–1.9 times), but simultaneous reduction of the content of free fatty acids (1.5–16.8 times) in the epicuticular waxes’ composition. General patterns of the leaf epicuticular waxes’ modification due to increased solar radiation and air temperature can indicate the adaptive metabolic responses of woody plants to changing climatic conditions.
Highlights
Climate is the key environmental factor which determines the ontogeny of plants and their geographical distribution (Ramirez-Valiente et al, 2015), so any variations in climate entail changes in plant growth and productivity
Accumulation of the epicuticular wax deposits on the surface of sun-adapted leaves significantly exceeded the indices for shaded leaves in both Ulmus species (1.6 and 2.6 times, respectively for U. pumila and U. minor, P < 0.05)
Analysis of the study results suggests that an increase in the proportion of aliphatic components with a longer chain in the epicuticular waxes of sun-adapted leaves can be considered as a general pattern for both U. minor (Fig. 2) and U. pumila (Fig. 3)
Summary
Climate is the key environmental factor which determines the ontogeny of plants and their geographical distribution (Ramirez-Valiente et al, 2015), so any variations in climate entail changes in plant growth and productivity. Due to their attached lifestyle, are permanently exposed to abiotic and biotic environmental factors that reflect on their state (Nazarenko & Lykholat, 2018; Nazarenko et al, 2018). Climatic changes observed in all the regions of the world are associated with an increase in the solar radiation intensity and temperature and simultaneous reduction in humidity (Bussotti et al, 2015; Lykholat et al, 2018b). Due to such circumstances, heating of the leaf surface and increasing water loss become inevitable dangerous effects, which are countered by the cuticle. The cuticle plays a role in minimizing the adhesion of dust, protecting tissues from UV radiation, microbes and insects (Müller & Riererer, 2005), powdery mildew fungus (Hansjakob et al, 2010), osmotic stress and pollution (Shepherd & Griffiths, 2006), and preventing deleterious fusions between different plant organs (Tanaka & Machida, 2013)
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