Ultrastructural leaf features of grapevine cultivars ( Vitis vinifera L. ssp. vinifera )

摘要

Aim: To investigate and compare of Vitis vinifera Linné subsp. vinifera leaves of cultivars important for the Austrian wine producers in order to learn more about their surface architectures in the microand nanoscale.Methods and results: Atomic force microscopy, binocular fluorescence microscopy, contact angle measurements, and environmental scanning electron microscopy were employed in order to assess physicochemical features of fresh plant material. Erect and prostrate trichomes are the most characteristic features present on the epidermal surfaces of grapevine leaves. These hairs occur in rather different densities from none to densely covering the whole surface. Contact angels are highly affected by these hairs, resulting in individual cases in values >150° in the presence of a high reclining hair density. On nanoscopic scale blades of the varieties differ with respect to their wax structures, in orientation, shape and size. Cuticular striae and epicuticular waxes, mostly granules and platelets, are the most conspicuous characteristics of grapevine leaf ultrastructure.Conclusion: The microscopy techniques applied are complementary, enabling morphological analysis at different scales. They are not only efficient tools for descriptive botanics and finding morphological adaptions to the environmental conditions, they provide also an insight into the habitat of leaf colonizing microbes, pathogenic as well as beneficial ones and may add to the understanding of the conditions they find on leaf surfaces.Significance and impact of the study: Leaf surface structures and chemicals are part of the defence system of the plant. Water-repellency can be advantageous for the plant as it creates unfavourable conditions for the successful colonization of pathogens. The knowledge of wetting properties of leaf surfaces will advance the insight in the interaction with additives, promoting the secure and optimal use of plant protection agents applied by spray deposition, especially under difficult weather conditions. The application of such research will be better contact and or penetration, better adhesion of pesticides and other plant protecting agents but also improved adhesion of plant promoting bacteria in biocontrol applications. 1. Introduction The cuticle forms the multifunctional interface of plant and environment. Most prominently, it is a transpiration barrier, but it also controls leaf carbon balance, solute loss and uptake. Physiology, morphology and density of grapevine stomata have been investigated with respect to water stress (Costa et al., 2012), soil temperatures and atmospheric carbon dioxide (Rogiers et al., 2011) and wind (Gokbayrak et al., 2008). But leaf surfaces are also habitats for a great variety of different organisms, including lichens, bryophytes, algae, fungi, cyanobacteria, yeasts and other microorganisms as well as small animals (Ruinen, 1961). Bacteria are representing the biggest group among them. Highly important for agricultural species, the cuticle works as the first contact point and barrier against pathogenic fungi (Mendoza-Mendoza et al., 2009), viruses (Khan et al., 2011), and bacteria (Marcell and Beattie, 2002), and it is responsible for host recognition by fungi as well as herbivorous insects (Powell et al., 1999) and their predators. Adhesion of bacteria and fungal spores relates to the physicochemical features of the cuticle and hence investigations of these are a highly significant topic for agricultural research. Thickness, structure and chemical composition of cuticular matrices and epicuticular and intracuticular waxes vary widely (Riederer and Schreiber, 2001; Koch et al., 2004). The different shapes of the wax crystals are determined by their chemistry, i.e., certain crystal types are formed by specific compounds (Koch et al., 2006). Barthlott et al. (1998) identified 23 types of epicuticular wax deposits and assigned to them high systematic significance mainly for higher taxonomic levels. The potential functional consequences of such differences are still poorly understood (Kerstiens, 2010). Fungal spores usually need free water or a relative humidity of 95% to germinate. Many fungi infect leaves via an infection drop - a drop of rainwater or dew (Blakeman, 1973). Thus water-repellency is advantageous for the plant as it creates unfavourable conditions for the successful colonization of pathogens and parasitic fungi (Bargel et al., 2006). Some pathogens are able to overcome the barrier of a leaf covered with epicuticular wax structures making it highly hydrophobic. Powdery mildews, for example, contain a small amount of water within their conidia which enables them to germinate on virtually dry surfaces (Barthlott and Neinhuis, 1997). Monteiro et al. (2013) and Santos et al. (2014) studied epidermis, stomata, hair distribution and mesophyll structure, finding significant differences between four red and four white grapevine cultivars from Portugal. Investigations on the