LAUSR

During daily aerobiological monitoring in Perugia (central Italy) in February 2018, unusual shapes of the cypress pollen have been observed. Under light microscopy observation, the presence of abnormal pink coloration of the cytoplasm was highlighted in more than 60% of cypress pollen. In these samples, exine was broken, but the thick layer of intine was intact (Fig. 1a). Normally, intine does not react with the sporopollenin stain (basic fuxine in glycerine) and prevents it to pass through and reach the cytoplasm (Fig. 1b). This occurrence could be related to a major permeability of cell membrane due to chilling stress. Each plant has an optimum set of temperatures for its proper growth and development. A particular set of temperature conditions, which are optimum for one plant, may be stressful for another plant. It has generally been noticed that plants native to warm habitats exhibit symptoms of injury upon exposure to non-freezing temperatures (Lynch 1990). For example, plants, such as maize (Zea mays) and soybean (Glycine max), show signs of injury already below 10–15 C (Guy 1990; Hopkins 1999). Conversely, cypress tree is widespread in all Mediterranean climates as it is robust and relatively adaptable to different ranges of temperatures. Although it prefers dry hot summers and mild winters, it can also tolerate more continental climates. Mature cypress can usually survive harsh winters with temperatures below 15 C, and there are records of resistance at 23 C, but under such conditions, severe damages may occur. Cold stress, which includes both chilling and freezing injuries, modifies the gene expression and plant metabolism with consequent effects on many biological functions (Shinozaki et al. 2003). During drastic cold exposure, freezing can induce extracellular ice formation, which leads to cell dehydration and may result in cell collapse. This could be related to the mechanical injury generated by the enlargement of ice crystals on the cell wall and the plasma membrane, ultimately leading to cell rupture (Lynch 1990; Suzuki et al. 2008). In the actual climate change scenario, the global warming is characterized by seasons altered with fast changes of temperature and occurrence of freezing that appears without any previous chilling period (Frenguelli et al. 2014; Rahmstorf et al. 2017). A sudden shift to extreme temperature can cause the damages on the biological systems depending on the sensitivity or tolerance to cold stress. The literature reports two types of low temperature stress, chilling and freezing stress (Mahajan and Tuteja 2005; Hopkins 1999). Chilling stress occurs when the plants are exposed to low but non-freezing temperatures. Instead, freezing stress can take place when plants E. Tedeschini (&) M. Mariani G. Frenguelli Department of Agriculture Food and Environmental Science, University of Perugia, Borgo XX giugno 74, 06121 Perugia, Italy e-mail: [email protected]