Bryophytes are widely used in monitoring environmental changes and various types of pollution. Features such as longevity and direct intake by the whole body make them very good models for bioindication. However, there is a considerable lack of knowledge on the coping, resistance and tolerance mechanisms to toxic elements within representatives of this second largest group of terrestrial plants. We tested two different growth form mosses, acrocarpous Atrichum undulatum and pleurocarpous Hypnum cupressiforme in axenic in vitro fully controlled laboratory conditions, thus eliminating additional side, antagonistic or synergistic effects. These mosses were exposed to three concentrations (including control) of zinc-, copper- or cadmium-acetate for a short and long period, and their growth, development and biochemical parameters were recorded. The results showed that reactions to stress are both species and metal-specific. Also, the short and long-term exposure times and the level of toxic elements played a role in species response and showed the differences between the two moss growth forms and species. Among the investigated parameters considered in the two mosses tested, the multiplication index proved to be the most useful and sensitive in detecting the metal pollution effects. On the other hand, the concentration of chl a seemed to vary over a rather small range between the stressed moss species. Overall, copper was shown to be quite toxic compared to the other two metals at lower applied concentration. However, the studied mosses demonstrated decreased viability according to all of the parameters tested in the media enriched with high concentrations of cadmium when compared with copper and zinc. These results suggest that species studies related to different metals/pollutants in small scale controlled conditions are urgently needed before application in broad areas monitored by mosses.

This study examined the morphogenesis of male inflorescences (catkins), staminate flowers, and pollen development in five walnut cultivars over two years. Differentiation of catkins began in spring with the formation of axillary meristems, followed by the successive development of bracts, floral meristems, the perianth, and stamens. Clear genotypic differences were observed in developmental dynamics: the cultivars ‘Sheynovo’ and ‘Champion’ entered the key stages of organogenesis earliest, whereas ‘Elit’ showed the latest differentiation and flowering. During the summer, catkins grew intensively until August, after which their growth slowed considerably. In the following spring, reproductive organ development resumed, with temperature conditions having a marked influence on growth rate. Histological analysis showed that the walnut anther develops through the differentiation of the epidermis, endothecium, middle layers, and tapetum, while microsporogenesis proceeds synchronously within the same microsporangium. Meiosis lasted 6-8 days, the tetrad stage 2-3 days, and the microspore and two-celled pollen stages 7-10 days each. Mature pollen grains were pantopororate, with a spinulate exine. The study was supported by photographic documentation of characteristic stages in the development of catkins, flowers, and anthers, as well as histological and cytological changes in the microsporangia. Strong correlations (r = 0.90-0.98**) were found between developmental stages and the morphometric parameters of catkins and anthers. These results contribute to a better understanding of walnut reproductive biology and may be significant for breeding and cultivar selection according to male flowering phenology.