Acta Biologica Cracoviensia s. Botanica

Salt stress is one of the main factors disturbing the physiology of organisms, including epigeic lichens inhabiting roadsides, due to de-icing salts used in winter seasons. The aim of the research was to study the effect of acute salt stress in various doses on the chlorophyll fluorescence parameters of chlorolichens, i.e., Cladonia furcata, C. mitis, Diposchistes muscorum, and cyanolichens, i.e., Peltigera didactyla, and P. rufescens, which naturally grow inland in the vicinity of roads. We also aimed to study changes in the photosynthetic efficiency of lichens over time and their responses to rainfall simulations in the days following exposure to salt stress to test whether liquid water supply improves photosynthetic efficiency. Salt stress led to a reduction of it in cyanolichens in most experimental groups, while in chlorolichens only treatment with 2.9-3.9M NaCl solutions significantly decreased F_V/F_M. Exposure to acute salt stress significantly affected fluorescence transient curves in all studied species. With respect to chlorolichens, a marked decrease of FM was observed and the flattened shape of the transient curves after treatment with the highest salt doses was the most apparent. Significantly greater disturbances were observed in cyanolichens in which the induction curve lost its sigmoid characteristics after treatment with solutions with a concentration greater than 0.35M. Furthermore, in all lichen species, increased values of ABS/RC and DI ₀/RC and decreases in PI _ABS, ET ₀/RC and TR0/RC as well as quantum yields and efficiencies were observed. Simulated rainfall resulted in a significant increase in the photosynthetic efficiency of chlorolichens to a level corresponding to healthy lichens almost throughout the duration of the whole experiment. On the contrary, in the case of cyanolichens, significant increases in F_V/F_M after water treatment were found only after exposure to low salt doses and, at the latest, 24 h after the stress. Although many cyanobacteria developed adaptations to survive in highly saline environments, cyanobionts present in inland lichen species seem to be highly susceptible to salt stress. We concluded that the time when rainfall occurs after exposure to salt stress is a crucial factor affecting the potential regeneration of PSII efficiency. Regeneration after rainfall is an important aspect for epigeic lichens occurring near roadsides, where, during the winter season, they are exposed to de-icing salt for a long time, and rainfall may partially compensate for their disturbances and increase their photosynthetic efficiency, enhancing the possibility of survival.

Assessment of photosynthetic activity is one of the quick and simple methods of verification whether the studied environmental factors have a stressful effect on photosynthetically active organisms. High-intensity light can be a stress factor that could have a potential impact on the maximum productivity of photosystem II. The purpose of the conducted research was to observe changes in photosynthetic activity of the lichen Cladonia mitis and the bryophyte Pleurozium schreberi exposed to artificial high-energy lighting under laboratory culture conditions. The obtained results showed variability of photosynthetic activity over time, depending on the amount of light energy supplied. C. mitis and P. schreberi at full exposure (light energy: 52.03 W m ^-2 and photosynthetically active radiation 167.24 μmol m ^-2) showed a slow downward trend in photosynthetic activity, while at half the light intensity periodic fluctuations were observed without changes in the controls. Long-term and high-light intensity exposure of photosynthetically active organisms may cause gradual degradation of the photosynthetic apparatus, which in turn leads to cell death. Low values of photosynthetic activity may indicate a situation in which, due to excess light, the rate of photosystem II damage exceeds the rate of its repair. This leads to irreversible damage to the photosynthetic apparatus.

Since silver nanoparticles (AgNPs) are used as nanofungicides and nanopesticides in agriculture, the toxicity of AgNPs as well as AgNO3 must be determined. Besides this, we evaluated the combined effects of salicylic acid (SA) and nitric oxide (NO) on responses of Phlomis tuberosa plants to Ag-induced stress. The results of growth parameters together with measurement of malondialdehyde (MDA) indicated that exposure to 1000 mg L–1 of AgNPs or AgNO3 exerted more toxicity, which was closely associated with the over– accumulation of ROS and the reduction of photochemical functioning. However, SNP (NO) and SA addition successfully alleviated adverse impact of AgNPs on Phlomis seedlings. Maximum amelioration of Ag-induced stress was found by combined treatments of SA+NO. Phlomis plants primed with SA+NO exhibited higher synthesis of chlorophyll b and carotenoid pigments to ameliorate AgNP-induced adverse effects on chlorophyll fluorescence parameters. SA+NO led to high levels of proline under both AgNPs and AgNO3 treatments. A further increase in antioxidants (phenolic compounds) was observed in NO-primed plants under AgNPs- induced stress, which was attendant with the high level of CAT and APX activities. Increase in total Ag translocation into shoot organs and cell survival were also enhanced by SA+NO under AgNPs stress. We concluded that SA+NO mitigated the inhibitory effects of AgNPs stress on the photosynthetic apparatus by increasing the phenolic compounds and carotenoids as well as by regulating accumulation of Ag, ROS and antioxidants. The present findings provide important knowledge to design strategies that minimize the negative impact of AgNPs and AgNO3 on crops.

The study was carried out to investigate the interactive effects of exogenous melatonin and excess amounts of zinc and copper on the growth and physiological parameters, antioxidant defense system and nutritional balance of cannabis seedlings. Cannabis sativa L. plants, grown under a completely randomized design, were irrigated with complete Hoagland’s nutrient solution. CuSO ₄ (0, 50 and 150 µM) and ZnSO ₄ (0, 50 and 100 µM) and their combinations were supplied to 21-day-old seedlings for 2 weeks. During the second week, melatonin was added to the nutrient solution at 100 μM. Zn and Cu stress led to reduced growth and physiological parameters, it promoted oxidative stress, changes in antioxidant enzymes activity and imbalance of mineral nutrients in cannabis seedlings. However, melatonin alleviated the growth retardation and physiological disorders of seedlings under normal conditions and heavy metal stress. The content of reduced glutathione and the activity of antioxidant enzymes such as glutathione reductase and ascorbate peroxidase were improved by melatonin. Excess amounts of zinc and copper changed the pattern of nutritional elements distribution in cannabis seedlings. Cu and Zn caused reduced content of Fe, Ca and K ions in shoots and roots. Melatonin treatment was able to adjust the nutrients content in metal-stressed seedlings up to the level of the control. Exogenous melatonin reduced toxic levels of Cu and Zn in seedlings overloaded with copper and zinc. MT also raised K, Ca and Fe concentrations in roots and shoots of seedlings under stress. Our results support the idea that melatonin acts as a powerful antioxidant, it can also be considered as a potent regulator of ion homeostasis in cannabis seedlings under heavy metal toxicity. Further studies still need to investigate the alleviatory effects of melatonin under field conditions.

The investigation described herein discusses the morpho-anatomical characteristics of xylem parenchyma cells of European ash stems undergoing heartwood formation. The research material comprised of cross and radial sections of wood obtained from stems at breast height of 91-year-old ash trees, half of which had visible ash dieback symptoms. The radial section of the wood samples was stained with acetocarmine to detect nuclei and with I2KI solution to observe starch grains in parenchyma cells, both of radial and axial systems. Additionally, microscopic slides were stained with Alcianblue Safranin-O, and fluorescence microscopy was applied to detect lignified cell walls. The color of sapwood and heartwood distinctly differed – heartwood extracts were detected in approx. 47 rings. Most of the parenchyma cells had nuclei present in both wood zones. Also starch grains were detected in the majority of the tree rings of the researched samples. All of the xylem parenchyma cell walls of axial and radial systems were lignified. The research revealed that lignification, parenchyma cells death and the release of heartwood extracts are processes remote in time and space. Furthermore, parenchyma cell walls lignification did not figure as a sign of the upcoming parenchyma cells death. Based on the current research, ash dieback disease might slightly impact the development paths of parenchyma cells. Compared with scores reported for other trees, European ash parenchyma cells longevity is indeed remarkable.