Marzenna Guzicka

Cytomixis in shoot apex of Norway spruce [Picea abies (L.) Karst.]

Atypical cell walls and nuclei were observed in the apex of Norway spruce shoots from late April to early May on the material collected from a few grafts of a clone of Norway spruce growing on an experimental area. Images of ultrastructure attest to cytomixis. The phenomenon of cytomixis has previously been described in various plant material, both in the meiotic and mitotic cells, but this is the first report of cytomixis in gymnosperms.

Limited variation found among Norway spruce half-sib families in physiological response to drought and resistance to embolism

Projections of future climates suggest that droughts (Ds) may become more frequent and severe in many regions. Genetic variation, especially within populations in traits related to D resistance, is poorly investigated in forest trees, but this knowledge is necessary to better understand how forests will respond to water shortages. In this study, we investigated variability among seven open-pollinated half-sib families of a single population and two population-level progenies of Norway spruce (Picea abies (L.) H. Karst.) in their gas exchange response to imposed D and xylem vulnerability to embolism. During their third growing season, saplings were subjected to three treatments-control (C), D (for 19 weeks) and broken drought (BD, 54 days without watering starting in mid-July, then well-watered). In response to D, all families reduced their stomatal conductance (gs) and light-saturated rates of photosynthesis (Amax) in a similar way. After rewatering, the xylem water potential (Ψ) recovered in the BD treatment, but gs and Amax remained lower than in C. Needle starch concentration was altered in both D treatments compared with C. Xylem of D-exposed trees was more vulnerable to embolism than in C. The minimum attained safety margin remained positive for all families, indicating that no catastrophic hydraulic failure occurred in stem xylem during D. Significant family variation was found for Ψ early in the D (midday Ψ between -1.2 and -1.8 MPa), and for needle damage, but not for sapling mortality. Family variation found at the initial stages of D, and not afterward, suggests that all families responded similarly to greater D intensity, exhibiting the species-specific response. Limited variation at the family level indicates that the response to D and the traits we examined were conservative within the species. This may limit breeding opportunities for increased D resistance in Norway spruce in light of expected climatic changes.

Strategies utilized by trophically diverse fungal species for Pinus sylvestris root colonization

Physiological changes in host plants in response to the broad spectrum of fungal modes of infection are still not well understood. The current study was conducted to better understand the infection of in vitro cultures of Pinus sylvestris L. seedlings by three trophically diverse fungal species, Fusarium oxysporum E. F. Sm. & Swingle, Trichoderma harzianum Rifai and Hebeloma crustuliniforme (Bull.) Quél. Biochemical methods and microscopy were utilized to determine (i) which factors (apoplastic and cellular pH, reactive oxygen species, glutathione and cell death) play a role in the establishment of pathogenic, saprotrophic and mycorrhizal fungi, and (ii) whether cell death is a common response of conifer seedling tissues when they are exposed to trophically diverse fungi. Establishment of the pathogen, F. oxysporum, was observed more frequently in the meristematic region of root tips than in the elongation zone, which was in contrast to T. harzianum and H. crustuliniforme. Ectomycorrhizal (ECM) hyphae, however, were occasionally observed in the studied root zone and caused small changes in the studied factors. Colonization of the meristematic zone occurred due to host cell death. Independently of the zone, changes in cellular pH resulting in an acidic cytoplasm conditioned the establishment of F. oxysporum. Additionally, cell death was negatively correlated with hydrogen peroxide (H2O2) in roots challenged by a pathogenic fungus. Cell death was the only factor uniquely associated with the colonization of host roots by a saprotrophic fungus. The mechanism may differ, however, between the zones since apoplastic pH was negatively correlated with cell death in the elongation zone, whereas in the meristematic zone, none of the studied factors explained cell death. Colonization by the ECM fungus, H. crustuliniforme, was associated with a decreasing number of cells with acidic apoplast and by production of H2O2 in the elongation zone resulting in cell death. Saprotrophic and ECM fungi had a greater effect on cell acidification in the meristematic zone than the pathogenic fungus.

Stomata on the pericarp of species of the genus Rosa L. (Rosaceae)

Achenes of 36 species representing all subgenera and sections of the genus Rosa were studied. All have stomata on the pericarp that seem to be normal in appearance. They are usually few, scattered, mostly on the upper part of fruit, and open or closed. This is the first report of stomata on fruits of Rosa.

Signalling regulators of abscisic and gibberellic acid pathways are involved in dormancy breaking of Norway maple (Acer platanoides L.) seeds

Physiological dormancy is a characteristic of the seeds of plants that are exposed to adverse harsh environmental conditions. Many tree seeds from the northern hemisphere have acquired deep dormancy as an adaptation to the winter period. Such kinds of dormancy can be removed by cold stratification. This physiological process is regulated through abscisic and gibberellic acids signal transduction, in which ABI5, 14-3-3 and RGL2 have a negative response to cold stratification and cause dormancy breaking. Our study is, to our knowledge, the first to report tissue localisation of ABI5 and RGL2 in deeply physiologically dormant seeds. Localisation of these proteins differs in time (weeks of stratification) and space (anatomy of the embryo root). Studies showed that changes occurred on three levels: (1) tissue, as the fluorescence signal throughout the weeks of stratification was localised in different regions of the embryo axes, and these changes were associated with changes in development regulation of the individual regions; (2) cell, either in nucleus or in cytoplasm, involving regulation of gene expression, and synthesis and inactivation in cytoplasm; and (3) organelle, specifically in nuclei/nucleoli, indicating transcription regulation of the specific genes. At the end of stratification, when dormancy is broken, ABI5 and RGL2 were not noticeable in the cells of the apical meristem. ABI5 likely blocked germination through inhibition of meristem activity, whereas RGL2 through blocking of procambial cell differentiation. We speculate that similar molecular and cellular mechanisms exist among other seeds characterised by physiological dormancy.