Andrzej Kornaś

LESION SIMULATING DISEASE1, ENHANCED DISEASE SUSCEPTIBILITY1, and PHYTOALEXIN DEFICIENT4 conditionally regulate cellular signaling homeostasis, photosynthesis, water use efficiency, and seed yield in Arabidopsis

Gene functions should be studied not only under stable laboratory conditions, but also in the environment abounding in multiple stresses. There is growing evidence that for a comprehensive insight into the function of plant genes, it is crucial to assess their functionalities under a wide range of conditions. In this study, we examined the role of LESION SIMULATING DISEASE1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), and PHYTOALEXIN DEFICIENT4 (PAD4) in the regulation of photosynthesis, water use efficiency, reactive oxygen species/hormonal homeostasis, and seed yield in Arabidopsis (Arabidopsis thaliana) grown in the laboratory and in the field. We demonstrate that the LSD1 null mutant (lsd1), which is known to exhibit a runaway cell death in nonpermissive conditions, proves to be more tolerant to combined drought and high-light stress than the wild type. Moreover, depending on growing conditions, it shows variations in water use efficiency, salicylic acid and hydrogen peroxide concentrations, photosystem II maximum efficiency, and transcription profiles. However, despite these changes, lsd1 demonstrates similar seed yield under all tested conditions. All of these traits depend on EDS1 and PAD4. The differences in the pathways prevailing in the lsd1 in various growing environments are manifested by the significantly smaller number of transcripts deregulated in the field compared with the laboratory, with only 43 commonly regulated genes. Our data indicate that LSD1, EDS1, and PAD4 participate in the regulation of various molecular and physiological processes that influence Arabidopsis fitness. On the basis of these results, we emphasize that the function of such important regulators as LSD1, EDS1, and PAD4 should be studied not only under stable laboratory conditions, but also in the environment abounding in multiple stresses.

Plastoquinone redox state modifies plant response to pathogen

The role of PQ (plastoquinione) redox state in establishment of response to pathogen infection (Botrytis cinerea) was tested along the regulation of main antioxidative enzymes (superoxide dismutase - SOD, catalase - CAT) and photochemistry of PSII (photosystem II) in Mesembryanthemum crystallinum plants performing C3 and CAM (Crassulacean acid metabolism) carbon metabolism. The redox state of PQ was modified by two inhibitors of photosynthetic electron transport resulting in a more oxidised (3-(3,4-dichlorophenyl)-1,1-dimethylurea; DCMU) or reduced (2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone; DBMIB) PQ redox state simulating darkness and high light conditions, respectively. Irrespective of the type of treatment (mock inoculation or pathogen inoculation) SOD activity depended on the PQ pool. Our results suggest that regarding changes in infection-induced CAT activity, plants developed response that is vital for hypersensitive-like (HR-like) response establishment only when PQ pool generated signal was similar to that in light presence (DBMIB pre-treatment). When PQ pool generated signal was similar to darkness, CAT activity response remained stress-independent, similarly to SOD. Fluorescence parameters of PSII, Qp (photochemical quenching coefficient) and NPQ (non-photochemical quenching) were affected only in the tissues treated with DCMU in stress-independent manner. We suggest that in case of abiotic and biotic stresses signals emerging from PQ pool indirectly orchestrate plant response and carbon metabolism affects this regulatory pathway.

Veinal-mesophyll interaction under biotic stress

According to microscopic observations, germinating hyphae of Botrytis cinerea, though easily penetrating Mesembryanthemum crystallinum mesophyll tissue, are limited in growth in mid-ribs and only occasionally reach vascular bundles. In mid-ribs of C3 and CAM leaves, we found significantly lower rbcL (large RubisCO subunit) abundance. Moreover, in CAM leaves, minute transcript contents for pepc1 (phosphoenolpyruvate carboxylase) and nadpme1 (malic enzyme) genes found in the mid-ribs suggest that they perform β-carboxylation at a low rate. The gene of the main H2O2-scavenging enzyme, catL (catalase), showed lower expression in C3 mid-rib parts in comparison to mesophyll. This allows maintenance of higher H2O2 quantities in mid-rib parts. In C3 leaves, pathogen infection does not impact photosynthesis. However, in CAM plants, the expression profiles of rbcL and nadpme1 were similar under biotic stress, with transcript down-regulation in mid-ribs and up-regulation in mesophyll (however, in case of rbcL not significant). After B. cinerea infection in C3 plants, transcripts for both antioxidative proteins strongly increased in mid-ribs, but not in mesophyll. In infected CAM plants, a significant transcript increase in the mesophyll was parallel to its decrease in the mid-rib region (however, in the case of catL this was not significant). Pathogen infection modified the expression of carbon and ROS metabolism genes in mid-ribs and mesophyll, resulting in the establishment of successful leaf defense.

Photosynthesis-Related Functions of Vasculature-Associated Chlorenchymatous Cells

In most biochemical, molecular, and genetic studies, a leaf is regarded as a uniformly responding unit, however leaves are not homogeneous in structure and function. Leaf venation is in continuity with the vascular system within leaf petiols and stems. Leaf veins are typically encircled by bundle sheath (BS) cells containing chloroplasts and photosynthetic cells adjacent to the vasculature are also found in petiols and stems. In C3 plants, BS cells have been shown to be preadapted for the role in C4 photosynthesis and this may explain the polyphyletic evolution of C4 photosynthesis. The photosynthetically active radiation (400–700 nm) reaching the chloroplast-containing cells adjacent to the vasculature in leaves, petiols, and stems is of lower intensity and enriched with longer wavelengths (~500–700 nm) when compared with that absorbed by mesophyll cells. The CO2 diffusion from the air to the vasculature-adjacent chlorenchymatous cells is also expected to be slow in comparison to mesophyll cells. However, the vasculature can be supplied with malate which releases CO2 after decarboxylation and with respiratory CO2 from heterotrophic tissues transported in the xylem. It could be expected that high CO2 concentration at the green cells around the vasculature supports carboxylation and photosynthesis. However, CO2-rich environment in stems impedes the photochemical activity of the photosynthetic vascular cells possibly through acidification of protoplasm and impairment of the pH-dependent excess energy quenching followed by reduction in the efficiency of heat dissipation. Light-dependent reduction in CO2 release, as shown in experiments on stems can predominantly be attributed to corticular refixation. All these can affect chloroplast ultrastructure, the composition of photosynthetic electron transport chain components, and the photosynthetic enzymatic machinery in these cells.

Foliar application of selenium for protection against the first stages of mycotoxin infection of crop plant leaves: Selenium application to protect against mycotoxin infection

BACKGROUND The aim of this study was to investigate whether the application of selenium (Se) ions directly to the leaf surface can protect plants against infection by the fungal toxin zearalenone (ZEA). The experiments were performed for the most common and agronomically important crops such as wheat, oat, and barley (both tolerant and sensitive varieties) because mycotoxin accumulation in plants is the cause of many diseases in animals and people. RESULTS ZEA at a concentration of 10 µmol L-1 either alone or in combination with Se (5 µmol L-1 Na2 SeO4 ) was applied to the second leaf of seedlings. Visualization of leaf temperature profiles by infrared thermography demonstrated a decrease in temperature at the location of ZEA infection that was more noticeable in sensitive genotypes. The presence of Se significantly suppressed changes at the site of ZEA application in all tested plants, especially the tolerant genotypes. Microscopic observations confirmed that foliar administration of ZEA resulted in its penetration to deeper localized cells and that damage induced by ZEA (mainly to chloroplasts) decreased after Se application. Analyses of antioxidant enzymes demonstrated the involvement of Se in antioxidation mechanisms, in particular by activating SOD and CAT under ZEA-induced stress conditions. CONCLUSION The foliar application of Se to seedling leaves may be a non-invasive method of protecting crops against the first steps of ZEA infection.

Withdrawal from functional Crassulacean acid metabolism (CAM) is accompanied by changes in both gene expression and activity of antioxidative enzymes

In Mesembryanthemum crystallinum, crassulacean acid metabolism (CAM) is seemingly reversible, but unequivocal evidence for functional CAM withdrawal has yet to be shown. In this study, we confirmed the rapid downregulation of PEPC1 expression just 1 h after the removal of NaCl from the plant growth media. At the same time, the Δ malate values in desalted plants rapidly (1 d) re-established to values typical for C3 plants. This phenomenon allowed us to confirm functional CAM withdrawal in the desalted plants. Desalting altered the expression of the genes of the main antioxidative enzymes and/or the activity of their respective proteins; for catalase (CAT), both gene expression and protein activity were restored to levels observed in C3 plants in response to desalting, while for cooper-zinc superoxide dismutase (CuZnSOD) and ascorbate peroxidase (APX), only protein activity was restored. Therefore, we conclude that during the C3→CAM transition the CAM-specific antioxidative enzyme activity profile constitutes a transient and fully reversible response to abiotic stress.

Determination of element composition and extraterrestrial material occurrence in moss and lichen samples from King George Island (Antarctica) using reactor neutron activation analysis and SEM microscopy

Seven lichens (Usnea antarctica and U. aurantiacoatra) and nine moss samples (Sanionia uncinata) collected in King George Island were analyzed using instrumental neutron activation analysis, and concentration of major and trace elements was calculated. For some elements, the concentrations observed in moss samples were higher than corresponding values reported from other sites in the Antarctica, but in the lichens, these were in the same range of concentrations. Scanning electron microscopy (SEM) and statistical analysis showed large influence of volcanic-origin particles. Also, the interplanetary cosmic particles (ICP) were observed in investigated samples, as mosses and lichens are good collectors of ICP and micrometeorites.