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Cryptogams of ten urban flatroofs, contrasting in their age and size, were studied between 2016 and 2018. Siliceous (bituminous felt, gravel, brick) and calcareous (concrete) substrata occurred at each site. Microclimate (T, RH) at two sites of contrasting shading was monitored from September 2016 to January 2017. Biomass of two differently aged, exposed flatroofs was sampled in October 2018. Taxa of Cladonia and Xanthoparmelia have been identified by spot tests and HPTLC. A total of 61 taxa (25 bryophytes, 36 lichens), mostly widespread synanthropic species, have been detected with an explicit difference of species composition between shaded and exposed sites. Floristically interesting species included acidophilous bryophytes (Hedwigia ciliata, Racomitrium canescens) and lichens (Xanthoparmelia conspersa, Stereocaulon tomentosum) of montane character. The most widespread lichen is Cladonia rei which accounted for a significant part of the biomass at selected sites. Species-area curves for bryophytes at exposed sites have become saturated at 100–150 m2. In contrast, saturation of lichen diversity has not been reached even at the largest sites. Flatroofs with traditional roofing techniques can harbour relatively diverse microhabitats and species-rich synanthropic vegetation. It is urgent to study these sites before renovation with modern roofing techniques eliminates them. Diversification of urban surroundings is possible in the future via application of various substrats in renovated and newly constructed roofs.

The present part of the series provides new records of 11 taxa, among them one diatom, six lichen-forming fungi and four bryophytes. The diatom Stauroneis blazenciciae is new to Romania, and it is the second record worldwide. The six lichen species have already been reported from Hungary, however they are quite rare. Additional interesting records are presented, e.g. Calicium notarisii and Pseudothelomma ocellatum are new for the Great Hungarian Plain, Cetrelia chicitae is new for the Velence Mts and for the Transdanubian Mountain Range, Petractis clausa is new for the Gerecse Mts, and Umbilicaria polyphylla is new for the Börzsöny Mts. Parmotrema perlatum has several interesting new occurrences. Regarding the bryophyte species, Marchantia polymorpha L. subsp. montivagans is new to Hungary, Sciuro-hypnum curtum is new for the Nyírség, Brachythecium capillaceum is reported from the Great Hungarian Plain for the first time. Pseudocampylium radicale is new for the Kismohos bog, its appearance seems to be a recent event.

Protein phosphatase PP2A is an enzyme complex consisting of C (catalytic), A (scaffold) and B (regulatory) subunits. B subunits are a large family of proteins that regulate activity, substrate specificity and subcellular localization of the holoenzyme. Knowledge on the molecular functions of PP2A in plants is less than for protein kinases, but it is rapidly increasing. B subunits are responsible for the large diversity of PP2A functioning. This paper intends to give a survey on their multiple regulatory mechanisms. Firstly, we give a short description on our current knowledge in terms of “B”-mediated regulation of metabolic pathways. Next, we present their subcellular localizations, which extend from the nucleus to the cytosol and membrane compartments. The next sections show how B subunits regulate cellular processes from mitotic division to signal transduction pathways, including hormone signaling, and then the emerging evidence for their regulatory (mostly modulatory) roles in both abiotic and biotic stress responses in plants. Knowledge on these issues should be increased in the near future, since it contributes to a better understanding of how plant cells work, it may have agricultural applications, and it may have new insights into how vascular plants including crops face diverse environmental challenges.

The protein phosphatase PP2A is essential for the control of integrated eukaryotic cell functioning. Several cellular and developmental events, e.g., plant growth regulator (PGR) mediated signaling pathways are regulated by reversible phosphorylation of vesicle traffic proteins. Reviewing present knowledge on the relevant role of PP2A is timely. We discuss three aspects: (1) PP2A regulates microtubule-mediated vesicle delivery during cell plate assembly. PP2A dephosphorylates members of the microtubule associated protein family MAP65, promoting their binding to microtubules. Regulation of phosphatase activity leads to changes in microtubule organization, which affects vesicle traffic towards cell plate and vesicle fusion to build the new cell wall between dividing cells. (2) PP2A-mediated inhibition of target of rapamycin complex (TORC) dependent signaling pathways contributes to autophagy and this has possible connections to the brassinosteroid signaling pathway. (3) Transcytosis of vesicles transporting PIN auxin efflux carriers. PP2A regulates vesicle localization and recycling of PINs related to GNOM (a GTP–GDP exchange factor) mediated pathways. The proper intracellular traffic of PINs is essential for auxin distribution in the plant body, thus in whole plant development. Overall, PP2A has essential roles in membrane interactions of plant cell and it is crucial for plant development and stress responses.

Jelen közlemény rövid áttekintést nyújt a mocsári kockásliliom (Fritillaria meleagris L.) nevezéktanáról, rendszertanáról, alak- és szövettanáról, életciklusáról, fenológiájáról, szaporodás-biológiájáról, élőhelyválasztásáról, biotikus interakcióiról, hatóanyagairól, mikroszaporításáról, felhasználási lehetőségeiről és veszélyeztetettségéről. Pontosítottuk a faj európai elterjedési térképét és kiegészítéseket teszünk a hazai előfordulásaihoz. Saját adatokat közlünk a növény magképzési sikeréről, ezermagtömegéről, hazai állományainak demográfiai jellemzőiről, valamint termőhelyeinek talaj-adottságairól.

We aimed to produce tissue cultures and plant regeneration from endangered Crocus species: C. scepusiensis, C. tommasinianus, C. vittatus (“Verni” series of the genus) and C. banaticus. For initiation of cultures we used a plant growth regulator (PGR) combination used for in vitro culture of saffron and its relatives: 10 mg L-1 α-naphthaleneacetic acid (NAA) and 1 mg L-1 6-benzyladenine (BA). Shoot tips of young seedlings (C. scepusiensis) and corms (for the rest of species) were used as explants. C. scepusiensis explants developed into organogenic calli. On media with decreased NAA and with or without increased BA concentration, calli produced stigma-like structures and/or shoots and whole plants. In the other species, callus initiation medium induced callus formation with abundant somatic embryos. In C. tommasinianus, embryos developed shoots when auxin content of medium was decreased. In C. banaticus, a decrease of auxin with or without an increase in cytokinin content led to shoot or whole plant regeneration, as in C. scepusiensis. In the case of C. vittatus and C. banaticus, initiation and/or maintenance of cultures on indole-3-butyric acid (IBA) and increased sucrose concentration stimulated whole plant regeneration and in vitro cormlet development. C. scepusiensis and the rest of cultures (organogenic vs. embryogenic) differed at the biochemical level: C. scepusiensis cultures had higher (yet still low) enzymatic antioxidant (catalase, peroxidase) activities. With respect to catalase isoenzyme patterns, C. banaticus was different from the rest of cultures, demonstrating its distinct taxonomical position. Besides germplasm preservation use of the present cultures, they have a potential biotechnological value.

Abiotic and biotic factors induce oxidative stress involving the production and scavenging of reactive oxygen species (ROS). This review is a survey of well-known and possible roles of serine-threonine protein phosphatases in plant oxidative stress signaling, with special emphasis on PP2A. ROS mediated signaling involves three interrelated pathways: (i) perception of extracellular ROS triggers signal transduction pathways, leading to DNA damage and/or the production of antioxidants; (ii) external signals induce intracellular ROS generation that triggers the relevant signaling pathways and (iii) external signals mediate protein phosphorylation dependent signaling pathway(s), leading to the expression of ROS producing enzymes like NADPH oxidases. All pathways involve inactivation of serine-threonine protein phosphatases. The metal dependent phosphatase PP2C has a negative regulatory function during ABA mediated ROS signaling. PP2A is the most abundant protein phosphatase in eukaryotic cells. Inhibitors of PP2A exert a ROS inducing activity as well and we suggest that there is a direct relationship between these two effects of drugs. We present current findings and hypotheses regarding PP2A-ROS signaling connections related to all three ROS signaling pathways and anticipate future research directions for this field. These mechanisms have implications in the understanding of stress tolerance of vascular plants, having applications regarding crop improvement.

Microcystin-LR (MCY-LR) is a heptapeptide toxin produced mainly by freshwater cyanobacteria. It strongly inhibits protein phosphatases PP2A and PP1. Functioning of the PIN family of auxin efflux carriers is crucial for plant ontogenesis and their functions depend on their reversible phosphorylation. We aimed to reveal the adverse effects of MCY-LR on PIN and auxin distribution in Arabidopsis roots and its consequences for root development. Relatively short-term (24 h) MCY-LR treatments decreased the levels of PIN1, PIN2 and PIN7, but not of PIN3 in tips of primary roots. In contrast, levels of PIN1 and PIN2 increased in emergent lateral roots and their levels depended on the type of PIN in lateral root primordia. DR5:GFP reporter activity showed that the cyanotoxin-induced decrease of auxin levels/responses in tips of main roots in parallel to PIN levels. Those alterations did not affect gravitropic response of roots. However, MCY-LR complemented the altered gravitropic response of crk5-1 mutants, defective in a protein kinase with essential role in the correct membrane localization of PIN2. For MCY-LR treated Col-0 plants, the number of lateral root primordia but not of emergent laterals increased and lateral root primordia showed early development. In conclusion, inhibition of protein phosphatase activities changed PIN and auxin levels, thus altered root development. Previous data on aquatic plants naturally co-occurring with the cyanotoxin showed similar alterations of root development. Thus, our results on the model plant Arabidopsis give a mechanistic explanation of MCY-LR phytotoxicity in aquatic ecosystems.

Horseradish allyl isothiocyanate (AITC, a volatile oil) and cyanobacterial microcystin-LR (MCY-LR, a cyclic heptapeptide) affect eukaryotic cell cycle. MCY-LR inhibits protein phosphatases PP1 and PP2A. We aimed to reveal the mechanisms of their cellular effects in a model eukaryote, Vicia faba. We have shown for the first time that AITC had minor effects on PP1 and PP2A activities in vitro, but it inhibited significantly PP1 in vivo. The combination of 10 μM AITC with 10 μM MCY-LR induced metaphase arrest after short-term (12 h) treatments. 10 μM AITC, 0.2–10 μM MCY-LR and their combinations induced histone H3 hyperphosphorylation, associated with the regulation of metaphase-anaphase transition. This hyperphosphorylation event occurred at any treatment which led to the inhibition of PP1 activity. 10 μM AITC + 10 μM MCY-LR increased the frequency of metaphase spindle anomalies, associated with metaphase arrest. We provide new insights into the mechanisms of metaphase-anaphase transition. Metaphase arrest is induced at the concomitant hyperphosphorylation of histone H3, alteration of metaphase spindle assembly and strong inhibition of PP1 + PP2A activity. Near-complete blocking of metaphase-anaphase transition by rapid protein phosphatase inhibition is shown here for the first time in plants, confirming a crucial role of serine-threonine phosphatases in this checkpoint of cell cycle regulation. Tissue-dependent differences in PP1 and PP2A activities induced by AITC and MCY-LR suggest that mainly regulatory subunits are affected. AITC is a potential tool for the study of protein phosphatase function and regulation. We raise the possibility that one of the biochemical events occurring during AITC release upon wounding is the modulation of protein phosphatase dependent signal transduction pathways during the plant defense response.