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  • 1.
    Ekblad, Alf
    et al.
    Umeå University, Umeå, Sweden.
    Lundquist, Per-Olof
    Sjöström, M
    Umeå University, Umeå, Sweden.
    Huss-Danell, Kerstin
    Umeå University, Umeå, Sweden.
    Day-to-day variation in nitrogenase activity of alnus-incana explained by weather variables: a multivariate time-series analysis1994In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 17, no 3, p. 319-325Article in journal (Refereed)
    Abstract [en]

    A modelling system is described that indicates the extent to which day-to-day variations in nitrogenase activity in young Alnus incana (L.) Moench, grown in defined conditions in the field, may be affected by weather conditions both during and prior to the day of measurement. Nitrogenase activity (acetylene reduction activity, ARA) was measured weekly on intact field-grown grey alder (A. incana) plants, 0.15–0.42 m tall at planting, nodulated with Frankia. The measurements were done at noon on two groups of plants in 1987 and on two other groups in 1988. Each group was made up of five or six plants. Seven weather variables: daily sunshine hours, daily mean, maximum and minimum air temperature, daily mean and 1300 h relative humidity, and daily rainfall were used. The relation between log(ARA/leaf area) and the weather variables were analysed using a PLS model (partial least squares projection to latent structures). The advantage of PLS is that it can handle x-variables that are correlated. Data from 1987 were chosen as a training set. Multivariate PLS time series analysis was made by adding, in a stepwise manner, the weather data up to 5 d before the day of measurement. This procedure gave six models with n * 7 x-variables (n= 1–6). With the models from the time series analysis of 1987 data, true predictions of ARA per leaf area were made from weather data 1988 (test set 1) and from ‘early-season’ weather data from 1987 and 1988 (test set 2). The variation in ARA/leaf area could be predicted from the weather conditions. The predictions of the two test sets improved when the weather conditions one and two days before the day of measurements were added to the model. The further addition of weather data from 3 to 5 d before the day of measurement did not improve the model. The good predictions of ARA/leaf area show that the alders responded to the variable weather conditions in the same way in 1988 as in 1987, despite the ten-fold difference in size (leaf area) at the end of the growing season. Among the weather variables, air temperature and the daily sunshine hours were positively correlated to ARA, while relative air humidity and rainfall were negatively correlated to ARA. The daily minimum temperature and rainfall appeared to have least impact on ARA. By use of PLS, we could extract information out of a data set containing highly correlated x-variables, information that is non-accessible with conventional statistical tools such as multiple regression. When making measurements of nitrogenase activities under field conditions, we propose that attention should be paid to the weather conditions on the days preceding the day of measurement. The day-to-day variation in nitrogenase activity is discussed with reference to known effects of stress factors under controlled conditions.

  • 2.
    Kalbin, Georgi
    et al.
    Örebro University, Department of Natural Sciences.
    Hidema, Jun
    Brosché, Mikael
    Kumagai, Tadashi
    Bornman, Janet F.
    Strid, Åke
    Örebro University, Department of Natural Sciences.
    UV-B-induced DNA damage and expression of defence genes under UV-B stress: tissue-specific molecular marker analysis in leaves2001In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 24, no 9, p. 983-990Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate the regulatory effect of ultraviolet-B (UV-B) radiation on a number of key stress response genes found in the epidermis and mesophyll of Pisum sativum L., Argenteum mutant. This mutant was chosen for the ease with which the entire epidermis can be removed from the mesophyll tissue. An additional goal was to explore the potential modifying effect of pre-acclimation of plants to UV-B radiation prior to exposure by UV-B during treatment. Results showed that mRNA accumulation was similar during acute short-term UV-B exposure for chalcone synthase (Chs) and short-chain alcohol dehydrogenase (SadA) in both epidermis and mesophyll. In contrast, the mRNA levels differed considerably between tissues for phenylalanine ammonia lyase, chalcone isomerase and lipid transfer protein. After 24 h incubation in visible light after cessation of UV-B exposure, the regulation of mRNA levels also differed between Chs and SadA, the former showing no expression in the epidermis and the latter none in the mesophyll. Acclimation to low UV-B levels before acute exposures resulted in delayed induction of Chs and SadA. Measurements of UV-B-induced cyclobutane pyrimidine dimers (CPDs) showed a greater formation in epidermis than in mesophyll. In addition, acclimation at low UV-B levels resulted in significantly higher basal levels of CPDs than in non-acclimated plants in both mesophyll and epidermis and also in increased damage in concomitant acute exposures. The lack of correlation between the number of CPDs and levels of transcripts for defence genes, indicates that DNA damage does not control transcription of these genes.

  • 3.
    Kalbina, Irina
    et al.
    Örebro University, Department of Natural Sciences.
    Strid, Åke
    Örebro University, Department of Natural Sciences.
    Supplementary ultraviolet-B irradiation reveals differences in stress responses between Arabidopsis thaliana ecotypes2006In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 29, no 5, p. 754-763Article in journal (Refereed)
    Abstract [en]

    Irradiation of Arabidopsis thaliana ecotypes C24, Wassilewskija (Ws) and Columbia-0 (Col-0) with supplementary ultraviolet-A+B (UV-A+B) radiation revealed ecotype-specific differences in expression of the gene for the pathogenesis-related protein PR-5. C24 showed an increased expression level of PR-5 (5- and 20-fold higher compared with Col-0 and Ws, respectively). Expression of other molecular markers such as CHS (encoding chalcone synthase), MEB5.2 [encoding a gene strongly up-regulated by ultraviolet-B (UV-B)] and PYROA [encoding a pyridoxine (Vitamin B6) biosynthesis enzyme] only showed slight differences between ecotypes. Oxidative stress during UVA+B exposure was monitored by staining for H2O2. This analysis also revealed important ecotype-specific differences. 'H2O2 hot spots' were found in C24, whereas an even distribution of H2O2 was found in Ws and Col-0. Necrotic lesions also appeared on C24 leaves after prolonged UV-B exposure. There was a reverse correlation between the H2O2 steady-state concentration and the PR-5 gene expression; Ws showed the highest level of H2O2 accumulation but the lowest expression level of the PR-5 gene. Furthermore, application of paraquat on the rosettes led to similar PR-5 expression and H2O2 accumulation patterns as were found after UV-A+B irradiation. The observed ecotypic differences were also reflected in a statistically significant UV-B-dependent decrease in biomass, rosette size and leaf area for Ws, but not for C24 and Col-0. Our results show that a significant ecotype-specific genetic variability in general UV-B responses in Arabidopsis exists. Moreover, the signal transduction or gene regulation pathway for PR-5 differs from the other molecular markers used in this study.

  • 4.
    Kalbina, Irina
    et al.
    Örebro University, Department of Natural Sciences.
    Strid, Åke
    Örebro University, Department of Natural Sciences.
    The role of NADPH oxidase and MAP kinase phosphatase in UV-B-dependent gene expression in Arabidopsis2006In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 29, no 9, p. 1783-1793Article in journal (Refereed)
    Abstract [en]

    Plant responses to supplementary UV-B irradiation have been reported to include formation of reactive oxygen species (ROS), hydrogen peroxide, in particular, and regulation by mitogen-activated protein kinase (MAPK) cascades which in turn are fine-tuned by MAPK phosphatases (MKPs). Here we present direct genetic evidence for the involvement of plasma membrane NADPH oxidase, a source of superoxide and hydrogen peroxide in the apoplasts, in UV-B signalling in Arabidopsis thaliana, by analysis of gene expression of the UV-B molecular markers in NADPH oxidase (atrbohD, F and DF) and MAP kinase phosphatase 1 (MKP1) knockout mutants (mkp1). Whereas the NADPH oxidase mutants were affected in UV-B-dependent CHS, PYROA and MEB5.2 gene expression, the mkp1 mutant was affected in the general expression pattern of the pathogenesis-related (PR) and PDF1.2 genes. The results indicate involvement of MKP1 in repressive action on gene expression of more general stress response pathways, similar to those activated by pathogen attack, while NADPH oxidase is involved in quantitative (rather than absolute) regulation of more UV-B-specific genes. The expressions of the molecular markers in the knockout mutant mkp1 and in its complemented lines (lines 6 and 10) were similar, as opposed to the responses of the corresponding wild-type Wassilewskija-4 (Ws-4). Lines 6 and 10 showed much higher MKP1 mRNA than Ws-4 but did not complement the mutant. This suggests a complex dependency of the MAPK phosporylation level of the PR and PDF1.2 genes. Both NADPH oxidase mutants and the mkp1 mutant phenotypically responded to UV-B by growth retardation.

  • 5.
    Mageroy, Melissa H.
    et al.
    Department of Molecular Plant Biology,Norwegian Institute of Bioeconomy Research, Ås, Norway.
    Christiansen, Erik
    Department of Molecular Plant Biology,Norwegian Institute of Bioeconomy Research, Ås, Norway.
    Långström, Bo
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Borg-Karlson, Anna-Karin
    Ecological Chemistry Group, Department of Chemistry, Royal Institute of Technology, Stockholm, Sweden.
    Solheim, Halvor
    Department of Molecular Plant Biology,Norwegian Institute of Bioeconomy Research, Ås, Norway.
    Björklund, Niklas
    Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Zhao, Tao
    Örebro University, School of Science and Technology.
    Schmidt, Axel
    Department of Biochemistry, Max Planck Institute for Chemical Ecology, Jena, Germany.
    Fossdal, Carl Gunnar
    Department of Molecular Plant Biology,Norwegian Institute of Bioeconomy Research, Ås, Norway.
    Krokene, Paal
    Department of Molecular Plant Biology,Norwegian Institute of Bioeconomy Research, Ås, Norway.
    Priming of inducible defenses protects Norway spruce against tree‐killing bark beetles2020In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 43, no 2, p. 420-430Article in journal (Refereed)
    Abstract [en]

    Plants can form an immunological memory known as defense priming, whereby exposure to a priming stimulus enables quicker or stronger response to subsequent attack by pests and pathogens. Such priming of inducible defenses provides increased protection and reduces allocation costs of defense. Defense priming has been widely studied for short–lived model plants such as Arabidopsis, but little is known about this phenomenon in long‐lived plants like spruce. We compared the effects of pre‐treatment with sub‐lethal fungal inoculations or application of the phytohormone methyl jasmonate (MeJA) on the resistance of 48‐year‐old Norway spruce (Picea abies) trees to mass attack by a tree‐killing bark beetle beginning 35 days later. Bark beetles heavily infested and killed untreated trees, but largely avoided fungus‐inoculated trees and MeJA‐treated trees. Quantification of defensive terpenes at the time of bark beetle attack showed fungal inoculation induced 91‐fold higher terpene concentrations compared to untreated trees, while application of MeJA did not significantly increase terpenes. These results indicate that resistance in fungus‐inoculated trees is a result of direct induction of defenses while resistance in MeJA‐treated trees is due to defense priming. This work extends our knowledge of defense priming from model plants to an ecologically important tree species.

  • 6.
    Morales, Luis Orlando
    et al.
    Division of Plant Biology, Department of Biosciences, University of Helsinki, Helsinki, Finland; School of Chemical Technology, Department of Forest Products Technology, Aalto University, Espo, Finland .
    Brosché, Mikael
    Division of Plant Biology, Department of Biosciences, University of Helsinki, Helsinki, Finland; Institute of Technology, University of Tartu, Tartu, Estonia .
    Vainonen, Julia P
    Division of Plant Biology, Department of Biosciences, University of Helsinki, Helsinki, Finland .
    Sipari, Nina
    Metabolomics Unit, Department of Biosciences, University of Helsinki, Helsinki, Finland .
    Lindfors, Anders
    Kuopio Unit, Finnish Meteorological Institute, Kuopio, Finland .
    Strid, Åke
    Örebro University, School of Science and Technology.
    Aphalo, Pedro J
    Division of Plant Biology, Department of Biosciences, University of Helsinki, Helsinki, Finland .
    Are solar UV-B- and UV-A-dependent gene expression and metabolite accumulation in Arabidopsis mediated by the stress response regulator RADICAL-INDUCED CELL DEATH1?2015In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 38, no 5, p. 878-891Article in journal (Refereed)
    Abstract [en]

    Wavelengths in the ultraviolet (UV) region of the solar spectrum, UV-B (280-315nm) and UV-A (315-400nm), are key environmental signals modifying several aspects of plant physiology. Despite significant advances in the understanding of plant responses to UV-B and the identification of signalling components involved, there is limited information on the molecular mechanisms that control UV-B signalling in plants under natural sunlight. Here, we aimed to corroborate the previous suggested role for RADICAL-INDUCED CELL DEATH1 (RCD1) in UV-B signalling under full spectrum sunlight. Wild-type Arabidopsis thaliana and the rcd1-1 mutant were used in an experimental design outdoors where UV-B and UV-A irradiances were manipulated using plastic films, and gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation and metabolite profiles were analysed in the leaves. At the level of transcription, RCD1 was not directly involved in the solar UV-B regulation of genes with functions in UV acclimation, hormone signalling and stress-related markers. Furthermore, RCD1 had no role on PDX1 accumulation but modulated the UV-B induction of flavonoid accumulation in leaves of Arabidopsis exposed to solar UV. We conclude that RCD1 does not play an active role in UV-B signalling but rather modulates UV-B responses under full spectrum sunlight.

  • 7.
    Palmqvist, K
    et al.
    Umeå University, Umeå, Sweden.
    Campbell, D
    Mount Allison University, Sackville, Canada.
    Ekblad, Alf
    Swedish University of Agricultural Sciences, Umeå, Sweden.
    Johansson, H
    Umeå University, Umeå, Sweden.
    Photosynthetic capacity in relation to nitrogen content and its partitioning in lichens with different photobionts1998In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 21, no 4, p. 361-372Article in journal (Refereed)
    Abstract [en]

    We tested the hypothesis that lichen species with a photosynthetic CO2-concentrating mechanism (CCM) use nitrogen more efficiently in photosynthesis than species without this mechanism. Total ribulose bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) and chitin (the nitrogenous component of fungal cell walls), were quantified and related to photosynthetic capacity in eight lichens. The species represented three modes of CO2 acquisition and two modes of nitrogen acquisition, and included one cyanobacterial (Nostoc) lichen with a CCM and N2 fixation, four green algal (Trebouxia) lichens with a CCM but without N2 fixation and three lichens with green algal primary photobionts (Coccomyxa or Dictyochloropsis) lacking a CCM. The latter have N2-fixing Nostoc in cephalodia. When related to thallus dry weight, total thallus nitrogen varied 20-fold, chitin 40-fold, Chl a 5-fold and Rubisco 4-fold among the species. Total nitrogen was lowest in three of the four Trebouxia lichens and highest in the bipartite cyanobacterial lichen. Lichens with the lowest nitrogen invested a larger proportion of this into photosynthetic components, while the species with high nitrogen made relatively more chitin. As a result, the potential photosynthetic nitrogen use efficiency was negatively correlated to total thallus nitrogen for this range of species. The cyanobacterial lichen had a higher photosynthetic capacity in relation to both Chl a and Rubisco compared with the green algal lichens. For the range of green algal lichens both Chl a and Rubisco contents were linearly related to photosynthetic capacity, so the data did not support the hypothesis of an enhanced photosynthetic nitrogen use efficiency in green-algal lichens with a CCM.

  • 8.
    Siipola, Sari M.
    et al.
    Plant Biology Division, Department of Biosciences, University of Helsinki, , Helsinki, Finland.
    Kotilainen, Titta
    Valoya Ltd, , Helsinki, Finland.
    Sipari, Nina
    Viikki Metabolomics Unit, Department of Biosciences, University of Helsinki, , Helsinki, Finland.
    Morales, Luis Orlando
    Plant Biology Division, Department of Biosciences, University of Helsinki, , Helsinki, Finland.
    Lindfors, Anders V.
    Kuopio Unit, Finnish Meteorological Institute, , Kuopio, Finland.
    Robson, Matthew
    Plant Biology Division, Department of Biosciences, University of Helsinki, , Helsinki, Finland.
    Aphalo, Pedro J.
    Plant Biology Division, Department of Biosciences, University of Helsinki, , Helsinki, Finland.
    Epidermal UV-A absorbance and whole leaf flavonoid composition in pea respond more to solar blue light than solar UV radiation2015In: Plant, Cell and Environment, ISSN 0140-7791, E-ISSN 1365-3040, Vol. 38, no 5, p. 941-952Article in journal (Refereed)
    Abstract [en]

    Plants synthesize phenolic compounds in response to certain environmental signals or stresses. One large group of phenolics, flavonoids, is considered particularly responsive to ultraviolet (UV) radiation. However, here we demonstrate that solar blue light stimulates flavonoid biosynthesis in the absence of UV‐A and UV‐B radiation. We grew pea plants (Pisum sativum cv. Meteor) outdoors, in Finland during the summer, under five types of filters differing in their spectral transmittance. These filters were used to (1) attenuate UV‐B; (2) attenuate UV‐B and UV‐A < 370 nm; (3) attenuate UV‐B and UV‐A; (4) attenuate UV‐B, UV‐A and blue light; and (5) as a control not attenuating these wavebands. Attenuation of blue light significantly reduced the flavonoid content in leaf adaxial epidermis and reduced the whole‐leaf concentrations of quercetin derivatives relative to kaempferol derivatives. In contrast, UV‐B responses were not significant. These results show that pea plants regulate epidermal UV‐A absorbance and accumulation of individual flavonoids by perceiving complex radiation signals that extend into the visible region of the solar spectrum. Furthermore, solar blue light instead of solar UV‐B radiation can be the main regulator of phenolic compound accumulation in plants that germinate and develop outdoors.

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