Drought affects the heat-hardening capacity of alpine plants as indicated by changes in xanthophyll cycle pigments, singlet oxygen scavenging, α-tocopherol and plant hormones

AbstractAlpine environments in Europe are increasingly affected by more erratic precipitation patterns, and more frequent drought and heat waves. Heat-hardening capacity is a key feature for survival of these abiotic stress factors, but it is poorly understood how heat and drought affect plant performance when combined. The main objectives of this study were (1) to determine maximum heat hardening capacity in 14 selected plant species and (2) to study how alpine plants respond to combined heat and drought stress compared to heat alone. (3) For risk assessment maximum leaf temperatures were measured in the field and (4) important methodological aspects of testing heat tolerance were evaluated. Heat hardening capacity was assessed by Tc, the heat threshold of photosystem II (PS II), and by heat tolerance tests based on visual inspection of leaf tissue damage or potential quantum efficiency of PS II (Fv/Fm). A purpose-built Heat Tolerance Testing System (HTTS) was used, which allows for controlled heat exposure of whole plants under nearly natural conditions. Additionally, in two species from contrasting habitats, Senecio incanus and Primula minima, the dynamics of heat hardening was studied during and after 8days exposure to heat (H), or to a combination of heat and severe drought (H+D) within a light-transmissive heat hardening chamber at the alpine field site. In both species, H treatment significantly increased heat tolerance (LT50), determined by the HTTS, to 58.0°C and 54.9°C, respectively, and was accompanied by elevated production of abscisic acid (ABA) and salicylic acid (SA), whereas jasmonic acid (JA) levels decreased. Under H+D the LT50 was only 56.5°C and 51.6°C, respectively, and levels of ABA were higher in S. incanus and SA lower in both species in comparison to H. Changes in xanthophyll cycle pigments, α-tocopherol and carotenoids:chlorophyll ratio were more pronounced in P. minima than in S. incanus. In P. minima both H and H+D significantly increased singlet oxygen (1O2) scavenging capacity, determined by electron paramagnetic resonance spectroscopy (EPR). In the field, the maximum half-hourly mean (HHM) leaf temperature of P. minima (32.2°C) was significantly lower than of S. incanus (46.5°C, a potentially harmful temperature). We conclude that the investigated species are well adapted to the prevailing temperature conditions in the field. They also possess an outstanding heat hardening capacity, but this can be curtailed when heat is combined with drought. As drought further increases leaf temperatures, the risk of suffering lethal heat damage of some species may increase in the future, particularly at south exposed, ruderal alpine sites with uncertain water supply

Redox feedback regulation of ANAC089 signaling alters seed germination and stress response

21 p.-4 fig.-2 tab. 1 graph. abst.The interplay between the phytohormone abscisic acid (ABA) and the gasotransmitter nitric oxide (NO) regulates seed germination and post-germinative seedling growth. We show that GAP1 (germination in ABA and cPTIO 1) encodes the transcription factor ANAC089 with a critical membrane-bound domain and extranuclear localization. ANAC089 mutants lacking the membrane-tethered domain display insensitivity to ABA,salt, and osmotic and cold stresses, revealing a repressor function. Whole-genome transcriptional profiling and DNA-binding specificity reveals that ANAC089 regulates ABA- and redox-related genes. ANAC089 truncated mutants exhibit higher NO and lower ROS and ABA endogenous levels, alongside an altered thiol and disulfide homeostasis. Consistently, translocation of ANAC089 to the nucleus is directed by changes in cellular redox status after treatments with NO scavengers and redox-related compounds. Our results reveal ANAC089 to be a master regulator modulating redox homeostasis and NO levels, able to repress ABA synthesis and signaling during Arabidopsis seed germination and abiotic stress.Wethank the Spanish networks BIO2015-68957-REDT and RED2018-102397-T for stimulating discussions, as well as Dr. José M. Carrasco and Dr. Pablo Vera (IBMCP-CSIC) for help with the protein-expression experiments of the PBM. This work was financed by grants EcoSeed Impacts of Environmental Conditions on Seed Quality ‘‘EcoSeed-311840’’ ERC.KBBE.2012.1.1-01;BIO2017-85758-R and CSD2007-00057 (TRANSPLANTA) from the Ministerio de Ciencia, Innovación y Universidades (MICIU) (Spain); SA313P18 and SA137P20 from Junta de Castilla y León; Escalera de Excelencia CLU-2018-04 co-funded by the P.O. FEDER of Castilla y León 2014–2020 Spain (to O.L.); and the PhD and University Teacher Training Fellowship, Spanish Ministry of Science and Education (to P.A.).Peer reviewe

Abscisic acid-determined seed vigour differences do not influence redox regulation during ageing

High seed quality is a key trait to achieve successful crop establishment required for optimum yield and sustainable production. Seed storage conditions greatly impact two key seed quality traits; seed viability (ability to germinate and produce normal seedlings) and vigour (germination performance). Accumulated oxidative damage accompanies the loss of seed vigour and viability during ageing, indicating that redox control is key to longevity. Here, we studied the effects of controlled deterioration at 40°C and 75% relative humidity (RH) (‘ageing’) under two different O2 concentrations (21 and 78% O2) in Brassica oleracea. Two B. oleracea genotypes with allelic differences at two QTLs that result in differences in abscisic acid (ABA) signalling and seed vigour were compared. Ageing led to a similar loss in germination speed in both genotypes that was lost faster under elevated O2. In both genotypes, an equal oxidative shift in the glutathione redox state and a minor loss of α-tocopherol progressively occurred before seed viability was lost. In contrast, ABA levels were not affected by ageing. In conclusion, both ABA signalling and seed ageing impact seed vigour but not necessarily through the same biochemical mechanisms

Foliar Phenolic Compounds in Norway Spruce with Varying Susceptibility to Chrysomyxa rhododendri: Analyses of Seasonal and Infection-Induced Accumulation Patterns

Secondary phenolic metabolites are involved in plant responses to various biotic stress factors, and are apparently important for the defense against fungal pathogens. In this study, we investigated their role in defense against the rust Chrysomyxa rhododendri in Norway spruce. The fungal pathogen undergoes a seasonal lifecycle with host shift; after overwintering in rhododendron shrubs, it attacks the sprouting current-year spruce needles and causes needle fall in autumn. Repeated infections lead to reduced timber yield and severe problems with rejuvenation in subalpine Norway spruce forests. Trees with varying susceptibility to infection by C. rhododendri were selected and foliar phenolic composition was assessed using UHPLC-MS. We report on seasonal accumulation patterns and infection-related changes in the concentrations of 16 metabolites, including flavonoids, stilbenes, simple phenylpropanoids and the precursor shikimic acid, and their correlation with the infection degree of the tree. We found significant variation in the phenolic profiles during needle development: flavonoids were predominant in the first weeks after sprouting, whereas stilbenes, picein and shikimic acid increased during the first year. Following infection, several flavonoids and resveratrol increased up to 1.8 fold in concentration, whereas picein and shikimic acid were reduced by about 70 and 60%, respectively. The constitutive and early stage infection-induced concentrations of kaempferol, quercetin and taxifolin as well as the late stage infection-induced concentrations of stilbenes and picein were negatively correlated with infection degree. We conclude that a combination of constitutive and inducible accumulation of phenolic compounds is associated with the lower susceptibility of individual trees to C. rhododendri. The potentially fungicidal flavonoid aglycones may limit hyphal growth and prevent development of infection symptoms, and high levels of stilbenes may impede the infection of older needles. The presented results underline a highly compound-specific seasonal accumulation and defense response of Norway spruce and may facilitate the selection of promising trees for breeding programs

The non-photochemical quenching protein LHCSR3 prevents oxygen-dependent photoinhibition in Chlamydomonas reinhardtii

Non-photochemical quenching (NPQ) helps dissipate surplus light energy, preventing formation of reactive oxygen species (ROS). In Chlamydomonas reinhardtii the thylakoid membrane protein LHCSR3 is involved in pH-dependent (qE-type) NPQ, deficient in the npq4 mutant. Preventing PSII repair revealed that npq4 lost PSII activity faster than wild-type (WT) in elevated O2, while no difference between strains was observed in O2-deplete conditions. Low Fv/Fm values remained 1.5 h after moving cells out of high light, and this qH-type quenching was independent of LHCSR3 and not accompanied by losses of maximum PSII activity. Culturing cells in historic O2 atmospheres (30-35%) increased the qE of cells, due to increased LHCSR1 and PsbS levels, and LHCSR3 in WT, showing that atmospheric O2 tensions regulate qE capacity. Colony growth of npq4 was severely restricted at elevated O2 and npq4 accumulated more reactive electrophile species (RES) than WT, which could damage PSI. Levels of PsaA (PSI) were lower in npq4 grown at 35 % O2 while PsbA (PSII) levels remained stable. We conclude that even at high O2 concentrations, the PSII repair cycle is sufficient to maintain net levels of PSII. However, LHCSR3 has an important function in protecting PSI against O2-mediated damage, e.g. via RES

Curvature Detection with an Optoelectronic Measurement System Using a Self-Made Calibration Profile

So far, no studies of material deformations (e.g., bending of sports equipment) have been performed to measure the curvature (w″) using an optoelectronic measurement system OMS. To test the accuracy of the w″ measurement with an OMS (Qualisys), a calibration profile which allowed to: (i) differentiates between three w″ (0.13˙ m−1, 0.2 m−1, and 0.4 m−1) and (ii) to explore the influence of the chosen infrared marker distances (50 mm, 110 mm, and 170 mm) was used. The profile was moved three-dimensional at three different mean velocities (vzero = 0 ms−1, vslow = 0.2 ms−1, vfast  = 0.4 ms−1) by an industrial robot. For the accuracy assessment, the average difference between the known w″ of the calibration profile and the detected w″ from the OMS system, the associated standard deviation (SD) and the measuring point with the largest difference compared to the defined w″ (=maximum error) were calculated. It was demonstrated that no valid w″ can be measured at marker distances of 50 mm and only to a limited extent at 110 mm. For the 170 mm marker distance, the average difference (±SD) between defined and detected w″ was less than 1.1 ± 0.1 mm−1 in the static and not greater than −3.8 ± 13.1 mm−1 in the dynamic situations. The maximum error in the static situation was small (4.0 mm−1), while in the dynamic situations there were single interfering peaks causing the maximum error to be larger (−30.2 mm−1 at a known w″ of 0.4 m−1). However, the Qualisys system measures sufficiently accurately to detect curvatures up to 0.13˙ m−1 at a marker distance of 170 mm, but signal fluctuations due to marker overlapping can occur depending on the direction of movement of the robot arm, which have to be taken into account

Classification of Alpine Skiing Styles Using GNSS and Inertial Measurement Units

In alpine skiing, four commonly used turning styles are snowplow, snowplow-steering, drifting and carving. They differ significantly in speed, directional control and difficulty to execute. While they are visually distinguishable, data-driven classification is underexplored. The aim of this work is to classify alpine skiing styles based on a global navigation satellite system (GNSS) and inertial measurement units (IMU). Data of 2000 turns of 20 advanced or expert skiers were collected with two IMU sensors on the upper cuff of each ski boot and a mobile phone with GNSS. After feature extraction and feature selection, turn style classification was applied separately for parallel (drifted or carved) and non-parallel (snowplow or snowplow-steering) turns. The most important features for style classification were identified via recursive feature elimination. Three different classification methods were then tested and compared: Decision trees, random forests and gradient boosted decision trees. Classification accuracies were lowest for the decision tree and similar for the random forests and gradient boosted classification trees, which both achieved accuracies of more than 93% in the parallel classification task and 88% in the non-parallel case. While the accuracy might be improved by considering slope and weather conditions, these first results suggest that IMU data can classify alpine skiing styles reasonably well

Association genetics of phenolic needle compounds in Norway spruce with variable susceptibility to needle bladder rust

Key message Accumulation of phenolic needle metabolites in Norway spruce is regulated by many genes with small and additive effects and is correlated with the susceptibility against fungal attack. Abstract Norway spruce accumulates high foliar concentrations of secondary phenolic metabolites, with important functions for pathogen defence responses. However, the molecular genetic basis underlying the quantitative variation of phenolic compounds and their role in enhanced resistance of spruce to infection by needle bladder rust are unknown. To address these questions, a set of 1035 genome-wide single nucleotide polymorphisms (SNPs) was associated to the quantitative variation of four simple phenylpropanoids, eight stilbenes, nine flavonoids, six related arithmetic parameters and the susceptibility to infection by Chrysomyxa rhododendri in an unstructured natural population of Norway spruce. Thirty-one significant genetic associations for the flavonoids gallocatechin, kaempferol 3-glucoside and quercetin 3-glucoside and the stilbenes resveratrol, piceatannol, astringin and isorhapontin were discovered, explaining 2259% of phenotypic variation, and indicating a regulation of phenolic accumulation by many genes with small and additive effects. The phenolics profile differed between trees with high and low susceptibility to the fungus, underlining the importance of phenolic compounds in the defence mechanisms of Norway spruce to C. rhododendri. Results highlight the utility of association studies in non-model tree species and may enable marker-assisted selection of Norway spruce adapted to severe pathogen attack.(VLID)456580

Changes in low-molecular-weight thiol-disulphide redox couples are part of bread wheat seed germination and early seedling growth

<p>The tripeptide antioxidant glutathione (γ-l-glutamyl-l-cysteinyl-glycine; GSH) essentially contributes to thiol-disulphide conversions, which are involved in the control of seed development, germination, and seedling establishment. However, the relative contribution of GSH metabolism in different seed structures is not fully understood. We studied the GSH/glutathione disulphide (GSSG) redox couple and associated low-molecular-weight (LMW) thiols and disulphides related to GSH metabolism in bread wheat (<i>Triticum aestivum</i> L.) seeds, focussing on redox changes in the embryo and endosperm during germination. In dry seeds, GSH was the predominant LMW thiol and, 15 h after the onset of imbibition, embryos of non-germinated seeds contained 12 times more LMW thiols than the endosperm. In germinated seeds, the embryo contained 17 and 11 times more LMW thiols than the endosperm after 15 and 48 h, respectively. This resulted in the embryo having significantly more reducing half-cell reduction potentials of GSH/GSSG and cysteine (Cys)/cystine (CySS) redox couples (E_GSSG/2GSH and E_CySS/2Cys, respectively). Upon seed germination and early seedling growth, Cys and CySS concentrations significantly increased in both embryo and endosperm, progressively contributing to the cellular LMW thiol-disulphide redox environment (E_{thiol-disulphide}). The changes in E_CySS/2Cys could be related to the mobilisation of storage proteins in the endosperm during early seedling growth. We suggest that E_GSSG/2GSH and E_CySS/2Cys can be used as markers of the physiological and developmental stage of embryo and endosperm. We also present a model of interaction between LMW thiols and disulphides with hydrogen peroxide (H₂O₂) in redox regulation of bread wheat germination and early seedling growth.</p