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3. Doktoritööd

Selle kollektsiooni püsiv URIhttp://hdl.handle.net/10492/2490

Sirvi

Sirvi 3. Doktoritööd Märksõna "abiootilised tegurid" järgi

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  • Pisipilt
    Kirje
    Differential regulation of release of leaf stress volatiles: from terpene synthase gene expression to emission responses under heat, ozone and wounding stresses
    (Eesti Maaülikool, 2018) Kanagendran, Arooran; Niinemets, Ülo; Uddling Fredin, Johan (oppopnent)
    Plants release a wide array of biogenic volatile organic compounds both constitutively and upon stress. BVOCs play key roles biologically and ecologically. In addition, the emission responses of stress volatiles act as one of the sensitive indicators for the degree of stress influenced by plants. Furthermore, there are three main photosynthetic traits, net assimilation rate, stomatal conductance to water vapour, and changes in maximum quantum yield of photosystem II, are also modified upon stress in parallel with volatile emissions. High temperature is one of the key abiotic stress factors negatively influencing the plant growth and productivity. Typically, high temperature strongly affect plant physiological and biochemical activities particularly photosynthesis, and biosynthesis and emission of volatile organic compounds. A fluctuating high temperature and in turn, the reduction of plant growth and productivity is a serious issue in tropical and mediterranean crop ecosystems. Ozone is a phytotoxic gas and one of the key abiotic stress factors. Tropospheric ozone is primarily formed through the reaction of nitrogen oxides NO and NO2 (NOX) and BVOCs in the presence of sunlight. Elevated ozone exerts oxidative stress in plants and thus, it alters biochemical adjustments and metabolic shifts. The current tropospheric ozone level is around 40 ppb in most parts of the world and this level of ozone is capable of causing oxidative stress in many plants, particularly in crop plants. Wounding is also a common mechanical stress factor, mainly caused by wind, falling debris and heavy precipitation in nature. Therefore, combined ozone and wounding treatments are predicted to result in synergistic effects on key plant physiological activities such as photosynthetic characteristics and volatile emission responses. There is a scarcity of information about the global scale of photosynthesis and volatile emission responses altered by oxidative stresses induced by heat, ozone, and wounding, and their relationship with concomitant changes in physical and chemical properties of atmosphere. In addition, there is limited information on the molecular basis of terpenoid biosynthesis upon different abiotic stresses. Therefore, understanding the gap between influence of stress and concomitant changes in plant eco-physiological activity is a vital. Aims of the study The specific aims of the Thesis were to: 1. study the impact of heat stress on time-dependent changes in photosynthetic characteristics and concomitant changes in mono- and sesquiteprene emission responses; analyze the effects of heat stress on the regulation of β-phellandrene and (E)-β-caryophyllene synthase genes in Solanum lycopersicum ‘Pontica’; and assess the correspondence between time-dependent modifications in mono-and sesquiterpene gene expression and terpenoid emissions through recovery (Paper I). 2. study the effect of combined ozone and wounding treatments on the changes in photosynthetic characteristics and stress volatile emission rates through recovery; and estimate the relationship between quantitative emission responses and stress severity, including ozone dose and stomatal ozone uptake rate in Eucalyptus globulus ‘Labil’ (Paper II). 3. assess the relationships between ozone concentration and modifications in foliage photosynthetic characteristics and emissions of LOX volatiles and mono- and sesquiterpenes; estimate the leaf ozone uptake between stomatal ozone uptake and non-stomatal ozone deposition; and relate the stomatal ozone flux and non-stomatal ozone deposition with the degree of elicitation of different volatiles in Nicotiana tabacum ‘Wisconsin’ (Paper III). Main results In this Thesis, we developed three model systems in our lab to understand the impact of abiotic stresses on primary and secondary metabolic processes of crop and economically important woody plants. • In S. lycopersicum leaves, mild heat stress did not have any significant impact on the changes in photosynthetic traits, but severe heat stress irreversibly declined photosynthetic characteristics. The modifications in foliage mono- and sesquiterpene emissions were associated with β-phellandrene and (E)-β-caryophyllene synthase gene expression at mild heat stress. Based on time-delay analysis of mono- and sesquiterpene synthase genes, the best correspondence between terpene synthase gene expression and emission was shifted by ca. 2h for mild heat stress, but the time-shift relationship between gene expression and emission was not clear-cut for severe heat stress, implying that severe heat stress significantly impair terpene metabolism (Paper I). • In E. globulus leaves, the physiological and biochemical responses to a combined effect of ozone and wounding through recovery were different from the responses in plants treated with ozone and wounding separately. Particularly, the reduction of photosynthetic characteristics such as A, gs and Fv/Fm, and increased stressed volatile emission responses were greater for combined ozone and wounding treatments followed by separate ozone and wounding treatments. Taken together, these key outcomes demonstrated that combined acute ozone and wounding treatments led to synergistic effects on leaf photosynthetic traits and stress volatile emissions. LOX emissions were scaled with the degree of stress applications, but there were no quantitative relationships observed between the severity of stress and emission responses for other stress volatiles. The absence of stress dose vs. emission relationship was likely due to removal of ozone in leaf intercellular air spaces and ROS in mesophyll cells by volatile isoprenoids through recovery (Paper II). • In N. tabacum ‘Wisconsin’ leaves, acute ozone exposure result in a dramatic decline of foliar gas-exchange characteristics, but the reductions in all these characteristics were almost fully reversible even at the highest ozone concentrations underscoring the high ozone resistance. The emission rate of LOX volatiles was dose-dependent, but dose-dependency was weaker for mono- and sesquiterpene emissions. In addition, non-stomatal ozone deposition contributed to the greater share of ozone flux into the leaf and this was associated with the release of terpenes, collectively implying that a greater share of terpenoid emission upon ozone exposures mostly reflected the modification of terpene release from trichomes on leaf surface (Paper III).
  • Pisipilt
    Kirje
    Influence of abiotic and biotic factors at patch and landscape scale on bumblebees (Bombus spp.) in semi-natural meadows
    (Eesti Maaülikool, 2011) Diaz Forero, Isabel
    Kimalasi on põhjalikumalt uuritud Lääne-Euroopa, Aasia ja Põhja-Ameerika põllumajandusmaastikes, vähem teistes piirkondades. Maastikumustri mõju kimalaste populatsioonidele metsastel aladel on käsitletud väga vähestes teadusuurigutes. Käesolev uurimus viidi läbi 22-l poollooduslikul niidul Ida-Virumaal, mis on suurte metsamassiivide ning suure looduslike elupaikade osatähtusega piirkond Kirde-Eestis. Uurimuse peamine eesmärk oli välja selgitada abiootiliste ja biootiliste faktorite mõju kimalaste arvukusele ja liigirikkusele nii elupaiga tasandil kui ka elupaika ümbritseva maastiku tasandil. Elupaiga tasandil uuriti taimkatte, taimkatte struktuuri, elupaiga pindala, perimeetri pikkuse ja kuju mõju kimalaste populatsioonidele. Maastiku tasandil uuriti 250 m, 500 m, 1000 m ja 2000 m raadiuses olevate maakattetüüpide ja erinevate maastikuindeksite seoseid kimalaste arvukuse ja liigirikkusega. Uurimistulemused näitasid, et õitsevate taimede suurem arvukus ja liigirikkus suurendab ka kimalaste arvukust ja liigirikkust. Maastiku tasandil ilmnes inimasustuse, eelkõige aedade ning looduslike ja poollooduslike niitude positiivne mõju kimalaste arvukusele ja liigirikkusele, samas vähendavad kimalaste arvukust ning liigirikkust ümbritsevas maastikus paiknevad avatud põllumaad, metsamassiivid ja võsa. Maakatte mõju kimalastele võib olla liigiti erinev. Mõned liigid (Bombus schrenki) eelistavad metsalaikudega maastikke ja servaalasid, teised liigid (B. vetereanus, B. terrestris) eelistavad avatud maastikke. Uurimus näitas, et kimalaste arvukus ja liigirikkus ei sõltu ainult bioloogilistest teguritest nagu näiteks toidu olemasolu, vaid sõltub ka elupaika ümbritseva maastiku mitmekesisusest ja kvaliteedist. Seega tuleb kimalaste kaitse korraldamisel ja põllumajanduskavade väljatöötamisel arvestada mitte ainult kitsalt elupaiga tingimustega vaid ka kimalaste elupaika ümbritseva maastiku mustriga.
  • Pisipilt
    Kirje
    Quantitative impacts of interactive biotic and abiotic stresses on plant performance: stress responses, priming, and acclimation
    (Estonian University of Life Sciences, 2023) Sulaiman, Hassan Yusuf; Niinemets, Ülo; Institute of Agricultural and Environmental Sciences; Staudt, Michael (opponent)
    Environmental stresses in plants result in emissions of volatile organic compounds (VOC) and reductions in photosynthesis. Plants experience multiple abiotic and biotic stresses sequentially or simultaneously and responses activated by one stress can alter responses activated by the other stress. The main aim of this thesis was to study the responses of plant physiological traits to interactive biotic and abiotic stresses depending on the severity of the different stresses, sequences, and duration in four model species. We used Achillea millefolium in the first experiment and O. vulgare in the second experiment to investigate the impact of moderate heat (35°C for 1 hr, heat priming) on foliage photosynthesis and VOC emissions responses through 72 h heat shock stress (45°C for 5 min) recovery period. Heat-primed plants demonstrated higher heat shock tolerance of photosynthetic activities, evident in smaller reductions in the rates of photosynthesis and faster recovery, and lower emissions of stress VOC indicating lower oxidative stress. In primed O. vulgare, a certain decrease in photosynthetic activity remained suggesting a sustained priming effect, and VOC emissions rose at later phases of recovery indicating the activation of biochemical defense in primed plants. In the third experiment, we studied how infestation with Trialeurodes vaporariorum alters photosynthesis and VOC emissions in O. vulgare through 48 h heat shock recovery period. In non-infested plants, photosynthesis did not recover, but in infested plants, photosynthesis recovered fully, indicating a greater heat stress tolerance. In infested plants, heat shock resulted in much lower stress VOC emissions that recovered to pre-stress levels at the end of the experiment. This suggests that insect phloem feeding decreased VOC emissions responses to heat shock and enhance the thermal acclimation of photosynthetic activities. In the fourth and fifth experiments, we quantified the impact of the biotrophic crown rust fungus, Puccinia coronata on foliage photosynthesis and VOC emissions with increasing the severity of infection in the primary host Avena sativa and the alternate host Rhamnus frangula. In A. sativa, decreases in photosynthesis were much greater and emissions of VOC were strongly enhanced with increased severity of infection, but the emissions decreased during severe infections due to an overall inhibition of physiological activity. In R. frangula, VOC emissions were elicited to a minor degree, but surprisingly, emissions of constitutive isoprene were strongly enhanced. These results suggest differential biochemical responses and varying fungal sensitivity in the two hosts. We argued that the greater infection sensitivity in A. sativa was due to fungal interaction with warm weather that might have enhanced the fungal virulence.