Maria Celeste Dias

Chromium (VI) induces toxicity at different photosynthetic levels in pea

In order to comprehensively characterize the effects of Cr (VI) on the photosynthetic performance of Pisum sativum, plants irrigated with Cr solutions (ranging from 20 to 2000 mg l(-1)) were evaluated using the following classical endpoints: gas exchange parameters, chlorophyll a (Chl a) fluorescence, leaf pigments, Rubisco activity, soluble sugars and starch content. Flow cytometry (FCM) was applied in an innovative approach to evaluate the morphological and fluorescence emission status of chloroplasts from plants exposed to Cr (VI). The parameters related to gas exchange, net CO(2) assimilation rate (A) and Rubisco activity were severally affected by Cr exposure, in some cases even at the lowest dosage used. While all biomarkers used to measure Chl a fluorescence indicated a decrease in fluorescence at the maximum dosage, pigment contents significantly increased in response to Cr (VI). The morphology of chloroplasts also was altered by Cr (VI) exposure, as a volume decrease was observed. Soluble sugars and starch showed an overall tendency to increase in Cr (VI) exposed plants, but sucrose and glucose decreased highly when exposed to 2000 mg l(-1). In conclusion, our results indicate that Cr (VI) affects photosynthesis at several levels, but the most Cr (VI)-sensitive endpoints were chloroplast morphology and biochemical processes; only at higher dosages the photochemical efficiency is compromised.

Limitations of photosynthesis in Phaseolus vulgaris under drought stress: gas exchange, chlorophyll fluorescence and Calvin cycle enzymes

In this article, the effects of drought stress (DS) on gas exchange, chlorophyll (Chl) a fluorescence and Calvin cycle enzymes in Phaseolus vulgaris are evaluated. Three-week-old plants were exposed to DS by receiving only so much water every evening to ensure 30% field capacity water content overnight. After three days under these conditions, we observed that DS induced a decline of the CO2 assimilation. Gas-exchange data showed that the closure of stomata during DS did not lead to a concomitant decline in calculated intercellular CO2 concentration. Moreover, DS plants showed a reduction of the photochemical Chl fluorescence quenching, photosystem II quantum yield and electron transport rate and a higher pH gradient and more heat dissipation as compared to controls. The activity of Calvin cycle enzymes, Rubisco, sFBPase, and Ru5PK, decreased strongly in DS plants as compared to controls. Data analysis suggest that the decrease of CO2 assimilation under drought conditions is not related to a diminished capacity of the use of NADPH and ATP but probably to the decline of enzyme activity involved in RuBP regeneration (Ru5PK).

Phytotoxicity: An Overview of the Physiological Responses of Plants Exposed to Fungicides

In the last decades, the use of fungicides in agriculture for fungi diseases control has become crucial. Fungicide research has produced a diverse range of products with novel modes of action. However, the extensive use of these compounds in the agriculture system raises public concern because of the harmful potential of such substances in the environment and human health. Moreover, the phytotoxic effects of some fungicides are already recognized but little is known about the impact of these compounds on the photosynthetic apparatus. This paper presents a comprehensive overview of the literature considering different classes of fungicides and their effects on plant physiology, with particular emphasis on photosynthesis.

Is the interplay between epigenetic markers related to the acclimation of cork oak plants to high temperatures

Trees necessarily experience changes in temperature, requiring efficient short-term strategies that become crucial in environmental change adaptability. DNA methylation and histone posttranslational modifications have been shown to play a key role in both epigenetic control and plant functional status under stress by controlling the functional state of chromatin and gene expression. Cork oak (Quercus suber L.) is a key stone of the Mediterranean region, growing at temperatures of 45°C. This species was subjected to a cumulative temperature increase from 25°C to 55°C under laboratory conditions in order to test the hypothesis that epigenetic code is related to heat stress tolerance. Electrolyte leakage increased after 35°C, but all plants survived to 55°C. DNA methylation and acetylated histone H3 (AcH3) levels were monitored by HPCE (high performance capillary electrophoresis), MS-RAPD (methylation-sensitive random-amplified polymorphic DNA) and Protein Gel Blot analysis and the spatial distribution of the modifications was assessed using a confocal microscope. DNA methylation analysed by HPCE revealed an increase at 55°C, while MS-RAPD results pointed to dynamic methylation-demethylation patterns over stress. Protein Gel Blot showed the abundance index of AcH3 decreasing from 25°C to 45°C. The immunohistochemical detection of 5-mC (5-methyl-2′-deoxycytidine) and AcH3 came upon the previous results. These results indicate that epigenetic mechanisms such as DNA methylation and histone H3 acetylation have opposite and particular dynamics that can be crucial for the stepwise establishment of this species into such high stress (55°C), allowing its acclimation and survival. This is the first report that assesses epigenetic regulation in order to investigate heat tolerance in forest trees.

Differential inhibition of photosynthesis under drought stress in Flaveria species with different degrees of development of the C4 syndrome

The effect of drought stress (DS) on photosynthesis and photosynthesis-related enzyme activities was investigated in F. pringlei (C3), F. floridana (C3–C4), F. brownii (C4-like), and F. trinervia (C4) species. Stomatal closure was observed in all species, probably being the main cause for the decline in photosynthesis in the C3 species under ambient conditions. In vitro ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and stromal fructose 1,6-bisphosphatase (sFBP) activities were sufficient to interpret the net photosynthetic rates (PN), but, from the decreases in PN values under high CO2 (Ca = 700 µmol mol− 1) it is concluded that a decrease in the in vivo rate of the RuBPCO reaction may be an additional limiting factor under DS in the C3 species. The observed decline in the photosynthesis capacity of the C3–C4 species is suggested to be associated both to in vivo decreases of RuBPCO activity and of the RuBP regeneration rate. The decline of the maximum PN observed in the C4-like species under DS was probably attributed to a decrease in maximum RuBPCO activity and/or to decrease of enzyme substrate (RuBP or PEP) regeneration rates. In the C4 species, the decline of both in vivo photosynthesis and photosynthetic capacity could be due to in vivo inhibition of the phosphoenolpyruvate carboxylase (PEPC) by a twofold increase of the malate concentration observed in mesophyll cell extracts from DS plants.

Changes in the metabolome of lettuce leaves due to exposure to mancozeb pesticide.

This paper describes a proton high resolution magic angle spinning (HRMAS) nuclear magnetic resonance (NMR) metabolomic study of lettuce (Lactuca sativa L.) leaves to characterise metabolic adaptations during leaf growth and exposure to mancozeb. Metabolite variations were identified through multivariate analysis and checked through spectral integration. Lettuce growth was accompanied by activation of energetic metabolism, preferential glucose use and changes in amino acids, phospholipids, ascorbate, nucleotides and nicotinate/nicotinamide. Phenylalanine and polyphenolic variations suggested higher oxidative stress at later growth stages. Exposure to mancozeb induced changes in amino acids, fumarate and malate, suggesting Krebs cycle up-regulation. In tandem disturbances in sugar, phospholipid, nucleotide and nicotinate/nicotinamide metabolism were noted. Additional changes in phenylalanine, dehydroascorbate, tartrate and formate were consistent with a higher demand for anti-oxidant defence mechanisms. Overall, lettuce exposure to mancozeb was shown to have a significant impact on plant metabolism, with mature leaves tending to be more extensively affected than younger leaves.

Photosynthetic parameters of Ulmus minor plantlets affected by irradiance during acclimatization

In order to set up large-scale acclimatization protocols of micropropagated plants, an in-depth knowledge of their physiological responses during in vitro to ex vitro transfer is required. This work describes the photosynthetic performance of Ulmus minor micropropagated plants during acclimatization at high irradiance (HI; 200 ± 20 μmol m−2 s−1 or low irradiance (LI; 100 ± 20 μmol m−2 s−1). During this experiment, leaf pigment content, chlorophyll a fluorescence, gas exchange, stomata morphology, the activity of the Calvin cycle enzymes and saccharides were measured in persistent and new leaves. The results indicated that HI induces a higher photosynthetic performance compared to LI. Therefore, plants acclimatized under HI are likely to survive better after field transfer.

Acclimatization of micropropagated plantlets induces an antioxidative burst: a case study with Ulmus minor Mill.

In this article, the effects of increased light intensities on antioxidant metabolism during ex vitro establishment of Ulmus minor micropropagated plants are investigated. Three month old in vitro plants were acclimatized to ex vitro conditions in a climate chamber with two different light intensities, 200 μmol m−2 s−1 (high light, HL) and 100 μmol m−2 s−1 (low light, LL) during 40 days. Immediately after ex vitro transfer, the increase of both malondialdehyde (MDA) and electrolyte leakage in persistent leaves is indicative of oxidative stress. As the acclimatization continues, an upregulation of the superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR) enzyme activities were also observed. Simultaneously, MDA content and membrane permeability stabilized, suggesting that the antioxidant enzymes decrease the deleterious effects of reactive oxygen species (ROS) generation. Unexpectedly, newly formed leaves presented a different pattern of antioxidative profile, with high levels of MDA and membrane leakage and low antioxidant enzyme activity. Despite these differences, both leaf types looked healthy (e.g. greenish, with no necrotic spots) during the whole acclimatization period. The results indicate that micropropagated U. minor plantlets develop an antioxidant enzyme system after ex vitro transfer and that, in general, LL treatment leads to lower oxidative stress. Moreover, new leaves tolerate higher levels of ROS without the need to activate the antioxidative pathway, which suggests that the environment at which leaves are exposed during its formation determinate their ability to tolerate ROS.

Acclimatization of secondary somatic embryos derived plants of Eucalyptus globulus Labill.: an ultrastructural approach

This paper reports the complete process from secondary emblings (SE-derived plants) regeneration to acclimatization of Eucalyptus globulus and describes histocytological changes that occur in leaves from in vitro to ex vitro acclimatization for a 3-month period. After elongation, plants were transferred to pots with sterilized peat:perlite and acclimatized in a phytotron, with progressive reduction of RH and increase of light intensity. Histocytological analyses were performed in fixed material using light microscopy and ultrastructural changes followed by electron microscopy (SEM and TEM). The protocol used allowed the successful acclimatization of the emblings. Plants looked morphologically normal and FCM screening revealed no ploidy or DNA content abnormalities. Histocytological analyses showed significant changes along time, mostly in stomata shape and aperture, starch reserves, chloroplast morphology and mesophyll differentiation. This is the first report concerning emblings acclimatization to ex vitro conditions in Eucalyptus. It was clearly demonstrated that during acclimatization emblings suffered profound changes in leaf morphology in order to successfully adapt to ex vitro conditions.

Effect of irradiance during acclimatization on content of proline and phytohormones in micropropagated Ulmus minor

This study aimed to investigate the effects of irradiance on plant growth and content of proline and phytohormones during ex vitro acclimatization of micropropagated Ulmus minor plants. In vitro rooted plants were acclimatized to ex vitro conditions in a climate chamber with two irradiances, 200 μmol m−2 s−1 (high irradiance, HI) and 100 μmol m−2 s−1 (low irradiance, LI) for 40 d. Immediately after the ex vitro transfer, the plants experienced a water deficit [wilting leaves with the reduced relative water content (RWC)], but following the experiment, the recovery of the RWC was more pronounced in the HI treatment. Also, the content of proline, ABA, and JA-Ile were higher in HI treatment. Growth analyses revealed that HI improved growth and biomass production.