No abstract

A comparative study of the effects of exposure to high Cd2+ (50 µM) and excess Zn2+ (600 µM) on photosynthetic performance of hydroponically-grown durum wheat seedlings was performed. At day 8, Cd and Zn were added to the nutrient solution. After 7-days exposure, the chosen concentrations of both metals resulted in similar relative growth rate (RGR) inhibitions of about 50% and comparable retardations of the CO2 assimilation rates (about 30%) in the second developed leaf of wheat seedlings. Analysis of chlorophyll a fluorescence indicated that both metals disturbed photosynthetic electron transport processes which led to a 4- to 5-fold suppression of the efficiency of energy transformation in Photosystem II. Non-specific toxic effects of Cd and Zn, which prevailed, were an inactivation of part of Photosystem II reaction centres and their transformation into excitation quenching forms as well as disturbed electron transport in the oxygen-evolving complex. The specificity of the Cd and Zn modes of action was mainly expressed in the intensity of the toxicity effects: despite the similar inhibitions of the CO2 assimilation rates, the wheat photochemistry showed much more sensitivity to Cd than to Zn exposure.

No abstract

Perennial ryegrass (Lolium perenne L.) belongs to the common cultivated grass species in Central and Western Europe. Despite being considered to be susceptible to drought, it is frequently used for forming the turf in urban green areas. In such areas, the water deficit in soil is recognized as one of the most important environmental factors, which can limit plant growth. The basic aim of this work was to explore the mechanisms standing behind the changes in the photosynthetic apparatus performance of two perennial ryegrass turf varieties grown under drought stress using comprehensive in vivo chlorophyll fluorescence signal analyses and plant gas exchange measurements. Drought was applied after eight weeks of sowing by controlling the humidity of the roots ground medium at the levels of 30, 50, and 70% of the field water capacity. Measurements were carried out at four times: 0, 120, and 240 h after drought application and after recovery (refilling water to 70%). We found that the difference between the two tested varieties’ response resulted from a particular re-reduction of P700+ (reaction certer of PSI) that was caused by slower electron donation from P680. The difference in the rate of electron flow from Photosystem II (PSII) to PSI was also detected. The application of the combined tools (plants’ photosynthetic efficiency analysis and plant gas exchange measurements) allowed exploring and explaining the specific variety response to drought stress.

16Phenotypic plasticity can maintain population fitness in novel or changing environments if it allows the 17 phenotype to track the new trait optimum. Understanding how adaptation to contrasting environments 18 determines plastic responses can identify how plasticity evolves, and its potential to be adaptive in response 19 to environmental change. We sampled 79 genotypes from populations of two closely related but ecologically 20 divergent ragwort species (Senecio, Asteraceae), and transplanted multiple clones of each genotype into four 21 field sites along an elevational gradient representing each species' native range, the edge of their range, and 22 conditions outside their native range. At each transplant site, we quantified differences in survival, growth, 23 leaf morphology, chlorophyll fluorescence and gene expression for both species. Overall, the two species 24 differed in their sensitivity to the elevational gradient. As evidence of plasticity, leaf morphology changed 25 across the elevational gradient, with changes occurring in opposite directions for the two species. Differential 26 gene expression across the four field sites also revealed that the genetic pathways underlying plastic 27 responses were highly distinct in the two species. Despite the two species having diverged recently, 28 adaptation to contrasting habitats has resulted in the evolution of distinct sensitivities to environmental 29 variation, underlain by distinct forms of plasticity. 30 genotype-by-environment interactions, phenotypic plasticity, physiological plasticity, specialisation 32 33 62when the environment is predictable, leading to adaptive plasticity within the environmental limits 63 experienced during adaptation (Bradshaw 1965; Schlichting 1986; Baythavong and Stanton 2010). Whether 64 such plasticity will continue to be adaptive when exposed to novel conditions, such as those imposed by 65 4 climate change, remains an empirical issue (Ghalambor et al. 2007). Strong stabilising selection created by 66 predictable environments is expected to lead to specific plastic responses and reduce genetic variation for 67 plasticity (Oostra et al. 2018). By contrast, populations adapted to a wider range of habitats that are more 68 spatially and temporally variable are predicted to maintain genetic variation in plastic responses, increasing 69 the potential for selection on plasticity (Chevin et al. 2010). Detecting and characterising patterns of G×E for 70 a range of naturally occurring genotypes can help us understand whether evolutionary responses can occur 71 even if plasticity is constrained in certain directions (Via 1993; Chevin and Hoffmann 2017). 72 The genetic architecture underlying variation in plasticity is largely unknown (Fusco and Minelli 2010). 73 Plastic responses at the gene expression level are most likely controlled either by epiallelic control of the 74 genes themselves or allelic variation in the regulators of the genes (Rockman and Kruglyak 2006). If allelic 75 (sequence changes) or epiallelic (e.g. DNA me...

No abstract

The herbicide imazamox may provoke temporary yellowing and growth retardation in IMI-R sunflower hybrids, more often under stressful environmental conditions. Although, photosynthetic processes are not the primary sites of imazamox action, they might be influenced; therefore, more information about the photosynthetic performance of the herbicide-treated plants could be valuable for a further improvement of the Clearfield technology. Plant biostimulants have been shown to ameliorate damages caused by different stress factors on plants, but very limited information exists about their effects on herbicide-stressed plants. In order to characterize photosynthetic performance of imazamox-treated sunflower IMI-R plants, we carried out experiments including both single and combined treatments by imazamox and a plant biostimulants containing amino acid extract. We found that imazamox application in a rate of 132 μg per plant (equivalent of 40 g active ingredient ha−1) induced negative effects on both light-light dependent photosynthetic redox reactions and leaf gas exchange processes, which was much less pronounced after the combined application of imazamox and amino acid extract.

The evolution of plastic responses to external cues allows species to maintain fitness in response to the environmental variations they regularly experience. However, it remains unclear how plasticity evolves during adaptation. To test whether distinct patterns of plasticity are associated with adaptive divergence, we quantified plasticity for two closely related but ecologically divergent Sicilian daisy species (Senecio, Asteraceae). We sampled 40 representative genotypes of each species from their native range on Mt. Etna and then reciprocally transplanted multiple clones of each genotype into four field sites along an elevational gradient that included the native elevational range of each species, and two intermediate elevations. At each elevation, we quantified survival and measured leaf traits that included investment (specific leaf area), morphology, chlorophyll fluorescence, pigment content, and gene expression. Traits and differentially expressed genes that changed with elevation in one species often showed little changes in the other species, or changed in the opposite direction. As evidence of adaptive divergence, both species performed better at their native site and better than the species from the other habitat. Adaptive divergence is, therefore, associated with the evolution of distinct plastic responses to environmental variation, despite these two species sharing a recent common ancestor.