Abstract

The photosynthesis in evergreen trees living in Mediterranean ecosystems is subjected to multiple climatic stresses due to water shortage and high temperatures during the summer and to low temperatures during the winter. Mediterranean perennials deploy different photoprotective mechanisms to prevent damage to the photosynthetic system. Wax accumulation in leaves is a primary response which by enhancing light scattering in the leaf surface reduces incident radiation in the mesophyll. The existence of high variability in wax accumulation levels between coexisting individuals of a species has a visual effect on colour that provides distinguishable green and glaucous phenotypes. We explored this variability in a Mediterranean evergreen tree Juniperus thurifera (L.) to evaluate the impact of epicuticular wax on optical and ecophysiological properties and on the abundance of photoprotective pigments throughout an annual cycle. Because of light attenuation by waxes, we expected that glaucous phenotypes would lower the need for photoprotective pigments. We evaluated the effect of phenotype and season on reflectance, defoliation levels, photochemical efficiency and photoprotective pigment contents in 20 green and 20 glaucous junipers. Contrary to our expectations, the results showed that glaucous trees suffered from a diminution in photochemical efficiency, but there was no reduction in photoprotective pigments. Differences between glaucous and green phenotypes were greater in winter, which is the most stressful season for this species. Glaucous individuals also showed the highest levels of leaf defoliation. The lower photochemical efficiency of glaucous trees, together with higher defoliation rates and equal or greater number of physiological photoprotective mechanisms, suggests that in spite of wax accumulation, glaucous trees suffer from more severe stress than green ones. This result suggests that changes in colouration in Mediterranean evergreens may be a decline indicator.

Summary

The lutein epoxide (Lx) cycle (Lx-L cycle), initially described in tomato fruits, remained unexplored during the following 25 years until it was re-discovered in the stems of the parasitic plant Cuscuta reflexa. Since then, 15 years of continuous research have revealed that the Lx-L cycle is present in a wide diversity of species, allowing us to make significant progress in our understanding of this carotenoid cycle. However, due to its absence in some traditional model plant species, much of its functional significance remains to be clarified. We have therefore provided an overview of the current knowledge of this cycle as well as an ecological perspective of the possible benefits derived from the possession of two xanthophyll cycles (all plants possess a xanthophyll cycle involving violaxanthin, antheraxanthin, and zeaxanthin, i.e., the VAZ cycle, whereas only some species possess the Lx-L cycle). In the Lx-L cycle, Lx is de-epoxidized upon illumination, by the action of violaxanthin de-epoxidase (VDE), and transformed into lutein (L). Correlative evidence supports a role for this newly formed L (ΔL) in the regulation of thermal energy dissipation as assessed from the non-photochemical quenching of chlorophyll fluorescence (NPQ). The reversibility of this reaction in darkness differentiates two modes of operation, one "completed" in which the initial Lx pool is restored and one "truncated" in which ΔL remains for a longer period. The first, described in sun and shade leaves of a few unrelated species, apparently provides fine-tuning for the adjustment of photoprotective energy dissipation complementary to that exerted by the VAZ cycle. On the other hand, the "truncated" cycle is widespread amongst woody plants, but is restricted to shaded environments where it may act as a rapid switch for the photosynthetic apparatus from a photosynthetically highly efficient state to a photoprotected one. The latter may be necessary for chloroplast acclimation after transition to high light, such as that which occurs following gap formation in forests or budbreak and subsequent leaf greening in trees.

bstract

Humans are continuously exposed to oxidative damage risk and in order to counteract it, the consumption of antioxidants and carotenoids of plant origin is recommended. Numerous studies show the need to include substantial amounts of the carotenoid zeaxanthin (Z) in the diet, because its deficiency provokes the development of macular degeneration, which leads to irreversible loss of vision. However, Z is a less-abundant carotenoid in plants, because most of its pool is rapidly converted to the carotenoid violaxanthin (V) via antheraxanthin (A), due to its involvement in the operation of the xanthophyll (V + A + Z) cycle. The aim of this paper, therefore, was to develop a protocol to enhance the Z content in spinach and rocket through two strategies: firstly, by applying stress (chilling, high light and drought) in order to enhance the total pool of V + A + Z and, secondly, by applying post-harvest treatments before consumption in order to enhance Z formation. The results showed that high light was the most beneficial stress, increasing the fresh weight production in rocket and showing the highest accumulation of V + A + Z and carotenoids in both species. An enhancement of α-tocopherol in rocket was, as well, accomplished by the environmental stress induction. Besides, with the second strategy (post-harvest treatments before consumption, such as boiling and vinegar dressing), both species showed Z enhancement. By combining both approaches in two-steps, the Z content can be enhanced up to 15-fold in spinach and 28-fold in rocket, increasing, as a result, the nutritional value of food.

Abstract

Tocochromanols are the most abundant lipid-soluble antioxidants in plants. Among them, α-tocopherol (α-Toc) shows a particularly high sensitivity to environmental stressors and its content is used as a stress biomarker even in non-photosynthetic tissues. Nevertheless, the presence of tocochromanols has not been described yet in the xylem of woody plants, even when their functions regarding cell membrane protection and the transport of photoassimilates may be crucial in this tissue and despite its potential utility in dendrometabolomics. Considering all these, we aimed to determine the presence and distribution of tocochromanols in the xylem of woody plants, to examine their responsiveness to high temperature and to evaluate their potential as environmental bioindicators. The analysis of 29 phyllogenetically diverse species showed that α-Toc is the most abundant and frequent tocochromanol in the xylem and is ubiquitously present in all the studied species, with a concentration ranging from 0.5 to 39.3 μg g−1 of dry weight. α-Tocopherol appeared to be mainly located in the parenchyma rays and was found in both the sapwood and the heartwood, suggesting that it is present even in dead parenchyma cells. The levels of α-Toc in the xylem did not change in response to locally induced xylem heating, but responded positively to the 3-year moving average of annual precipitation. The present findings suggest that α-Toc may be linked to changes in climatic stress. This should enhance further research on the environmental controls of α-Toc variation in the xylem as a first step towards a deeper understanding of dendrometabolomics.

Abstract

Rooted cuttings of Eridano and I-214 Populus clones were treated in hydroponics with high [Zn] to establish their phytoextraction capacity and physiological responses for phytoremediation. The Bio-concentration factor, Uptake ratio and Translocation factor revealed that the highest Zn accumulation occurred in roots. Lower accumulation at 1 mM [Zn] in Eridano aerial parts limited Zn toxicity on photosynthetic machinery. Increasing [Zn] negatively affected growth, net photosynthesis, stomatal conductance, maximum quantum yield, chlorophyll content and hydric parameters. The physiological impairment in I-214 at 1 mM [Zn] indicated a greater sensitivity to high [Zn] than Eridano. At 5 mM [Zn], high toxicity for both clones occurred. Upregulation of photoprotective and antioxidant responses was a consequence of Zn stress rather than a Zn tolerance mechanism. Increased de-epoxidation state of the xanthophyll-cycle, α-Tocopherol and reduced glutathione and decreased total phenolics in I-214 at 1 mM [Zn] suggested that it responded earlier to oxidative stress when compared to Eridano.

Abstract

Eucryphia cordifolia Cav. is a long-lived evergreen tree species, commonly found as a canopy emergent tree in the Chilean temperate rain forest. This species displays successive leaf cohorts throughout the entire growing season. Thus, full leaf expansion occurs under different environmental conditions during growing such as air temperature, vapor pressure deficit and the progress of moderate water stress (WS). These climate variations can be reflected as differences in anatomical and physiological characteristics among leaf cohorts. Thus, we investigated the potential adaptive role of different co-existing leaf cohorts in seedlings grown under shade, drought stress or a combination of the two. Photosynthetic and anatomical traits were measured in the first displayed leaf cohort and in a subsequent leaf cohort generated during the mid-season. Although most anatomical and photosynthetic pigments did not vary between cohorts, photosynthetic acclimation did occur in the leaf cohort and was mainly driven by biochemical processes such as leaf nitrogen content, Rubisco carboxylation capacity and maximal Photosystem II electron transport rather than CO2 diffusion conductance. Cohort acclimation could be relevant in the context of climate change, as this temperate rainforest will likely face some degree of summer WS even under low light conditions. We suggest that the acclimation of the photosynthetic capacity among current leaf cohorts represents a well-tuned mechanism helping E. cordifolia seedlings to face a single stress like shade or drought stress, but is insufficient to cope with simultaneous stresses.

Abstract

Lipophilic antioxidants play dual key roles in edible seeds (i) as preservatives of cell integrity and seed viability by preventing the oxidation of fats, and (ii) as essential nutrients for human and animal life stock. It has been well documented that plant domestication and post-domestication evolution frequently resulted in increased seed size and palatability, and reduced seed dormancy. Nevertheless, and surprisingly, it is poorly understood how agricultural selection and cultivation affected the physiological fitness and the nutritional quality of seeds. Fabaceae have the greatest number of crop species of all plant families, and most of them are cultivated for their highly nutritious edible seeds. Here, we evaluate whether evolution of plants under cultivation has altered the integrated system formed by membranes (fatty acids) and lipophilic antioxidants (carotenoids and tocopherols), in the ten most economically important grain legumes and their closest wild relatives, i.e.: Arachis (peanut), Cicer (chickpea), Glycine (soybean), Lathyrus(vetch), Lens (lentil), Lupinus (lupin), Phaseolus (bean), Pisum (pea), Vicia (faba bean) and Vigna (cowpea).

Abstract

Globally, over 7.4 million accessions of crop seeds are stored in gene banks, and conservation of genotypic variation is pivotal for breeding. We combined genetic and biochemical approaches to obtain a broad overview of factors that influence seed storability and ageing in barley (Hordeum vulgare). Seeds from a germplasm collection of 175 genotypes from four continents grown in field plots with different nutrient supply were subjected to two artificial ageing regimes. Genome-wide association mapping revealed 107 marker trait associations, and hence, genotypic effects on seed ageing. Abiotic and biotic stresses were found to affect seed longevity. To address aspects of abiotic, including oxidative, stress, two major antioxidant groups were analysed. No correlation was found between seed deterioration and the lipid-soluble tocochromanols, nor with oil, starch and protein contents. Conversely, the water-soluble glutathione and related thiols were converted to disulphides, indicating a strong shift towards more oxidizing intracellular conditions, in seeds subjected to long-term dry storage at two temperatures or to two artificial ageing treatments. The data suggest that intracellular pH and (bio)chemical processes leading to seed deterioration were influenced by the type of ageing or storage. Moreover, seed response to ageing or storage treatment appears to be significantly influenced by both maternal environment and genetic background.