Overexpression of beta-carotene hydroxylase enhances stress tolerance in Arabidopsis

Plant stress caused by extreme environmental conditions is already a principal reason for yield reduction in crops. The threat of global environment change makes it increasingly important to generate crop plants that will withstand such conditions. Stress, particularly stress caused by increased sunlight, leads to the production of reactive oxygen species that cause photo-oxidative cell damage. Carotenoids, which are present in the membranes of all photosynthetic organisms, help protect against such light-dependent oxidative damage. In plants, the xanthophyll cycle (the reversible interconversion of two carotenoids, violaxanthin and zeaxanthin) has a key photoprotective role and is therefore a promising target for genetic engineering to enhance stress tolerance. Here we show that in Arabidopsis thaliana overexpression of the chyB gene that encodes -carotene hydroxylase—an enzyme in the zeaxanthin biosynthetic pathway—causes a specific twofold increase in the size of the xanthophyll cycle pool. The plants are more tolerant to conditions of high light and high temperature, as shown by reduced leaf necrosis, reduced production of the stress indicator anthocyanin and reduced lipid peroxidation. Stress protection is probably due to the function of zeaxanthin in preventing oxidative damage of membranes

The moss Bryum argenteum var. muticum Brid. is well adapted to cope with high light in continental Antarctica

The net photosynthetic rate (NP), chlorophyll fluorescence, carotenoid content and chlorophyll content of the cosmopolitan moss Bryum argenteum were measured in the field at Botany Bay, southern Victoria Land, continental Antarctica (77°S). Comparisons were made between sun- and shade-adapted forms, and changes were followed as the moss emerged from under the snow and during exposure of shade and sun forms to ambient light. Shade forms had lower light compensation and saturation values for NP but little difference in maximal NP rates. Shade forms exposed to ambient light changed rapidly (within five days) towards the performance of the sun forms. Surprisingly, this change was not by acclimation of shoots but by the production of new shoots. Chlorophyll and carotenoid levels measured on a molar chlorophyll basis showed no difference between sun and shade forms and also little change during emergence. The constant molar relationship between carotenoids and chlorophyll plus the high levels of the xanthophyll cycle pigments suggest that protection of the chlorophyll antenna was constitutive. This is an adaptation to the very high light levels that occur when the plants are active in continental Antarctica and contrasts to the situation in more temperate areas where high light is normally avoided by desiccation

Modified atmosphere packaging and dark/light refrigerated storage in green leafy vegetables have impact on nutritional value

The consumption of zeaxanthin (Z) through a vegetable-rich diet is recommended to reduce the progression of age-related macular degeneration. Due to Z’s intrinsic dynamic character that results from its participation in the photoprotective xanthophyll cycle involving the carotenoids violaxanthin, antheraxanthin and zeaxanthin (VAZ), post-harvest handling practices and storage usually retain low amounts of this bioactive compound (compared to the rest of phytochemicals that are, in general, more stable). Thus, the aim of this work was to investigate in important consumed leafy vegetables the effects of different storage conditions on carotenoids (mainly Z) including i) packaging under three modified atmospheres (MAs), ii) light refrigerated supermarket storage and iii) dark refrigerated domestic storage. The results showed that an MA with low O2 and high CO2 enhanced the Z content under light. Moreover, both light and dark refrigerated storage showed dynamic and circadian pigment changes that enhanced the total VAZ pool. These results can contribute to generating practical recommendations for industries, supermarkets, and consumers when high Z content is a nutritional target.RE received a Juan de la Cierva-incorporación grant IJCI-2014-21452. JB is a holder of a PhD fellowship from the Public University of Navarre. This research was supported by research BFU 2010-15021 and CTM2014- 53902-C2-2-P from the Ministry of Education and Science of Spain and the ERDF (FEDER) and research project UPV/EHU IT-1018-16. Technical and human support by Eroski supermarkets and “Fundación Tecnova” is gratefully acknowledged

A minimal mathematical model of nonphotochemical quenching of chlorophyll fluorescence

Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.Peer reviewedPreprin

Ecophysiological adaptations of the lichen genera pseudocyphellaria and sticta to south temperate rainforests

Temperate rainforests are a poorly researched habitat with respect to lichen ecophysiology in comparison to desert and polar regions. The evergreen, broadleaf forests provide a dim, moist environment that is relatively stable throughout the year. Lichens are abundant in both quantity and species diversity with the large foliose genera Sticta and Pseudocyphellaria normally being dominant, visually and in terms of biomass. These lichens exhibit a great diversity of both form and habitat range. Physiological and morphological adaptation has also been demonstrated. Pseudocyphellaria dissimilis shows changes in thallus water storage capacity with evaporative demand and is also highly shade-adapted. The species has the lowest light saturation and compensation values for photosynthesis yet known for lichens (20 and 1-μmol m−2s−1, PAR, respectively). Unexpectedly it is also highly desiccation-sensitive with some thalli being killed after only 20 h exposure to 15% relative humidity. Photobiont versatility is also a feature of these genera. Photosymbiodemes occur, i.e. a single thallus containing both green algal and cyanobacterial sectors. Because the different sectors have the same fungal partner and grow in the same habitat, it is possible to investigate whether particular physiological traits are photobiont determined. The ability to recover photosynthetic activity in humid air is confined to thalli with green algal photobionts whilst the inability of thalli containing cyanobacterial photobionts to tolerate high light stress may be related to their lack of a protective xanthophyll cycle

Silk oak flowers as a source of β-carotene

The pigment of the yellow flowers of the silk oak (Grevillea robusta, Cunningham) does not appear to have been investigated heretofore. If the dried material is extracted with ether, the solution shows typical absorption maxima at 483 and 453 mµ,corresponding to the spectrum of p-carotene. The rather blurred borders of these bands indicate, however, the presence of other polyenic pigments in small quantities. After saponification a photometric analysis of the total extract gave values which would correspond to 270 mg. of β-carotene in 1 kilo of the dry flowers if no other pigments were present. After a chromatographic separation the true β-carotene content was found to be about 215 mg. per kilo. Two-thirds of this amount was isolated as crystals; lycopene or γ- and α-carotene were not present [1]. The non-carotene fraction is a complicated xanthophyll mixture in which no single compound predominates. From this fraction two very small amounts of crystalline material were isolated, one of which was kryptoxanthin and the other a new carotenoid possessing a remarkably short wave-length spectrum. For the separation and study of carotenoids contained in extracts we suggest the systematic use of the ultraviolet lamp which has been so helpful in the chromatography of colorless substances (2). Plant pigments are frequently accompanied by large amounts of colorless material which prevent the formation of sharp pigment zones in the Tswett column and thus a satisfactory separation of the components. Furthermore, the crystallization of some carotenoids may be hindered. Fortunately many such colorless substances show an intense fluorescence (3). An observation made in ultraviolet light during the chromatographic separation of the pigments may furnish a good indication of the best method and optimum extent of developing the chromatogram. The distribution of the fluorescence may also indicate the lines at which it is best to cut the column. By sacrificing small amounts of pigment large portions of colorless associated material may be eliminated in this simple way

Knock-Out of the Genes Coding for the Rieske Protein and the ATP-Synthase δ-Subunit of Arabidopsis

In Arabidopsis, the nuclear genes PetC and AtpD code for the Rieske protein of the cytochrome b6/f (cyt b6/f) complex and the δ-subunit of the chloroplast ATP synthase (cpATPase), respectively. Knock-out alleles for each of these loci have been identified. Greenhouse-grown petc-2 and atpd-1 mutants are seedling lethal, whereas heterotrophically propagated plants display a high-chlorophyll (Chl)-fluorescence phenotype, indicating that the products of PetC and AtpD are essential for photosynthesis. Additional effects of the mutations in axenic culture include altered leaf coloration and increased photosensitivity. Lack of the Rieske protein affects the stability of cyt b6/f and influences the level of other thylakoid proteins, particularly those of photosystem II. In petc-2, linear electron flow is blocked, leading to an altered redox state of both the primary quinone acceptor QA in photosystem II and the reaction center Chl P700 in photosystem I. Absence of cpATPase-δ destabilizes the entire cpATPase complex, whereas residual accumulation of cyt b6/f and of the photosystems still allows linear electron flow. In atpd-1, the increase in non-photochemical quenching of Chl fluorescence and a higher de-epoxidation state of xanthophyll cycle pigments under low light is compatible with a slower dissipation of the transthylakoid proton gradient. Further and clear differences between the two mutations are evident when mRNA expression profiles of nucleus-encoded chloroplast proteins are considered, suggesting that the physiological states conditioned by the two mutations trigger different modes of plastid signaling and nuclear response

Recovery kinetics of winter stressed conifers: The effects of growth light environment, extent of the season, and species.

Evergreens undergo a dramatic reduction in their maximal photochemical efficiency (measured as Fv/Fm) during winter, which is largely due to increases in a sustained form of thermal energy dissipation. Upon removing winter-stressed leaves to room temperature and low light, Fv/Fm recovers over several days and can include both a rapid phase (reversing in minutes) and a slow phase (reversing over days). Both phases are associated with reversal of sustained energy dissipation. Preliminary examination of recovery of evergreens monitored in January in Minnesota showed an absence of the rapid component to recovery. Our goal was to monitor recovery kinetics of sun and shade evergreens in Minnesota throughout winter in order to assess whether the rapid phase of recovery exists early in the winter and converts to the slowly reversible form as winter progresses. Four species of conifers (sun and shade needles) were monitored during the winter of 2007/08: eastern white pine (_Pinus strobus_ L.), balsam fir [_Abies balsamea_ (L.) P. Mill], _Taxus cuspidata_ (L.) and blue spruce (_Picea pungens_ Engelm.). Fv/Fm was measured on dark acclimated needles in the field, twigs were collected, brought indoors and maintained at room temperature and low light where Fv/Fm was monitored for six days. 

The results demonstrated that all species, and both sun and shade needles, showed a rapidly reversible component to recovery in early winter (November). In the sun needles this component was rarely present later in the season, while in the shade needles it was present (although only a small fraction of the total sustained energy dissipation) on most days monitored during winter. The slowly reversible component to sustained energy dissipation was present in both sun and shade needles of all species beginning in November. In all cases, shade needles recovered significantly faster than sun needles. There was a significant slowing of recovery (the slowly reversible component) as winter progressed in both sun and shade needles, and significant differences between species in their recovery response. The results indicate a relatively small contribution of the rapidly reversible component of sustained energy dissipation compared with earlier studies on evergreens growing in the milder winter conditions of Colorado. The results also provide evidence that the rapid component to recovery diminishes as the season progresses, particularly in needles growing in full sun where the slowly reversible component of sustained energy dissipation accounts for most or all of the observed sustained energy dissipation. 
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Investigating Leaf Pigments

The purpose of this resource is to explore what pigments exist in leaves and their importance. Students will conduct an experiment using paper chromatography to separate pigments present in leaves. Educational levels: Middle school, High school