Search

Background and Aims Condensed tannins, responsible for berry and wine astringency, may have been selected during grapevine domestication. This work examines the phylogenetic distribution of condensed tannins throughout the Vitaceae phylogenetic tree. Methods Green berries and mature leaves of representative true-to-type members of the Vitaceae were collected before ‘véraison’, freeze-dried and pulverized, and condensed tannins were measured following depolymerization by nucleophilic addition of 2-mercaptoethanol to the C4 of the flavan-3-ol units in an organic acidic medium. Reaction products were separated and quantified by ultrahigh pressure liquid chromatography/diode array detection/mass spectrometry. Key Results and Conclusions The original ability to incorporate epigallocatechin (EGC) into grapevine condensed tannins was lost independently in both the American and Eurasian/Asian branches of the Vitaceae, with exceptional cases of reversion to the ancestral EGC phenotype. This is particularly true in the genus Vitis, where we now find two radically distinct groups differing with respect to EGC content. While Vitis species from Asia are void of EGC, 50 % of the New World Vitis harbour EGC. Interestingly, the presence of EGC is tightly coupled with the degree of leaf margin serration. Noticeably, the rare Asian EGC-forming species are phylogenetically close to Vitis vinifera, the only remnant representative of Vitis in Eurasia. Both the wild ancestral V. vinifera subsp. sylvestris as well as the domesticated V. vinifera subsp. sativa can accumulate EGC and activate galloylation biosynthesis that compete for photoassimilates and reductive power.

Iron (Fe) is an essential transition metal. Based on its redox-active nature under biological conditions, various Fe compounds serve as cofactors in redox enzymes. In plants, the photosynthetic machinery has the highest demand for Fe. In consequence, the delivery and incorporation of Fe into cofactors of the photosynthetic apparatus is the focus of Fe metabolism in leaves. Disturbance of foliar Fe homeostasis leads to impaired biosynthesis of chlorophylls and composition of the photosynthetic machinery. Nevertheless, mitochondrial function also has a significant demand for Fe. The proper incorporation of Fe into proteins and cofactors as well as a balanced intracellular Fe status in leaf cells require the ability to sense Fe, but may also rely on indirect signals that report on the physiological processes connected to Fe homeostasis. Although multiple pieces of information have been gained on Fe signalling in roots, the regulation of Fe status in leaves has not yet been clarified in detail. In this review, we give an overview on current knowledge of foliar Fe homeostasis, from the chemical forms to the allocation and sensing of Fe in leaves.

As the first national network of early-career researchers marks its 21st birthday, the founders of Hungary’s describe how and why they set up theirs in 2019. As the first national network of early-career researchers marks its 21st birthday, the founders of Hungary’s describe how and why they set up theirs in 2019.

Chlorococcum is a coccoid green algal genus, which contains almost 50 species. The genus is polyphyletic, but in a traditional sense, the cells are coccoid and non-motile with a cup-shape chloroplast in the vegetative stage, while the spores have chlamydomonad appearance. They are distributed worldwide mainly in terrestrial habitats, and the biotechnological potential of several strains has been reported. In this study, three new green algal strains from a shallow, temporary freshwater lake in Hungary are characterized using microscopic (light and transmission electron microscopy) and DNA-based methods (phylogenetic analysis of the ribosomal ITS region, the 18S ribosomal RNA and rbcL genes, and ITS secondary structure comparison). Based on the obtained results, one of the three new isolates is considered to represent a new species, which is described here as Chlorococcum szentendrense sp. nov.

High levels of soil salinity affect plant growth, reproduction, water and ion uptake, and plant metabolism in a complex manner. In this work, the effect of salt stress on vegetative growth, photosynthetic activity, and chloroplast ultrastructure of spearmint (Mentha spicata L. var. crispa “Moroccan”) was investigated. After 2 weeks of low concentration treatments (5, 25, and 50 mM NaCl) of freshly cut shoots, we observed that the stem-derived adventitious root formation, which is a major mean for vegetative reproduction among mints, was completely inhibited at 50 mM NaCl concentration. One-week-long, high concentration (150 mM NaCl) salt stress, and isosmotic polyethylene glycol (PEG) 6000 treatments were compared in intact (rooted) plants and freshly cut, i.e., rootless shoots. Our data showed that roots have an important role in mitigating the deleterious effects of both the osmotic (PEG treatment) and specific ionic components of high salinity stress. At 50 mM NaCl or above, the ionic component of salt stress caused strong and irreversible physiological alterations. The effects include a decrease in relative water content, the maximal and actual quantum efficiency of photosystem II, relative chlorophyll content, as well as disorganization of the native chlorophyll-protein complexes as revealed by 77 K fluorescence spectroscopy. In addition, important ultrastructural damage was observed by transmission electron microscopy such as the swelling of the thylakoid lumen at 50 mM NaCl treatment. Interestingly, in almost fully dry leaf regions and leaves, granum structure was relatively well retained, however, their disorganization occurred in leaf chloroplasts of rooted spearmint treated with 150 mM NaCl. This loss of granum regularity was also confirmed in the leaves of these plants using small-angle neutron scattering measurements of intact leaves of 150 mM NaCl-stressed rooted plants. At the same time, solid-phase microextraction of spearmint leaves followed by gas chromatography and mass spectrometry (GC/MS) analyses revealed that the essential oil composition of spearmint was unaffected by the treatments applied in this work. Taken together, the used spearmint cultivar tolerates low salinity levels. However, at 50 mM NaCl concentration and above, the ionic components of the stress strongly inhibit adventitious root formation and thus their clonal propagation, and severely damage the photosynthetic apparatus.

Researchers with children or carer roles have struggled more than others during the pandemic, amplifying existing inequalities, argue Edyta Swider-Cios and colleagues. This survey has been conducted in the contact ofthe CALIPER projectand produced three key findings (the full survey data are availablehere). &nbsp

The formation of different intracellular compartments is necessary for the physical separation of various biochemical reactions, their products as well as different ions by barriers made up by memb...

In variable light environments, plants adjust light use in photosynthetic electron transport and photoprotective dissipation in the thylakoid membrane. In this respect, roles of the K+/H+ antiporter KEA3, the Cl− channel/transporter CLCe and the voltage-dependent Cl− channel VCCN1 have been unraveled in Arabidopsis thaliana. Here we report that they independently adjust photosynthesis on the basis of analyses using single and higher order loss-of-function mutants. In short experiments of photosynthetic response on transition from dark to low light, we reveal a sequential functioning of VCCN1 and CLCe in the activation of photoprotection and of KEA3 in its downregulation to a low steady state while adjusting the electron transport. On transition from low to high light, VCCN1 accelerates the activation of photoprotection, whereas KEA3 slows it down on transition from high to low light. Based on parallel electrochromic band shift measurements, the mechanism behind is that VCCN1 builds up a pH gradient across the thylakoid membrane, whereas KEA3 dissipates this gradient, which affects photoprotection. CLCe regulates photosynthesis by a pH-independent mechanism likely involving Cl− homeostasis. Nevertheless, all genotypes grow well in alternating high and low light. Taken together, the three studied ion channels/transporters function independently in adjusting photosynthesis to the light environment.

NADPH:protochlorophyllide (Pchlide) oxidoreductase (POR) is a key enzyme of chlorophyll biosynthesis in angiosperms. It is one of few known photoenzymes, which catalyzes the light-activated trans-reduction of the C17-C18 double bond of Pchlide’s porphyrin ring. Due to the light requirement, dark-grown angiosperms cannot synthesize chlorophyll. No crystal structure of POR is available, so to improve understanding of the protein’s three-dimensional structure, its dimerization, and binding of ligands (both the cofactor NADPH and substrate Pchlide), we computationally investigated the sequence and structural relationships among homologous proteins identified through database searches. The results indicate that α4 and α7 helices of monomers form the interface of POR dimers. On the basis of conserved residues, we predicted 11 functionally important amino acids that play important roles in POR binding to NADPH. Structural comparison of available crystal structures revealed that they participate in formation of binding pockets that accommodate the Pchlide ligand, and that five atoms of the closed tetrapyrrole are involved in non-bonding interactions. However, we detected no clear pattern in the physico-chemical characteristics of the amino acids they interact with. Thus, we hypothesize that interactions of these atoms in the Pchlide porphyrin ring are important to hold the ligand within the POR binding site. Analysis of Pchlide binding in POR by molecular docking and PELE simulations revealed that the orientation of the nicotinamide group is important for Pchlide binding. These findings highlight the complexity of interactions of porphyrin-containing ligands with proteins, and we suggest that fit-inducing processes play important roles in POR-Pchlide interactions.

It is unclear whether light affects the structure and activity of exogenous secretory tissues like glandular hairs. Therefore, transmission electron microscopy was used to study plastid differentiation in glandular hairs and leaves of light-grown rosemary (Rosmarinus officinalis ’Arp’) plants kept for 2 weeks under ambient light conditions or in complete darkness. The basal cells of both capitate and peltate glandular hairs of light-grown leaves contained chloroplasts, while leucoplasts were observed in the other cells of both hair types, with tubuloreticular membrane structures resembling prolamellar bodies appearing only in stalk cell plastids of peltate glandular hairs. From the originally light-grown shoot tips of so-called dark-forced adult plants occasionally (typically at the end of summer or winter) new shoots with elongated internodes and pale leaves developed in the dark. Absorption and fluorescence spectroscopic analyses of the chlorophyllous pigment contents, the native arrangement of the pigment-protein complexes and photosynthetic activity confirmed that the first and second pairs of leaf primordia of dark-forced shoots were partially etiolated: in addition to low amounts of photoactive and non-photoactive protochlorophyllide pigment complexes they contained low amounts of residual chlorophylls, had etio-chloroplasts with prolamellar bodies and low grana and impaired photosynthesis. Darkness did not influence plastid structure in fifth leaves or secretory tissues with the exception of head cells of peltate glandular hairs in which rarely tubuloreticular membranes were observed. The cotyledons of 2-week-old dark-germinated rosemary seedlings accumulated high amounts of photoactive protochlorophyllide pigments and contained no chlorophylls, their etioplasts had highly regular prolamellar bodies similar to mesophyll etio-chloroplasts of leaves and clearly different from tubuloreticular membranes of secretory cells. Analyses of the essential oil composition obtained after solid phase microextraction and gas chromatography-mass spectroscopy showed that in addition to light, the age of the studied organ (i.e. first leaf primordia and leaf tip vs. fifth, fully developed green leaves) and the type of the organ (cotyledon vs. leaves) also strongly influenced the essential oil composition. Our data outline that light and developmental stage are both important factors to be considered in case of potential therapeutic, culinary or aromatic uses of rosemary leaves and their essential oils.

During arbuscular mycorrhizal symbiosis, arbuscule-containing root cortex cells display a proliferation of plastids, a feature usually ascribed to an increased plant anabolism despite the lack of studies focusing on purified root plastids. In this study, we investigated mycorrhiza-induced changes in plastidic pathways by performing a label-free comparative subcellular quantitative proteomic analysis targeted on plastid-enriched fractions isolated from Medicago truncatula roots, coupled to a cytological analysis of plastid structure. We identified 490 root plastid protein candidates, among which 79 changed in abundance upon mycorrhization, as inferred from spectral counting. According to cross-species sequence homology searches, the mycorrhiza-responsive proteome was enriched in proteins experimentally localized in thylakoids, whereas it was depleted of proteins ascribed predominantly to amyloplasts. Consistently, the analysis of plastid morphology using transmission electron microscopy indicated that starch depletion associated with the proliferation of membrane-free and tubular membrane-containing plastids was a feature specific to arbusculated cells. The loss of enzymes involved in carbon/nitrogen assimilation and provision of reducing power, coupled to macromolecule degradation events in the plastid-enriched fraction of mycorrhizal roots that paralleled lack of starch accumulation in arbusculated cells, lead us to propose that arbuscule functioning elicits a nutrient starvation and an oxidative stress signature that may prime arbuscule breakdown.

In variable light environments, plants adjust light use in photosynthetic electron transport and photoprotective dissipation in the thylakoid membrane. In this respect, roles of the K+/H+ antiporter KEA3, the Cl− channel/transporter CLCe and the voltage-dependent Cl− channel VCCN1 have been unraveled in Arabidopsis thaliana. Here we report that they independently adjust photosynthesis on the basis of analyses using single and higher order loss-of-function mutants. In short experiments of photosynthetic response on transition from dark to low light, we reveal a sequential functioning of VCCN1 and CLCe in the activation of photoprotection and of KEA3 in its downregulation to a low steady state while adjusting the electron transport. On transition from low to high light, VCCN1 accelerates the activation of photoprotection, whereas KEA3 slows it down on transition from high to low light. Based on parallel electrochromic band shift measurements, the mechanism behind is that VCCN1 builds up a pH gradient across the thylakoid membrane, whereas KEA3 dissipates this gradient, which affects photoprotection. CLCe regulates photosynthesis by a pH-independent mechanism likely involving Cl− homeostasis. Nevertheless, all genotypes grow well in alternating high and low light. Taken together, the three studied ion channels/transporters function independently in adjusting photosynthesis to the light environment.

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of differences in respect of how they look (color, size, and ultrastructure), and what their specific function and molecular composition is. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition, to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization.

Plastids represent a largely diverse group of organelles in plant and algal cells that have several common features but also a broad spectrum of differences in respect of how they look (color, size, and ultrastructure), and what their specific function and molecular composition is. Plastids and their structural and metabolic diversity significantly contribute to the functionality and developmental flexibility of the plant body throughout its lifetime. In addition, to the multiple roles of given plastid types, this diversity is accomplished in some cases by interconversions between different plastids as a consequence of developmental and environmental signals that regulate plastid differentiation and specialization.

International audience; AbstractFood production has to be significantly increased in order to feed the fast growing global population estimated to be 9.1 billion by 2050. The Green Revolution and the development of advanced plant breeding tools have led to a significant increase in agricultural production since the 1960s. However, hundreds of millions of humans are still undernourished, while the area of total arable land is close to its maximum utilization and may even decrease due to climate change, urbanization, and pollution. All these issues necessitate a second Green Revolution, in which biotechnological engineering of economically and nutritionally important traits should be critically and carefully considered. Since the early 1990s, possible applications of plastid transformation in higher plants have been constantly developed. These represent viable alternatives to existing nuclear transgenic technologies, especially due to the better transgene containment of transplastomic plants. Here, we present an overview of plastid engineering techniques and their applications to improve crop quality and productivity under adverse growth conditions. These applications include (1) transplastomic plants producing insecticidal, antibacterial, and antifungal compounds. These plants are therefore resistant to pests and require less pesticides. (2) Transplastomic plants resistant to cold, drought, salt, chemical, and oxidative stress. Some pollution tolerant plants could even be used for phytoremediation. (3) Transplastomic plants having higher productivity as a result of improved photosynthesis. (4) Transplastomic plants with enhanced mineral, micronutrient, and macronutrient contents. We also evaluate field trials, biosafety issues, and public concerns on transplastomic plants. Nevertheless, the transplastomic technology is still unavailable for most staple crops, including cereals. Transplastomic plants have not been commercialized so far, but if this crop limitation were overcome, they could contribute to sustainable development in agriculture.

Background Since the industrial revolution, the consumption of processed food increased dramatically. During processing, food material loses many of its natural properties. Objective The simple restoration of the original properties of the processed food as well as fortification require food supplementation with compounds prepared chemically or of natural origin. The observations that natural food additives are safer and better accepted by consumers than synthetic ones have strongly increased the demand for natural compounds. Because some of them have only a low abundance or are even rare, their market price can be very high. This is the case for most carotenoids of natural origin to which this review is dedicated. The increasing demand for food additives of natural origin contributes to an accelerated depletion of traditional natural resources already threatened by intensive agriculture and pollution. To overcome these difficulties and satisfy the demand, alternative sources for natural carotenoids have to be found. In this context, photosynthetic microalgae present a very high potential because they contain carotenoids and are able to produce particular carotenoids under stress. Their potential also resides in the fact that only ten thousands of microalgal strains have been described while hundred thousands of species are predicted to exist. Carotenoids have been known for ages for their antioxidant and coloring properties, and a large body of evidence has been accumulated about their health potential. Conclusion This review summarizes both the medicinal and food industry applications of microalgae with emphasis on the former. In addition, traditional and alternative microalgal sources used for industrial carotenoid extraction, the chemical and physical properties, the biosynthesis and the localization of carotenoids in algae are also briefly discussed.

Background & objective Cannabis is one of the earliest cultivated plants. Cannabis of industrial utility and culinary value is generally termed as hemp. Conversely, cannabis that is bred for medical, spiritual and recreational purposes is called marijuana. The female marijuana plant produces a significant quantity of bio- and psychoactive phytocannabinoids, which regained the spotlight with the discovery of the endocannabinoid system of the animals in the early 90's. Nevertheless, marijuana is surrounded by controversies, debates and misconceptions related to its taxonomic classification, forensic identification, medical potential, legalization and its long-term health consequences. Method In the first part, we provide an in-depth review of the botany and taxonomy of Cannabis. We then overview the biosynthesis of phytocannabinoids within the glandular trichomes with emphasis on the role of peculiar plastids in the production of the secreted material. We also compile the analytical methods used to determine the phytocannabinoid composition of glandular trichomes. In the second part, we revisit the psychobiology and molecular medicine of marijuana. Results & conclusion We summarize our current knowledge on the recreational use of cannabis with respect to the modes of consumption, short-term effects, chronic health consequences and cannabis use disorder. Next, we overview the molecular targets of a dozen major and minor bioactive cannabinoids in the body. This helps us introduce the endocannabinoid system in an unprecedented detail: its up-todate molecular biology, pharmacology, physiology and medical significance, and beyond. In conclusion, we offer an unbiased survey about cannabis to help better weigh its medical value versus the associated risks.

BACKGROUND & OBJECTIVE Thylakoids and chloroplasts harbor several vital metabolic processes, but are most importantly associated with photosynthesis. The undisturbed functioning of this process necessitates the ceaseless synthesis of photosynthetic pigments, including closed tetrapyrroles such as chlorophylls (Chls). Chls probably represent the most abundant natural pigment molecules which are via photosynthesis not only crucial for the autotrophic production of food sources for heterotrophic organisms but have also contributed to oxygen production essential for aerobic metabolism. This review first briefly discusses the physico-chemical properties, biosynthesis, occurrence, in vivo localization and roles of the different Chl pigments. Then we provide a detailed overview of their potential applications in the food industry and medicine. These include the use of Chls and their derivatives (different chlorophyllins) as food colorants (identified as E140 and E141 in the European Union). METHOD Different sources used for industrial extraction as well as different factors influencing pigment stability during processing are also critically reviewed. The problems surrounding the nomenclature, the production and the composition of different chlorophyllin mixtures are also discussed. RESULTS & CONCLUSION Finally, a comprehensive overview of the health benefits and potential medicinal applications of these pigments and the future directions of research in these fields are provided.

Background Open tetrapyrroles termed phycobilins represent the major photosynthetic accessory pigments of several cyanobacteria and some eukaryotic algae such as the Glaucophyta, Cryptophyta and Rhodophyta. These pigments are covalently bound to so-called phycobiliproteins which are in general organized into phycobilisomes on the thylakoid membranes. Objective & methods In this work we first briefly describe the physico-chemical properties, biosynthesis, occurrence, in vivo localization and roles of the phycobilin pigments and the phycobiliproteins. Then the potential applications and uses of these pigments, pigment-protein complexes and related products by the food industry (e.g., as LinaBlue® or the so-called spirulina extract used as coloring food), by the health industry or as fluorescent dyes are critically reviewed. Conclusion In addition to the stability, bioavailability and safety issues of purified phycobilins and phycobiliproteins, literature data about their antioxidant, anticancer, anti-inflammatory, immunomodulatory, hepatoprotective, nephroprotective and neuroprotective effects, and their potential use in photodynamic therapy (PDT) are also discussed.

A novel Rab GTPase protein in Arabidopsis thaliana, CPRabA5e (CP = chloroplast localized) is located in chloroplasts and has a role in transport. Transient expression of CPRabA5e:EGFP fusion protein in tobacco (Nicotiana tabacum) leaves, and immunoblotting using Arabidopsis showed localization of CPRabA5e in chloroplasts (stroma and thylakoids). Ypt31/32 in the yeast Saccharomyces cerevisiae are involved in regulating vesicle transport, and CPRabA5e a close homolog of Ypt31/32, restores the growth of the ypt31Δ ypt32 ts mutant at 37 °C in yeast complementation. Knockout mutants of CPRabA5e displayed delayed seed germination and growth arrest during oxidative stress. Ultrastructural studies revealed that after preincubation at 4 °C mutant chloroplasts contained larger plastoglobules, lower grana, and more vesicles close to the envelopes compared to wild type, and vesicle formation being enhanced under oxidative stress. This indicated altered thylakoid development and organization of the mutants. A yeast-two-hybrid screen with CPRabA5e as bait revealed 13 interacting partner proteins, mainly located in thylakoids and plastoglobules. These proteins are known or predicted to be involved in development, stress responses, and photosynthesis related processes, consistent with the stress phenotypes observed. The results observed suggest a role of CPRabA5e in transport to and from thylakoids, similar to cytosolic Rab proteins involved in vesicle transport.

‘Chlorella’ and ‘Nannochloris’ were traditional genera of minute coccoid green algae with numerous species described in the past century, including isolates used as experimental test organisms. In the last few years, the introduction of DNA-based phylogenetic analyses resulted in a large number of taxonomic revisions. We investigated and reclassified a taxonomically problematic group within the Trebouxiophyceae (comprising ‘Nannochloris eucaryotum’ UTEX 2502, ‘N. eucaryotum’ SAG 55.87 and ‘Chlorella minutissima’ SAG 1.80), distantly related to the recently described Chloroparva isolates (97.5–97.9 % 18S rRNA gene pairwise similarity). Cryopreserved material of SAG 55.87 was selected as holotype for a novel species – Pseudochloris wilhelmii Somogyi, Felfoldi & Voros – whose phylogenetic position confirmed the proposal of a new genus. Pseudochloris wilhelmii had spherical to oval cells with an average diameter of 2.6 × 2.8 µm and a simple ultrastructure characteristic of small green algae. Vegetative cells ...

Equipe DAVEM = Diversité et Adaptation de la Vigne et des Espèces Méditerranéennes; International audience; Background and Aims Condensed tannins (also called proanthocyanidins) are widespread polymers of catechins and are essential for the defence mechanisms of vascular plants (Tracheophyta). A large body of evidence argues for the synthesis of monomeric epicatechin on the cytosolic face of the endoplasmic reticulum and its transport to the vacuole, although the site of its polymerization into tannins remains to be elucidated. The aim of the study was to re-examine the cellular frame of tannin polymerization in various representatives of the Tracheophyta. Methods Light microscopy epifluorescence, confocal microscopy, transmission electron microscopy (TEM), chemical analysis of tannins following cell fractionation, and immunocytochemistry were used as independent methods on tannin-rich samples from various organs from Cycadophyta, Ginkgophyta, Equisetophyta, Pteridophyta, Coniferophyta and Magnoliophyta. Tissues were fixed in a caffeine-glutaraldehyde mixture and examined by TEM. Other fresh samples were incubated with primary antibodies against proteins from both chloroplastic envelopes and a thylakoidal chlorophyll-carrying protein; they were also incubated with gelatin-Oregon Green, a fluorescent marker of condensed tannins. Coupled spectral analyses of chlorophyll and tannins were carried out by confocal microscopy on fresh tissues and tannin-rich accretions obtained through cell fractionation; chemical analyses of tannins and chlorophylls were also performed on the accretions. Key Results and Conclusions The presence of the three different chloroplast membranes inside vacuolar accretions that constitute the typical form of tannin storage in vascular plants was established in fresh tissues as well as in purified organelles, using several independent methods. Tannins are polymerized in a new chloroplast-derived organelle, the tannosome. These are formed by pearling of the thylakoids into 30 nm spheres, which are then encapsulated in a tannosome shuttle formed by budding from the chloroplast and bound by a membrane resulting from the fusion of both chloroplast envelopes. The shuttle conveys numerous tannosomes through the cytoplasm towards the vacuole in which it is then incorporated by invagination of the tonoplast. Finally, shuttles bound by a portion of tonoplast aggregate into tannin accretions which are stored in the vacuole. Polymerization of tannins occurs inside the tannosome regardless of the compartment being crossed. A complete sequence of events apparently valid in all studied Tracheophyta is described.

Summary The transformation of desiccoplasts into etioplasts and the parallel appearance of protochlorophyllide (Pchlide) forms were observed with transmission electron microscopy and 77 K fluorescence spectroscopy, when air-dried detached leaves of the poikilochlorophyllous desiccation tolerant plant Xerophyta humilis were floated in water in the dark. After 1 week of rehydration, pregranal plastids with newly synthesized prothylakoid (PT) lamellae and mainly non-photoactive Pchlide forms developed, while etioplasts with prolamellar bodies (PLBs) and photoactive, 655 nm emitting Pchlide form accumulated primarily in the basal leaf regions after 2 weeks of regeneration. When these latter leaves were illuminated with continuous light for 3 days, the etioplasts transformed into regular chloroplasts and the fluorescence emission bands characteristic of green leaves appeared. These results show that, upon rehydration, the dehydrated chlorenchyma cells are able to regenerate pregranal plastids and etioplasts from desiccoplasts in the dark, which can transform into regular chloroplasts when they are illuminated. This means that the differentiation of pregranal plastids and etioplasts and their greening process is a basic property of fully differentiated cells of X. humilis. Consequently, these processes are not merely characteristic for seedlings with meristematic and differentiating young tissues.

The world population is expected to increase from approximately 2.5 billion in 1950 to almost 10 billion in 2050, exhibiting the highest population growth rates in history. Securing the supply of wood and timber from sustainable sources without competing for agricultural land and food production has already become a challenge in many parts of the world. South America has had the advantage of being a large continent with a relatively small population, of which a large share lives in urban areas. Historically, these conditions have permitted inefficient land-use systems such as extensive livestock grazing for beef production. However, in recent decades export-oriented industrial agriculture has become the main driver of South American land use patterns, increasing the pressure for more efficient and intensive production systems. Specialization and intensification in the land use sector have brought economic and productive benefits at a cost. They have caused the massive destruction of natural ecosystems while at the same time making national economies highly dependent on a reduced number of export products. Therefore opportunities for intensification on extensive grazing land and other inefficient land uses (often on marginal land) have to be considered. Particularly in times of pressing global environmental change and increasingly complex trade relationships, land use intensification has to take into account economic, environmental and social objectives and increase the resilience of the system as a whole.

The maintenance but substantial transformation of plastids was found in lowermost hypocotyl segments of soil-grown bean plants (Phaseolus vulgaris cv. Magnum) during a 60-day cultivation period. Although the plants were grown under natural light–dark cycles, this hypocotyl segment was under full coverage of the soil in 5–7 cm depth, thus it was never exposed to light. The 4-day old plants were fully etiolated: amyloplasts, occasionally prolamellar bodies, protochlorophyllide (Pchlide) and protochlorophyll (Pchl) were found in the hypocotyls of these young seedlings. The 633 and 654 nm bands in the 77 K fluorescence emission spectra indicated the presence of Pchlide and Pchl pigments. During aging, both the Pchlide and Pchl contents increased, however, the Pchl to Pchlide ratio gradually increased. In parallel, the contribution of the 654 nm form decreased and in the spectra of the 60-day-old samples, the main band shifted to 631 nm, and a new form appeared with an emission maximum at 641 nm. The photoactivity had been lost; bleaching took place at continuous illumination. The inner membranes of the plastids disappeared, the amount of starch storing amyloplasts decreased. These data may indicate the general importance of plastids for plant cell metabolism, which can be the reason for their maintenance. Also the general heterogeneity of plastid forms can be concluded: in tissues not exposed to light, Pchl accumulating plastids develop and are maintained even for a long period.

Chloride ions can be translocated across cell membranes through Cl(-) channels or Cl(-)/H(+) exchangers. The thylakoid-located member of the Cl(-) channel CLC family in Arabidopsis thaliana (AtCLCe) was hypothesized to play a role in photosynthetic regulation based on the initial photosynthetic characterization of clce mutant lines. The reduced nitrate content of Arabidopsis clce mutants suggested a role in regulation of plant nitrate homeostasis. In this study, we aimed to further investigate the role of AtCLCe in the regulation of ion homeostasis and photosynthetic processes in the thylakoid membrane. We report that the size and composition of proton motive force were mildly altered in two independent Arabidopsis clce mutant lines. Most pronounced effects in the clce mutants were observed on the photosynthetic electron transport of dark-adapted plants, based on the altered shape and associated parameters of the polyphasic OJIP kinetics of chlorophyll a fluorescence induction. Other alterations were found in the kinetics of state transition and in the macro-organization of photosystem II supercomplexes, as indicated by circular dichroism measurements. Pre-treatment with KCl but not with KNO3 restored the wild-type photosynthetic phenotype. Analyses by transmission electron microscopy revealed a bow-like arrangement of the thylakoid network and a large thylakoid-free stromal region in chloroplast sections from the dark-adapted clce plants. Based on these data, we propose that AtCLCe functions in Cl(-) homeostasis after transition from light to dark, which affects chloroplast ultrastructure and regulation of photosynthetic electron transport.

Macro-organisation of the protein complexes in plant thylakoid membranes plays important roles in the regulation and fine-tuning of photosynthetic activity. These delicate structures might, however, undergo substantial changes during isolating the thylakoid membranes or during sample preparations, e.g., for electron microscopy. Circular-dichroism (CD) spectroscopy is a non-invasive technique which can thus be used on intact samples. Via excitonic and psi-type CD bands, respectively, it carries information on short-range excitonic pigment-pigment interactions and the macro-organisation (chiral macrodomains) of pigment-protein complexes (psi, polymer or salt-induced). In order to obtain more specific information on the origin of the major psi-type CD bands, at around (+)506, (-)674 and (+)690 nm, we fingerprinted detached leaves and isolated thylakoid membranes of wild-type and mutant plants and also tested the effects of different environmental conditions in vivo. We show that (i) the chiral macrodomains disassemble upon mild detergent treatments, but not after crosslinking the protein complexes; (ii) in different wild-type leaves of dicotyledonous and monocotyledonous angiosperms the CD features are quite robust, displaying very similar excitonic and psi-type bands, suggesting similar protein composition and (macro-) organisation of photosystem II (PSII) supercomplexes in the grana; (iii) the main positive psi-type bands depend on light-harvesting protein II contents of the membranes; (iv) the (+)506 nm band appears only in the presence of PSII-LHCII supercomplexes and does not depend on the xanthophyll composition of the membranes. Hence, CD spectroscopy can be used to detect different macro-domains in the thylakoid membranes with different outer antenna compositions in vivo.

An increasing number of soils of poor quality with unbalanced metal concentrations are used worldwide for crop cultivation. Even though plants are able to develop strategies to cope with metal stress, either metal deficiency or excess, this unbalance affects the whole plant. Chloroplasts are key organelles for organic matter synthesis and biomass production. Under metal stress, chloroplasts suffer severe alterations of their ultrastructure, associated with profound molecular and metabolic damages. These alterations are accompanied by unbalanced metal distribution in plants, in particular in edible crop organs. Toxic metals get either accumulated or there is a deficiency of nutrients, resulting in a weak nutritional value. Nonetheless, there is more and more knowledge on the functioning and regulation of metal transporters in plants. Such knowledge will allow growing crops with well-balanced metal concentrations in edible parts even on metal unbalanced soils. This review shows that almost all vital functions of chloroplasts, such as photosynthesis, CO2 fixation, nitrogen and sulfur assimilation, and protein and nucleic acid metabolism, require metals. Therefore, the uptake of essential metals is necessary for the proper functioning of chloroplasts and, in turn, for crop productivity. We describe nutrient uptake mechanisms of plants and processes that influence essential and non-essential metal concentrations in different plant organs. We present an overview of metal transporters in chloroplasts. Several questions still need to be elucidated about the uptake and the trafficking of essential and non-essential metals into and within chloroplasts. Similarly to transporters present in other cellular compartments, the carriers are often not metal-specific. Therefore, essential and non-essential metals may compete for carriers. As a result, unbalanced soil metal concentrations can be reflected in the plants and in the chloroplasts. Metal deficiency or excess causes reduced growth and decreased productivity of crops. It can lead to human malnutrition. Several complex physiological processes can be responsible for the reduced biomass observed in plants with unbalanced metal concentration. In this review, we have focused on the structural and functional alterations of chloroplasts under metal deficiency or excess. Interestingly, besides specific differences, our data indicate several similarities in the response of chloroplasts to metal deficiency or excess. Indeed, oxidative stress and several ultrastructural alterations, e.g., increase in the number and size of plastoglobuli, disorganized grana and disturbed thylakoids, and swelling of the intrathylakoidal space, are observed in both cases. This indicates that changes in chloroplast ion homeostasis rather than the specific effect of a metal are responsible for decreased plant productivity. Therefore, sustainable agriculture has to take into consideration solutions that enable undisturbed metal and ion homeostasis in chloroplasts of crop plants grown even in soils with unbalanced metal concentrations.