Are active oxygen species involved in induction of β-carotene in Dunaliella bardawil?

The purpose of this work was to test whether induction of massive -carotene synthesis in the alga Dunaliella bardawil is triggered by oxygen radicals. The following results were obtained: (i) The induction of -carotene synthesis is preceded by a lag period of about 4 h during which the cells swell and photosynthesis is partially inhibited, (ii) Addition of promoters of oxygen radicals or of azide (an inhibitor of catalase and superoxide dismutase) during the induction period, under conditions which are suboptimal for massive -carotene accumulation, greatly enhances -carotene synthesis, photodegradation of chlorophyll and inhibition of photosynthesis, (iii) High irradiance, which induces massive -carotene accumulation, also induces a high catalase activity. It is suggested that photosynthetically produced oxygen radicals are involved in triggering massive -carotene accumulation in D. bardawil.     

Effects of altered α‐ and β‐branch carotenoid biosynthesis on photoprotection and whole‐plant acclimation of Arabidopsis to photo‐oxidative stress

Functions of α‐ and β‐branch carotenoids in whole‐plant acclimation to photo‐oxidative stress were studied in Arabidopsis thaliana wild‐type (wt) and carotenoid mutants, lut ein deficient (lut2, lut5), n on‐p hotochemical q uenching1 (npq1) and s uppressor of z eaxanthin‐l ess1 (szl1) npq1 double mutant. Photo‐oxidative stress was applied by exposing plants to sunflecks. The sunflecks caused reduction of chlorophyll content in all plants, but more severely in those having high α‐ to β‐branch carotenoid composition (α/β‐ratio) (lut5, szl1npq1). While this did not alter carotenoid composition in wt or lut2, which accumulates only β‐branch carotenoids, increased xanthophyll levels were found in the mutants with high α/β‐ratios (lut5, szl1npq1) or without xanthophyll‐cycle operation (npq1, szl1npq1). The PsbS protein content increased in all sunfleck plants but lut2. These changes were accompanied by no change (npq1, szl1npq1) or enhanced capacity (wt, lut5) of NPQ. Leaf mass per area increased in lut2, but decreased in wt and lut5 that showed increased NPQ. The sunflecks decelerated primary root growth in wt and npq1 having normal α/β‐ratios, but suppressed lateral root formation in lut5 and szl1npq1 having high α/β‐ratios. The results highlight the importance of proper regulation of the α‐ and β‐branch carotenoid pathways for whole‐plant acclimation, not only leaf photoprotection, under photo‐oxidative stress.     

Genetic variation in the β, β‐carotene‐9′, 10′‐dioxygenase gene and association with fat colour in bovine adipose tissue and milk

β, β‐carotene‐9′, 10′‐dioxygenase (BCO2) plays a role in cleaving β‐carotene eccentrically, and may be involved in the control of adipose and milk colour in cattle. The bovine BCO2 gene was sequenced as a potential candidate gene for a beef fat colour QTL on chromosome (BTA) 15. A single nucleotide base change located in exon 3 causes the substitution of a stop codon (encoded by the A allele) for tryptophan⁸⁰ (encoded by the G allele) (c. 240G>A, p.Trp80stop, referred to herein as SNP W80X). Association analysis showed significant differences in subcutaneous fat colour and beta‐carotene concentration amongst cattle with different BCO2 genotypes. Animals with the BCO2 AA genotype had more yellow beef fat and a higher beta‐carotene concentration in adipose tissues than those with the GA or GG genotype. QTL mapping analysis with the BCO2 SNP W80X fitted as a fixed effect confirmed that this SNP is likely to represent the quantitative trait nucleotide (QTN) for the fat colour‐related traits on BTA 15. Moreover, animals with the AA genotype had yellower milk colour and a higher concentration of beta‐carotene in the milk.     

Characterization of carotenes in a combination of a C18 HPLC column with isocratic elution and absorption spectra with a photodiode-array detector

Carotenes have attracted much attention in recent years for their biological function in processes such as photosynthesis. The characterization of carotenes is difficult, however, because they consist of only carbon and hydrogen atoms, without oxygen. In the present study, we systematically examined the chemical structures of more than 30 carotenes, including most of the carotenes found in phototrophic organisms, and observed their elution order using a Novapak C₁₈ HPLC column with simple isocratic elution. The elution order of the carotenes was C₃₀, C₄₀,C₄₅ then C₅₀. The C₄₀ carotenes with fewer conjugated double bonds (N) had longer retention times. With respect to the end groups, the carotenes eluted in the following order: φ, Ψ, ∈ then β end groups. Furthermore, absorption spectra in the HPLC eluent used were recorded with a photodiode-array detector. A greater N value was associated with a longer absorption maximum wavelength. Since the conjugated end groups (φ and β) influenced the absorption spectra and the non-conjugated end groups (Ψ and ∈) did not, the number of conjugated end groups (zero, one and two) was clearly distinguishable. Therefore, the chemical structures of carotenes can be easily determined by a combination of the HPLC retention times and the absorption spectra. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effect of modification of soybean lipoxygenase-1 with N-bromosuccinimide on linoleate oxidation,pigment bleaching and carbonyl production

Essential tryptophan residues were specifically modified in soybean lipoxygenase-1 by N-bromosuccinimide (NBS). Both linoleate oxidation and pigment bleaching (β-carotene or chlorophyll a) activities were significantly reduced with the modified enzyme under aerobic conditions. However, the effect on the reduction of linoleate oxidation was more marked. Pigment bleaching under anaerobic conditions was almost completely blocked with the modified enzyme. On the basis of spectral studies it was elucidated that soybean lipoxygenase-1 contains two essential tryptophan residues in its active site.     

The capacity of antioxidant protection during modulated ageing of bean (Phaseolus vulgaris L.) cotyledons. 2. The low-molecular weight antioxidants

The aim of the present work was to evaluate non-enzymic antioxidants during natural and artificially modulated senescence. Senescence of bean (Phaseolus vulgaris L. cv. Jantar) cotyledons was modulated by UV C irradiation or by the decapitation of plants apices. The content of beta-carotene and zeaxanthin decreased in control and decapitated plants but in UV C irradiated plants these contents increased. The degree of de-epoxidation increased in all cultivations with age. The content of total glutathione (sum of reduced and oxidized) sharply decreased in bean cotyledons grown in all conditions. Interestingly, the content of total ascorbate increased at the end of cotyledon life span of control and decapitated plants but decreased in UV plants. Decrease of reduced/oxidized ratio of ascorbate and glutathione during cotyledon ageing confirmed increasing oxidative stress during senescence in all cultivations.     

Milking microalga Dunaliella salina for beta-carotene production in two-phase bioreactors

A new method was developed for production of beta-carotene from Dunaliella salina. Cells were grown in low light intensity and then transferred to a production bioreactor illuminated at a higher light intensity. It was a two-phase bioreactor consisting of an aqueous and a biocompatible organic phase. Mixing of the cells and extraction were performed by recirculation of the organic phase. Two experiments were performed. In the first experiment, bioreactors were operated at two different solvent recirculation rates of 150 and 200 mL min(-1). The beta-carotene extraction rate increased significantly at the higher recirculation rate, without exerting any influence on cell number and viability. A second experiment was carried out at a recirculation rate (200 mL min(-1)) appropriate for the study of long-term production of beta-carotene. The results show that D. salina at high light intensity remained viable for a long period (>47 days) in the presence of a biocompatible organic phase; however, cell growth was very slow. beta-Carotene could be continuously extracted to the organic phase; the cells continued to produce beta-carotene and the extracted molecules were continuously reproduced. As a result, beta-carotene was continuously removed ("milked") from the cells. beta-Carotene extraction efficiency in this system was >55%, and productivity was 2.45 mg m(-2) day(-1), much higher than that of commercial plants.     

Lutein epoxide cycle, light harvesting and photoprotection in species of the tropical tree genus Inga

Dynamics and possible function of the lutein epoxide (Lx) cycle, that is, the reversible conversion of Lx to lutein (L) in the light-harvesting antennae, were investigated in leaves of tropical tree species. Photosynthetic pigments were quantified in nine Inga species and species from three other genera. In Inga , Lx levels were high in shade leaves (mostly above 20 mmol mol⁻¹ chlorophyll) and low in sun leaves. In Virola surinamensis , both sun and shade leaves exhibited very high Lx contents (about 60 mmol mol⁻¹ chlorophyll). In Inga marginata grown under high irradiance, Lx slowly accumulated within several days upon transfer to deep shade. When shade leaves of I. marginata were briefly exposed to the sunlight, both violaxanthin and Lx were quickly de-epoxidized. Subsequently, overnight recovery occurred only for violaxanthin, not for Lx. In such leaves, containing reduced levels of Lx and increased levels of L, chlorophyll fluorescence induction showed significantly slower reduction of the photosystem II electron acceptor, Q _A, and faster formation as well as a higher level of non-photochemical quenching. The results indicate that slow Lx accumulation in Inga leaves may improve light harvesting under limiting light, while quick de-epoxidation of Lx to L in response to excess light may enhance photoprotection.