Diatoms possess several genes for proteins of the cryptochrome/photolyase family. A typical sequence for a plant cryptochrome was not found in our analysis of the Phaeodactylum tricornutum genome, but one protein grouped with higher plant and green algal cryptochromes. This protein, CryP, binds FAD and 5,10-methenyltetrahydrofolate, according to our spectroscopic studies on heterologously expressed protein. 5,10-Methenyltetrahydrofolate binding is a feature common to both cyclobutane pyrimidine dimer photolyases and DASH cryptochromes. In recombinant CryP, however, the FAD chromophore was present in its neutral radical state and had a red-shifted absorption maximum at 637 nm, which is more characteristic for a DASH cryptochrome than a cyclobutane pyrimidine dimer photolyase. Upon illumination with blue light, the fully reduced state of FAD was formed in the presence of reductant. Expression of CryP was silenced by antisense approaches, and the resulting cell lines showed increased levels of proteins of light-harvesting complexes, the Lhcf proteins, in vivo. In contrast, the levels of proteins active in light protection, the Lhcx proteins, were reduced. Thus, CryP cannot be directly grouped with known members of the cryptochrome/photolyase family. Of all P. tricornutum proteins, it is the most similar in sequence to a plant cryptochrome, and is involved in the regulation of light-harvesting protein expression, but shows spectroscopic features and a chromophore composition that are most typical of a DASH cryptochrome.

The diatom Cyclotella meneghiniana Kütz. (SAG 1020-a) was cultured under high-light (HL) and low-light (LL) conditions with either high (12 μM) or low (1 μM) iron in the media. Changes in cell morphology, especially cell volume and chloroplast size, were observed in cells grown under low iron. In contrast, HL had a much stronger influence on the photosynthetic apparatus. PSII function was unimpaired under lowered iron supply, but its quantum efficiency and reoxidation rate were reduced under HL conditions. As reported before, HL induced changes in antenna polypeptide composition. Especially the amount of Fcp6, an antenna protein related to LI818 and known to be involved in photoprotection, was increased under HL but was significantly reduced under lowered iron. The diatoxanthin content correlated with the amount of Fcp6 in isolated FCPa antenna complexes and was thus increased under HL and reduced under low iron as well. While the diatoxanthin (Dt) content of whole cells was enhanced under HL, no decrease was observed under lowered iron supply, ruling out the possibility that the decreased amounts in FCPa were due to a hampered diadinoxanthin de-epoxidase activity under these conditions. Thus, diatoxanthin not bound to FCPa has to be responsible for protection under the slight reduction in iron supply used here.

No abstract

Analysis of photosystem I (PSI) complexes from Cyclotella meneghiniana cultured under different growth conditions led to the identification of three groups of antenna proteins, having molecular weights of around 19, 18, and 17 kDa. The 19-kDa proteins have earlier been demonstrated to be more peripherally bound to PSI, and their amount in the PSI complexes was significantly reduced when the iron supply in the growth medium was lowered. This polypeptide was almost missing, and thus the total amount of fucoxanthin-chlorophyll proteins (Fcps) bound to PSI was reduced as well. When treating cells with high light in addition, no further changes in antenna polypeptide composition were detected. Xanthophyll cycle pigments were found to be bound to all Fcps of PSI. However, PSI of high light cultures had a significantly higher diatoxanthin to diadinoxanthin ratio, which is assumed to protect against a surplus of excitation energy. PSI complexes from the double-stressed cultures (high light plus reduced iron supply) were slightly more sensitive against destruction by the detergent treatment. This could be seen as a higher 674-nm emission at 77 K in comparison to the PSI complexes isolated from other growth conditions. Two major emission bands of the Fcps bound to PSI at 77 K could be identified, whereby chlorophyll a fluorescing at 697 nm was more strongly coupled to the PSI core than those fluorescing at 685 nm. Thus, the build up of the PSI antenna of several Fcp components enables variable reactions to several stress factors commonly experienced by the diatoms in vivo, in particular diatoxanthin enrichment under high light and reduction of antenna size under reduced iron conditions.

Background New genomic techniques (NGTs) allow new genotypes and traits to be developed in different ways and with different outcomes compared to previous genetic engineering methods or conventional breeding (including non-targeted mutagenesis). EU GMO regulation requires an assessment of their direct and indirect effects that may be immediate, delayed or cumulative. Such effects may also result from the interactions of NGT organisms simultaneously present in a shared receiving environment or emerge from a combination of their traits. This review elaborates such potential interactions based on a literature review and reasoned scenarios to identify possible pathways to harm. Main findings NGT organisms might be introduced into the environment and food chains on a large-scale, involving many traits, across a broad range of species and within short periods of time. Unavoidably, this would increase the likelihood that direct or indirect effects will occur through interactions between NGT organisms that are, for example simultaneously present within a shared environment. It has to be assumed that the cumulative effects of these NGT organisms may exceed the sum of risks identified in the distinct ‘events’. Consequently, risk assessors and risk managers not only need to consider the risks associated with individual NGT organisms (‘events’), but should also take account of risks resulting from their potential interactions and combinatorial effects. In addition, a prospective technology assessment could help the risk manager in defining criteria to minimize potential unintended interactions between NGT organisms through limiting the scale of releases. Conclusions If genetically engineered (GE) organisms derived from NGTs are released into the environment, their potentially negative impacts need to be minimized. As with all GE organisms, it is, therefore, crucial to not only assess the risks of the individual events, but also their potential interactions which can trigger direct and indirect effects with adverse impacts. It is necessary to develop hypotheses and specific scenarios to explore interactions between NGT organisms and possible pathways to harm from the perspective of the precautionary principle. In addition, the introduction prospective technology assessment could provide an instrument for the risk manager to control the scale of releases of NGT organisms.