Klaus J. Appenroth

The Spirodela polyrhiza genome reveals insights into its neotenous reduction fast growth and aquatic lifestyle

The subfamily of the Lemnoideae belongs to a different order than other monocotyledonous species that have been sequenced and comprises aquatic plants that grow rapidly on the water surface. Here we select Spirodela polyrhiza for whole-genome sequencing. We show that Spirodela has a genome with no signs of recent retrotranspositions but signatures of two ancient whole-genome duplications, possibly 95 million years ago (mya), older than those in Arabidopsis and rice. Its genome has only 19,623 predicted protein-coding genes, which is 28% less than the dicotyledonous Arabidopsis thaliana and 50% less than monocotyledonous rice. We propose that at least in part, the neotenous reduction of these aquatic plants is based on readjusted copy numbers of promoters and repressors of the juvenile-to-adult transition. The Spirodela genome, along with its unique biology and physiology, will stimulate new insights into environmental adaptation, ecology, evolution and plant development, and will be instrumental for future bioenergy applications.

Kinetics of chromium(V) formation and reduction in fronds of the duckweed Spirodela polyrhiza — a low frequency EPR study

The uptake of chromate by the duckweed Spirodela polyrhiza was investigated with atomic absorption spectroscopy and the reduction of Cr(VI) to Cr(V) was measured using low frequency EPR spectroscopy. The biphasic kinetics of the uptake was fitted to parameters of a proposed kinetic model. Another model was developed to simulate chromate reduction. The first step of chromate reduction was found to be much faster than the uptake of Cr(VI) from the free space. Most probably, this step occurs already in the cell wall or on the cell membrane surface. Further reduction of Cr(V) to Cr(III) was estimated to be slower. The disappearance of the Cr(V) signal, following transfer of the plants into a Cr-free solution, lasted several tens of hours; the kinetics was mono- or biexponential depending on the length of Cr loading. The rate constants for Cr reduction in living plants were determined for the first time.

Complex and shifting interactions of phytochromes regulate fruit development in tomato

Tomato fruit ripening is a complex metabolic process regulated by a genetical hierarchy. A subset of this process is also modulated by light signalling, as mutants encoding negative regulators of phytochrome signal transduction show higher accumulation of carotenoids. In tomato, phytochromes are encoded by a multi-gene family, namely PHYA, PHYB1, PHYB2, PHYE and PHYF; however, their contribution to fruit development and ripening has not been examined. Using single phytochrome mutants phyA, phyB1 and phyB2 and multiple mutants phyAB1, phyB1B2 and phyAB1B2, we compared the on-vine transitory phases of ripening until fruit abscission. The phyAB1B2 mutant showed accelerated transitions during ripening, with shortest time to fruit abscission. Comparison of transition intervals in mutants indicated a phase-specific influence of different phytochrome species either singly or in combination on the ripening process. Examination of off-vine ripened fruits indicated that ripening-specific carotenoid accumulation was not obligatorily dependent upon light and even dark-incubated fruits accumulated carotenoids. The accumulation of transcripts and carotenoids in off-vine and on-vine ripened mutant fruits indicated a complex and shifting phase-dependent modulation by phytochromes. Our results indicate that, in addition to regulating carotenoid levels in tomato fruits, phytochromes also regulate the time required for phase transitions during ripening.

Thermochromism and photochromism of aryl substituted acyclic azines1: Uncatalised and acid-catalised thermal isomerisation

Abstract The photochemical E-Z isomerisation of the benzophenone-9-anthraldehyde azine (1), benzophenone-9-acridine aldehyde azine (2) and 9-anthraldehyde azine (3) is thermally reversible. The thermal reaction gives the same isomers as the photochemical reaction. We have studied the mechanism of the thermal isomerisation of these azines. Our results are in accordance with an inversion of the N atom which is connected with a rotation movement about the N-N single or the CN double bond.

Thermochromism and photochromism of aryl-substituted acyclic azines II: Photokinetics

Abstract Acyclic azines with higher condensed aromatic and heterocyclic substituents are photochromic and show both thermal isomerization and photochemical isomerization. From the point of view of formal kinetics the azines can be divided into four reaction types depending on the substituents R i . The correspondence of the expected formal kinetic behaviour of the azines with the experimental results is a direct proof of a photochemical E – Z isomerization of these compounds. We investigated acyclic azines which fulfil all criteria of a complicated unitary photoreaction of the type A ⇌ B as well as those azines showing a reversible consecutive photoreaction A ⇌ B ⇌ C. All quantum yields were determined using formal kinetics.

Thermochromism and photochromism of aryl-substituted acyclic azines III: Investigations on the mechanism of photochemical isomerization

Abstract We studied the reaction mechanism of the unsensitized as well as the sensitized photochemical E — Z and Z — E isomerizations of benzophenone-9-anthraldehyde azine. The photochemistry of this compound follows a unitary E ⇌ Z reaction. For qualitative investigations we used benzophenone-9-acridinealdehyde azine, 9-anthranyl-2-pyridinealdehyde azine, 9-anthranyl-3-quinolinealdehyde azine, 9-anthranyl-9-acridinealdehyde azine and 9-acridinealdehyde azine. The experimental results are consistent with the following mechanism for the photoisomerization of azines. In the photochemical E — Z isomerization the S 1 state of the E isomer is reactive; sensitization of the triplet state does not induce the reaction. A singlet mechanism is also very probable for the Z — E isomerization. The most effective photophysical processes competing with isomerization are intersystem crossing in the E isomer and radiationless internal conversion in the Z isomer.

Nutritional value of duckweeds (Lemnaceae) as human food

Duckweeds have been consumed as human food since long. Species of the duckweed genera, Spirodela, Landoltia, Lemna, Wolffiella and Wolffia were analysed for protein, fat, and starch contents as well as their amino acid and fatty acid distribution. Protein content spanned from 20% to 35%, fat from 4% to 7%, and starch from 4% to 10% per dry weight. Interestingly, the amino acid distributions are close to the WHO recommendations, having e.g. 4.8% Lys, 2.7% Met+Cys, and 7.7% Phe+Tyr. The content of polyunsaturated fatty acids was between 48 and 71% and the high content of n3 fatty acids resulted in a favourable n6/n3 ratio of 0.5 or less. The phytosterol content in the fastest growing angiosperm, W. microscopica, was 50mgg(-1) lipid. However, the content of trace elements can be adjusted by cultivation conditions. Accordingly, W. hyalina and W. microscopica are recommended for human nutrition.

Different regulation of β-amylase and starch phosphorylase by light in dormant and non-dormant turions of Spirodela polyrhiza

Summary The influence of single red light pulses and of continuous red light on the activity of two enzymes, i.e. β-amylase (EC 3.2.1.2) and starch phosphorylase (EC 2.4.1.1), was investigated in dormant and non-dormant turions of Spirodela polyrhiza. The activity of β-amylase was induced by continuous red light but not by red light pulses in dormant turions. In non-dormant turions, however, the activity of β-amylase following a single red light pulse was two times higher than after continuous red light. This high effectiveness of a single red light pulse, as compared with continuous red, represents a novel mode of regulation of enzyme activity by light. It is suggested that a low fluence response of phytochrome is abolished by a high irradiance response elicited by continuous red light. The light-induced increase in the activity of β-amylase is due to de novo synthesis of the enzyme as shown by Western blot analysis using polyclonal antibodies raised against β-amylase from Spirodela polyrhiza. The presence of light-activable precursor was excluded by showing that cysteine added to the extraction medium did not influence the activity of β-amylase. In contrast, the activity of starch phosphorylase was induced by continuous red light in dormant turions but decreased in non-dormant turions. During the cold after-ripening treatment turions qualitatively changed their response to light, becoming light-insensitive when partly after-ripened (21 days). In all instances, a red light pulse was ineffective in inducing starch phosphorylase. Isoforms of β-amylase and starch phosphorylase were separated by non-denaturating PAGE. No special induction by light of any specific isoform of β-amylase and starch phosphorylase was found in turions. Since both enzymatic activities and their regulation by light do not correlate with the breakdown of starch, we conclude that they are not directly involved in the regulation of starch degradation in turions.

Thermochromism and photochromism of aryl-substituted acyclic azines VII: solvent effect on photochemical E-Z isomerization

Abstract In the E-Z isomerization of benzophenone-9-anthraldazine and benzophenone-9-acridinealdazine there is a significant relation between φE → Z and the solvent acceptor number AN, whereas a significant relation between φZ → E and AN could not be detected. These results are interpreted in terms of the effect of solvent polarity on the energy levels of the E-Z isomers of the azine.

Thermochromism and photochromism of aryl-substituted acylic azines X: Relationship between molecular geometry and fluorescence of anthranyl-substituted compounds

The EE and EZ isomers of 9-anthraldehyde azine (II) do not show any fluorescence either at room temperature or at low temperatures. The ZZ isomer shows monomer—excimer fluorescence strongly dependent on temperature as is characteristic of bridged anthracene compounds. The differences in fluorescence behaviour are discussed with respect to the molecular geometry of the three isomers of II.