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Cuscuta reflexa induces a variety of reaction in its hosts. Some of these are visual reactions, and it is clear that these morphological changes are preceded by events at the molecular level, where signal transduction is one of the early processes. Calcium (Ca2+) release is the major second messenger during signal transduction, and we therefore studied Ca2+ spiking in tomato during infection with C. reflexa. Bioluminescence in aequorin-expressing tomato was monitored for 48 h after the onset of Cuscuta infestation. Signals at the attachment sites were observed from 30 to 48 h. Treatment of aequorin-expressing tomato leaf disks with Cuscuta plant extracts suggested that the substance that induced Ca2+ release from the host was closely linked to parasite haustoria. [ABSTRACT FROM AUTHOR]

Aquaporins are membrane-intrinsic proteins that facilitate membrane transport of water and small solutes or even gases. Aquaporin genes are found in almost all living organisms. In plants the proteins account for water uptake and transport as well as CO 2 availability for photosynthesis. These processes are subjected to diurnal or circadian regimes. Expression and even function of aquaporins also follows day – night rhythms. Significance of aquaporin function in chronobiology has been provided by recent publications, which are summarised here. Examples of the significance of aquaporins in processes related to chronobiology are given for root water transport and leaf movement in several plant species. [ABSTRACT FROM AUTHOR]

ABSTRACTYoung maize seedlings (Zea mays L. cv.Giza 2) were exposed to moderate salinity in hydroponic culture. NADH-nitrate reductase (NR) activity (E.C. 1·6.6·1), NR activation state, NR-mRNA-steady state levels and major solute contents in leaves and roots were investigated. With increasing external salt concentration, Na+, Cl-, sugars, amino acids and quarternary ammonium compounds accumulated in leaves and roots, with concentrations in leaves exceeding those in roots. The nitrate content of leaves decreased, but increased in roots. The diurnal pattern of NR activity and of NR-mRNA was also changed under salinity, but the NR activation state was not affected. In the first light phase, maximum NR activity increased rapidly in leaves of control plants, but was much slower in leaves from salinized plants. Thus, integrated over the whole day, the NR activity of salt-stressed plants was lower than in control plants. NR transcript levels of control plants were low in the early night phase, started to increase in the second night phase, followed by a distinct peak at 2 h into the light period. This large ‘early morning peak’ of NR-mRNA was hardly affected by salinity, whereas the initial slow increase of m-RNA levels in the early night phase was almost absent in salinized plants. This is considered as one reason for the low NR activity of salinized plants in the first half of the day. It is also suggested that nitrate is a major signal affecting NR expression and activity under salinity. Sugars and amino acids appeared less important. [ABSTRACT FROM AUTHOR]

The plasmalemma of Arabidopsis thaliana contains several different aquaporins. These members of the major-intrinsic-protein family are permeable and selective for water. The apparent redundancy of aquaporins might be explained by tissue-specific expression of the corresponding gene. In order to investigate and compare the expression levels of five genes for plasma membrane-intrinsic proteins (PIP), PIP1a, PIP1b, PIP1c, PIP2a, and PIP2b, gene-specific RNA probes were generated by transcription of 3' untranslated regions. The probes were applied in RNase protection assays with RNA from different tissues of A. thaliana. The experiments revealed that PIP1b-RNA is the prominent PIP messenger in all tissues investigated. The expression levels of the remaining PIPs in comparison to PIP1b are low or very low. The findings indicate, that an explanation for the redundancy of plasma membrane aquaporin genes could not be found in an organ-specific expression of them in adult plants. [ABSTRACT FROM AUTHOR]

Abstract Background Plant infestation with parasitic weeds like Cuscuta reflexa induces morphological as well as biochemical changes in the host and the parasite. These modifications could be caused by a change in protein or gene activity. Using a comparative macroarray approach Cuscuta genes specifically upregulated at the host attachment site were identified. Results One of the infestation specific Cuscuta genes encodes a cysteine protease. The protein and its intrinsic inhibitory peptide were heterologously expressed, purified and biochemically characterized. The haustoria specific enzyme was named cuscutain in accordance with similar proteins from other plants, e.g. papaya. The role of cuscutain and its inhibitor during the host parasite interaction was studied by external application of an inhibitor suspension, which induced a significant reduction of successful infection events. Conclusions The study provides new information about molecular events during the parasitic plant - host interaction. Inhibition of cuscutain cysteine proteinase could provide means for antagonizing parasitic plants.

Discusses findings concerning the sensitivity of aquaporins to heavy metal ions and their possible consequences to plant physiology. Significance of membrane water permeability regulation; Selectivity of plasma membrane aquaporins.

Background Information: Aquaporins are H 2 O-permeable membrane protein pores. However, some aquaporins are also permeable to other substances such as CO 2 . In higher plants, overexpression of such aquaporins has already led to an enhanced photosynthetic performance due to improved CO 2 mesophyll conductance. In this work, we investigated the effects of such aquaporins on unicellular photosynthetically active organisms, specifically cyanobacteria., Results: Overexpression of aquaporins NtAQP1 or hAQP1 that might have a function to improve CO 2 membrane permeability lead to increased photosynthesis rates in the cyanobacterium Synechococcus sp. PCC7002 as concluded by the rate of evolved O 2 . A shift in the Plastoquinone pool state of the cells supports our findings. Water permeable aquaporins without CO 2 permeability, such as NtPIP2;1, do not have this effect., Conclusions and Significance: We conclude that also in single cell organisms like cyanobacteria, membrane CO 2 conductivity could be rate limiting and CO 2 -porins reduce the respective membrane resistance. We could show that besides the tobacco aquaporin NtAQP1 also the human hAQP1 most likely functions as CO 2 diffusion facilitator in the photosynthesis assay., (© 2024 The Authors. Biology of the Cell published by Wiley‐VCH GmbH on behalf of Société Française des Microscopies and Société de Biologie Cellulaire de France.)

The increased use of wireless technology causes a significant exposure increase for all living organisms to radio frequency electromagnetic fields (RF-EMF). This comprises bacteria, animals, and also plants. Unfortunately, our understanding of how RF-EMF influences plants and plant physiology remains inadequate. In this study, we examined the effects of RF-EMF radiation on lettuce plants ( Lactuca sativa ) in both indoor and outdoor environments using the frequency ranges of 1890-1900 MHz (DECT) at 2.4 GHz and 5 GHz (Wi-Fi). Under greenhouse conditions, RF-EMF exposure had only a minor impact on fast chlorophyll fluorescence kinetics and no effect on plant flowering time. In contrast, lettuce plants exposed to RF-EMF in the field showed a significant and systemic decrease in photosynthetic efficiency and accelerated flowering time compared to the control groups. Gene expression analysis revealed significant down-regulation of two stress-related genes in RF-EMF-exposed plants: violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). RF-EMF-exposed plants had lower Photosystem II's maximal photochemical quantum yield (F V /F M ) and non-photochemical quenching (NPQ) than control plants under light stress conditions. In summary, our results imply that RF-EMF might interfere with plant stress responses and reduced plant stress tolerance.

In Chlamydomonas reinhardtii, ketocarotenoid biosynthesis is limited to the diploid zygospore stage. In this study, we attempted to engineer the ketocarotenoid pathway into Chlamydomonas haploid vegetative green cells by overexpressing the key enzyme ß-carotene ketolase (CrBKT). We chose strain CC-4102 for the approach; competitive pathways, α-carotene biosynthesis and xanthophyll cycle are silenced in this strain. Driven by the strong constitutive HSP70/RBCS2 promoter CrBKT overexpression resulted in the production of canthaxanthin, the ketolation product from ß-carotene as well as a drastic reduction in the chlorophyll concentration. Intriguingly, these phenotypes could only be detected from lines transformed and grown heterotrophically in the dark. Once exposed to light, these transformants lost the aforementioned phenotypes as well as their antibiotic resistance. This phenomenon is in agreement with the fact that we were unable to recover any canthaxanthin-producing line among light-selected transformants.

Aquaporins are important and well-studied water channel membrane proteins. However, being membrane proteins, sample preparation for functional analysis is tedious and time-consuming. In this paper, we report a new approach for the co-translational insertion of two aquaporins from Escherichia coli and Nicotiana tabacum using the CFPS system. This was done in the presence of liposomes with a modified procedure to form homogenous proteo-liposomes suitable for functional analysis of water permeability using stopped-flow spectrophotometry. Two model aquaporins, AqpZ and Nt PIP2;1, were successfully incorporated into the liposome in their active forms. Shifted green fluorescent protein was fused to the C-terminal part of AqpZ to monitor its insertion and status in the lipid environment. This new fast approach offers a fast and straightforward method for the functional analysis of aquaporins in both prokaryotic and eukaryotic organisms.