Aquaporins of the PIP2 class are required for efficient anther dehiscence in tobacco

Several processes during sexual reproduction in higher plants involve the movement of water between cells or tissues. Before flower anthesis, anther and pollen dehydration takes place before the release of mature pollen at dehiscence. Aquaporins represent a class of proteins that mediates the movement of water over cellular membranes. Aquaporins of the plasmamembrane PIP2 family are expressed in tobacco (Nicotiana tabacum) anthers and may therefore be involved in the movement of water in this organ. To gain more insight into the role these proteins may play in this process, we have analyzed their localization using immunolocalizations and generated plants displaying RNA interference of PIP2 aquaporins. Our results indicate that PIP2 protein expression is modulated during anther development. Furthermore, in tobacco PIP2 RNA interference plants, anther dehydration was slower, and dehiscence occurred later when compared with control plants. Together, our results suggest that aquaporins of the PIP2 class are required for efficient anther dehydration prior to dehiscence.     

Use of 1H NMR to study transport processes in porous biosystems

The operation of bioreactors and the metabolism of microorganisms in biofilms or soil/sediment systems are strongly dictated by the transport processes therein. Nuclear magnetic resonance (NMR) spectroscopy or magnetic resonance imaging (MRI) allow nondestructive and noninvasive quantification and visualisation (in case of MRI) of both static and dynamic water transport phenomena. Flow, mass transfer and transport processes can be measured by mapping the (proton) displacement in a defined time interval directly in a so-called pulsed field gradient (PFG) experiment. Other methods follow the local intensity in time-controlled sequential images of water or labelled molecules, or map the effect of contrast agents. Combining transport measurements with relaxation-time information allows the discrimination of transport processes in different environments or of different fluids, even within a single picture element in an image of the porous biosystem under study. By proper choice of the applied NMR method, a time window ranging from milliseconds to weeks (or longer) can be covered. In this paper, we present an overview of the principles of NMR and MRI techniques to visualise and unravel complex, heterogeneous transport processes in porous biological systems. Applications and limitations will be discussed, based on results obtained in (model) biofilms, bioreactors, microbial mats and sediments. Journal of Industrial Microbiology & Biotechnology (2001) 26, 43–52. Received 20 April 2000/ Accepted in revised form 14 August 2000     

Argulus izintwala n. sp. (Crustacea: Branchiura) from Lake St Lucia,South Africa

During surveys of the fish parasites of Lake St Lucia on the coast of northern KwaZulu-Natal, specimens of an hitherto undescribed argulid were found on the skin of the kelee shad Hilsa kelee (Cuvier). This, only the fourth argulid species to be found in South African coastal waters, is here described as Argulus izintwala n. sp.     

MRI of intact plants

Nuclear magnetic resonance imaging (MRI) is a non-destructive and non-invasive technique that can be used to acquire two- or even three-dimensional images of intact plants. The information within the images can be manipulated and used to study the dynamics of plant water relations and water transport in the stem, e.g., as a function of environmental (stress) conditions. Non-spatially resolved portable NMR is becoming available to study leaf water content and distribution of water in different (sub-cellular) compartments. These parameters directly relate to stomatal water conductance, CO₂ uptake, and photosynthesis. MRI applied on plants is not a straight forward extension of the methods discussed for (bio)medical MRI. This educational review explains the basic physical principles of plant MRI, with a focus on the spatial resolution, factors that determine the spatial resolution, and its unique information for applications in plant water relations that directly relate to plant photosynthetic activity.     

Pregnancy-associated venous insufficiency course with placental and systemic oxidative stress

The development of lower extremity venous insufficiency (VI) during pregnancy has been associated with placental damage. VI is associated with increased oxidative stress in venous wall. We have investigated potential disturbance/dysregulation of the production of reactive oxygen species (ROS) in placenta and its eventual systemic effects through the measurement of malondialdehyde (MDA) plasma levels in women with VI. A total of 62 women with VI and 52 healthy controls (HCs) were studied. Levels of nicotinamide adenine dinucleotide phosphate-oxidase 1 (NOX1), 2 (NOX2), inducible nitric oxide synthase (iNOS), endothelial (eNOS), poly(ADP-ribose) polymerase PARP (PARP) and ERK were measured in placental tissue with immunohistochemistry and RT-qPCR. Plasma and placental levels of MDA were determined by colorimetry at the two study times of 32 weeks of gestation and post-partum. Protein and gene expression levels of NOX1, NOX2, iNOS, PARP and ERK were significantly increased in placentas of VI. eNOS activity was low in both study groups, and there were no significant differences in gene or protein expression levels. Women with VI showed a significant elevation of plasma MDA levels at 32 weeks of gestation, and these levels remained elevated at 32 weeks post-partum. The MDA levels were significantly higher in placentas of women with VI. Placental damage that was found in the women with VI was characterized by overexpression of oxidative stress markers NOX1, NOX2, and iNOS, as well as PARP and ERK. Pregnant women with VI showed systemic increases in oxidative stress markers such as plasma MDA levels. The foetuses of women with VI had a significant decrease in their venous pH as compared to those from HC women. The situation of oxidative stress and cellular damage created in the placenta is in coexpression with the production of a pH acidification.     

Influence of steroid hormone progesterone on the properties of phosphatidyl serine monolayers and thin liquid films

In this work the capability of Progesterone (Prog) to penetrate to phosphatidyl serine (PS) monolayers (detected by equilibrium and dynamic surface tensions) and to induce rupture of PS thin liquid films (TLFs, known as foam films) in presence of Ca(2+) ions is studied. TLF studies reveal that the presence of Ca(2+) ions changes the type of PS films from thicker common black films to bilayer Newton black films and that the addition of Prog results in film destabilization and rupture. The effects of Prog in presence of Ca(2+) ions were observed with the films consisting of negatively charged PS but not of neutral phospholipids. The results correlate with the proposed physiological role of Prog and Ca(2+) in the acrosome reaction. The model of TLFs is used for the first time to study membrane fusion during acrosome reaction and proposes several new qualitative and quantitative parameters for studying of this reaction.     

Analysis of diffusion and relaxation behavior of water in apple parenchymal cells

It has been demonstrated by an example of apple parenchymal cells that NMR spectroscopy can be used to analyze the relaxation and diffusion of water molecules in plant cells. With small diffusion times, three relaxation components have been distinguished, which correspond to water in a vacuole, in the cytoplasm, and in intercellular liquid. The coefficient of self-diffusion corresponding to these components have been determined. With large diffusion times, it is possible to distinguish two components. For the slowly relaxing component (which corresponds to water in a vacuole), the regime of restricted diffusion was observed. For a quickly relaxing component, an anomalous increase in the coefficient of self-diffusion with the time of diffusion took place.     

Combined analysis of diffusion and relaxation behavior of water in apple parenchyma cells

With apple parenchymal cells as an example, we demonstrate the expedience of combined analysis of the relaxation and diffusion of water molecules in plant cells by NMR spectroscopy. At small diffusion times, our approach discerns three relaxation components pertaining to water in the vacuole, cytoplasm, and intercellular space. The corresponding self-diffusion coefficients are determined. At long diffusion times, it is possible to distinguish two components. For the slow-relaxing component (vacuolar water) we observe the mode of restricted diffusion. For the fast-relaxing components, the diffusion coefficient anomalously increases with time.