Molecular cloning and transcriptional activity of a new Petunia calreticulin gene involved in pistil transmitting tract maturation, progamic phase, and double fertilization

Calreticulin (CRT) is a highly conserved and ubiquitously expressed Ca2+-binding protein in multicellular eukaryotes. As an endoplasmic reticulum-resident protein, CRT plays a key role in many cellular processes including Ca2+ storage and release, protein synthesis, and molecular chaperoning in both animals and plants. CRT has long been suggested to play a role in plant sexual reproduction. To begin to address this possibility, we cloned and characterized the full-length cDNA of a new CRT gene (PhCRT) from Petunia. The deduced amino acid sequence of PhCRT shares homology with other known plant CRTs, and phylogenetic analysis indicates that the PhCRT cDNA clone belongs to the CRT1/CRT2 subclass. Northern blot analysis and fluorescent in situ hybridization were used to assess PhCRT gene expression in different parts of the pistil before pollination, during subsequent stages of the progamic phase, and at fertilization. The highest level of PhCRT mRNA was detected in the stigma–style part of the unpollinated pistil 1 day before anthesis and during the early stage of the progamic phase, when pollen is germinated and tubes outgrow on the stigma. In the ovary, PhCRT mRNA was most abundant after pollination and reached maximum at the late stage of the progamic phase, when pollen tubes grow into the ovules and fertilization occurs. PhCRT mRNA transcripts were seen to accumulate predominantly in transmitting tract cells of maturing and receptive stigma, in germinated pollen/growing tubes, and at the micropylar region of the ovule, where the female gametophyte is located. From these results, we suggest that PhCRT gene expression is up-regulated during secretory activity of the pistil transmitting tract cells, pollen germination and outgrowth of the tubes, and then during gamete fusion and early embryogenesis

Femtosecond near-infrared laser pulse induced strand breaks in mammalian cells.

Multiphoton laser scanning microscopy (MPLSM) is based on non-resonant simultaneous absorption of two or three near infrared (NIR) photons by a fluorophore in the subfemtoliter focal volume of a high numerical aperture (N.A. 1.3) objective. The higher penetration depth of NIR radiation enables optical sectioning across thick biological specimens and because of the absence of efficient single photon absorbers in the NIR spectral region of 700 to 1200 nm there is hardly any out-of-focus photodamage and photobleaching. Recent in vitro studies (14) have demonstrated that irradiation of supercoiled plasmid DNA with intense multiphoton NIR 810 nm of 140 fs pulse width, 76 MHz pulse repetition rate results in single strand breaks as a result of simultaneous absorption of three or more photons. Herein, we have investigated the influence of 800 nm NIR 170 fs laser pulses, 80 MHz pulse repetition frequency at mean powers of 2 to 20 mW on nuclear DNA of unlabelled PtK2 cells. In situ TdT-mediated dUTP-nick end labelling (TUNEL) revealed that cells exposed to the NIR irradiation above > or =5 mW mean laser power alone contained TUNEL-positive nuclei. The intensity of TUNEL fluorescence was relatively higher at increased mean NIR laser power. These results provide evidence that DNA strand breaks also occur in vivo when mammalian cells are exposed to high average power > or =5 mW NIR irradiation during MPLSM possibly due to multiphoton absorption process. Because intense DNA fragmentation is one of the hall marks of programmed cell death it is hypothesised that NIR induced cell death is by apoptosis

Femtosecond near-infrared lasers as a novel tool for non-invasive real-time high-resolution time-lapse imaging of chloroplast division in living bundle sheath cells of Arabidopsis.

Non-linear excitation of fluorophores by contemporaneous absorption of two or more near-infrared (NIR) photons following diffraction-limited focusing with high-numerical-aperture objectives circumvents out-of-focus fluorescence (without a confocal pinhole) and spatially limits photobleaching and photodamage to the minute sub-femtoliter focal volume. This is in contrast to optical events in conventional confocal imaging systems using ultraviolet (UV) or visible laser sources wherein the entire sectors of the specimen above and below the plane of focus experience massive photostress and photodamage. In addition, NIR wavelengths penetrate deeper into the highly scattering environs of plant tissue than UV and visible wavelengths. We delineate a novel non-invasive technique using NIR femtosecond laser pulses at lambda = 740, 760, 780, and 800 nm for induction of chlorophyll fluorescence by the two-photon effect as well as for intra-tissue time-lapse vital three-dimensional imaging of fundamental events of chloroplast division in deeply seated bundle sheath cells of Arabidopsis thaliana (L.) Heynh. leaves. Our findings establish that (i) mature bundle sheath chloroplasts are indeed capable of division, (ii) the dividing chloroplasts assume a distinct constricted/dumbbell-shaped profile with an average lifespan of 20-25 min, (iii) the complete division of the pre-existing chloroplasts occurs within 50 min, and (iv) the two derivative daughter chloroplasts are invariably unequal in size. This novel NIR-laser-based technique has any number of potential applications, including (i) non-invasive intra-vital imaging of molecular and ion dynamics, (ii) non-destructive screening of mutants impaired in photosynthesis, (iii) diagnosis of physiological states of plants and (iv) bio-optical taxonomy

Technical advance: near-infrared femtosecond laser pulses as a novel non-invasive means for dye-permeation and 3D imaging of localised dye-coupling in the Arabidopsis root meristem.

We have used near-infrared femtosecond Titanium: Sapphire laser pulses as novel non-invasive means for dye loading into various cell types of the Arabidopsis root meristem, and by 3D imaging have assessed the extent of dye coupling between the meristematic cells. The post-embryonic primary root of Arabidopsis thaliana has an invariant ontogeny and fixed cellular organisation which makes it an attractive model system to study developmental events involving cell fate determination, cellular differentiation and pattern formation. Local intercellular communication and local transmission of positional signals are likely to play a pivotal role in cell proliferation and regulation of differentiation. We have therefore examined the extent to which the constituent cells in the root meristem are symplastically coupled. Following laser-assisted loading of membrane impermeate fluorescent dye propidium iodide (PI) in single cells, we show by time-lapse and 3D imaging that in the root tip all undifferentiated cells are dye-coupled. When PI is permeated into the central cells, it rapidly moved into the adjacent initials of the columella, cortex, pericycle and stele. Interestingly, when only either of the initials were loaded with the dye, it never moved into any of the central cells. Amongst the epidermal cells, the differentiated hair cells are symplastically isolated. Our data provide evidence (1) for differential dye-coupling behaviour between quiescent centre cells and the neighbouring initials; (2) that cells in the root are coupled during stages at which the cell-lineage pattern is formed and that it becomes progressively secluded as they differentiate and the pattern is fixed. Taken together, our NIR-laser mediated approach is highly efficient and has numerous potential applications for non-invasive permeation of dyes in different cell types

In situ 3D characterization of membrane fouling by yeast suspensions using two-photon femtosecond near infrared non-linear optical imaging

In situ non-invasive 3D characterization of membrane fouling was achieved using femtosecond near infrared non-linear optical imaging together with a novel crossflow filtration module. Washed fluorophore-labelled yeast suspensions were filtered through Millipore 0.22 μm mixed cellulose ester membranes and the fouling layer was imaged at different times throughout the experiment. Based on the 3D femtosecond images, it has been possible to identify fine structural features of the cake and to measure the thickness of the filter cake formed on the microfiltration (MF) membranes. Our findings reveal that low concentration feeds result in the initial formation of a patchy monolayer of cells leading to a multilayered cake, whilst at higher concentrations a multilayer cake forms rapidly. For patchy cakes, the technique offers greater resolution than that which is achievable with the direct observation through membrane technique. Deposited cell aggregates and broken fragments of cells can clearly be imaged. For thick cakes, it has been possible to image up to depths 45 μm below the cake surface in the present work. © 2006 Elsevier B.V. All rights reserved

Noninvasive 3D vital imaging and characterization of notochordal cells of the intervertebral disc by femtosecond near-infrared two-photon laser scanning microscopy and spatial-volume rendering.

The central region of the intervertebral disc (IVD) in infant humans is made and maintained by notochordal cells (NCs). These cells disappear during maturation to be replaced by mature chondrocyte-like cells. NCs are completely different morphologically from the mature chondrocyte-like IVD cells and have complex and essential functions but little is known about them. Recently, two-photon laser scanning microscopy (TPLSM) using near-infrared (NIR) femtosecond pulsed lasers has emerged as a promising noninvasive optical technique for observing unfixed living 3D biological specimens in situ and in vitro. Several lines of evidence suggest that compared with conventional laser scanning confocal microscopy (LSCM), femtosecond NIR laser-based TPLSM has any number of advantages including 3D resolution without a spatial filter (confocal pinhole), minimal photobleaching, and photodamage above and below the focal plane, and importantly, greater depth penetration. We have thus taken advantage of these unique features of femtosecond laser-based TPLSM for vital 3D imaging in conjunction with advanced spatial-volume rendering modalities to compare morphologies of NCs/clusters from pig caudal discs with chondrocyte-like IVD cells from bovine caudal discs, both in ex vivo tissue and when isolated and grown in vitro within 3D alginate scaffolds. Our results provide evidence that (a) ex vivo notochordal tissue consists of areas with NC clusters, and those dominated by tubular structures of low cell density (b) within 3D in vitro scaffolds the morphology of NC is heterogeneous and the cells contain distinct cytoplasmic vacuole-like structures occasionally including acidic subinclusions (c) a quantitative determination based on 3D spatial and volumetric-rendering reveals an average NC diameter of 22.05 microm (range 11.96-46.63 microm) and NC volume of 9701 microm(3) (2041-36427 microm(3)) whereas chondrocyte-like cells have a mean volume of 3279 microm(3) and diameter of 12.20 microm. Taken together, this study demonstrates that femtosecond TPLSM has unique advantages over other conventional histological and in particular LSCM for high resolution noninvasive vital characterization of notochordal and chondrocyte-like cells of IVD over extended depths beyond 300-500 microm