Pollination and embryo development in Brassica rapa L. in microgravity

Plant reproduction under spaceflight conditions has been problematic in the past. In order to determine what aspect of reproductive development is affected by microgravity, we studied pollination and embryo development in Brassica rapa L. during 16 d in microgravity on the space shuttle (STS-87). Brassica is self-incompatible and requires mechanical transfer of pollen. Short-duration access to microgravity during parabolic flights on the KC-135A aircraft was used initially to confirm that equal numbers of pollen grains could be collected and transferred in the absence of gravity. Brassica was grown in the Plant Growth Facility flight hardware as follows. Three chambers each contained six plants that were 13 d old at launch. As these plants flowered, thin colored tape was used to indicate the date of hand pollination, resulting in silique populations aged 8-15 d postpollination at the end of the 16-d mission. The remaining three chambers contained dry seeds that germinated on orbit to produce 14-d-old plants just beginning to flower at the time of landing. Pollen produced by these plants had comparable viability (93%) with that produced in the 2-d-delayed ground control. Matched-age siliques yielded embryos of equivalent developmental stage in the spaceflight and ground control treatments. Carbohydrate and protein storage reserves in the embryos, assessed by cytochemical localization, were also comparable. In the spaceflight material, growth and development by embryos rescued from siliques 15 d after pollination lagged behind the ground controls by 12 d; however, in the subsequent generation, no differences between the two treatments were found. The results demonstrate that while no stage of reproductive development in Brassica is absolutely dependent upon gravity, lower embryo quality may result following development in microgravity.

ASTROCULTURE (TM) root metabolism and cytochemical analysis

Physiology of the root system is dependent upon oxygen availability and tissue respiration. During hypoxia nutrient and water acquisition may be inhibited, thus affecting the overall biochemical and physiological status of the plant. For the Astroculture (TM) plant growth hardware, the availability of oxygen in the root zone was measured by examining the changes in alcohol dehydrogenase (ADH) activity within the root tissue. ADH activity is a sensitive biochemical indicator of hypoxic conditions in plants and was measured in both spaceflight and control roots. In addition to the biochemical enzyme assays, localization of ADH in the root tissue was examined cytochemically. The results of these analyses showed that ADH activity increased significantly as a result of spaceflight exposure. Enzyme activity increased 248% to 304% in dwarf wheat when compared with the ground controls and Brassica showed increases between 334% and 579% when compared with day zero controls. Cytochemical staining revealed no differences in ADH tissue localization in any of the dwarf wheat treatments. These results show the importance of considering root system oxygenation in designing and building nutrient delivery hardware for spaceflight plant cultivation and confirm previous reports of an ADH response associated with spaceflight exposure.

[Chromosome aberration of pollen mother cell of broccoli (Brassica oleralea var. Italica) induced by space flight]

OBJECTIVE

To study the cytogenetic effect of space flight on broccoli seeds and the mechanism of mutations of the plant.

METHOD

Dry seeds of broccoli were sent to the space on board a recoverable satellite for 8 days. After recovery the seeds were planted in the field. Chromosome behaviour of pollen mother cell (PMC) samples were observed following the method of ZHU Cheng, 1982. Pollen samples were stained and embeded in lacto-phenol fuchsin for fertility determination.

RESULT

Unequal chromosome numbers of broccoli's PMC were found in the diakinesis stage, such as reducing n = 6, 7 or increasing n = 11 (earth-control number is n = 9); inversion or translocation of chromosomes occurred, and lagging chromosome were found in the anaphase and telophase of PMC meiosis growing rate and growing potential of the seeds were observed after recovery.

CONCLUSION

Leaves cexaceous decrease and aberrations in the chromosome of PMC are found in broccoli after space flight.

DNA content and differentiation of root apical cells of Brassica rapa plants grown in microgravity

Root cap is proposed to be a graviperceptive tissue in the plant root, and it is composed of several cell types. One such cell type, the columella cells, are thought to initiate the gravity-induced signal transduction cascade, and these cells arise from the activity of the meristematic zone of the root cap. There is, in fact, a continuum of cells in the central column of the root cap representing the meristematic cells, developing columella cells, mature cells, and those that will soon be sloughed off into the soil. In order to study the functional roles of the root cap cells in gravity-sensing, we compared the ultrastructural organization, differentiation, and DNA content in the meristematic, elongating, and differentiating cells of root tips in Brassica rapa plants grown in space microgravity and at 1g. The experiments were also designed to determine the reactions of root cap cells in both main roots (in which the original root cap was present in an embryonic form within the seed) and lateral roots (in which the root cap formed completely in space after seed germination on orbit) to the space microgravity. This study (ROOTS) was performed in collaboration with the B-PAC experiment on the Space shuttle "Columbia" mission STS-87 (Collaborative US/Ukrainian Experiment (CUE) during November 19-December 5, 1997.

Simulated weightlessness and hyper-g results in opposite effects on the regeneration of the cortical microtubule array in protoplasts from Brassica napus hypocotyls

Enzymatic digestion of the cell wall of Brassica napus hypocotyls gave a heterogeneous suspension of protoplasts with the cortical microtubules (CMTs) randomly organised or CMTs organised in parallel. The effect of variable g-influences has been tested on CMT organisation. In contrast to the 1 g-protoplasts, which reorganised the CMTs into parallel arrays during the 96 h test period, the frequency of randomly-oriented CMTs in the protoplasts exposed to simulated weightlessness (0 g) on a 2-D clinostat increased significantly during the same period. The opposite effect was obtained when the protoplasts were exposed to hyper-g (7 or 10 g), where the reorganisation of the CMTs into parallel arrays was accelerated compared to the 1 and 0 g-protoplasts. These results indicate that a unidirectional gravity force is a necessity for the reorganisation of CMTs in protoplasts to parallel arrays and that CMTs act as responding elements that are able to sense different levels of gravity. Besides the inability of the protoplasts to reorganise the CMTs into parallel arrays, the quantity of CMTs in the individual protoplast decreased during 4 days of simulated weightlessness, both compared to the CMTs quantity in the protoplasts immediately after isolation and compared to the 1 g- and hyper-g-protoplasts after 24 and 48 h of g-exposure. The size of the protoplasts was also affected by the g-exposure. Protoplasts exposed to simulated 0 g increased significantly after 24 and 48 h, whereas the 1 g- and 10 g-protoplasts maintained the same size during the 48 h test period.

Effects of clinorotation on the polysaccharide content of resynthesized walls of protoplasts

Changes in cellulose and callose content during cell wall regeneration in Brassica oleracea protoplasts have been examined by cytofluorimetry following their exposure to the conditions of the horizontal clinostat (2 r.p.m.) for 10 days. In comparison with controls, cellulose content decreased 4-fold and 28% of the protoplasts failed to resynthesize a wall in the clinorotated sample. The callose content was almost doubled in clinostated cells. Callose synthesis fluctuated in both control and clinorotated protoplasts. The results support the idea that inhibition of cellulose synthesis in protoplasts grown on the clinostat is caused by a change of plasmalemma fluidity and functioning, and also by a disturbance to the state of cytoplasmic calcium under conditions of simulated microgravity.

Disruption of the phosphate-starvation response of oilseed rape suspension cells by the fungicide phosphonate

The influence of the anti-fungal agent phosphonate (Phi) on the response of oilseed rape (Brassica napus L. cv. Jet Neuf) cell suspensions to inorganic phosphate (Pi) starvation was examined. Subculture of the cells for 7 d in the absence of Pi increased acid phosphate (APase; EC 3.1.3.2) and pyrophosphate (PPi)-dependent phosphofructokinase (PFP; EC 2.7.1.90) activities by 4.5- and 2.8-fold, respectively, and led to a 19-fold increase in Vmax and a 14-fold decrease in Km (Pi) and Pi uptake. Addition of 2 mM Pi to the nutrient media caused dramatic reductions in the growth and Pi content of the Pi-starved, but not Pi-sufficient cells, and largely abolished the Pi-starvation-dependent induction of PFP, APase, and the high-affinity plasmalemma Pi translocator. Immunoblotting indicated the cells contain three APase isoforms that are synthesized de novo following Pi stress, and that Pi treatment represses this process. Phosphonate treatment of Pi-starved cells significantly altered the relative extent of in-vivo 32P-labelling of polypeptides having M(rs) of 66, 55, 45 and 40 kDa. However, Phi had no effect on the total adenylate pool of Pi-starved cells which was about 32% lower than that of Pi-sufficient cells by day 7. Soluble protein levels, and activities of pyruvate kinase (EC 2.7.1.40) and ATP-dependent phosphofructokinase (EC 2.7.1.11) were unaffected by Pi starvation and/or Phi treatment. The effects of Phi on the growth, and APase and PFP activities of Pi-starved B. napus seedlings were similar to those observed in the suspension cells. The results re consistent with the hypothesis that a primary site of Phi action in higher plants is at the level of the signal transduction chain by which plants perceive and respond to Pi stress at the molecular level.

Isolation of viable egg cells of rape (Brassica napus L.)

The isolation of viable egg cells of rape (Brassica napus L.) has been achieved from microdissected ovules. The non-gametic cells of the embryo sac, synergids and central cells have also been isolated. Their morphology corresponded to that of these cells in situ, making a discrimination from isolated sporophytic cells possible. Two hours after isolation the egg cells were still viable. Viable egg cells have been reproducibly isolated with a frequency of 25% per dissected ovule.

The response to auxin of rapeseed (Brassica napus L.) roots displaying reduced gravitropism due to transformation by Agrobacterium rhizogenes

It has recently been documented that, compared to untransformed controls, the roots of oilseed rape (Brassica napus L. CV CrGC5) seedlings transformed by Agrobacterium rhizogenes A4 show a reduced gravitropic reaction (Legue et al. 1994, Physiol Plant 91: 559-566). After stimulation at 90 degrees C or 135 degrees, the transformed root tips curve. but never reach a vertical orientation. In the present study, we investigated the causes of reduced gravitropic bending observed in stimulated transformed root tips. First, we localized the gravitropic curvature in normal and in transformed roots after 1.5 h of stimulation. The cells involved in root curvature (target cells) corresponded at the cellular level to the apical part of the zone of increasing cell length. In transformed roots grown in the vertical position, these cells showed a reduction in cell length compared to controls. Because auxin is considered to be the gravitropic mediator, the response of normal and transformed roots to exogenous auxin was studied. Indole-3-acetic acid (IAA) was applied along the first 3 mm using resin beads loaded with the hormone. In comparison to normal roots, transformed roots showed reduced bending toward the bead at all points of bead application. Moreover, the cells which responded to IAA corresponded to the target cells involved in the gravitropic reaction. The level of endogenous IAA was lower in transformed roots. Thus, it was concluded that the modified behavior of transformed roots during gravitropic stimulation could be due to differences either in IAA levels or in reactivity of the target cells to the message from the cap.

Monoclonal antibody TeM 106 reacts with a tonoplast intrinsic protein of 106 kDa from Brassica oleracea L

A monoclonal antibody, designated TeM 106, that recognizes an intrinsic protein from the vacuole membrane (tonoplast) of cauliflower (Brassica oleracea L. var. botrytis) is described. Mice were immunized with a tonoplast fraction that had been purified from differentiating meristematic cells from the cauliflower head. Hybridomas were generated and screened by means of Enzyme Linked Immuno Sorbent Assays for differential reactivity to tonoplast over non-related proteins (bovine serum albumin). One out of 14 reactive murine clones was selected on the basis of its stability, secretory efficiency, and high affinity of the secreted antibodies. TeM 106 is an IgM which was shown by indirect immunofluorescence microscopy of frozen thin sections to bind specifically to the tonoplast of highly vacuolated cells as well as to the tonoplast of small vacuoles in meristematic cells. The molecular specificities of TeM 106 were preliminarily determined using electrophoretic transfer procedures (immunoblotting). TeM 106 reacted with a single protein band of 106,000 M(r) from the tonoplast of cauliflower. Using two-dimensional gel electrophoresis, it was shown that the epitope is borne by a single polypeptide. The antigen is a glycopeptide containing mannose and/or glucose residues in the oligosaccharide side chain but the epitope, resistant to the metaperiodate oxidation, is contained in the polypeptide backbone. Salt elution experiments indicated that the antigen, unlike several proteins from the tonoplast, is not eluted from the membrane by KCl treatments and is, therefore, tentatively considered as a tonoplast intrinsic protein, designated TIP 106.

[Preparation and characterization of low protein, cell structural material. II. Materials with cellular structure from carrot and white cabbage]

The molecular parameters and functional properties of low-protein materials with a cellular structure are determined by both the conditions of preparation and the kind of raw material used. Compared to alcohol-insoluble substance, the conditions of preparation were modified. When an alkaline extraction and a favorable combination of processing steps is used, materials with special low protein and high pectin contents result. In addition, such functional properties as water binding capacity and cation exchange capacity of the materials are improved. After having prepared various materials with a cellular structure from apple, carrot, and white cabbage, it was found that the amount of solvent needed and the yield, as well as the molecular parameters and the functional properties were also determined by the kind of raw materials used. For instance, material with a cellular structure from apple is low in protein and high in water binding capacity. Whereas, materials with a cellular structure from carrot, which contains a deesterified pectin component, is characterized by a good yield, a high pectin content, and an excess of 1.5 mmol/g of free carboxyl groups.

Preparatory tests for immunodetection of microtubules in protoplasts during IML-2

Preparatory tests to improve methods for detection of cortical microtubules (cMTs) in rapeseed protoplasts for the IML-2 experiment "TRANSFORM" were undertaken. This study is based on the results obtained in the "PROTO" experiment onboard the shuttle Discovery during an 8-day IML-1 flight in 1992. The use of free-floating protoplasts on IML-1 made it technically impossible for the astronauts to remove the glutaraldehyde fixative during the orbital period resulting in high background fluorescence which made it very difficult to detect MTs. In order to avoid this on the IML-2 mission, protoplasts will be immobilized in alginate beads. The effect of variable concentrations and fixation periods for two different fixatives on the preservation of cMTs was tested. Best results were obtained using 3.5% paraformaldehyde (PFA) for 1 hour, but 1% glutaraldehyde (GA) also gave acceptable results. The effect of low temperatures on microtubule depolymerization was also examined as freshly isolated protoplasts have to be kept at 5 degrees C for up to 20 hours pre-launch and before activation of Biorack. Only slight changes in cMT-appearance were observed at 4 degrees C indicating a minor depolymerization compared to the cMTs in non-chilled protoplasts.

Development of plant protoplasts during the IML-1 mission

During the 8 day IML-1 mission, regeneration of cell walls and cell divisions in rapeseed protoplasts were studied using the Biorack microscope onboard the Space Shuttle "Discovery". Samples from microgravity and 1g protoplast cultures were loaded on microscope slides. Visual microscopic observations were reported by the payload specialist Roberta Bondar, by down-link video transmission and by use of a microscope camera. Protoplasts grown under microgravity conditions do regenerate cell walls but to a lesser extent than under 1g. Cell divisions are delayed under microgravity. Few cell aggregates with maximum 4-6 cells per aggregate are formed under microgravity conditions, indicating that microgravity may have a profound influence on plant cell differentiation.

Mosaic disease induced by turnip yellow mosaic Tymovirus

Mosaic disease is one of the most common consequences of infection of plants by viruses. Most such mosaics include islands of dark green tissue, which are normal in appearance, contain little or no virus and are resistant to superinfection at least for a period of weeks. The mosaic pattern that develops in successive expanded leaves of larger plants is variable and unpredictable. Therefore it has not been possible to investigate the early events in leaf primordia that lead to the formation of dark green tissue. Here we describe an experimental system which should allow the application of molecular techniques to the study of the nature of dark green tissue.

The effect of exposure to microgravity on the development and structural organisation of plant protoplasts flown on Biokosmos 9

Preparatory experiments for the IML-1 (International Microgravity Laboratory) mission to be flown on the Space Shuttle in January, 1992, were performed on a 14 day flight on Biokosmos 9 (Kosmos 2044) in September 1989. The purpose of the experiment was to study the effect of weightlessness on protoplast regeneration. Problems with late access to the space vehicle meant that the newly isolated protoplasts from hypocotyl cells of rapeseed (Brassica napus L. cv Niklas) and suspension cultures of carrot (Daucus carota L, cv Nobo) had to be stored at 4 degrees C for 36 h prior to the launch of the biosatellite, in order to delay cell wall regeneration until the samples were in orbit. In the flight samples and the ground controls, a portion of the total number of protoplasts regenerated cell walls. The growth of flight rapeseed cells was only 56% compared to the ground control; the respective growth of carrot cells in orbit was 82% of the ground control. Analysis demonstrated that the peroxidase activity and the amount of protein was lower in the flight samples than in the ground controls. The number of different isoenzymes was also decreased in the flight samples. A 54% decrease in the production of cellulose was found in rapeseed, and a 71% decrease in carrot. Hemicellulose production was also decreased in the flight samples compared to the ground controls. Ultrastructural analysis of the cell aggregates from the protoplasts cultured in orbit, demonstrated that hydrolysis and disappearance of reserve starch occurred in the flight cell plastids. The mitochondria were more varied in appearance in the flight samples than in the ground control cells. An increased frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds was also observed. Fluorescence analysis showed a decrease of the calcium content in cell cultures under space flight compared to the ground controls. One general effect of the stay onboard the space vehicle was a retardation of the regeneration processes. Callus cultures obtained from the flight samples grew very slowly compared to callus regenerated from the ground controls, and two years after the Biokosmos 9 flight there appears to be no further growth in the samples exposed to microgravity. Callus cultures from the ground controls, however, continue to grow well. A simulation experiment for IML-l performed in January 1990 at ESTEC (European Space Technology Center), The Netherlands, has resulted in regenerated plants. These observations are discussed and compared to the results obtained on Biokosmos 9.

Structural and functional organisation of regenerated plant protoplasts exposed to microgravity on Biokosmos 9

Preparatory experiments for the IML-1 mission using plant protoplasts, were flown on a 14-day flight on Biokosmos 9 in September 1989. Thirty-six hours before launch of the biosatellite, protoplasts were isolated from hypocotyl cells of rapeseed (Brassica napus) and suspension cultures of carrot (Daucus carota). Ultrastructural and fluorescence analysis of cell aggregates from these protoplasts, cultured under microgravity conditions, have been performed. In the flight samples as well as in the ground controls, a portion of the total number of protoplasts regenerated cell walls. The processes of cell differentiation and proliferation under micro-g did not differ significantly from those under normal gravity conditions. However, in micro-g differences were observed in the ultrastructure of some organelles such as plastids and mitochondria. There was also an increase in the frequency of the occurrence of folds formed by the plasmalemma together with an increase in the degree of complexity of these folds. In cell cultures developed under micro-g conditions, the calcium content tends to decrease, compared to the ground control. Different aspects of using isolated protoplasts for clarifying the mechanisms of biological effects of microgravity are discussed.

The effect of microgravity on the development of plant protoplasts flown on Biokosmos 9

An experiment using plant protoplasts has been accepted for the IML-1 Space Shuttle mission scheduled for 1991. Preparatory experiments have been performed using both fast and slow rotating clinostats and in orbit to study the effect of simulated and real weightlessness on protoplast regeneration. Late access to the space vehicles before launch has required special attention since it is important to delay cell wall regeneration until the samples are in orbit. On a flight on Biokosmos 9 ("Kosmos-2044") in September 1989 some preliminary results were obtained. Compared to the ground control, the growth of both carrot and rapeseed protoplasts was decreased by 18% and 44% respectively, after 14 days in orbit. The results also indicated that there is less cell wall regeneration under micro-g conditions. Compared to the ground controls the production of cellulose in rapeseed and carrot flight samples was only 46% and 29% respectively. The production of hemicellulose in the flight samples was 63% and 67% respectively of that of the ground controls. In both cases all samples reached the stage of callus development. The peroxidase activity was also found to be lower in the flight samples than in the ground controls, and the number of different isoenzymes was decreased in the flight samples. In general, the regeneration processes were retarded in the flight samples with respect to the ground controls. From a simulation experiment for IML-1 performed in January 1990 at ESTEC, Holland, regenerated plants have been obtained. These results are discussed and compared to the results obtained on Biokosmos 9. Protoplast regeneration did not develop beyond the callus stage in either the flight or the ground control samples from the Biokosmos 9 experiment.

Molecular cloning and characterization of genes expressed in shoot apical meristems

The above-ground portion of a plant develops from the shoot apical meristem. An abundant source of apical meristems was obtained from cauliflower heads. Meristematic cDNAs were identified by differential screening and used to isolate corresponding Arabidopsis thaliana genes. Transcriptional promoters from Arabidopsis clones were fused to the beta-glucuronidase (GUS) reporter gene and introduced into plants, and GUS expression was used to analyze temporal and spatial regulation of the promoters. One promoter (meri-5) directed GUS expression in the meristematic dome and not the surrounding leaf primordia. The meri-5 promoter also directed GUS expression at branching points in the shoot and root. A second meristematic gene was found to be a histone (H3) gene. The H3 promoter was isolated and fused to GUS. Expression of the H3-GUS fusion in transgenic tobacco showed preferential expression in the peripheral zone and a lack of noticeable staining in the central zone.

Comparative effectiveness of a clinostat and a slow-turning lateral vessel at mimicking the ultrastructural effects of microgravity in plant cells

The object of this research was to determine how effectively the actions of a clinostat and a fluid-filled, slow-turning lateral vessel (STLV) mimic the ultrastructural effects of microgravity in plant cells. We accomplished this by qualitatively and quantitatively comparing the ultrastructures of cells grown on clinostats and in an STLV with those of cells grown at 1 g and in microgravity aboard the Space Shuttle Columbia. Columella cells of Brassica perviridis seedlings grown in microgravity and in an STLV have similar structures. Both contain significantly more lipid bodies, less starch, and fewer dictyosomes than columella cells of seedlings grown at 1 g. Cells of seedlings grown on clinostats have significantly different ultrastructures from those grown in microgravity or in an STLV, indicating that clinostats do not mimic microgravity at the ultrastructural level. The similar structures of columella cells of seedlings grown in an STLV and in microgravity suggest that an STLV effectively mimics microgravity at the ultrastructural level.

The S-locus specific glycoproteins of Brassica accumulate in the cell wall of developing stigma papillae

Self-incompatibility in Brassica oleracea is now viewed as a cellular interaction between pollen and the papillar cells of the stigma surface. In this species, the inhibition of self-pollen occurs at the stigma surface under the influence of S-locus specific glycoproteins (SLSG). We used antibodies specific for a protein epitope of SLSG to study the subcellular distribution of these molecules in the stigmatic papillae. The antibodies have uncovered an interesting epitope polymorphism in SLSG encoded by subsets of S-alleles, thus providing us with useful genetic controls to directly verify the specificity of the immunolocalization data. Examination of thin sections of Brassica stigmas following indirect immunogold labeling showed that SLSG accumulate in the papillar cell wall, at the site where inhibition of self-pollen tube development has been shown to occur. In addition, the absence of gold particles over the papillar cell walls in the immature stigmas of very young buds, and the intense labeling of these walls in the stigmas of mature buds and open flowers, correlates well with the acquisition of the self-incompatibility response by the developing stigma.

Preparatory studies for the use of plant protoplasts in space research

An experiment using plant protoplasts has been accepted for the IML-1 mission to be flown on a space shuttle in 1991. Preparatory experiments include studies of cell wall formation, cell division, the effect of simulated weightlessness using fast and slow rotating clinostats, and the development and testing of hardware for the IML-1 mission. After 24 h at 25 degrees C, protoplasts isolated from hypocotyls or leaves of rapeseed seedlings, or from carrot suspension cells, show 60, 20 and 15% cell wall formation, respectively. The time course of formation of the cell wall and cell division could be delayed by treatment at low temperatures or immobilization in alginate or agarose. This aspect is of importance in connection with problems of late access to the space shuttle before launch. At 4 degrees C only 18% of the rapeseed hypocotyl protoplasts had formed cell walls after 24 h. Protoplasts immobilised in agarose or alginate gradually regain their cell division capacity and after 72 h the frequencies are 51 and 26%, respectively, compared to non-immobilised control protoplasts. A significant decrease in cell division activity is observed after rotation for 6 h on the slow clinostat. A similar effect is not observed on the fast clinostat. Protoplasts, cultured in the specially designed plant chamber for up to 14 days established cell aggregates which have further developed into plants.

Isolation and characterisation of satellite DNA from Brassica juncea (L.) Czern

Nuclear DNA isolated from hypocotyls (H), proliferating callus (PC) and differentiating callus (DC) of Brassica juncea contains a satellite DNA which can be resolved in actinomycin-D/CsCl gradients. The satellite DNA undergoes changes, when an in vitro culture is raised from hypocotyl tissue and forms a higher percentage of the genome in PC and DC than in mature differentiated tissue (hypocotyl). All the three satellite DNAs are GC-rich compared to main band DNAs. Satellite DNA of H has higher Tm and GC content than that of the PC and DC satellites. A 200 bp basic repeat unit from hypocotyl nuclear DNA has been cloned and characterised.

Laser-induced fusion of mammalian cells and plant protoplasts

An ultraviolet-laser microbeam was shown to be suitable for inducing fusion of individually selected plant protoplasts or of B-lymphocytes with myeloma cells. The fusion took place in normal culture medium and the fusogenic condition perturbed the cells only for a fraction of a millisecond. Without manipulating the cell culture except for exposing the cells to laser light, fusion products between preselected individual pairs may be produced.

Model system for studies of microbial dynamics at exuding surfaces such as the rhizosphere

An autoclavable all-glass system for studying microbial dynamics at permeable surfaces is described. Standard hydrophobic or hydrophilic membranes (46-mm diameter) of various pore sizes were supported on a glass frit through which nutrient solutions were pumped by a peristaltic pump. The pump provided a precisely controlled flow at speeds of 0.5 to 500 ml of defined or natural cell exudates per h, which passed through the membrane into a receiving vessel. The construction allowed a choice of membranes, which could be modified. The system was tested with a bacterium, isolated from rape plant roots (Brassica napus L.), that was inoculated on a hydrophilic membrane filter and allowed to develop into a biofilm. A defined medium with a composition resembling that of natural rape root exudate was pumped through the membrane at 0.5 ml/h. Scanning electron microscopic examinations indicated that the inoculum formed microcolonies embedded in exopolymers evenly distributed over the membrane surface. The lipid composition and content of poly-beta-hydroxybutyrate in free-living and adhered cells were determined by gas chromatography. The bacterial consumption of amino acids in the exudate was also studied.

Pollen-stigma interaction in Brassica oleracea: the role of stigmatic proteins in pollen grain adhesion

The adhesion of pollen grains to the stigmas of Brassica oleracea was assayed after treatment of the stigmas wiuth protease and/or cycloheximide. Treatment with protease alone adversely affected pollen grain adhesion. However, the adhesive properties of the stigma recovered fully if the stigmas were not pollinated until 2 h after treatment. Immersion of the stigmas in cycloheximide after protease treatment prevented any recoveryt of the stigmas' adhesive properties. Cycloheximide treatment alone prevented pollen grain adhesion when pollination occurred later than 1–2 h after treatment but did not affect pollen grain adhesion if pollination occurred immediately after treatment. These results indicated not only that the surface-held proteins of the stigma are involved in pollen grain adhesion, but also that their turnover rate is rapid. Isoelectric focusing of extracts derived from stigmas after protease and cycloheximide treatment showed a marked decrease in staining intensity of 3 protein bands, one of which, a glycoprotein, is known to be present only when the self-incompativility system is fully functional. These observations suggest a specificity of adhesion between higher plant cells in the presence of the cell wall.