Densitometric analysis of nuclear DNA content in lentil roots grown in space

Lentil seedlings were grown for 28 h in space, on board Spacelab (IML 1 Mission) and growth of the primary root was analysed. The length of cortical cells was less in near weightlessness than on the 1 g centrifuge (flight control) and mitotic index was lower but there was no apparent perturbation in the mitosis. To further investigate which phase of cell cycle was modified, densitometric analysis of nuclear DNA content in cortical cells was carried out by the mean of an image processing system (SAMBA). In microgravity there was a decrease in DNA synthesis and a promotion of the arrest in the G2 phase of cell cycle. These results, and other ones obtained elsewhere on a slowly rotating clinostat, led us to think that in microgravity the perturbation of the gravisensing cells and/or the absence of convection could account for the modification of cell growth registered in the primary root.     

Sensitivity to gravistimulus of lentil seedling roots grown in space during the IML 1 Mission of Spacelab

The gravitropic curvature of seedlings of lentil ( Lens culinaris L. cv. Verte du Puy) grown in microgravity and stimulated on the 1 g centrifuge for 5 to 60 min was followed by time lapse photography in near weightlessness in the frame of the IML 1 Mission of Spacelab. In microgravity, the root tip could overshoot the direction of the 1 g acceleration after bending, whereas roots stimulated on the ground did not reach the direction of the gravity vector. On earth, there is, therefore, a regulation (inhibition of root curvature), which is gravity dependent. In space, the initial rate of curvature as well as the amplitude of curvature varied as a function of the quantity of stimulation (Q, in g min). For a given quantity of stimulation, the rate of curvature remained constant for 80 min. The bending has thus a certain inertia, which is linked to the mechanism of differential growth. The presentation time (Tp) of the lentil root was calculated by extrapolation to zero curvature of the regression line representing either the initial rate of curvature or the amplitude of curvature at 2 h after the end of the stimulation. Tp was estimated to 27 and 26 s. respectively. These results confirm the values of Tp obtained by clinostats, and they also lead to a reconsideration of the causes of the kinetics of root curvature.     

Polarity of statocytes in lentil seedling roots grown in space (Spacelab D1 Mission)

A morphometric analysis of root statocytes was performed on seedlings of lentil ( Lens culinaris L., cv. Verte du Puy) in order to determine the effects of microgravity on the polarity of these cells. Seedlings were grown: (1) on the ground, (2) in microgravity, (3) on a 1 g centrifuge in space, (4) first in microgravity and then placed on a 1 g centrifuge for 3 h. Dry seeds were hydrated in space (except for the ground control) for 25 h in darkness at 22°C in the Biorack facility developed by the European Space Agency. At the end of the experiment, the seedlings were photographed and fixed in glutaraldehyde in the Biorack glove box. The average shape of the statocytes and the location of endoplasmic reticulum, amyloplasts and nucleus in the cells were analysed in the four samples. By considering the cell shape, it appears that the morphology of the statocytes on the ground was different from that observed in the space samples. Cell polarity was similar in microgravity and in the centrifuged samples except for the distribution of the amyloplasts. These organelles were not distributed at random in near zero gravity, and they were more numerous in the proximal than in the distal half. Moreover, the statoliths were more voluminous in microgravity than in the centrifuged samples. The nucleus was closer to the cell center in the statocytes of roots grown in microgravity than in statocytes of roots grown in microgravity and then placed on the 1 g centrifuge for 3 h. It is hypothesized that the nucleus is attached to the cell periphery and that its location is dependent upon gravity.     

Graviperception of lentil seedling roots grown in space (Spacelab Dl Mission)

The growth and graviresponsiveness of roots were investigated in lentil seedlings (Lens culinaris L. cv. Verte du Puy) grown (1) in microgravity, (2) on a 1 g centrifuge in space, (3) in microgravity and then placed on the 1 g centrifuge for 3 h, (4) on the ground. Dry seeds were hydrated in space (except for the ground control) and incubated for 25 h at 22°C in darkness. At the end of the experiment, the seedlings were photographed and fixed in glutaraldehyde in a Biorack glove box. Root length was similar for seedlings grown in space and for the ground and the 1 g centrifuge controls. The direction of root growth in the microgravity sample deviated strongly from the initial orientation of the roots of the dry seeds. This deviation could be due to spontaneous curvatures similar to those observed on clinostats. When lentil seedlings were first grown in microgravity for 25 h and then placed on the 1 g centrifuge for 3 h, their roots bent strongly under the effect of the centrifugal acceleration. The amplitude of root curvature on the centrifuge was not significantly different from that observed on ground controls growing in the vertical position and placed in the horizontal position for 3 h. The gravisensitivity of statocytes differentiated in microgravity was similar to that of statocytes differentiated on earth. There were no qualitative differences in the ultrastructural features of the gravisensing cells in microgravity and in the 1 g centrifuge and ground controls. However, the distribution of statoliths in the gravisensing cells was different in microgravity: most of them were observed in the proximal part of these cells. Thus, these organelles were not distributed at random, which is in contradiction with results obtained with clinostats. The distal complex of endoplasmic reticulum in the statocytes was not in contact with the amyloplasts. Contact and pressure of amyloplasts on the tubules were not prerequisites for gravisensing. The results obtained are not in agreement with the hypothesis that the distal endoplasmic reticulum would be the transducer of the action of the statoliths.     

Oscillatory growth movements of roots in weightlessness

The gravitropic curvature of lentil roots ( Lens culinaris L. cv. Verte du Puy), grown in near weightlessness and stimulated on a 1-g centrifuge for 5 to 60 min was followed by time lapse photography. The experiment was carried out in the frame of the IML 1 Mission of Spacelab. Due to the applied acceleration field, the tip of the roots bent and reoriented with respect to the acceleration vector. However, visual inspection of the data could indicate an oscillatory movement superimposed on the gravitropic reorientation.
We applied two signal processing techniques, fast Fourier transform (FFT) and maximum entropy spectral analysis (MESA), to provide quantitative data about the oscillatory movements of the lentil roots under gravity free conditions. In the case with very few data points in the time series the MESA method is superior to the conventional FFT. In the lentil root movements, the Fourier analysis could not extract and resolve the oscillatory signals present in the time series. The MESA approach revealed oscillations with periods around 35 and 50 min for the present lentil roots.
Circumnutations are, therefore, present in roots also in weightlessness.     

Phenotypic characterization of Aspergillus niger and Candida albicans grown under simulated microgravity using a three-dimensional clinostat

The living and working environments of spacecraft become progressively contaminated by a number of microorganisms. A large number of microorganisms, including pathogenic microorganisms, some of which are fungi, have been found in the cabins of space stations. However, it is not known how the characteristics of microorganisms change in the space environment. To predict how a microgravity environment might affect fungi, and thus how their characteristics could change on board spacecraft, strains of the pathogenic fungi Aspergillus niger and Candida albicans were subjected to on-ground tests in a simulated microgravity environment produced by a three-dimensional (3D) clinostat. These fungi were incubated and cultured in a 3D clinostat in a simulated microgravity environment. No positive or negative differences in morphology, asexual reproductive capability, or susceptibility to antifungal agents were observed in cultures grown under simulated microgravity compared to those grown in normal earth gravity (1 G). These results strongly suggest that a microgravity environment, such as that on board spacecraft, allows growth of potentially pathogenic fungi that can contaminate the living environment for astronauts in spacecraft in the same way as they contaminate residential areas on earth. They also suggest that these organisms pose a similar risk of opportunistic infections or allergies in astronauts as they do in people with compromised immunity on the ground and that treatment of fungal infections in space could be the same as on earth.     

Development of the primary root and mobilisation of reserves in etiolated seedlings of Brassica napus grown on a slowly rotating clinostat

The effect of the slow rotating clinostat (1 rpm) on the growth of the primary root was studied on Brassica napus seedlings. After 5 d in darkness, the primary root was longer and thinner in seedlings grown on the clinostat than in seedlings grown in the vertical position. However, the breakdown of lipid reserves, sucrose level and transport of 14C-labeled sucrose from the cotyledons to the primary root, were not altered by growth on the clinostat. Moreover, the activity of isocitrate lyase, one of the two enzymes necessary for the conversion of lipids into glucids also was also not modified in the cotyledons of clinorotated seedlings. Thus, there was clear evidence that clinorotation had a direct effect on the growth of the primary root that was independent of the mobilisation of lipid reserves in the cotyledons. As a sink, the primary root had the same strength on the clinostat as in the vertical position, but the reserves were used in a different way. The increase in root elongation on the clinostat could be due to the slight, but continuous, omnilateral gravitropic stimulation due to the rotation of the seedlings about a horizontal axis.     

Photomorphogenesis and pigment induction in lentil seedling roots exposed to low light conditions

Although roots are normally hidden in soil, they may inadvertently be exposed to low light levels in experiments or in natural conditions through cracks or light transmittance through the soil. Light has been implicated in root morphogenesis. Thus, effects of low light conditions on lentil (Lens culinaris L. cv. Verte du Puy) root morphology and root pigmentation were studied. Lentil seedlings were grown in peat or transparent, nutrient-fortified agar at a 12-h light (PAR 240 μmol · m(-2) · s(-1)), 12-h dark cycle. Roots were exposed to low levels (≈ 1-10 μmol · m(-2) · s(-1)) of broadband white light, either directly or indirectly by aboveground light penetrating the growth medium. Control roots were grown in darkness. In situ spectroscopy was used to measure transmittance and reflectance spectra of intact root tissue by mounting the upper part of the primary root directly in a spectrophotometer equipped with an integrating sphere attachment. The transmittance and reflectance spectra were used to calculate the in situ root absorbance spectrum. Absorbance bands were found in the regions 480-500 nm and 650-680 nm, possibly due to low levels of root-localised carotenoids and chlorophylls, respectively. Low light levels (≈ 1-10 μmol · m(-2) · s(-1) ) transmitted through the growth medium significantly increased root pigment concentration and root biomass, and altered root morphology by enhancing lateral root formation and inhibiting root elongation relative to roots grown in complete darkness. The light-induced changes in root morphogenesis and pigmentation appear to be primarily due to upper root light perception.     

兵豆萌发过程中初生根皮层细胞的细胞周期活动的动态分析

观察了兵豆(Lens culinaris Medic.)初生根原皮层组织的细胞周期在其种子萌发过程中时间和空间上的动态变化.免疫组织化学和细胞学证据表明,原皮层细胞分别在种子吸胀大约13 h和17 h开始DNA复制和细胞分裂.最早进行DNA复制和细胞分裂的细胞位于远基端1 mm附近,但这些分裂细胞的DNA复制是在种子成熟过程中完成的,而不是在萌发后.第一个细胞周期的激活样式表明,这些细胞并不同步激活,而是依次进入细胞周期,且进入的次序与自身在根尖中的相对位置有关.在兵豆初生根原皮层组织中,邻近位置上的细胞的细胞周期同步化程度较高.     

兵豆萌发过程中初生根皮层细胞的细胞周期活动的动态分析

观察了兵豆 (LensculinarisMedic.)初生根原皮层组织的细胞周期在其种子萌发过程中时间和空间上的动态变化。免疫组织化学和细胞学证据表明 ,原皮层细胞分别在种子吸胀大约 13h和 17h开始DNA复制和细胞分裂。最早进行DNA复制和细胞分裂的细胞位于远基端 1mm附近 ,但这些分裂细胞的DNA复制是在种子成熟过程中完成的 ,而不是在萌发后。第一个细胞周期的激活样式表明 ,这些细胞并不同步激活 ,而是依次进入细胞周期 ,且进入的次序与自身在根尖中的相对位置有关。在兵豆初生根原皮层组织中 ,邻近位置上的细胞的细胞周期同步化程度较高。     

Automorphosis of maize shoots under simulated microgravity on a three-dimensional clinostat

Seedlings of maize ( Zea mays L. cv. Golden Cross Bantam T-51) were grown under microgravity conditions simulated by a three-dimensional clinostat. On the clinostat, maize shoots exhibited curvatures in three different portions: (1) the basal transition zone connecting roots and mesocotyls, (2) the coleoptile node located between mesocotyls and coleoptiles, and (3) the elongating region of the coleoptiles. Even non-clinostatted control shoots showed some degree of curvature away from the caryopsis in the transition zone and bending toward the caryopsis in the coleoptile node. Clinostat rotation greatly stimulated these curvatures. Control coleoptiles elongated almost straightly, whereas coleoptiles on the clinostat bent either away from or toward the caryopsis depending on the timing of rotation. The curvature in all three portions became larger with time, both in control and clinostatted seedlings. There was no difference in the osmotic concentration of the cell sap between the convex and the concave halves of any portion. However, in coleoptile nodes and coleoptiles, the faster-expanding convex side exhibited a higher extensibility of the cell wall than the opposite side, and this appears to be a cause of the curvature. Thus, changes in the cell wall metabolism may be involved in automorphosis, which governs the life cycle of plants under a microgravity environment.     

Fibroblast growth factor receptor signaling is essential for lens fiber cell differentiation

The vertebrate lens provides an excellent model to study the mechanisms that regulate terminal differentiation. Although fibroblast growth factors (FGFs) are thought to be important for lens cell differentiation, it is unclear which FGF receptors mediate these processes during different stages of lens development. Deletion of three FGF receptors (Fgfr1-3) early in lens development demonstrated that expression of only a single allele of Fgfr2 or Fgfr3 was sufficient for grossly normal lens development, while mice possessing only a single Fgfr1 allele developed cataracts and microphthalmia. Profound defects were observed in lenses lacking all three Fgfrs. These included lack of fiber cell elongation, abnormal proliferation in prospective lens fiber cells, reduced expression of the cell cycle inhibitors p27^kip1 and p57^kip2, increased apoptosis and aberrant or reduced expression of Prox1, Pax6, c-Maf, E-cadherin and α-, β- and γ-crystallins. Therefore, while signaling by FGF receptors is essential for lens fiber differentiation, different FGF receptors function redundantly.     

Effect of benzylaminopurine on in vitro and in vivo root development in lentil, Lens culinaris Medik

The effect of benzylaminopurine (BAP) on the formation of roots from lentil shoots regenerated on media containing BAP was studied. Seedling shoot tips, first nodes and bractlets, and immature seeds cultured on the initiation media containing 2.25 or 0.225 mg/l of BAP regenerated multiple bud shoots. The regenerated shoots formed roots in percentages ranging from 4.6 to 39.9% on a rooting medium (R medium) containing 2 mg/l of indoleacetic acid. Rooting success on R medium depended upon the cytokinin used in the initiation media, its concentration, and the time elapsed during shoot formation on these media prior to transplanting regenerated shoots to R medium. In vivo study of root growth of lentil seedlings demonstrated the strong inhibitory effect of BAP on root growth reflected in a drastic reduction of the mitotic index of the root meristem. Received: 27 August 1996 / Revision received: 12 December 1996 / Accepted: 15 January 1997     

细胞生长和表面精蛋白的N－糖链中核心岩藻糖的关系

细胞生长和表面精蛋白的Ｎ－糖链中核心岩藻糖的关系董素才,杨小平,陈惠黎（上海医科大学生物化学教研室,２０００３２）关键词精蛋白Ｎ—糖链,核心岩藻糖,小扁豆凝集素,细胞生长细胞表面精蛋白Ｎ一糖链的结构与细胞生长、分化、恶变有密切关系,除糖链的类型和天线...     

Sef is a negative regulator of fiber cell differentiation in the ocular lens

Growth factor signaling, mediated via receptor tyrosine kinases (RTKs), needs to be tightly regulated in many developmental systems to ensure a physiologically appropriate biological outcome. At one level this regulation may involve spatially and temporally ordered patterns of expression of specific RTK signaling antagonists, such as Sef (similar expression to fgfs). Growth factors, notably FGFs, play important roles in development of the vertebrate ocular lens. FGF induces lens cell proliferation and differentiation at progressively higher concentrations and there is compelling evidence that a gradient of FGF signaling in the eye determines lens polarity and growth patterns. We have recently identified the presence of Sef in the lens, with strongest expression in the epithelial cells. Given the important role for FGFs in lens developmental biology, we employed transgenic mouse strategies to determine if Sef could be involved in regulating lens cell behaviour. Over-expressing Sef specifically in the lens of transgenic mice led to impaired lens and eye development that resulted in microphthalmia. Sef inhibited primary lens fiber cell elongation and differentiation, as well as increased apoptosis, consistent with a block in FGFR-mediated signaling during lens morphogenesis. These results are consistent with growth factor antagonists, such as Sef, being important negative regulators of growth factor signaling. Moreover, the lens provides a useful paradigm as to how opposing gradients of a growth factor and its antagonist could work together to determine and stabilise tissue patterning during development and growth.