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  • 1
    Electronic Resource
    Electronic Resource
    Autotropism, automorphogenesis, and gravity (1998)
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 102 (1998), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Segments of organs that have undergone gravitropic curvature later straighten during the course of gravitropism or after the g-vector becomes randomized on a clinostat. Little is known about the mechanisms underlying these and perhaps related phenomena which have been described with various overlapping terms such as autotropism, autotropic straightening, automorphosis, automorphogenesis, automorphic curvature, and gravitropic straightening. The types of phenomena that historically have been named by the above terms are reviewed critically with respect to an interaction with gravitropism. We suggest that the term “autotropism” should not be applied to the phenomenon of organ straightening that occurs during the course of gravitropism, since this straightening is part of a complex series of local growth adjustments overall through time, and since this phenomenon is not itself a tropistic response to a directional exogenous stimulus. It is suggested that the term autotropism should be used only for the phenomenon of organ straightening that occurs after the g-vector is randomized on a clinostat or withdrawn in the microgravity conditions of spaceflight. Usage of the term automorphogenesis is most appropriate for describing curvatures or orientations that result from morphological relationships such as in nastic curvatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1399-3054.1998.1020222.x
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  • 2
    Electronic Resource
    Electronic Resource
    Amyloplast sedimentation kinetics in gravistimulated maize roots (1985)
    Springer
    Planta 165 (1985), S. 295-300 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast sedimentation ; Root (gravistimulation) ; Graviperception ; Zea (graviperception)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Amyloplast sedimentation in gravistimulated maize (Zea mays L.) roots was measured using the change in angle from the center of the cell to each amyloplast as an index of sedimentation. Using tissue fixed after gravistimulation, the relationship between mean amyloplast angle and the duration of gravistimulation was found to be linear when plotted on a logarithmic time scale. Extrapolated values for the onset of angular change are 5.9 s after the start of gravistimulation for the entire population of amyloplasts and 11.8 s for lead amyloplasts. By multiplying the instantaneous angular velocity (in radians) by the cell center to amyloplast radius, it is possible to calculate the initial sedimentation velocity to be 19.1 μm min-1 at 5.9 s. During sedimentation, the mean amyloplast angles surpass the calculated cell corner angle of 123° at 2.2 min for all amyloplasts and at 19 s for lead amyloplasts near the new lower wall. Thus, substantial sedimentation occurs within the presentation time, calculated to be 4.1 min. These kinetics are consistent with several hypotheses of graviperception.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392225
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  • 3
    Electronic Resource
    Electronic Resource
    Amyloplasts are necessary for full gravitropic sensitivity in roots of Arabidopsis thaliana (1989)
    Springer
    Planta 177 (1989), S. 198-206 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast ; Arabidopsis ; Gravitropism ; Gravity ; Mutant (gravitropism) ; Plastid and graviperception ; Starch and graviperception ; Statolith
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The observation that a starchless mutant (TC7) of Arabidopsis thaliana (L.) Heynh. is gravitropic (T. Caspar and B.G. Pickard, 1989, Planta 177, 185–197) raises questions about the hypothesis that starch and amyloplasts play a role in gravity perception. We compared the kinetics of gravitropism in this starchless mutant and the wild-type (WT). Wild-type roots are more responsive to gravity than TC7 roots as judged by several parameters: (1) Vertically grown TC7 roots were not as oriented with respect to the gravity vector as WT roots. (2) In the time course of curvature after gravistimulation, curvature in TC7 roots was delayed and reduced compared to WT roots. (3) TC7 roots curved less than WT roots following a single, short (induction) period of gravistimulation, and WT, but not TC7, roots curved in response to a 1-min period of horizontal exposure. (4) Wild-type roots curved much more than TC7 roots in response to intermittent stimulation (repeated short periods of horizontal exposure); WT roots curved in response to 10 s of stimulation or less, but TC7 roots required 2 min of stimulation to produce a curvature. The growth rates were equal for both genotypes. We conclude that WT roots are more sensitive to gravity than TC7 roots. Starch is not required for gravity perception in TC7 roots, but is necessary for full sensitivity; thus it is likely that amyloplasts function as statoliths in WT Arabidopsis roots. Furthermore, since centrifugation studies using low gravitational forces indicated that starchless plastids are relatively dense and are the most movable component in TC7 columella cells, the starchless plastids may also function as statoliths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392808
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  • 4
    Electronic Resource
    Electronic Resource
    Reduced gravitropic sensitivity in roots of a starch-deficient mutant ofNicotiana sylvestris (1989)
    Springer
    Planta 180 (1989), S. 123-130 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast ; Gravitropism ; Mutant (gravitropism) ; Nicotiana (gravitropism) ; Plastid and graviperception ; Starch and graviperception ; Statolith
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Gravitropism was studied in seedlings ofNicotiana sylvestris Speg. et Comes wild-type (WT) and mutant NS 458 which has a defective plastid phosphoglucomutase (EC 2.7.5.1). Starch was greatly reduced in NS 458 compared to the WT, but small amounts of starch were detected in root-cap columella cells in NS 458 by light and electron microscopy. The roots of WT are more sensitive to gravity than mutant NS 458 roots since: (1) in mutant roots, curvature was reduced and delayed in the time course of curvature; (2) curvature of mutant roots was 24–56% that of WT roots over the range of induction periods tested; (3) in intermittent-stimulation experiments, curvature of mutant roots was 37% or less than that of WT roots in all treatments tested. The perception time, roots in all treatments tested. The perception time, determined by intermittent-stimulation experiments, was ≤5 s for WT roots and 30–60 s for mutant roots. The growth rates for WT and NS 458 roots were essentially equal. These results and our previous results with WT and starchless mutantArabidopsis roots (Kiss et al. 1989, Planta177, 198–206) support the conclusions that a full complement of starch is necessary for full gravitropic sensitivity and that amyloplasts function in gravity perception. Since a presumed relatively small increase in plastid buoyant mass (N. sylvestris mutant versusArabidopsis mutant) significantly improves the orientation of theN. sylvestris mutant roots, we suggest that plastids are the likeliest candidates to be triggering gravity perception in roots of both mutants.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02411418
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  • 5
    Electronic Resource
    Electronic Resource
    Gravitropism and gravimorphism during regeneration from protoplasts of the moss Ceratodon purpureus (Hedw.) Brid. (1998)
    Springer
    Planta 205 (1998), S. 352-358 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Ceratodon (graviresponse) ; Gravimor-phism ; Gravitropism ; Plastid ; Polarity ; Protoplast
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Wild-type (WT) protonemata of the moss Ceratodon purpureus grow upwards in darkness (negative gravitropism), whereas protonemata of the mutant, wrong-way response (wwr-1) grow down. Since Ceratodon protoplasts regenerate to form new protonemata, we analyzed whether the direction of filament emergence was influenced by gravity (gravimorphism) and determined the cytological events that correlated with the onset of gravitropism in WT and wwr-1 filaments formed de novo. In the WT the direction of filament emergence appeared to be gravimorphic as more than 66% of the new filaments emerged above the horizontal. In contrast, the direction of filament emergence was random in wwr-1. Tip-growing cells of both genotypes became gravitropic within a total of one to two cell divisions. Gravitropic curvature in wwr-1 was opposite in direction to that of WT, and the timing of curvature was comparable, indicating that the wwr-1 mutation acts during the onset of gravitropic competence. In time-lapse studies of both genotypes, neither a plastid-free zone nor obvious and extensive plastid sedimentation characteristic of mature dark-grown protonemata was observed in the new filaments prior to gravitropic curvature. Thus, it appears that these latter two features are not required for gravitropism in new protonemal filaments from protoplasts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050330
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  • 6
    Electronic Resource
    Electronic Resource
    Irradiance-dependent regulation of gravitropism by red light in protonemata of the moss Ceratodon purpureus (1999)
    Springer
    Planta 209 (1999), S. 299-307 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Ceratodon (protonema ; tropism) ; Micro-gravity ; Phototropism ; Phytochrome ; Polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Apical cells of protonemata of the moss Ceratodon purpureus (Hedw.) Brid. are negatively gravitropic in the dark and positively phototropic in red light. Various fluence rates of unilateral red light were tested to determine whether both tropisms operate simultaneously. At irradiances ≥140 nmol m−2 s−1 no gravitropism could be detected and phototropism predominated, despite the presence of amyloplast sedimentation. Gravitropism occurred at irradiances lower than 140 nmol m−2 s−1 with most cells oriented above the horizontal but not upright. At these low fluence rates, phototropism was indistinct at 1 g but apparent in microgravity, indicating that gravitropism and phototropism compete at 1 g. The frequency of protonemata that were negatively phototropic varied with the fluence rate and the duration of illumination, as well as with the position of the apical cell before illumination. These data show that the fluence rate of red light regulates whether gravitropism is allowed or completely repressed, and that it influences the polarity of phototropism and the extent to which apical cells are aligned in the light path.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050636
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  • 7
    Electronic Resource
    Electronic Resource
    Fluorescence microscopy and radiolabeling of C3 and C4 chloroplasts using diisothiocyanatostilbene disulfonic acid as a marker for the phosphate translocator (1989)
    Springer
    Planta 179 (1989), S. 137-147 
    Details
    ISSN: 1432-2048
    Keywords: Anion transport ; Chloroplast membrane (phosphate translocator) ; 4,4′-Diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) ; Fluorescence microscopy ; Spinacia (chloroplast membrane) ; Zea (chloroplast membrane)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The usefulness of 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) for in-situ studies of the chloroplast phosphate translocator was evaluated by fluorescence microscopy and radiolabeling of spinach (Spinacia oleracea L.) (C3 plant) and maize (Zea mays L.) (C4 plant) chloroplasts. In maize mesophyll and bundle-sheath chloroplasts and in spinach chloroplasts that were either intact, broken or swollen, DIDS fluorescence was only associated with the chloroplast envelope. Intact chloroplasts often had fluorescent patches corresponding to concave regions of the chloroplast which we assume to be regions enriched in DIDS-binding sites. Incubation of intact or broken spinach chloroplasts or maize mesophyll chloroplasts with [3H2]DIDS resulted in the labeling of a single polypeptide (relative molecular mass, Mr, ∼30 kDa) in the envelope fraction, in each case. Label in the stromal fraction was not detected when intact chloroplasts were incubated with [3H2]DIDS. However, when broken chloroplasts were incubated with [3H2]DIDS, several polypeptides of various molecular masses were labeled, but not the 30×31-kDa polypeptide. In thylakoid fractions from both broken and intact chloroplasts, a single 30×31-kDa polypeptide was labeled inconsistently. When a mixture of intact maize mesophyll and bundle-sheath chloroplasts was labeled with [3H2]DIDS, extracts of whole chloroplasts displayed radioactivity only in the 30×31-kDa band. We conclude that DIDS is a valuable probe for the in-situ identification and characterization of the ∼30-kDa protein — the presumptive phosphate translocator — in C3 and C4 chloroplasts since DIDS (1) does not penetrate the inner membrane of the envelope of intact chloroplasts and, therefore, (2) does not bind internal sites in intact chloroplasts, and (3) only binds the ∼30-kDa protein in the inner membrane of the envelope.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00393683
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  • 8
    Electronic Resource
    Electronic Resource
    Amyloplasts as possible statoliths in gravitropic protonemata of the moss Ceratodon purpureus (1990)
    Springer
    Planta 181 (1990), S. 71-77 
    Details
    ISSN: 1432-2048
    Keywords: Amyloplast ; Bryophytes ; Gravitropism ; Gravity perception ; Ceratodon ; Protonema (moss), gravitropism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The kinetics of gravitropism and of amyloplast sedimentation were studied in dark-grown protonemata of the moss Ceratodon purpureus (Hedw.) Brid. The protonemata grew straight up at a rate of 20–25 μm·h− in nutrient-supplemented agar. After they were oriented to the horizontal, upward curvature was first detected after 1–1.5 h and reached 84° by 24 h. The tip cells exhibited an amyloplast zonation, with a tip cluster of nonsedimenting amyloplasts, an amyloplast-free zone, and a zone with pronounced amyloplast sedimentation. This latter zone appears specialized more for lateral than for axial sedimentation since amyloplasts sediment to the lower wall in horizontal protonemata but do not fall to the basal wall in vertical protonemata. Amyloplast sedimentation started within 15 min of gravistimulation; this is within the 12–17-min presentation time. The data support the hypothesis that some amyloplasts function as statoliths in these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00202326
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  • 9
    Electronic Resource
    Electronic Resource
    A positively gravitropic mutant mirrors the wild-type protonemal response in the moss Ceratodon purpureus (1997)
    Springer
    Planta 202 (1997), S. 149-154 
    Details
    ISSN: 1432-2048
    Keywords: Key words:Ceratodon (mutant) ; Gravitropism ; Mutant (gravitropism ; moss) ; Plastid ; Polarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Wild-type Ceratodon purpureus (Hedw.) Brid. protonemata grow up in the dark by negative gravitropism. When upright wild-type protonemata are reoriented 90°, they temporarily grow down soon after reorientation (“initial reversal”) and also prior to cytokinesis (“mitotic reversal”). A positively gravitropic mutant designated wrong-way response (wwr-1) has been isolated by screening ultraviolet light-mutagenized Ceratodon protonemata. Protonemata of wwr-1 reoriented from the vertical to the horizontal grow down with kinetics comparable to those of the wild-type. Protonemata of wwr-1 also show initial and mitotic reversals where they temporarily grow up. Thus, the direction of gravitropism, initial reversal, and mitotic reversal are coordinated though each are opposite in wwr-1 compared to the wild-type. Normal plastid zonation is still maintained in dark-grown wwr-1 apical cells, but the plastids are more numerous and plastid sedimentation is more pronounced. In addition, wwr-1 apical cells are wider and the tips greener than in the wild-type. These data suggest that a functional WWR gene product is not necessary for the establishment of some gravitropic polarity, for gravitropism, or for the coordination of the reversals. Thus, the WWR protein may normally transduce information about cell orientation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004250050113
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  • 10
    Electronic Resource
    Electronic Resource
    Plastids and gravitropic sensing (1997)
    Springer
    Planta 203 (1997), S. S63 
    Details
    ISSN: 1432-2048
    Keywords: Key words: Gravitropism ; Amyloplast ; Sedimentation ; Gravity sensing ; Starch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Data and theories about the identity of the mass that acts in gravitropic sensing are reviewed. Gravity sensing may have evolved several times in plants and algae in processes such as gravitropism of organs and tip-growing cells, gravimorphism, gravitaxis, and the regulation of cytoplasmic streaming in internodal cells of Chara. In the latter and in gravitaxis, the mass of the entire cell may function in sensing. But gravitropic sensing appears to rely upon the mass of amyloplasts that sediment since (i) the location of cells with sedimentation is highly regulated, (ii) such cells contain other morphological specializations favoring sedimentation, (iii) sedimentation always correlates with gravitropic competence in wild-type plants, (iv) magnetophoretic movement of rootcap amyloplasts mimics gravitropism, and (v) starchless and intermediate starch mutants show reduced gravitropic sensitivity. The simplest interpretation of these data is that gravitropic sensing is plastid-based.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00008116
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