Relation entre réaction géotropique et évolution du statenchyme dans la racine d'Asperge

Relationship between the Geotropic Response and the Evolution of the Statenchyma in Roots of Asparagus officinalis. The evolution of the statenchyma in roots of Asparagus of ficinalis seedlings, grown in obscurity, was followed during the first 17 days. After 7 days of etiolation, a decrease of both the average diameter of the amyloplasts and the average number of these organelles was observed in the central root cap cells. If the seedlings were illuminated (with white light) from the 7th day, the average number of statoliths increased rapidly in the statocytes. The volume of these organelles undergoes the same variation in etiolated and in illuminated plants. The initial rate of curvature (V_i) of the roots (stimulated in a horizontal position) and the volume of amyloplasts (V_ac) in their caps were analysed as a function of the time of germination in obscurity (from the 8th to the 17th day). It was found that V_i increased as a linear function of the logarithm of V_ac, which confirms that the weight of the amyloplasts of the statocytes may play a role in the geotropic stimulation of the roots.     

Gibberellic-acid-induced cell elongation in pea epicotyls: Effect on polyploidy and DNA content

In gibberellic-acid(GA₃)-treated epicotyls of dwarf peas (Pisum sativum L.) grown in the light, DNA (per cell and per epicotyl) is followed. Histofluorometric DNA determinations show that GA₃-promoted cell elongation is not accompanied by increased endomitosis, but chemical estimations show an increased DNA content per epicotyl. This difference must therefore be the result of increased mitotic activity in the GA₃-treated tissue. Epicotyls of seedlings grown with or without cotyledons under continuous light with GA₃ are tetraploid, as are those of ecotylized embryos grown in darkness. These epicotyls reach no more than half the length of octaploid epicotyls of seedlings grown in darkness. This result provides evidence for a relationship between polyploidy and final possible cell length.     

The Mechanism of Geoperception in Lentil Roots

The sediment of the amyloplasts in the statocytes of lentilroots was analysed in two different samples of seedlings. Theroots of the first sample (HP) were grown in a horizatal position,whereas thoes of the second sample (VP+20) were grown in a horizontalposition and then exposure to give a response). It is demonstratedthat the statolish can almost enter into contact with the plasmamembrane lining the longitudinal wall of the statocytes of theHP sample. However, these organelles in the VP+20 sample areable to provoke a geotropic stimulation though they are sedimentedat a distance of 0.1350–0.2600 µm from the plasmalemma.From these data it is concluded that the cytoplasmic structureswhich may play a role in the geotropic stimulation are: (1)the endoplasmic reticulum located along the longitudianl wallof the statocytes and (2) the microtubules or the plasmalemmaif the action of the statoliths is transmitted by the parietalcytoplasm. The large aggregations of endoplasmic reticulum whichare situated in the distal part of the central root cap cellswould not have any role in the perception of gravity by roots.These results are discussed in the light of recent work showingthe action of a growth inibitor in the geotropic reaction ofroots.     

Respiration metabolism in mitochondria of pea seedlings of different age under water deficit and rewatering

The effects of an osmoticum (mannitol) on growth, water content, respiration, and proline content in epicotyls of etiolated two-day-old (S₂) and three-day-old (S₃) pea (Pisum sativum L., cv. Flora-2) seedlings were studied. Water deficit was produced by placing plant roots in 0.6 M mannitol for 2–4 days. Control S₃ epicotyls contained more water than S₂ epicotyls; they were also characterized by more intense mitochondrial activity (in state 3, V ₃) and by the higher value of the respiratory control (RC) due to a fourfold decrease of proportion of weakly phosphorylating cyanide-resistant respiration (CRR). After 2-day-long treatment with the osmoticum, S₂ epicotyls lost more water than S₃; water deficit in them attained 40% (28% in S₃). In S₃ treatment, epicotyls continued to grow at the almost unchanged rate, and the content of proline in them changed insignificantly, whereas in S₂ seedlings epicotyl growth stopped, and proline accumulated in them. In the presence of the osmoticum, V ₃ and RC reduced, but in S₃ treatment they retained higher than in treatment S₂. In mitochondria of S₃ subjected to dehydration, the proportion of the cytochromic pathway of oxidation (V _cyt) remained high, but the absolute values of the respiration rate reduced, whereas in S₂ both these indices reduced and the proportion of CRR increased. After rewatering, indices of mitochondrial activity (the rate of substrate oxidation, RC value) were restored, but in S₃ they were higher. The ratio of V _cyt to CRR in S₃ shifted toward CRR, whereas in S₂, in contrast, it was shifted toward V _cyt. When temperature during seedling growth and experiment performing was declined from 22°C (in control) to 18°C, growth of S₃ epicotyls was retarded to the rate characteristic of S₂ at 22°C. Under the effect of osmoticum, they, like S₂, acquired a capacity to accumulate proline. Nevertheless, mitochondrial activity in such S₃ turned out to be higher than in S₂ grown at 22°C. The results obtained than, as distinct from traditional notes, 3-day-old pea seedlings manifested the higher tolerance to water deficit than 2-day-old seedlings.     

Distribution of labeled auxin in geotropically stimulated steins of cucumber and pea

The distribution of IAA-2-¹⁴C or IAA-5-³H applied to the apexin the upper and lower (with respect to gravity) halves of geotropicallystimulated stems of cucumber and pea was examined and the resultsobtained are as follows: 1. A larger amount of IAA-2-¹⁴C or IAA-5-³H was detected inthe lower than upper half of cucumber hypocotyls with 3-hr geostimulation. 2. A larger amount of IAA-2-¹⁴C was distributed in the lowerthan upper epidermis of pea epicotyls with 1-hr geostimulation. 3. Freezing autoradiography revealed that IAA-2-¹⁴C was concentratedin the vascular bundles and epidermis of cucumber hypocotyls,the distribution being affected by geostimulation only in thelatter. 4. Application of 1% TIBA in lanolin inhibited the distributionof IAA-2-¹⁴C in the lower epidermis of pea epicotyls, causingsuppression of geotropic curvature. 5. From these results, we concluded that IAA which accumulatedin the lower epidermis of the stem upon geostimulation causedthe negative geotropic curvature of the stem. (Received October 13, 1975; )     

Circumnutation and distribution of phytohormones in <Emphasis Type="Italic">Vigna angularis</Emphasis> epicotyls

Circumnutation is a plant growth movement in which the tips of axial organs draw a circular orbit. Although it has been studied since the nineteenth century, its mechanism and significance are still unclear. Greened adzuki bean (Vigna angularis) epicotyls exhibited a clockwise circumnutation in the top view with a constant period of 60 min under continuous white light. The bending zone of circumnutation on the epicotyls was always located in the region 1–3 cm below the tip, and its basal end was almost identical to the apical end of the region where the epicotyl had completely elongated. Therefore, epidermal cells that construct the bending zone are constantly turning over with their elongation growth. Since exogenously applied auxin transport inhibitors and indole-3-acetic acid (IAA) impaired circumnutation without any effect on the elongation rate of epicotyls, we attempted to identify the distribution pattern of endogenous auxin. Taking advantage of its large size, we separated the bending zone of epicotyls into two halves along the longitudinal axis, either convex/concave pairs in the plane of curvature of circumnutation or pre-convex/pre-concave pairs perpendicular to the plane. By liquid chromatography–mass spectrometry, we found, for the first time, that IAA and gibberellin A₁ were asymmetrically distributed in the pre-convex part in the region 1–2 cm below the tip. This region of epicotyl sections exhibited the highest responsiveness to exogenously applied hormones, and the latent period between the hormone application and the detection of a significant enhancement in elongation was 15 min. Our results suggest that circumnutation in adzuki bean epicotyls with a 60 min period is maintained by differential growth in the bending zone, which reflects the hormonal status 15 min before and which is shifting sequentially in a circumferential direction. Cortical microtubules do not seem to be involved in this regulation.     

Effect of gibberellic acid combined with saponin on shoot elongation of Asparagus officinalis

Effect of gibberellic acid (GA₃) combined with saponin on shoot elongation of Asparagus officinalis was evaluated in tissue culture. Addition of saponin to GA₃ supplemented Murashige and Skoog (MS) basal medium showed a dose depended effect on shoot length of Asparagus officinalis. However, increasing concentration of saponin above 3.0 mg dm⁻³ decreased shoot length and showed yellowing and thinning of shoots. Saponin (3.0 mg dm⁻³) + GA₃ (0.2 mg dm⁻³) mixture treated by variable duration of sonication (0, 1, 3, 5, 7, 9, 11, 13 and 15 min) were evaluated for shoot elongation on MS basal medium. The highest shoot lengths (14.4 ± 0.3 and 15.1 ± 0.1 cm) were found after 5 and 7 min sonication.     

Dorsiventralität der Statocyten in plagiogeotropen Seitenwurzeln von Lepidium sativum L.

Summary The calyptra of plagiotropic lateral roots of Lepidium sativum L. is composed of three rows of cells. Movable amyloplates, possibly functioning as statoliths, are located only a few central cells of the ontogenetic youngest cell row. Beside the lateral root axis the two innermost statocytes contain a stable complex of rough endoplasmic reticulum, which is preferentially located in the central distal cell corner. In the statocytes lying above the lateral root axis the amyloplasts are sedimented on the ER-complex during growth in direction of the geotropic liminal angle. In the statocyte below the axis the ER-complex is free of amyloplasts. Thus a dorsiventrality exists in the statocytes located above and below the root axis in regard to the arrangement of their organelles.

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Herrn Professor Dr. Maximilian Steiner zum 70. Geburtstag.     

Restitution of polarity in statocytes from centrifuged roots*

Abstract The structural polarity of statocytes from cress roots is changed by centrifugation. Upon low- dose centrifugation (3000 g min), the extent of stratification depends on statocyte position, i.e., central statocytes are affected more than lateral ones. Upon higher doses of centrifugation (60,000 and 360,000 g min), a uniform density gradient is established in all statocytes. If, after centrifugation, the roots are exposed to gravity again, the endoplasmic reticulum (ER) cisternae are relocated parallel to the periclinal cell walls within a few minutes; this relocation is independent of the direction of gravity in relation to the root axis, and independent of the previously applied centrifugation dose. This supports the notion that polarity is determined genetically. Cytochalasin B treatment, before and during centrifugation, totally inhibits the relocation of ER. After removing the drug by rinsing the roots, the statocytes restore cell polarity and relocate ER. These results indicate that relocation of ER cisternae may be mediated by microfilaments. When centrifuged roots are exposed to 1 g in the horizontal position, the latent period of gravitropism increases by 8–10 min relative to controls, regardless of the previously applied centrifugation doses. The kinetics of curvature are virtually identical. Since the increase in the latent period coincides with the time needed for most statocytes to restore the distal cell pole, it is evident that perception of gravity is correlated to the integrity of the distal cell pole.     

Amyloplast development in etiolated and ethylene-treated pea epicotyls

The amyloplasts found in the apical hook cells of etiolated pea (Pisum sativum L.) epicotyls were randomly distributed. Sedimentation of endodermal amyloplasts in the direction of gravity became apparent in the transition from the hook to the top of the main axis of the epicotyl. Cortical amyloplasts in this region were not, however, sedimented. These patterns of sedimentation could not be related to changes in amyloplast size, and it is proposed that cytoplasmic properties determine amyloplast behaviour.The differentiation of plastids in the hook differed between the amyloplast-containing endodermal cells and the cortical cells, in which amoeboid plastids predominated over amyloplasts. Amyloplasts disappeared from the cortical cells in the main axis of the epicotyl, but in the endodermal cells sedimented amyloplasts were found throughout the upper epicotyl.Etiolated epicotyls induced to grow horizontally by treatment with ethylene had a normal content of amyloplasts, sedimented in the direction of gravity.     

Growth initiation in the geotropic response of the wheat node

Summary The geotropic response in stems of Triticum aestivum occurs at the leaf sheath bases. Growth is initiated in the lower halves of these organs after orientation into the horizontal position. Lateral transport of growth hormone is not involved in the development of curvature. Continuous stimulation is necessary to maintain the response.Growth can be initiated in small pieces of tissue excised from the leaf sheath base but this is entirely dependent upon the precise orientation of the tissue in the gravitational field. Growth occurs only when the segment is orientated horizontally with the outer epidermis facing downwards. IAA is able to initiate growth in nongeo-induced tissue segments of the leaf sheath base but this effect appears to differ from the geo-induced growth.IAA-Indole-3-acetic acid; ABA-RS(±) abscisic acid; CFM-chlorofluorenol methyl ester; GA₃-gibberellic acid.     

Effects of abscisic acid on the orientation and cold stability of cortical microtubules in epicotyl cells of the dwarf pea

Summary The effects of abscisic acid (ABA) on the orientation and cold stability of cortical microtubules (MTs) in epidermal cells of epicotyls of the dwarf pea,Pisum sativum L. cv. Little Marvel, were examined by immunofluorescence microscopy. The effect of ABA on the elongation of epicotyls and on the orientation of cortical MTs was opposite to that of gibberellin A₃ (GA₃). Treatment with ABA, which reduced the promotion of epicotyl elongation by GA₃, eliminated the GA₃-induced predominance of transverse MTs and resulted in a predominance of longitudinal MTs. The effect of ABA on the cold stability of cortical MTs was also opposite to that of GA₃. ABA increased the cold stability of MTs, while GA₃ decreased it. The predominance of longitudinal MTs brought about by ABA may have some relationship to ABA-induced inhibition of the elongation of the epicotyl. ABA may alter membrane proteins to stabilize cortical MTs and induce cold hardiness of plants.Abbreviations ABA abscisic acid - DMSO dimethylsulfoxide - FITC fluorescein isothiocyanate - GA₃ gibberellin A₃ - MT microtubule - PBS phosphate-buffered saline Dedicated to the memory of Professor Oswald Kiermayer     

Effect of red light on geotropism in pea epicotyls

Dose response curves were determined for phytochrome phototransformation and for a phytochrome-controlled decrease in geotropic curvature in epicotyls of dark-grown Pisum sativum L. cv. Alaska. Ten times as much light was required to produce a spectrophotometrically detectable transformation of phytochrome as was required to produce a significant change in the geotropic response. The red light energy required for a 50% phytochrome transformation caused a 90% change in the physiological response.     

Joining forces: The interface of gravitropism and plastid protein import

In flowering plants, gravity perception appears to involve the sedimentation of starch-filled plastids, called amyloplasts, within specialized cells (the statocytes) of shoots (endodermal cells) and roots (columella cells). Unfortunately, how the physical information derived from amyloplast sedimentation is converted into a biochemical signal that promotes organ gravitropic curvature remains largely unknown. Recent results suggest an involvement of the Translocon of the Outer Envelope of (Chloro) plastids (TOC) in early phases of gravity signal transduction within the statocytes. This review summarizes our current knowledge of the molecular mechanisms that govern gravity signal transduction in flowering plants and summarizes models that attempt to explain the contribution of TOC proteins in this important behavioral plant growth response to its mechanical environment.Key words: gravitropism, root, amyloplast, TOC complex, TOC132, TOC75     

Effect of root length on epicotyl dormancy release in seeds of Paeonia ludlowii,Tibetan peony

Background and Aims

Epicotyl dormancy break in seeds that have deep simple epicotyl morphophysiological dormancy (MPD) requires radicle emergence and even a certain root length in some species. However, the mechanisms by which root length affects epicotyl dormancy break are not clear at present. This study aims to explore the relationship between root length and epicotyl dormancy release in radicle-emerged seeds of Tibetan peony, Paeonia ludlowii, with discussion of the possible mechanisms.

Methods

Radicle-emerged seeds (radicle length 1·5, 3·0, 4·5 and 6·0 cm) were incubated at 5, 10 and 15 °C. During the stratification, some seeds were transferred to 15 °C and monitored for epicotyl–plumule growth. Hormone content was determined by ELISA, and the role of hormones in epicotyl dormancy release was tested by exogenous hormone and embryo culture.

Key Results

Cold stratification did not break the epicotyl dormancy until the root length was ≥6 cm. The indole-3-actic acid (IAA) and GA₃ contents of seeds having 6 cm roots were significantly higher than those of seeds with other root lengths, but the abscisic acid (ABA) content was lowest among radicle-emerged seeds. GA₃ (400 mg L⁻¹) could break epicotyl dormancy of all radicle-emerged seeds, while IAA (200 mg L⁻¹) had little or no effect. When grown on MS medium, radicles of naked embryos grew and cotyledons turned green, but epicotyls did not elongate. Naked embryos developed into seedlings on a mixed medium of MS + 100 mg L⁻¹ GA₃.

Conclusions

A root length of ≥6·0 cm is necessary for epicotyl dormancy release by cold stratification. The underlying reason for root length affecting epicotyl dormancy release is a difference in the GA₃/ABA ratio in the epicotyl within radicle-emerged seeds, which is mainly as a result of a difference in ABA accumulation before cold stratification.     

Relation of Phytochrome-enhanced Geotropic Sensitivity to Ethylene Production

Brief exposure of etiolated pea (Pisum sativum cv. Alaska) seedlings to red light enhances subsequent development of geotropic curvature of the stem. Both this response and inhibition of ethylene production by red light become maximal 8 hours after illumination. Very low concentrations of applied ethylene inhibit development of geotropic curvature, whereas hypobaric treatment enhances geotropic sensitivity by removing endogenous ethylene. Increased geotropic sensitivity after illumination is accompanied by increased lateral migration of ³H-indoleacetic acid in response to gravity, and ethylene inhibits this lateral migration. It is suggested, therefore, that red light-enhanced geotropic sensitivity is caused by increased lateral auxin transport resulting from a reduction in ethylene production after illumination.     

Identification of two markers linked to the sex locus in dioecious <Emphasis Type="Italic">Asparagus officinalis</Emphasis> plants

One hundred decamer primers of random-amplified polymorphic DNA were tested on dioecious Asparagus officinalis plants to identify sex-linked molecular markers. One primer (S368) produced two markers (S368-928 and S368-1178) in female plants. These two DNA markers were identified in 30 male and female plants, respectively, and a S368-928 marker was proved to be linked to the female sex locus. The female-linked S368-928 marker was sequenced and specific primers were synthesized to generate a 928 bp marker of sequence characterized amplified regions (SCAR) in female plants, SCAR₉₂₈. SCAR₉₂₈ could be used to correctly screen homozygous mm female plants of A. officinalis. However, results of Southern blot analysis suggest that the hybridization pattern of S368-928 was presented in both sex plants. This text was submitted by the authors in English.     

Geotropic curvature of decapitated Avena coleoptiles after application of tips of maize roots,tips of Avena coleoptiles,indoleacetic acid,or abscisic acid

Isolated Avena coleoptiles were decapitated at different distances from the tip and then placed horizontally, after which the geotropic curvature was measured. No geotropic curvature could be detected during the first 3 h. Later, upward curvature occurred which was found to depend inversely on the length of the decapitated tips. When the tips of maize roots or Avena coleoptiles were placed on the cut surface of decapitated Avena coleoptiles, the coleoptiles showed a significantly stronger upward curvature as compared to controls which had been provided with agar blocks on the cut surface. The same upward curvature was found with decapitated coleoptiles provided with agar blocks containing 10^-6 or 10^-7 M indoleacetic acid (IAA). After application of abscisic acid (ABA) at concentrations of 10^-6 and 10^-8 M to the decapitated coleoptiles, the curvature observed was not different from that of the controls; at higher concentrations of ABA the curvature was found to be lower than that of the controls. It is concluded that root tips secrete a substance which may replace the effect of IAA in coleoptiles. The results are discussed in view of the validity of the Cholodny-Went hypothesis for the geotropic reaction of roots.Abbreviations ABA abscisic acid - IAA 3-indoleacetic acid     

Responses of intact and excised young bean plants to fusicoccin

The effect of fusicoccin (FC) on the growth of epicotyls and leaves of Phaseolus vulgaris L. intact and excised seedlings has been examined, and several unexpected responses were observed. FC was added either to small wounds on one side of the epicotyl of 10 day old red-light grown seedlings or to the base of shoots excised at the base of the hypocotyl. Plants were kept in either dim red light (4 mol m^-2sec^-1) or bright white light (175 mol m^-2sec^-1) during the FC treatment. FC added to the base of the shoots was found to inhibit leaf expansion in either light condition. At the same time stem elongation was enhanced. The active concentration range was 10^-7–10^-5M. The basal fed FC caused a rapid and severe bending of the epicotyl starting at the base of the elongation zone. The direction of curvature was random, not related to the plane of the cotyledons or the direction of the gravity vector. Application of FC to one side of the epicotyl caused a similar but smaller bending away from the treated side. The bending occurred at either end of the elongation zone in accordance with site of FC application above or anywhere below it along the epicotyl and hypocotyl. It is concluded that the curvature of the epicotyl induced by FC fed in the transpiration stream may either be due to a differential loss of the capacity of cells at the base of the elongation zone to grow in response to FC or as a result of elongation of the first responsive cells encountered by the FC.