共查询到10条相似文献,搜索用时 109 毫秒
1.
Temperature-dependent internode elongation in vegetative plants of Arabidopsis thaliana lacking phytochrome B and cryptochrome 1 总被引:1,自引:0,他引:1
Vegetative plants of Arabidopsis thaliana (L.) Heynh. form a compact rosette of leaves in which internode growth is virtually arrested. Rapid extension of the internodes
occurs after flower buds are present in the reproductive apex. Under natural radiation, continuous light from fluorescent
lamps, or short photoperiods of light from fluorescent lamps, plants of the phyB cry1 double mutant (lacking both phytochrome B and cryptochrome 1) did not form normal rosettes because all the internodes showed
some degree of elongation. Internode elongation was weak in the phyB single mutant and absent in the cry1 mutant, indicating redundancy between phytochrome B and cryptochrome 1. The absence of phytochrome A caused no effects. The
failure to form normal rosettes was conditional because internode elongation was arrested at low temperatures in all the mutant
combinations. In contrast, the temperature dependence of phytochrome B and cryptochrome 1 effects on hypocotyl growth was
weak. The elongation of the internodes in phyB cry1 was not accompanied by early flowering as showed by the lack of effects on the final number of leaves. Apex dissection indicated
that in phyB cry1 double mutants internode elongation anticipated the transition from the vegetative to the reproductive stage. Thus, stem
growth in Arabidopsis thaliana is not fully dependent on the program of reproductive development.
Received: 2 June 1999 / Accepted: 13 August 1999 相似文献
2.
Takahashi H Kamada M Yamazaki Y Fujii N Higashitani A Aizawa S Yoshizaki I Kamigaichi S Mukai C Shimazu T Fukui K 《Planta》2000,210(3):515-518
Seedlings of most cucurbitaceous plants develop a peg (protuberance caused by cell outgrowth) on the transition zone between
the hypocotyl and root. The peg is necessary for removing the seed coat after germination. In our spaceflight experiments
on the STS-95 space shuttle, Discovery, we found that cucumber (Cucumis sativus L.) seedlings grown under microgravity conditions developed two pegs symmetrically at the transition zone. Thus, cucumber
seedlings potentially develop two pegs and do not require gravity for peg formation itself, but on the ground the development
of one peg is suppressed in response to gravity. This may be considered as negative control of morphogenesis by gravity.
Received: 17 August 1999 / Accepted: 4 October 1999 相似文献
3.
Inactivation of DNA replication origins by the cell cycle regulator, trigonelline, in root meristems of Lactuca sativa 总被引:4,自引:0,他引:4
The effects of trigonelline (TRG) on the cell cycle in root meristems of Lactuca sativa L. were examined in the knowledge that TRG is a cell cycle regulator that causes cell arrest in G2, and prevents ligation
of replicons in S-phase. The hypothesis was tested that continuous exposure to TRG would perturb DNA replication which, in
turn, would lengthen the cell cycle and impair root elongation. Using DNA fibre autoradiography, mean replicon size was 31
and 13 μm in the TRG (3 mM) and control treatments, respectively. Trigonelline also resulted in a lengthening of both S-phase
and the cell cycle and a decrease in primary root elongation. Hence, replicon inactivation was responsible for the protracted
S-phase. Trigonelline treatment also resulted in a 1.6-fold increase in fork rate (13.8 μm h−1) compared with the control (8.4 m h−1). The faster fork rate in the larger replicons is in accord with the highly significant positive relationship already established
between fork rate and replicon size for various unrelated higher plants.
Received: 11 October 1999 / Accepted: 23 December 1999 相似文献
4.
Somatic embryogenesis induced by the simple application of abscisic acid to carrot (Daucus carota L.) seedlings in culture 总被引:3,自引:0,他引:3
Seedlings of carrot (Daucus carota L. cv. Red Cored Chantenay) formed somatic embryos when cultured on medium containing abscisic acid (ABA) as the sole source
of growth regulator. The number of embryos per number of seedlings changed depending on the concentration of ABA added to
the medium, with a maximum embryo number at 1 × 10−4 M ABA. Seedling age was critical for response to exogenous ABA; no seedling with a hypocotyl longer than 3.0 cm was able to
form an embryo. Removal of shoot apices from seedlings completely inhibited the embryogenesis induced by application of exogenous
ABA, suggesting that the action of ABA requires some substance(s) that is translocated basipetally from shoot apices through
hypocotyls. Histologically, somatic embryos shared common epidermal cells and differentiated not through the formation of
embryogenic cell clumps, but directly from epidermal cells. These morphological traits are distinct from those of embryogenesis
via formation of embryogenic cell clumps, which has been found in embryogenic carrot cultures established using 2,4-dichlorophenoxyacetic
acid or other auxins. These results suggest that ABA acts as a signal substance in stress-induced carrot seedling somatic
embryogenesis.
Received: 22 April 2000 / Accepted: 8 June 2000 相似文献
5.
The role of gibberellins (GAs) in the regulation of shoot elongation is well established but the phytohormonal control of
dry-matter production is poorly understood. In the present study, shoot elongation and dry-matter production were resolved
by growing Brassica napus L. seedlings under five light intensities (photon flux densities) ranging from 25 to 500 μmol m−2 s−1. Under low light, plants were tall but produced little dry weight; as light intensity was increased, plants were progressively
shorter but had increasing dry weights. Endogenous GAs in stems of 16- and 17-d-old plants were analyzed by gas chromatography-selected
ion monitoring with [2H2] internal standards. The contents of GAs increased dramatically with decreasing light intensity: GA1, GA3, GA8 and GA20 were 62, 15, 16 and 32 times higher, respectively, under the lowest versus highest light intensities. Gibberellin A19 was not measured at 25 μmol m−2 s−1 but was 9␣times greater in the 75 compared to 500 μmol m−2 s−1 treatment. Shoot and hypocotyl lengths were closely positively correlated with (log) GA concentration (for example: r
2 = 0.93 for GA1 and hypocotyl length) but shoot dry matter was negatively correlated with GA concentration. The application of gibberellic
acid (GA3) produced elongation of plants grown under high light, indication that their low level of endogenous GA was limiting shoot
elongation. Although endogenous GA20 showed the greatest influence of light treatment, metabolism of [3H]GA20 and of [3H]GA1 was only slightly influenced by light intensity, suggesting that neither 2β- nor 3β-hydroxylation were points of metabolic
regulation. The results of this study indicate that GAs control shoot elongation but are not directly involved in the regulation
of shoot dry weight in Brassica. The study also suggests a role of GAs in photomorphogenesis, serving as an intermediate between light condition and shoot
elongation response.
Received: 18 June 1998 / Accepted: 29 July 1998 相似文献
6.
Hypaphorine, the major indolic compound isolated from the ectomycorrhizal fungus Pisolithus tinctorius, controls the elongation rate of root hairs. At inhibitory concentrations (100 μM), hypaphorine induced a transitory swelling
of root hair tips of Eucalyptus globulus Labill. ssp. bicostata. When the polar tip growth resumed, a characteristic deformation was still visible on elongating hairs. At higher hypaphorine
concentrations (500 μM and greater), root hair elongation stopped, only 15 min after application. However, root hair initiation
from trichoblasts was not affected by hypaphorine. Hypaphorine activity could not be mimicked by related molecules such as
indole-3-acetic acid (IAA) or tryptophan. While IAA had no activity on root hair elongation, IAA was able to restore the tip
growth of root hairs following inhibition by hypaphorine. These results suggest that hypaphorine and endogenous IAA counteract
in controlling root hair elongation. During ectomycorrhiza development, the absence of root hairs might be due in part to
fungal release of molecules, such as hypaphorine, that inhibit the elongation of root hairs.
Received: 27 October 1999 / Accepted: 14 March 2000 相似文献
7.
Summary. Nitric oxide (NO) has been shown to regulate neurotransmitter release in the brain; both inhibitory and excitatory effects
have been seen. Taurine is essential for the development and survival of neural cells and protects them under cell-damaging
conditions. In the brain stem, it regulates many vital functions such as cardiovascular control and arterial blood pressure.
Now we studied the effects of the NO-generating compounds hydroxylamine (HA), S-nitroso-N-acetylpenicillamine (SNAP) and sodium
nitroprusside (SNP) on the release of preloaded [3H]taurine under normal and ischemic conditions in slices prepared from the mouse brain stem from developing (7-day-old) to
young adult (3-month-old) mice. In general, the effects of NO on the release were somewhat complex and difficult to explain,
as expected from the multifunctional role of NO in the central nervous system. The basal initial release under normal conditions
was enhanced by the NO donors 5 mM HA and 1.0 mM SNAP at both ages, but SNP was inhibitory in developing mice. The release
was markedly enhanced by K+ stimulation. The effects of HA, SNAP and SNP on the basal release were not antagonized by the NO synthase inhibitor NG-nitro-L-arginine (L-NNA, 1.0 mM), demonstrating that mechanisms other than NO synthesis are involved. Taurine release in
developing mice in the presence of SNP was reduced by the inhibitor of soluble guanylate cyclase, 1H-(1,2,3)oxadiazolo(4,3-a)quinoxalin-1-one
(ODQ), indicating the possible involvement of cGMP. In normoxia, N-methyl-D-aspartate (NMDA, 1.0 mM) enhanced the SNAP- and
HA-evoked taurine release in developing mice and the HA-evoked release in adults. In ischemia, both K+ stimulation and NMDA potentiated the NO-induced release, particularly in the immature mice, probably without the involvement
of the NO synthase or cGMP. The substantial release of taurine in the developing brain stem evoked by NO donors together with
NMDA might represent signs of important mechanisms against excitotoxicity which protect the brain stem under cell-damaging
conditions.
Authors’ address: Prof. Pirjo Saransaari, Brain Research Center, Medical School University of Tampere, Tampere, FIN-3 3014,
Finland 相似文献
8.
The auxin-resistant diageotropica mutant of tomato responds to gravity via an auxin-mediated pathway
Hypocotyls of the diageotropica (dgt) mutant of tomato (Lycopersicon esculentum Mill.) do not elongate in response to exogenous auxin, but can respond to gravity. This appears paradoxical in light of the
Cholodny-Went hypothesis, which states that shoot gravicurvature results from asymmetric stimulation of elongation by auxin.
While light-grown dgt seedlings can achieve correct gravitropic reorientation, the response is slow compared to wild-type seedlings. The sensitivity
of dgt seedlings to inhibition of gravicurvature by immersion in auxin or auxin-transport inhibitors is similar to that of wild-type
plants, indicating that both an auxin gradient and auxin transport are required for the gravitropic response and that auxin
uptake, efflux, and at least one auxin receptor are functional in dgt. Furthermore, dgt gravicurvature is the result of asymmetrically increased elongation as would be expected for an auxin-mediated response.
Our results suggest differences between elongation in response to exogenous auxin (absent in dgt) and elongation in response to gravistimulation (present but attenuated in dgt) and confirm the presence of two phases during the gravitropic response, both of which are dependent on functional auxin
transport.
Received: 16 July 1999 / Accepted: 24 September 1999 相似文献
9.
Kocsy G von Ballmoos P Suter M Rüegsegger A Galli U Szalai G Galiba G Brunold C 《Planta》2000,211(4):528-536
The role of glutathione (GSH) in protecting plants from chilling injury was analyzed in seedlings of a chilling-tolerant
maize (Zea mays L.) genotype using buthionine sulfoximine (BSO), a specific inhibitor of γ-glutamylcysteine (γEC) synthetase, the first enzyme
of GSH synthesis. At 25 °C, 1 mM BSO significantly increased cysteine and reduced GSH content and GSH reductase (GR: EC 1.6.4.2)
activity, but interestingly affected neither fresh weight nor dry weight nor relative injury. Application of BSO up to 1 mM
during chilling at 5 °C reduced the fresh and dry weights of shoots and roots and increased relative injury from 10 to almost
40%. Buthionine sulfoximine also induced a decrease in GR activity of 90 and 40% in roots and shoots, respectively. Addition
of GSH or γEC together with BSO to the nutrient solution protected the seedlings from the BSO effect by increasing the levels
of GSH and GR activity in roots and shoots. During chilling, the level of abscisic acid increased both in controls and BSO-treated
seedlings and decreased after chilling in roots and shoots of the controls and in the roots of BSO-treated seedlings, but
increased in their shoots. Taken together, our results show that BSO did not reduce chilling tolerance of the maize genotype
analyzed by inhibiting abscisic acid accumulation but by establishing a low level of GSH, which also induced a decrease in
GR activity.
Received: 9 November 1999 / Accepted: 17 February 2000 相似文献
10.
To test the hypothesis that the contribution of phosphoribulokinase (PRK) to the control of photosynthesis changes depending
on the light environment of the plant, the response of transgenic tobacco (Nicotiana tabacum L.) transformed with antisense PRK constructs to irradiance was determined. In plants grown under low irradiance (330 μmol m−2 s−1) steady-state photosynthesis was limited in plants with decreased PRK activity upon exposure to higher irradiance, with a
control coefficient of PRK for CO2 assimilation of 0.25 at and above 800 μmol m−2 s−1. The flux control coefficient of PRK for steady-state CO2 assimilation was zero, however, at all irradiances in plant material grown at 800 μmol m−2 s−1 and in plants grown in a glasshouse during mid-summer (alternating shade and sun 300–1600 μmol m−2 s−1). To explain these differences between plants grown under low and high irradiances, Calvin cycle enzyme activities and metabolite
content were determined. Activities of PRK and other non-equilibrium Calvin cycle enzymes fructose-1,6-bisphosphatase, sedoheptulose-1,7-bisphosphatase
and ribulose-1,5-bisphosphate carboxylase-oxygenase were twofold higher in plants grown at 800 μmol m−2 s−1 or in the glasshouse than in plants grown at 330 μmol m−2 s−1. Activities of equilibrium enzymes transketolase, aldolase, ribulose-5-phosphate epimerase and isomerase were very similar
under all growth irradiances. The flux control coefficient of 0.25 in plants grown at 330 μmol m−2 s−1 can be explained because low ribulose-5-phosphate content in combination with low PRK activity limits the synthesis of ribulose-1,5-bisphosphate.
This limitation is overcome in high-light-grown plants because of the large relative increase in activities of sedoheptulose-1,7-bisphosphatase
and fructose-1,6-bisphosphatase under these conditions, which facilitates the synthesis of larger amounts of ribulose-5-phosphate.
This potential limitation will have maintained evolutionary selection pressure for high concentrations of PRK within the chloroplast.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献