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1.
When seedlings of Pharbitis nil are presented with an inductive dark period at varying times, they show a circadian fluctuation in the number of flower buds initiated. This study determines if this fluctuation is due to the plant's perception, at the time of the inductive dark period, of either a rhythmic, external, environmental stimulus or of an endogenous rhythm. Using experimental designs in which the time of planting, the time of seedling emergence from the soil, and the time at which the presentation of an inductive dark period are varied, this fluctuation in flower bud formation is shown to be due to an endogenous rhythm initiated or synchronized by some event associated with the emergence of the seedlings from the soil. The results are inconsistent with the hypothesis that the plants are responding to rhythmic external stimuli.  相似文献   

2.
The Inhibition of Flowering by Non-Induced Cotyledons of Pharbitis nil   总被引:1,自引:0,他引:1  
Inhibitory effects on flowering of a non-induced cotyledon havebeen examined in Pharbitis nil seedlings. The photoperiodicinduction of one cotyledon was accomplished by wrapping it inaluminium foil for 13 to 15 h while the seedling remained inthe light. The presence of the other cotyledon in the lightblocked this inductive stimulus. The timing of its inhibitoryeffect suggested that its action was to block the expressionof the inductive stimulus, presumably at the shoot apex. Byvarying the area of the non-induced cotyledon parallel inhibitoryeffects were shown on export of stimulus and of 14C-labelledassimilate to the apex from the induced cotyledon. Thus, partof the inhibition was by interference with assimilate/stimulusco-transport in the phloem. However, an additional inhibitoryeffect was also evident and for this second component therewas no relationship between assimilate and stimulus transport.This latter inhibition was generated by brief light interruptionsof darkness given to one cotyledon only whilst the other waswrapped. The control treatment, removal of the unwrapped cotyledon,did not alter flowering compared to seedlings with intact, darkenedcotyledons. Thus, these studies show that the brief night interruptionsacted to trigger a photoperiodically sensitive inhibitor notto block induction. The implications of these findings are discussedin relation to models of time measurement in the photoperiodiccontrol of flowering. (Received March 20, 1989; Accepted November 16, 1989)  相似文献   

3.
An extract of cotyledons of Pharbitis nil, which had been exposedto short-day conditions, was tested for flower-promoting activityin a shoot-tip assay system in vitro. The crude extract hadno flower-promoting activity, however, after partitioning ofthe crude extract with dichloromethane, the resulting aqueousfraction had flower-promoting activity. This activity was separatedinto two fractions by column chromatography on Toyopearl HW-40.One active fraction was identified as dihydrokaempferol-7-O-rß-D-glucoside(DHK-glc). This compound exhibited flower-promoting activityat the extremely low concentration of 4.4x10-9. (Received April 25, 1995; Accepted August 11, 1995)  相似文献   

4.
The light requirements for induction of flowering by a long dark period were investigated in dark-grown seedlings of Pharbitis nil Chois, cv. Violet. The cotyledons bcame photoperiodically sensitive to a 24 h dark period by two 1 min red irradiations (6.3 μmol m−2 S−1) separated by a 24 h dark period. The reversibility of the effect of brief red irradiations, and the effectiveness of low energies of red irradiation suggest the involvement of phytochrome in the induction of photoperiodic sensitivity. Partial de-etiolation occurred after these brief periods of red irradiation but the seedlings were not capable of net CO2 uptakeeven 7 h after the start of the main light period that followed the critical dark period. A changing response to the duration of the priod of darkness given between the two short red irradiations showed the the correct phasing of an endogenous photoperiodic rhythm is needed for the attainment of photoperiodic snsitivity.  相似文献   

5.
Cyclic adenosine diphosphate ribose (cADPR) is a potent endogenous calcium-mobilizing agent synthesized from NAD+ by ADP-ribosyl cyclases described for several animal cells. Pharmacological studies suggest that cADPR is an endogenous modulator of Ca2+-induced Ca2+ release channels. There is also information about the sub-micromolar concentration of cADPR in plant cells. Whether cADPR can act as a Ca2+-mobilizing intracellular messenger in plant tissue is an unresolved question. Despite the obvious importance of monitoring cADPR cellular levels under various physiological conditions in plants, its measurement has been technically difficult and requires specialized reagents. In the present study a widely applicable sensitivity assay for cADPR is described. We show that Pharbitis nil tissue from cotyledons contains a certain cADPR level. To explain the possible roles of this second messenger in photoperiodic flower induction, some physiological experiments were also performed. The exogenous applications of cADPR to Pharbitis nil plants, which were exposed to a 12-h-long subinductive night, significantly increased flowering response. Nevertheless 8-Br-cADPR inhibited flowering when these compounds were applied during a 16-h-long inductive night. The effect of ruthenium red, a calcium channel blocker and ryanodine, a calcium channel stimulator, on the photoperiodic induction of flowering was also studied. Ruthenium red, when applied before and during an inductive 16-h dark period, slightly inhibited flowering, whereas ryanodine, when applied before and during a 12-h long subinductive night, stimulated flower bud formation. We also confirmed evidence that Ca2+ ions are involved in the photoperiodic induction of flowering. Thus, the obtained results may suggest the involvement of cyclic ADPR-activated Ca2+ mobilization in the photoperiodic flower induction process in Pharbitis nil.  相似文献   

6.
7.
EGTA, a specific Ca(2+) chelator, inhibited the flowering response of Pharbitis nil when applied to the cotyledons immediately before the inductive dark period. Calcium sprayed 30 minutes after the EGTA blocked the effect of EGTA. The length of the critical dark period was increased both by EGTA and by LaCl(3). The calmodulin antagonists W-7 and chlorpromazine also reduced the flowering response. On the other hand, A23187, a calcium ionophore, increased the flowering response. Both EGTA and A23187 were effective at certain times of the photoperiod but had almost no effect when applied at other times. The results indicate that the level of endogenous Ca(2+) may be limiting for floral induction in Ph. nil. Ca(2+) seems to play a role during the early stages of the inductive dark period.  相似文献   

8.
Since labelling of ureides from adenine-8-14C is higher in dark than in light, the influence of light on the deamination and the oxidation of adenylic compounds by cotyledon discs of Pharbitis nit was investigated. Among the three possible adenylic precursors for the deaminative step, adenine was found to be the best compound for the study of the deaminative rate, adenosine being easily hydrolyzed into adenine, and AMP undergoing an apparent complete hydrolysis before entering the cells. By analysis of adenine-8-14C metabolism for brief periods, it was determined that the rate of deamination of adenylic compounds was faster in light than in dark. In contrast, the activity of xanthine dehydrogenase was much higher in the dark than in light. The level of the activity of uricase was the same in both light and dark.  相似文献   

9.
10.
Rhythmicity of Flowering in Pharbitis nil   总被引:1,自引:0,他引:1  
When young seedlings of Pharbitis nil are grown under continuous light, except for a single inductive dark period, they flower to a varying degree, depending on when this dark period is given. Plants become sensitive to this induction approximately three days after the seedlings emerge from the soil. The expression of flowering varies in a rhythmic fashion for three or more cycles, when an inductive dark period is given at progressively later times. The time between maximum expression of flowering is 24 hours or somewhat longer. It appears necessary that the inductive dark period be of sufficient duration, to only partially induce the plants to flower for this rhythm to be expressed. Under the conditions employed in this study, this duration is 12 hours. If this rhythm is endogenous, it exists at least from when the plants emerged from the soil since no environmental cues are given after that time, and it raises questions of the interpretations of data from previous studies with this organism.  相似文献   

11.
Seedlings of Pharbitis nil, strain Kidachi, were grown undercontinuous light at 20°C in vessels containing 5,000-mlnutrient solution, 24 plants per vessel. NAA (0.005–0.5µM), GA3 (0.1–0.5 µM), kinetin (0.5–5µM), benzyladenine (0.05–5 µM) or abscisicacid (4 µM) added to the nutrient solution induced long-dayflowering, and the flowering was always accompanied by suppressionof root elongation. 3,4-Dichlorobenzoic acid (0.05–10µM) and some other benzoic acid derivatives which arehighly effective for the induction of flowering in Lemna paucicostataalso showed similar effects. Neither NAA, kinetin nor 3,4-dichlorobenzoicacid applied via the apical part of the hypocotyl could causeflowering or suppression of root elongation. Thus, the flower-inducingeffect of the above substances was presumed to be secondaryto the suppression of root elongation. Ethrel (1–50 µM)added to the nutrient solution suppressed root elongation, butdid not induce flowering probably because it has flower-inhibitingactivity. 1 This paper is dedicated to the memory of Dr. Joji Ashida,the first president of the Japanese Society of Plant Physiologists. (Received December 15, 1982; Accepted February 25, 1983)  相似文献   

12.
In dark-grown Pharbitis nil seedlings, far-red light (FR) irradiationof 48 h or less promotes Chl a accumulation in the first 2-hof a subsequent white light (WL) period, without a lag phaseof Chl a accumulation. However, continuous FR irradiation of72 h or more, causes the so-called FR-induced lag phase. A 5-minWL given 4 h before the onset of the continuous WL promotesChl a accumulation irrespective of the length of the precedingFR irradiation period, if a 4-h dark period is inserted betweenthe 5-min WL and continuous WL. This suggests that the effectof the brief WL is independent of and additive to the effectof the preceding FR irradiation, although the effect of theFR irradiation changes from promotive to inhibitory with anincrease in the irradiation period. Red light (R) is more active than blue light (B) in this brieflight effect. The R effect is reversed by subsequent exposureto FR when the period of the preceding FR irradiation is 24h, but not when it is 72 h. The relative effectiveness of Bto R increases after prolonged FR irradiation. (Received August 6, 1986; Accepted March 12, 1987)  相似文献   

13.
Flowering of Pharbitis nil plants was slightly inhibited byexposure to the light of the full moon for 8 or more hours witha single dark period of 16, 14 or 13 h. It is suggested thatin the natural environment moonlight may have at most only aslight delaying effect on the time of flower induction in short-dayplants. Flowering, moonlight, night-break, Pharbitis nil, photoperiodism, short day plants  相似文献   

14.
Two new gibberellins, gibberellins A26 and A27 were isolated from immature seeds of Japanese morning-glory (Pharbitis nil) and their structures were elucidated as I and IX.  相似文献   

15.
Flower buds of Pharbitis nil cut from plants growing in thefield open rapidly when subjected to darkness (20–25°C)or low temperature (20°C) in light. Petals of the buds arethe sites of photo- and thermo-perception; flower-opening iscaused mainly by the epinasty of petal midribs. 1Dedicated to Professor Dr. Erwin Bunning on the occasion ofhis 75th birthday. (Received October 23, 1980; Accepted December 15, 1980)  相似文献   

16.
LYNDON  R. F. 《Annals of botany》1979,43(5):539-551
The growth of the flower and its constituent parts was measuredin Silene coeli-rosa plants, induced at 13, 20 and 27 °C,in order to try and identify those processes which consistentlyoccurred and would therefore be more likely to be essentialfor flower formation. The increased growth rate of the apical dome just before orabout the time of sepal initiation was not maintained in theflower, the growth rate of which was comparable to that of avegetative apex until all the carpels had been initiated, whenit decreased further. The primordia of the same whorl all hadsimilar growth rates so that the relative sizes of the primordiareflected their relative ages since their initiation. The relativegrowth rate of the stamens was the same (13 and 20 °C) orless (27 °C) than that of the sepals, but the relative growthrate of the petals was lower than either. The growth rate ofthe flower axis was least at the sepal node and increased bothdistally and proximally from this region. The plastochron during sepal initiation was shorter than forleaf initiation and tended to be shorter still during initiationof stamens and petals. Increasing temperature increased therate of primordial initiation but at 27 °C the growth ratesof the primordia were lowest although the rates of primordiainitiation were highest. The form of the flower, as exemplifiedby the relative sizes of the primordia at the moment when allcarpels had been initiated, was constant despite the differinggrowth rates and sizes of the primordia on initiation in differenttemperatures. It is concluded that neither the initiation ofthe primordia in the flower nor the form of the flower is determinedprimarily by the relative growth rates of its component parts. Silene coeli-rosa, flower development, primordia initiation, growth  相似文献   

17.
The inhibitory effect of ethylene on photoperiodic flower inductionin Pharbitis nil was investigated in relation to the time ofethylene application. Ethylene applied during an 18-h dark periodnot only made the dark period non-inductive, but also greatlyinhibited the flower-inducing effect of the 2nd 18-h dark periodgiven 6 h after the end of the first dark period. The seconddark period was inductive when it was given 30 h after the endof the first dark period, during which ethylene was applied.Ethylene applied during the light period prior to an inductivedark period had no inhibitory effect, suggesting that ethylenegiven during the dark period produces some flower-inhibitingentity. (Received April 17, 1987; Accepted June 17, 1987)  相似文献   

18.
The object of study was the regeneration of Pharbitis nil by direct and indirect organogenesis. From fragments of roots, cotyledons, hypocotyls and epicotyls on Murashige and Skoog nutrient solution (MS) supplemented with naphtalenacetic acid (NAA) or indolylacetic acid (IAA; both at 0.1 mg·dm−3 concentration) in the presence of benzylaminopurine (BAP), zeatin or kinetin (all at 5 mg·dm−3 concentration) only root organogenesis was obtained. Likewise, when using the two-step method (2 or 5 days exposure to NAA or IAA at 2 mg·dm−3 concentration followed by exposure to BAP or zeatin at 1 or 2 mg·dm−3 concentration) root organogenesis was observed in all types of explants. Moreover, shoot buds were formed on fragments of epicotyl exposed vertically in relation to the medium. However, attempts at regenerating complete plants from them failed, so did the regeneration of P. nil from callus. The roots were formed in callus cultures only.  相似文献   

19.
The properties of phytochrome have been measured by dual-wavelength spectropho-tometry in the cotyledons of the short-day plant Pharbitis nil Choisy cv. Violet, where it is known to play a role in flower induction. In plants de-etiolated by a single white light period (4 h or longer), destruction of the far-red absorbing form of phytochrome (Pfr) was twice as rapid as after 10 min red light. A small fraction of Pfr was stable. After de-etiolation by a period of white light (6 h or longer) the rapid decrease of Pfr during the first 30 min was accompanied by a rapid increase of the red absorbing form of phytochrome (Pfr). This rapid increase of Pfr is probably due to dark reversion. Long term synthesis of phytochrome was inhibited by the presence of Pfr. Phytochrome synthesised in darkness showed the etiolated-plant type characteristics and underwent rapid destruction upon photoconversion to Pfr. The stable Pfr identified here is possibly that pool of phytochrome associated with the long term promotive process in flower induction, and the rapidly reverting Pfr is that pool associated with the night break inhibition of flowering.  相似文献   

20.
A new gibberellin, gibberellin A20 (GA20), was isolated from immature seeds of morning-glory (Pharbitis nil). Its structure was established as 4aα, 7α-dihydroxy-1β-methyl-8-methylenegibbane-1α, 10β-dicarboxylic acid-1→4a lactone (I) on the basis of its physicochemical analysis as well as chemical evidences. GA20 shows marked growth promoting activities on dwarf maize d2 and d5 but weak activities on d1, rice seedling and dwarf pea.  相似文献   

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