Ethylene and IAA interactions in the inhibition of photoperiodic flower induction of Pharbitis nil
Jacek KęsyBeata MaciejewskaMagdalena Sowa-KućmaMagdalena SzumilakKrzysztof KawałowskiMaja BorzuchowskaJan Kopcewicz
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Pharbitis nil
Flower induction
Plant Physiology
Flowering responses to a single photoperiod, of various durations and irradiances, followed by an inductive dark period were investigated with dark-grown seedlings of Pharbitis nil Choisy. The number of flower buds induced in each plant (NFB) increased with the increase of both duration and irradiance of the photoperiod. Reciprocity did not hold for this photoresponse within the range of 0-16 h and 2.5-10 W-m-2, NFB depending on the duration rather than the irradiance. With lengthening of the dark period following a photoperiod of 8 h or less, two different phases alternately appeared so that NFB sharply increased at 20-24 h and 40-43 h after the onset of the photoperiod, then gradually decreased. When the photoperiod was longer than 8 h, NFB sharply increased at 12–16 h after the end of the photoperiod and remained around the saturated value with longer dark periods. Far-red light given immediately after the photoperiod inhibited flowering, the inhibitory effect being stronger the shorter the photoperiod. This far-red effect is mediated by phytochrome and PFR seems to be required during the inductive dark period following a short photoperiod for floral induction.
Pharbitis nil
Phytochrome
Flower induction
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Abstract ‘Chandler’ strawberry plants (Fragaria X ananassa Duch.) were greenhouse grown under natural lighting and then placed into growth chambers at two constant temperatures of 16 °C and 26 °C and two day lengths of 9 h (SD) and 9 h photoperiod (NI) which was night interrupted with 3 h of incandescent radiation at 30-45 μmol s ∼ 1m ∼ 2 PAR. Plants were given different numbers of inductive cycles in growth chambers and then moved to the greenhouse where flowering and growth were monitored. Flowering was completely inhibited at 26 °C, regardless of pretreatment growing conditions such as pot sizes and plant ages, photoperiod and inductive cycles. At 16 °C, SD promoted floral induction compared to NI under all inductive cycles except a 7-day induction. The minimum number of inductive cycles required at 16 °C for floral induction was dependent on photoperiod and prior greenhouse treatment. Flowering rate was also affected by greenhouse treatment, photoperiod and inductive cycles. Runner production was affected by photoperiod and temperature Xinductive cycle.
Flower induction
Day length
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Flower induction
Vernalization
Long day
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The content of endogenous ethylene in the seedlings of <em>Pharbitis nil</em> subjected to 16-hour long inductive night is low during the first half of a dark period, then it increases considerably in the second half of the night. Ethrel, the compound releasing ethylene, applied to the cotyledons of the seedlings, increases the amount of endogenous ethylene in them and at the same time inhibits the flowering, especially when ethrel was applied during the first half of an inductive night, when the content of endogenous ethylene in the seedlings is low. The auxin, inhibiting the flowering of <em>Pharbitis</em>, causes at the same time the increase in the production of endogenous ethylene. PCIB, an inhibitor of auxin action reverses the inhibiting influence of ethrel on flowering. On the other hand the combined application of ethrel and TIBA, the inhibitor of auxin polar transport, causes the increase of the flowering inhibition. CoCl<sub>2</sub>, the inhibitor of ethylene biosynthesis, and AgNO<sub>3</sub>, the inhibitor of ethylene action, reverse partly the inhibiting influence of auxin. It suggests that ethylene could take part in auxininhibition of flowering. The all obtained results seem to suggest the participation of ethylene in the control of the flower photoperiodic induction.
Pharbitis nil
Flower induction
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The interaction between day/night temperature (DT/NT) and irradiance during the photoperiod prior to the inductive night on Pharbitis nil (L.) cv. Violet flower induction was studied. Plants exposed to 12 or 18 °C NT did not flower regardless of DT. When NT was 24 or 30 °C, percent flowering plants increased progressively as DT increased from 12 to 30 °C. Percent flowering plants and total flower bud number per plant was greatest when seedlings were induced with a 24 or 30 °C DT/30 °C NT regime. DT/NT did not affect the node number to first flower. Irradiance did not affect flowering. Temperature effects on P. nil flowering could be described as a function of average daily temperature, where flowering increased as temperature rose from 22 to 30 °C.
Pharbitis nil
Flower induction
Day length
Long day
Bud
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Pharbitis [Ipomoea] nil cv. Violet is an excellent model plant for the study of photoperiodic induction of flowering because it can be induced flowering by a single short-day. However there are few molecular-level studies of the induction of flowering in Pharbitis. To gain insight into the photoperiodic induction of flowering, we isolated an APETALA1-like gene (PnAP1), which showed high similarity to SQUAMOSA (SQUA) and AP1. PnAP1 expression at the shoot apex was induced only under flowering-inductive conditions, and PnAP1 expression was induced from 24 h after the start of the inductive dark period. Both night-break and low ambient temperature during the dark period effectively repressed PnAP1 expression and flowering. Timing of PnAP1 expression assessed through induced cotyledon removal indicated that the floral stimulus began to move from cotyledons 14 h after the start of the inductive dark period. The results indicate that floral transitions begin immediately after the inductive dark period and that PnAP1 is a good molecular marker of floral transition.
Pharbitis nil
Flower induction
Ipomoea
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The control of night-break timing was studied in dark-grown seedlings of Pharbitis nil (Choisy cv. Violet) following a single continuous or skeleton photoperiod. There was a rhythmic response to a red (R) interruption of an inductive dark period, and the phasing of the rhythm was influenced by the preceding light treatment.Following a continuous white light photoperiod of 6 hours or less, the points of maximum inhibition of flowering were constant in real time. Following a continuous photoperiod of more than 6 hours, maximum inhibition occurred at 9 and 32.5 hours after the end of the light period. The amplitude of the rhythm during the second circadian cycle was much reduced following prolonged photoperiods.Following a skeleton photoperiod, the time of maximum sensitivity to a R interruption was always related to the second pulse of the skeleton, R(2), with the first point of maximum inhibition of flowering occurring after 12 to 18 hours and the second after 39 hours. Without a second R pulse, the time of maximum sensitivity to a R interruption was related to the initial R(1) pulse. A ;light-off' or dusk signal was not mimicked by a R pulse ending a skeleton photoperiod; such a pulse only generated a ;light-on' signal and initiated a new rhythm.It is concluded that the timing of sensitivity to a R interruption of an inductive dark period in Pharbitis nil is controlled by a single circadian rhythm initiated by a light-on signal. After 6 hours in continuous white light, the phase of this rhythm is determined by the transition to darkness. Following an extended photoperiod, the timing characteristics were those of an hourglass; this seemed to be due to an effect on the coupling or expression of a single circadian timer during the second and subsequent cycles, rather than to the operation of a different timing mechanism.In addition to the effects on timing, the photoperiod affected the magnitude of the flowering response.
Pharbitis nil
Darkness
Dusk
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`Chandler' strawberry plants ( Fragaria Xananassa Duch.) were greenhouse grown under natural lighting and then placed into growth chambers at two constant temperatures of 16 and 26 °C and 2 daylengths of 9 h (SD) and 9-h photoperiod (NI) which was night interrupted with 3 hours of incandescent radiation at 30-45 μmol·s -1 ·m -2 PAR. Plants were given different numbers of inductive cycles in growth chambers and then moved to the greenhouse. Flowering and growth were monitored. Flowering was completely inhibited at 26 °C, regardless of pretreatment growing conditions such as pot sizes and plant ages, photoperiod, and inductive cycles. At 16 °C, SD promoted floral induction compared to NI under all inductive cycles except a 7-day induction. The minimum number of inductive cycles required at 16 °C for floral induction was dependent on photoperiod and prior greenhouse treatment. Flowering rate was also affected by greenhouse treatment, photoperiod, and inductive cycles. Runner production was affected by photoperiod and temperature × inductive cycle.
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ABSTRACT Experiments were carried out to determine whether a semidian (12 h) rhythm in flowering response operates in Pharbitis nil as the basis for photoperiodic time measurement. The effect of 5 min far‐red light followed by 85 min dark (FRD) given 4, 8,14 and 22 h before the end of a 48 h photoperiod on night‐break timing and critical night length was determined. When given 4 h before the end of a 48 h photoperiod, an interruption with FRD advanced the phase of the circadian rhythm in the night‐break inhibition of flowering. In contrast, earlier interruptions of the photoperiod had no effect on the phase of the rhythm. The critical night length was modified by FRD given 4 h (shortened) or 8 h (lengthened) before the end of the photo‐period; when given at other times FRD did not alter the critical night length. The results are discussed in relation to the basis for photoperiodic timekeeping, with particular reference to suggestions for the involvement of a semidian rhythm. A circadian model based on the concept of limit cycles is described.
Pharbitis nil
Infradian rhythm
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The endogenous content of ABA in the cotyledons of <em>Pharbitis nil</em> is high during the light phase before an inductive 16-h-long dark period. During the night, however, at the beginning, the level of ABA is relatively low with the tendency to increase during the second half of an inductive dark period. The dual effect of exogenous ABA on the <em>Pharbitis nil</em> flowering has been observed. ABA applied to the cotyledons on subthreshold photoperiod (12-h-long night) stimulates flower bud formation. On the other hand, however, ABA applied during an inductive (16-h-long) dark period, as well as applied to the medium of cultured plantlets, inhibits flowering. Thus, the flowering effect of ABA is clearly dependent on the state of flower induction which is different in plants growing on various photoperiods.
Pharbitis nil
Flower induction
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