Changes in the carbohydrate content of the leaf and the apical bud of Sinapis during transition to flowering

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Nanogram tissue samples from apical meristems of Sinapis alba were assayed for sucrose, total soluble hexosyl equivalents (-glucose and fructose plus hexoses from sucrose hydrolysis), and total soluble glucosyl equivalents (-glucose plus glucose from sucrose hydrolysis). On dry weight basis, sucrose concentration increased by more than 50% within 10 hours after the start ofeither a long photoperiod or a short photoperiod displaced by 10 hours in the 24-hour cycle ('displaced short day'). (These treatments induce flower initiation) Glucose and fructose concentrations were close to zero in vegetative meristems and remained low compared to sucrose in meristems of induced plants. Within a single meristem, the peripheral and the central zones had similar concentrations of sucrose. Our results indicate that an early physiological event in floral transition is the accumulation of sucrose in the meristem.The transition of a vegetative meristem to a floral meristem is marked by several histological, cellular, physiological, and molecular changes (2); those events that are associated with an irreversible commitment of the meristem to initiate flowers constitute the 'evocation' (12). One physiological change that is associated with floral transition in photoperiodic-and coldrequiring plants is an increase of the soluble carbohydrate concentration in the apical bud (7). In Sinapis alba, this increase has been observed regardless of the environmental inductive treatment (3,4) peripheral zone (13,17,19). At floral evocation, both the central and the peripheral zones are activated mitotically and the pithrib meristem progressively vacuolates and disappears (2,13).At least in Tradescantia paludosa, the mitotic activity of the central zone is influenced by nutritional factors (27). Thus, one possibility is that the central zone of the vegetative meristem is relatively deprived ofnutrients and that an increase ofassimilates in it is a prerequisite for floral transition (23). However, there are no data in support of this hypothesis.The highly sensitive methods for quantitative histochemical analysis described by Lowry and Passonneau (16, see also 20) are well suited to study the metabolite content of the meristem. Using these methods, we have measured the sucrose content of the peripheral zone and central zone of the apical meristem of Sinapis plants, which were induced to flower by one LD or by one displaced SD. Total soluble hexosyl equivalents and total soluble glucosyl equivalents were measured also, but with less morphological resolution. MATERIALS AND METHODSPlant Material. Sinapis alba plants were cultured as described elsewhere (3). Vegetative plants were maintained by growing them under 8-h photoperiods (SD). Sixty-five-d-old plants were induced to flower either by one 22-h LD or by one 8-h displaced SD (Fig. 1). Subsequently, the induced plants were returned to the standard SD regime. The meristem of induced plants will be referred to as 'evoked' to signify that the meristem ofthese plants is undergoing evocat...

mentioning

confidence: 92%

mentioning

confidence: 92%

“…One physiological change that is associated with floral transition in photoperiodic-and coldrequiring plants is an increase of the soluble carbohydrate concentration in the apical bud (7). In Sinapis alba, this increase has been observed regardless of the environmental inductive treatment (3,4) peripheral zone (13,17,19). At floral evocation, both the central and the peripheral zones are activated mitotically and the pithrib meristem progressively vacuolates and disappears (2,13).…”

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confidence: 97%

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Elevation in the Sucrose Content of the Shoot Apical Meristem of Sinapis alba at Floral Evocation

Bodson

Outlaw²

1985

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“…It is concluded that sucrose may be an important controlling factor determining floral initiation in Brassica. found in cauliflower (6,17) and Sinapis (3,4). Direct addition of sucrose to the medium in which stem tips of the LD plant Sinapis were grown in sterile culture induced flowering under SD (5), suggesting that under some conditions floral initiation may be causally dependent on carbohydrate supply.…”

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confidence: 99%

Promotion of Flowering in Brassica campestris L. cv Ceres by Sucrose

Friend

Bodson²,

Bernier³

1984

Flower initiation of the quantitative long-day plant Brassica campestris cv Ceres was earlier and at a lower final leaf number when sucrose was added to the medium in which plants were grown in sterile culture. The optimal concentration of sucrose was 40 to 80 millimolar. This flowerpromoting effect of sucrose was not osmotic, as mannitol, sodium chloride, and polyethylene glycol were not effective at equal osmotic potentials.Seedlings grown heterotrophically after treatment with 4-chloro-5- found in cauliflower (6, 17) and Sinapis (3, 4). Direct addition of sucrose to the medium in which stem tips of the LD plant Sinapis were grown in sterile culture induced flowering under SD (5), suggesting that under some conditions floral initiation may be causally dependent on carbohydrate supply.The quantitative LD plant Brassica campestris cv Ceres was selected for its small size, seedling sensitivity to daylength, and rapid response (9). Floral initiation is earlier, the higher the photon flux density under which plants are grown, and both HIR and phytochrome responses are involved (7). A linear relationship between the reciprocal of daylength and time to floral initiation and the equal effectiveness of fluorescent and incandescent light given at equal PAR, suggested that photosynthesis plays a quantitative role in the induction of flowering (8).These experiments were designed to determine whether increasing the carbohydrate supply of either green plants or plants treated with Sandoz 6706 to prevent Chl accumulation would increase the quantitative effects of daylength and photon flux density on flower initiation in Brassica seedlings. The effect of reducing the carbohydrate supply was studied by using C02-free air to restrict the rate of photosynthesis.

“…Numerous studies with monocarpic and polycarpic species showed that flower initiation and development have apparently higher light flux requirements than continued leaf initiation (18). There is also considerable evidence, for many photoperiodic species, that high photon flux may replace all or part of the day length requirements for the transition from vegetative to reproductive development (2,3,9,15,18). Since the high light flux is generally in the photosynthetically active range, it seemed as ifchanged levels ofphotosynthesis, or assimilates derived therefrom, played an important role in inductive processes in the leaves and/or as a morphogenetic signal in the shoot apical meristem (5,10 (16,17).…”

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confidence: 99%

Flowering in Bougainvillea

Ramina

Hackett²,

Sachs³

1979

Early concepts of the control of reproductive development emphasized the importance of nutritional parameters (7,8,11,14), particularly C/N ratios in the entire plant (12). Many of these ideas were not sustained in subsequent studies (13), and, hence, nutritional hypotheses were assigned a supportive rather than regulatory role in reproductive development. Numerous studies with monocarpic and polycarpic species showed that flower initiation and development have apparently higher light flux requirements than continued leaf initiation (18). There is also considerable evidence, for many photoperiodic species, that high photon flux may replace all or part of the day length requirements for the transition from vegetative to reproductive development (2,3,9,15,18). Since the high light flux is generally in the photosynthetically active range, it seemed as ifchanged levels ofphotosynthesis, or assimilates derived therefrom, played an important role in inductive processes in the leaves and/or as a morphogenetic signal in the shoot apical meristem (5, 10). Bodson (2) obtained evidence for an early increase, before cytological evidence for evocation, in carbohydrate levels in apical buds of Sinapis following induction by LD3 or displaced SD.In a comprehensive review of the effects of nutritional factors, acting as substrates or osmotica, on tissue differentiation and organogenesis, Allsopp (1) assigned a determining, not merely ' Permanent address: