Experimental Cytology of the Shoot Apical Cells during Vegetative Growth and Flowering

Nougarède, Arlette

doi:10.1016/s0074-7696(08)60815-3

Cited by 99 publications

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“…Since this change is ubiquitous, it may re¯ect the unfolding within the SAM at¯oral transition of a single ®eld with increased Pd connectivity. Increased Pd connectivity may be related to increased cell homogeneity, corresponding possibly to the so-called`pre¯oral phase' during which the zonation fades away in transitional SAMs, including the Sinapis SAM (NougareÁ de 1967;Bernier et al 1981b;Lyndon 1998). A similar increase in Pd frequency was reported for the CZ of the transitional SAM of Rudbeckia bicolor, an LD plant of the family Asteraceae Nikiforova 1995, 1996).…”

Section: Discussionmentioning

confidence: 99%

“…A similar increase in Pd frequency was reported for the CZ of the transitional SAM of Rudbeckia bicolor, an LD plant of the family Asteraceae Nikiforova 1995, 1996). Although the Rudbeckia SAM was examined at a single time point of the¯oral transition (8 d after the start of the LD induction; at a stage corresponding apparently to the pre¯oral phase; Milyaeva et al 1991), the PZ was not studied in Rudbeckia, and the structural details of the¯oral transformation of the SAM are very di erent in Asteraceae and Brassicaceae (NougareÁ de 1967;Bernier et al 1981b). However, it is noteworthy that the Pd frequency changes were in the same direction in Rudbeckia and Sinapis.…”

Section: Discussionmentioning

confidence: 99%

“…In particular, its cytohistological zonation fades away and ultimately disappears (NougareÁ de 1967;Lyndon 1998), and the pattern of gene activity is completely changed. For instance, up-regulation of some genes like Arabidopsis TFL1 or Sinapis SaMADS A and FPF1 is observed at particular times and in particular areas of the transitional SAM (Menzel et al 1996;Bradley et al 1997;Kania et al 1997).…”

Section: Introductionmentioning

confidence: 99%

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The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition

Orménèse

Havelange

Deltour

et al. 2000

Planta

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Abstract. The frequency of plasmodesmata increases in the shoot apical meristem of plants of Sinapis alba L. induced to¯ower by exposure to a single long day. This increase is observed within all cell layers (L1, L2, L3) as well as at the interfaces between these layers, and it occurs in both the central and peripheral zones of the shoot apical meristem. The extra plasmodesmata are formed only transiently, from 28 to 48 h after the start of the long day, and acropetally since they are detectable in L3 4 h before they are seen in L1 and L2. These observations indicate that (i) in the Sinapis shoot apical meristem at¯oral transition, there is an unfolding of a single ®eld with increased plasmodesmatal connectivity, and (ii) this event is an early e ect of the arrival at this meristem of the¯oral stimulus of leaf origin. Since (i) the wave of increased frequency of plasmodesmata is 12 h later than the wave of increased mitotic frequency (A. Jacqmard et al. 1998, Plant cell proliferation and its regulation in growth and development, pp. 67±78; Wiley), and (ii) the increase in frequency of plasmodesmata is observed in all cell walls, including in walls not deriving from recent divisions (periclinal walls separating the cell layers), it is concluded that the extra plasmodesmata seen at¯oral transition do not arise in the forming cell plate during mitosis and are thus of secondary origin.Key words: Floral transition ± Plasmodesmata formation ± Secondary plasmodesmata ± Shoot apical meristem ± Sinapis (¯oral transition) IntroductionThe vegetative shoot apical meristem (SAM) in dicots has the shape of a dome and consists of a relatively small number of undi erentiated dividing cells arranged in layers (Lyndon 1998). Cells of the two most super®cial layers, L1 and L2, divide anticlinally (perpendicular to the meristem surface), except those L2 cells in the peripheral sectors involved in organogenesis that may divide periclinally (parallel to the meristem surface). Layers L1 and L2 collectively form the tunica which is responsible for surface growth of the SAM. The L3 cells, i.e. all cells below L1 and L2, divide in all planes and collectively form the corpus which is responsible for the growth in SAM volume. Given this pattern of orientation of cell divisions, cell walls in the SAM are not all of the same age: anticlinal walls in the tunica and all walls in the corpus are younger, i.e. derive from more recent divisions, than the periclinal walls in the tunica. A cytohistological zonation is usually superimposed on this layered structure, with the centrally located cells of both the tunica and corpus dividing less frequently and having less RNA and protein than the peripherally located cells of these tissues (Steeves and Sussex 1989;Lyndon 1998).During the¯oral transition, although the layered structure persists, other aspects of SAM structure and activity are profoundly altered (Lyndon 1998). In particular, its cytohistological zonation fades away and ultimately disappears (NougareÁ de 1967;Lyndon 1998), and the pattern o...

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition

Orménèse

Havelange

Deltour

et al. 2000

Planta

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“…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).…”

Section: Introductionmentioning

confidence: 99%

“…Within the meristem, there are three different histological regions: (a) the central zone at the summit of the dome; (b) the peripheral zone-which is the site of organogenesis-on the flanks of the meristem; and (c) the pith-rib meristem located internally just underneath the central zone 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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Elevation in the Sucrose Content of the Shoot Apical Meristem of Sinapis alba at Floral Evocation

Bodson

Outlaw²

1985

Plant Physiol.

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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...

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Apical Meristems

Francis¹

2008

Encyclopedia of Life Sciences

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Apical meristems are regarded generically, as the growing tips of the higher plant. However, neither the shoot apical meristem (SAM) nor the root apical meristem (RAM) is apical, the former is protected by young unexpanded leaves and the RAM by the root cap. The SAM is an exponentially growing morphogenetic centre, it initiates leaves, flowers, nodes and internodes and in culture can regenerate a whole plant. Genes that regulate the SAM include the homeodomain genes, WUSCHEL ( WUS ), SHOOTMERISTEMLESS ( KNOTTED ), KNOTTED‐like genes and the WUS‐related WOX9 together with the nonhomeodomain CLAVATA gene family. Leaf initiation, an event characterized by an early change in the plane of cell division on the flanks of the SAM, is characterized by the expression of MGOUN while AINTEGUMENTA expression is restricted to the primordium. The RAM shows steady‐state growth kinetics and roots in culture form more roots. QUIESCENT CENTRE HOMOBOX ( QHB ) is a gene expressed in the quiescent centre, a population of slowly dividing founder cells that is located at the pole of the RAM. QHB may function in a manner analogous to WUS . However, ROOTMERISTEMLESS is a nonhomeodomain gene that is also central to normal function of the RAM .

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Experimental Cytology of the Shoot Apical Cells during Vegetative Growth and Flowering

Cited by 99 publications

References 296 publications

The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition

The frequency of plasmodesmata increases early in the whole shoot apical meristem of Sinapis alba L. during floral transition

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

Apical Meristems

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