Activation of replicon origins as a possible target for cytokinins in shoot meristems of Sinapis

Houssa, Claude; Jacqmard, A.; Bernier, Georges

doi:10.1007/bf00195883

Cited by 33 publications

(12 citation statements)

References 22 publications

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“…1A) and previously reported for maize endosperm (Jones ct al., 1990). Hence, these data are consistent with the hypoihesis that cytokinin may play a role in stimulating cell dlvision, as has been proposed in other tissue systems (Fosket and Short, 1973;Nishinari and Syono, 1986;Houssa et al, 1990).…”

Section: Time Course Of Developmental Eventssupporting

confidence: 79%

Role of Auxin in Maize Endosperm Development (Timing of Nuclear DNA Endoreduplication, Zein Expression, and Cytokinin)

1993

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The timing of developmental events and regulatory roles of auxin were examined in maize (Zea mays 1.) endosperms. Zeatin, zeatin riboside, and indole-3-acetic acid (IAA) levels were determined by enzyme-linked immunosorbent assay (ELISA). Zeatin and zeatin riboside increased to maximal concentrations at an early stage (9 d after pollination [DAP]), corresponding to the stage when cell division rate was maximal. In contrast, IAA concentration was low at 9 DAP and abruptly increased from 9 to 11 DAP, thus creating a sharp decline in the cytokinin to auxin ratio. Coincident with the increase in IAA was an increase in DNA content per nucleus, attributed to postmitotic DNA replication via endoreduplication. Exogenous application of 2,4-dichlorophenoxyacetic acid (2,4-D) at 5 or 7 DAP hastened the time course of DNA accumulation per nucleus and increased the average nuclear diameter, whereas 2-(para-ch1orophenoxy)isobutyric acid delayed such development. Exogenously applied 2,4-D hastened the accumulation of the zein polypeptides of apparent molecular masses of 12, 14, and 16 k D and the expression of mRNA hybridizing with a zein DNA probe.We conclude that an abrupt increase in auxin induces cellular differentiation events in endosperm, including endoredupliction and expression of particular zein storage proteins..Endosperm constitutes the majority of kemel dry matter in maize (Zea mays L.) and is the predominate sink for photosynthate and other assimilates during reproductive growth. Studies of the cytology and morphology of maize endosperm have indicated that its development, starting with the formation of the triploid primary endosperm nucleus at the time of fertilization, consists of several sequential stages: (a) mitosis, (b) cell enlargement and differentiation, (c) storage material accumulation, and (d) desiccation and maturation. The developmental events that precede rapid storage material accumulation are crucial for establishing the capacity for endosperm growth. Studies of genotypes differing in endosperm size and of environmental treatments that affect endosperm growth have indicated that cell number, cell size, and starch granule number are correlated with endosperm mass at maturity (Reddy and Daynard, 1983). Thus, the Supported in part by a fellowship from the Ministry of Education, Taiwan, Republic of China, to H.-S. L. and funds provided by U.S. Department of Agriculture, regional projects NE-157 and NE-175.

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Section: Time Course Of Developmental Eventssupporting

confidence: 79%

Role of Auxin in Maize Endosperm Development (Timing of Nuclear DNA Endoreduplication, Zein Expression, and Cytokinin)

1993

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“…(Table 1) (Fig. 4, Table 1), as was also the case in Sinapis where F was only slightly reduced (Houssa et al 1990).…”

Section: Methodsmentioning

confidence: 60%

“…For the purpose of replication, the eukaryotic chromosomal DNA is composed of many tandemly-joined replication units, or replicons, each with an origin where replication starts and proceeds in opposite directions at divergent forks (Van't Hof 1985;Campbell 1986). In Sinapis meristematic cells we found that the cytokinin halved the replicon size, implying that it activated latent replicon origins while it only slightly affected the fork-progression rate (Houssa et al 1990). …”

Section: Introductionmentioning

confidence: 96%

“…Using the vegetative shoot apical meristem of the dicotyledonous species Sinapis alba, we have previously observed that the most dramatic effect of a single application of a cytokinin was a 3.5-fold reduction in the dura-* Present address: Laboratoire de Cytog~n~tique, D~partement de Biologie, Universit6 Catholique de Louvain, Place Croix du Sud, 5, bte 13, B 1348 Louvain-la-Neuve, Belgium Abbreviations: BAP=benzylaminopurine; F=fork-progression rate; R = replicon size; TdR=thymidine Correspondence to: A. Jacqmard; FAX: 32(41)563831 tion of the S phase of DNA replication of the cell cycle (Houssa et al 1990). For the purpose of replication, the eukaryotic chromosomal DNA is composed of many tandemly-joined replication units, or replicons, each with an origin where replication starts and proceeds in opposite directions at divergent forks (Van't Hof 1985;Campbell 1986).…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Activation of latent DNA-replication origins: a universal effect of cytokinins

Houssa¹,

Bernier²,

Pieltain³

et al. 1994

Planta

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In a previous study (Houssa et al., 1990, Planta 181, 324-326) we observed that a single application of a low dose of benzylaminopurine, a cytokinin, resulted in the halving of the size of the units of DNA replication in the vegetative shoot meristem of Sinapis alba L., a dicotyledonous plant. The effect was due to the recruitment by the hormone of latent replication origins in the chromosomal DNA. Here we report that benzylaminopurine has the same effect in both the vegetative shoot meristem of a monocotyledonous species, Lolium temulentum L., and the tomato (Lycopersicon esculentum Mill.) ovule, a dicotyledonous reproductive meristem. It is thus tentatively concluded that activation of latent replication origins is an universal effect of cytokinins in the regulation of the cell-division cycle.

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“…During this period, secondary initiation sites of DNA replication are switched on [43], S-phase shortens [34] and the cell cycle becomes synchronous [8 ]. In Sinapis, the activation of secondary origins is a response to a component of the floral stimulus which may be a cytokinin [40]. What might be the function of such an activation is unknown, although the reordering of initiation sites may well facilitate changes in gene expression which are necessary for flower initiation to begin.…”

Section: Cell Cycle and Developmental Switchingmentioning

confidence: 99%