The Role of the Cell Cycle Machinery in Resumption of Postembryonic Development

Abstract

Cell cycle activity is required for plant growth and development, but its involvement in the early events that initiate seedling development remains to be clarified. We performed experiments aimed at understanding when cell cycle progression is activated during seed germination, and what its contribution is for proper seedling establishment. To this end, the spatial and temporal expression profiles of a large set of cell cycle control genes in germinating seeds of Arabidopsis (Arabidopsis thaliana) and white cabbage (Brassica oleracea) were analyzed. The in vivo behavior of the microtubular cytoskeleton was monitored during Arabidopsis seed germination. Flow cytometry of Arabidopsis germinating seeds indicated that DNA replication was mainly initiated at the onset of root protrusion, when germination reached its end. Expression analysis of cell cycle genes with mRNA in situ localization, b-glucuronidase assays, and semiquantitative reverse transcription-polymerase chain reaction showed that transcription of most cell cycle genes was detected only after completion of germination. In vivo green fluorescent protein analysis of the microtubule cytoskeleton demonstrated that mitosis-specific microtubule arrays occurred only when the radicle had started to protrude, although the assembly of the microtubular cytoskeleton was promptly activated once germination was initiated. Thus, seed germination involves the synthesis and/or activation of a reduced number of core cell cycle proteins, which only trigger DNA replication, but is not sufficient to drive cells into mitosis. Mitotic divisions are observed only after the radicle has protruded and presumably rely on the de novo production of other cell cycle regulators.Seed germination is the process by which the plant embryo resumes growth after a period of quiescence. Under favorable conditions, rapid growth of the embryo culminates in rupture of the covering layers and emergence of the radicle, which is considered the completion of germination. At this stage, the decision of individual embryo cells to reenter the cell cycle or to remain arrested is crucial to determine seedling formation. The building of plant shape and function depends on the ability of the embryo cells to resume division and differentiate. Understanding how the cell cycle genes work at this particular phase of plant development might help to clarify the cellular and structural events that bring a quiescent embryo to a metabolically active plant.Cell cycle is a coordinated cyclic series of events, occurring between the end of subsequent cell divisions, by which cellular material is duplicated and divided between daughter cells. Thus, cell cycle consists of two major events, DNA replication (S phase) and mitosis (M phase) separated by two gap phases, G1 and G2 (for review, see Dewitte and Murray, 2003). The G1 phase is assumed to be the gate through which most cells resume cell cycle progression after a nonproliferative period. Additionally, G1-to-S transition is the central target of the cross-talk betwe...

Plant-derived smoke induced activity of amylases, DNA replication and β-tubulin accumulation before radicle protrusion of dormant Avena fatua L. caryopses

“…There are data showing that radicle protrusion does not require the cell cycle activation (Baíza et al 1989;Jing et al 1999), whereas others indicate that activation of the cell cycle takes place prior to radicle protrusion (de Castro et al 2000;Barrôco et al 2005;Masubelele et al 2005;Gendreau et al 2008). In dry and dormant A. fatua caryopses imbibed in water at 20°C, 93% of cells in the radicle with coleorhiza (RC) were arrested at the G 1 phase (Table 5; Cembrowska-Lech and Kępczyński 2016).…”

Screening of Antioxidant Compounds During Sprouting of Brassica oleracea L. var. costata DC

“…As observed with B. oleracea leaves and seeds [20,[30][31] shikimic (6) and fumaric (7) acids were present in small amounts, representing less than 0.5 and 2% of total acids, respectively ( Table 3). While fumaric acid showed behaviour similar to that exhibited by malic acid, shikimic acid displayed an opposite tendency, significantly decreasing until 6 days of germination.…”

“…In this process triggered by the imbibition of water, the plant embryo resumes growth after a period of quiescence [6]. The germination process implies a series of active and complex biochemical and physiological reactions, resulting in extensive changes in composition and/or morphology [7,8].…”

“…Previous work with B. oleracea sprouts concerned the genetic characterization of seed germination [25,26], monitorization of cell cycle modifications during the first divisions of the seeds [6], sensitivity to hypoxia [18], and the ability of seeds produced under a drought to germinate normally [27]. Other studies have dealt with the ability of seeds to biosynthesize and incorporate erucic acid into triacylglycerols [28] and the activity and distribution of peroxidases isozymes in germinating seeds [29].…”

Plant growth inhibitory activity of medicinal plant Hyptis suaveolens: could<br>allelopathy be a cause?

“…The germination bioassay was laid out using a completely randomized design with three replications. Seeds that showed the emergence of the radical by rupturing the seed coat were considered to be germinated as described by Barrôco et al (2005) and Faria et al (2005). Germination of seeds was recorded at every 12 h intervals for four days.…”