[beta]-Tubulin Accumulation and DNA Replication in Imbibing Tomato Seeds

Abstract

The activation of the cell cycle in embryo root tips of imbibing tomato (Lycopersicon esculentum Mill. cv Lerica) seeds was studied by flow cytometric analyses of the nuclear DNA content and by immunodetection of p-tubulin. With dry seeds, flow cytometric profiles indicated that the majority of the cells were arrested at the C , phase of the cell cycle. In addition, p-tubulin was not detectable on western blots. Upon imbibition of water, the number of cells in C , started to increase after 24 h, and a 55-kD fl-tubulin signal was detected between 24 and 48 h. Two-dimensional immunoblots revealed at least three different p-tubulin isotypes. Thus, p-tubulin accumulation and DNA replication were induced during osmotic priming. These processes, as well as seed germination rate, were enhanced upon subsequent imbibition of water, compared with control seeds that imbibed but were not primed. By contrast, when aged seeds imbibed, DNA replication, P-tubulin accumulation, and germination were delayed. In all cases studied, both DNA replication and p-tubulin accumulation preceded visible germination. We suggest that activation of these cell-cycle-related processes is a prerequisite for tomato seed germination. Furthermore, p-tubulin expression can be used as a parameter for following the initial processes that are activated during seed imbibition.

Exploring the Mechanism of Physcomitrella patens Desiccation Tolerance through a Proteomic Strategy

“…7) and the disappearance of tubulin (spots D1, D2, and D4), along with evidence presented earlier (Pressel et al, 2006;Proctor et al, 2007), indicate that the microtubules might be incompatible with the desiccated state. Interestingly, angiosperm embryos also lose microtubules at maturation (de Castro et al, 1995).…”

Cell Division and Subsequent Radicle Protrusion in Tomato Seeds Are Inhibited by Osmotic Stress But DNA Synthesis and Formation of Microtubular Cytoskeleton Are Not

“…cv Moneymaker) with a moisture content of 6.0% Ϯ 0.1% (on a fresh weight basis) were used in the present study. Seed cleaning, drying, and storage were as previously described (de Castro et al, 1995). Dry seeds were imbibed in water or Germination analysis was conducted on four replicates of 50 seeds placed on top of two layers of filter paper soaked with 6 mL of distilled water or Ϫ1.0 MPa PEG-6000 at 25°C Ϯ 1°C in darkness for 7 d. Germination was expressed as the percentage of seeds that exhibited 1-mm radicle protrusion.…”

“…With all samples, at least 10,000 nuclei were analyzed. Extraction and detection of ␤-tubulin by western blotting were conducted as described previously (de Castro et al, 1995(de Castro et al, , 1998.…”

“…The transition from quiescence to that of cell proliferation occurs during imbibition. In tomato seeds it is characterized by increasing numbers of radicle tip cells that are in the G 2 phase of the cell cycle (Bino et al, 1992;de Castro et al, 1995). This increase is accompanied by an accumulation of ␤-tubulin, not only during seed imbibition (i.e.…”

“…prior to radicle protrusion), but also during incubation in a solution of polyethylene glycol (M r 6,000) that prevents radicle protrusion (de Castro et al, 1995(de Castro et al, , 1998. Both the relative number of cells in G 2 and the level of ␤-tubulin are correlated with enhanced seed performance after osmotic treatment ("priming effect") (de Castro et al, 1995).…”