Comparison of the Disruption of Mitosis and Cell Plate Formation in Oat Roots by DCPA, Colchicine and Propham

Holmsen, J. D. and Hess, F. D. 1985. Comparison of the disruptionof mitosis and cell plate formation in oat roots by DCPA, colchicineand propham.—J. exp. Bot. 36: 1504–1513. Concentrationsof DCPA, propham and colchicine were selected to cause from0% to greater than 60% inhibition of oat (Avena sativa L. ‘Victory’)root growth after 24 h exposure. Root growth progressively declinedas concentrations were raised from 1·0 to 5·6mmol m^–3 DCPA, 1·0–5·0 mmol m^–3propham, and 50–500 mmol m^–3 colchicine. In additionto inhibiting root growth each mitotic disrupter caused theroot tips to swell to an extent dependent upon concentration.All three compounds effectively disrupted mitosis at concentrationsthat caused less than maximal root growth inhibition. Mitoticdisruption was manifest as a reduction in the number of normalmitotic figures and an increase in the number of condensed prophase,multipolar and anaphase bridge division figures. The frequencyof each type of division figure was different for each of thethree compounds. DCPA disrupted mitosis more effectively whencompared with propham and colchicine at concentrations whichcaused the same amount of root growth inhibition. Each mitoticdisrupter also induced the formation of aberrant cell walls.DCPA was the most effective at disrupting cell plate formation,whereas colchicine was least effective. These data suggest thatthe mechanism of action of DCPA is distinct from the mechanismof colchicine or propham Key words: Avena sativa L., mitotic disruption, DCPA, colchicine, propham     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

The cytochemical localization of oxidative enzymes. II. Pyridine nucleotide-linked dehydrogenases

Methods are presented for the intramitochondrial localization of various diphosphopyridine nucleotide and triphosphopyridine nucleotide-linked dehydrogenases in tissue sections. The cytochemical reactions studied involve the oxidation of the substrates by a specific pyridino-protein. The electron transfer of tetrazolium salt is mediated by the diaphorase system associated with the dehydrogenase. The final electron acceptor was either p-nitrophenyl substituted ditetrazole (nitro-BT) or N-thiazol-2-yl monotetrazole (MTT), the latter giving rise to metal formazan in the presence of cobaltous ions. Mitochondrial localization of the formazan precipitate could be achieved by using hypertonic incubating media containing high concentrations of substrate and co-enzyme. A fast reduction of tetrazolium salt was obtained by chemically blocking the respiratory chain enzymes beyond the flavoproteins. Although diaphorase systems are implicated in the reduction of tetrazolium salts, specific dehydrogenases are solely responsible for the distinct distribution pattern obtained in tissues with various substrates. The present findings in tissue sections are discussed in conjunction with existing biochemical evidence from differential centrifugation experiments.