Effects of osmotic preconditioning on nuclear replication activity in seeds of pepper {Capsicum annuum). -Physiol. Plant. 89: 433-440.Flow cytometric determination of nuclear DNA contents in embryos of dry, fully matured pepper seeds revealed only 2C signals. Therefore, pepper belongs to those species in which the quiescent embryo arrests nuclear division in the presynthetic G, phase. In whole seeds, two other peaks were observed which corresponded with the 3C and 6C DNA content and originated from the triploid endosperm. After 36 to 48 h of imbibition in water (48 to 60 h before visible germination), a rise in the 4C signal was observed in the root tip of the embryo. Osmotic preconditioning (priming) of pepper seeds for 7, 14 or 21 days in polyethylene glycol (PEG) or KNO3 + K3PO4 considerably reduced the time to 50% germination (t^,,) and the mean germination time, and the effect was proportional to the duration of the priming treatments. An induction of the 4C signal was firstly observed after 10 days osmopriming in either PEG or KNO3 + K3PO4. For both priming methods, a positive correlation was found between the efficiency of the treatment to reduce the mean germination time, and the induction of DNA synthesis, measured as the amount of 4C versus 2C, at 12 h before radicle protrusion. Apart from the quantitative effect, there was also a temporal influence of priming on DNA synthetic activity. When primed seeds were subsequently imbibed in water,'the induction of DNA synthesis started about 12 h earlier than in untreated seeds. This was also found for seeds primed for 7 days, when no induction of DNA synthesis had yet occurred. Apparently, during priming of pepper seeds there is a lag period of 9 days in which physiological processes other than DNA synthesis can take place. These processes sustain a rapid inception of nuclear replicative activity upon imbibition. By comparing the relative nuclear DNA contents of dry, imbibed and primed seeds, we provide information about the relation between the percentage of cells in seeds which have entered the replication stage of nuclear division, and germination performance. >>

Ageing of tomato seeds involves glutathione oxidation. -Physiol. Plant. 92: 131-139.The effect of seed ageing on the oxidation of reduced glutathione (GSH) and the role of GSH oxidation in ageing-induced deterioration were studied in seeds of tomato (Lycopersicon esculentum Mill, cv, Lerica, Moneymaker and Cromco). Both long-term storage al 15=C/305f relative humidity (RH) and artificial ageing at 20°CA759i: RH, 30<'C/45% RH and 60°C/45% RH resulted in a marked loss of GSH and a simultaneous, though not propottional, increase in its oxidized form GSSG. The glutathione thiol-disuifide status shifted towards a highly oxidized form, while the total glutathione pool decreased. The extent of GSH oxidation differed between ageing conditions and was not directly related to ihe extent of seed deterioration. Thiobarbituric acid-reactive substances did not increase in ageing tomato seeds, suggesting that lipid peroxidation did not take place. Hydration of seeds, either upon imbibition in water or by priming in an osmotic soiution. resulted in a rapid decrease in GSSG. a shift of the glutathione redox couple to a mainly reduced status and an increase in the glutathione pool, in both control and aged seeds. The results indicate that, in tomato seeds, (1) seed ageing involves GSH oxidation into GSSG, which is indicative of oxidative .stress, (2) ageing does not affect the GSSG reduction capacity upon subsequent imbibition, and (3) the lowered viabilitv of aged seeds cannot directly be ascribed to the decreased GSH pool or to the highly oxidized glutathione redox status.