RESUMEN
Peak levels of 1-aminocyclopropane-l-carboxylic acid (ACC) in flower parts of ageing carnations (Dianthus caryophyllus L. cv Scanea 3C) were detected 6 to 9 days after flower opening. The ethylene climacteric and the first visible sign of wilting was observed 7 days after opening. The concentration of conjugated ACC in these same tissues peaked at day three with reduction of 70% by day 4. From day 5 to day 9 all parts followed a diurnal pattern of increasing in conjugate levels 1 day and decreasing the next. Concentrations of conjugated ACC were significantly higher than those of ACC in all ageing parts. Preclimacteric petals treated with ACC or 1-(malonylamino)-cycloprane-1-carboxylic acid (MACC), started to senesce 30 to 36 hours after treatment. When petals were treated with MACC plus by 0.1 millimolar aminoethyoxyvinylglycine, premature senescence was induced, while ethylene production was suppressed relative to MACC-treated petals. Petals treated with MACC and silver complex produced ethylene, but did not senesce. The MACC-induced ethylene was inhibited by the addition of 1.0 millimolar CoC1(2). These results demonstrate MACC-induced senescence in preclimacteric petals. The patterns of ACC and MACC detected in the flower parts support the view that an individual part probably does not export an ethylene precursor to the remainder of the flower inducing senescence.
RESUMEN
After 48 hours at 2 degrees C, hypocotyls from chill-sensitive Cucumis sativus seedlings showed a burst of O(2) uptake. The alternative pathway became engaged to close to 45% full capacity during this postchilling respiratory burst. However, it only accounted for up to 50% of this increased respiratory O(2) uptake. By 24 hours after chilling, when the seedlings were fully recovered from visible symptoms of chilling injury, the flux through the alternative pathway was back to the level (about 10%) found before chilling. Blocking chilling-induced ethylene production with aminoethoxyvinylglycine had no effect on this increased utilization of the alternative pathway.The direct effects of temperature on respiration rates and the effects of inhibitors suggested that there was a rapid increase in alternative pathway activity and decrease in the cytochrome pathway activity. The possibility that the alternative pathway represents a compensatory mechanism for the more labile cytochrome pathway is discussed.
RESUMEN
Embryos, excised from seed coats of soybeans (Glycine max Merr. cv. ;Wayne'), leak profusely during the first minutes of imbibition. A discontinuity of temperature/leakage patterns occurs between 10 and 15 C; as embryos imbibe at 10 C or lower, disproportionately more solutes leak out per unit of water imbibed. Short periods of imbibition at or below 12 to 14 C reduce embryo germination and axis elongation; injury results from imbibition at 2 C for as little as 5 minutes. Humidifying embryos to 35 to 50% moisture before imbibition reduced leakage during imbibition and imparted some resistance to imbibitional chilling injury.The period of profuse leakage is interpreted as a time of membrane reorganization. Imposing a low temperature during this period prolongs the rapid leakage, suggesting delayed or faulty membrane reorganization. Reduced cold sensitivity of embryos with an initial 35 to 50% moisture content is presumed to be due to at least partial membrane reorganization in the embryo before imbibition. These data collectively are taken to indicate that low temperature interferes with normal membrane reorganization during imbibition, probably by modifying the physical state of membrane phospholipids, and that the consequent abnormal organization of membranes is a basic cause of low temperature injury.
RESUMEN
Effects of CO(2) on mitochondrial activity of apple (Malus pumila Mill. var. Richared Delicious) were studied in two ways. Immediate effects were determined by imposing 3 to 18% CO(2)-bicarbonate mixtures on isolated apple mitochondria, and long term effects were determined by extracting mitochondria from apples that had been stored for intervals in atmospheres containing 6 or 12% CO(2) plus 3% O(2). The CO(2)-bicarbonate systems had immediate and broad effects on mitochondrial oxidations: 18% CO(2) stimulated malate oxidation about 10%; suppressed alpha-ketoglutarate, citrate, and NADH oxidations about 10%; and suppressed fumarate, pyruvate, and succinate oxidations about 32%. The effects of lower CO(2) concentrations varied with substrates. Mitochondria isolated from fruit stored in 6 or 12% CO(2) possessed a reduced capacity to oxidize added succinate or NADH, but retained a marked sensitivity to CO(2)-bicarbonate mixtures. Respiratory control in these mitochondria was somewhat reduced, but CO(2) had not acted as a strong uncoupling agent.
RESUMEN
Seedlings of corn (Zea mays) were tested for recovery from chilling injury incurred at 0.3 +/- 0.3 C. At 0.3 C visual leaf injury appeared in 36 hours, whereas stem and root injuries appeared later. Appearance of leaf injury was preceded by a rise in O(2) uptake and a lessened effect of 2,4-dinitrophenol on O(2) uptake by leaf segments and was accompanied by increased ion leakage from the leaves. These effects were reversible, in that transfer of seedlings to 21 C after 36 hours at 0.3 C produced a return of O(2) uptake, 2,4-dinitrophenol stimulation, and ion leakage to the levels of unchilled leaves, as well as a disappearance of leaf symptoms, within 72 hours. For most seedlings, transfer to 21 C after 48 to 60 hours at 0.3 C reversed the chilling effects on O(2) uptake, 2,4-dinitrophenol stimulation, and injury symptoms but not on ion leakage within 108 hours. However, some seedlings collapsed during 48 to 60 hours of chilling, and these never recovered. Transfer to 21 C after 72 hours at 0.3 C did not produce recovery from any symptom of chilling injury examined, and these seedlings soon died. No growth occurred at 0.3 C, but growth began soon after transfer to 21 C. Seedlings chilled 24 or 36 hours grew at reduced rates during the first 72 hours at 21 C, but within 96 hours at 21 C were growing at the same rate as nonchilled seedlings. These results demonstrate considerable capacity of growing plants to recover from short chilling treatments even though significant physiological changes occurred at low temperatures.