Inhibition by polyamines of macromolecular synthesis and its implication for ethylene production and senescence processes

Polyamine content of long-keeping alcobaca tomato fruit

Fruit of tomato landrace Alcobaca, containing the recessive allele alc, ripen more slowly, with a reduced level of ethylene production, and have prolonged keeping qualities. The levels of polyamines in pericarp tissues of alc and ;wild type' Alc (cv Rutgers and Alcobaca-red) fruit were measured by HPLC in relation to ripening. Putrescine was the predominant polyamine with a lower content of spermidine, while spermine was just detectable. The level of putrescine was high at the immature green stage and declined in the mature green stage. In Alc fruit the decline persisted but in alc fruit the putrescine level increased during ripening to a level similar to that present at the immature green stage. There was no pronounced change or difference in spermidine levels. The enhanced polyamine level in alc fruit may account for their ripening and storage characteristics.

The effect of chemical facilitators on the frequency of electrofusion of tobacco mesophyll protoplast

Trypsin, pronase, protease, dispase, spermine, spermidine, and DMSO were characterized for their effect on the frequency of electrofusion of tobacco mesophyll protoplasts. Protease (Boehringer Mannheim) and Sigma pronase (1.26 mg/ml; 15 min incubation) increased the fusion frequency from 7% (control) to 20.7% (2.9X increase). Following protease and pronase were trypsin (2.8X), spermine (2.4X), dispase (2.1X), DMSO (2.0X), and spermidine (1.4X). BM Protease and polyamines caused the least amount of damage, followed by DMSO and trypsin (26% and 24% decrease in viability respectively), pronase (41%) and dispase (57%). Callus formed from all but dispase-treated protoplasts. Shoots regenerated from calli of all but trypsin-treated protoplasts.

Effects of polyamines on cyclic AMP-mediated stimulation of amino acid transport in isolated rat hepatocytes

The effects of natural polyamines on cyclic AMP-mediated stimulation of amino acid transport in isolated rat hepatocytes were analyzed. Despite the fact that polyamines could directly compete with alpha-aminoisobutyric acid (AIB) for uptake, preincubation of hepatocytes with polyamines did not significantly alter basal AIB transport. The stimulatory effect of glucagon or cyclic AMP analogs was differently affected by polyamines, since it was reduced in the presence of spermine and, inversely, potentiated by spermidine, putrescine, and cadaverine. Dose-dependence analysis showed that half maximal and maximal effects occurred with 2-3 and 6-10 mM external concentrations, respectively. None of the polyamine effects could be ascribed to transstimulation or transinhibition of amino acid uptake. The inhibitory effect exerted by spermine correlated its capacity to inhibit [3H]-leucine incorporation into proteins partially. The potentiating effect of the other polyamines did not result from stabilization of newly synthesized carrier proteins. Instead, the increase in Vmax of the high affinity transport component suggested that more carriers became available, presumably because polyamines facilitated their synthesis by interacting directly with one or several steps controlled by cyclic AMP. Polyamines appear to represent a new class of factors capable of modulating the cyclic AMP-mediated stimulation of amino acid transport, in hepatocytes.