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Changes in the rotational motion of paramagnetic and fluorescent lipid-soluble probes were used to assess the effects of putrescine, spermidine and spermine on the fluidity of microsomal membranes from primary leaves of bean (Phaseolus vulgaris L.). Surface probes were more strongly immobilized by physiological concentrations of the polyamines than probes that partitioned deep into the bilayer interior. Spermidine and spermine were more effective than putrescine at reducing membrane fluidity, and at equimolar concentrations, the polyamines and calcium had similar effects on the mobility of the membrane probes. Spermine had essentially equivalent effects on the fluidity of native membranes, heat-denatured membranes and liposomes prepared from the total lipid extract of the membranes, indicating that polyamines associate with membrane lipid. These results raise the possibility that some of the physiological effects previously attributed to exogenously added polyamines could reflect membrane rigidification rather than a true physiological response.

1986. Senescence in cut carnation flowers: Temporal and physiological relationships among water status, ethylene, abscisic acid and membrane permeability. -Physioi Plantarum 68' 323-328. Changes in water status, membrane permeability, ethylene production and levels of abscisic acid (ABA) were measured during senescence of cut carnation flowers (Dianthus caryophyllus L. cv. White Sim) in order to clarify the temporal sequence of physiological events during this post-harvest period. Ethylene production and ABA content of the petal tissue rose essentially in parallel during natural senescence and after treatment of young flowers with exogenous ethylene, indicating that their syntheses are not widely separated in time. However, solute leakage, refiecting membrane deterioration, was apparent well before the natural rise in ethylene and ABA had begun. In addition, there were marked changes in water status of the tissue, including losses in water potential {%fj and turgor (ijip), that preceded the rise in ABA and ethylene. As senescence progressed, ijj, continued to decline, but ijtp returned to normal levels. These temporal relationships were less well resolved when senescence of young flowers was induced by treatment with ethylene, presumably because the time-scale had been shortened. Thus changes in membrane permeability and an associated water stress in petal tissue appear to be earlier symptoms of flower senescence than the rises in ABA or ethylene. These observations support the contention that the climacteric-like rise in ethylene production is not the initial or primary event of senescence and that the rise in ABA titre may simply be a response to changes in water status.Additional key words -Plant growth regulators, post-harvest physiology, osmotic and water potentials.