Abstract
Inhibition of ethylene biosynthesis in apple fruit discs by calcium and spermine differed in character in at least three respects: (i) as the fruit ripened inhibition due to spermine decreased whereas that by calcium increased; (ii) inhibition by calcium was transitory, whereas that by spermine was persistent; (iii) at temperatures below 12°C calcium inhibited more than spermine whereas above 12°C the reverse was true. Temperature-dependence of the spermine and calcium effect on ethylene biosynthesis was correlated with specific changes induced by them in the microviscosity of microsomal membranes of apple tissue. Pretreatment with calcium resulted in lower microviscosity of the membranes compared to those of buffer-treated discs and in both cases microviscosity increased with increase in temperature of incubating solution containing fruit discs. Spermine stabilized membrane fluidity in apple discs incubated at temperatures above 4°C, thereby preventing the natural increase in microviscosity which occurred with increasing incubation temperature. These effects of calcium and spermine on membrane microviscosity required preincubation of fruit discs with the test compound since addition of spermine or calcium directly to microsomal membranes immediately before assay had no effect on their microviscosity.
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