No abstract

The volatile constituents of kiwifruit (Actinidia chinensis Planch.) have been investigated. The volatiles were collected and concentrated using vacuum steam distillation and freeze concentration. The concentrated distillate was analysed by gas chromatography, gas chromatography-mass spectrometry and reaction gas chromatography. Apart from methyl benzoate, all the components identified were alkyl and alkenyl esters, alcohols, aldehydes and ketones. The most abundant component was trans hex-2-enal. Odour evaluation of the components at the exit port of the gas chromatograph indicated that ethyl butanoate, hexanal and trans hex-2-enal are important contributors to the aroma of kiwifruit. One other component which does not show a peak in the chromatogram and which is not yet completely characterised may have particular significance.

The kinetics of phosphate uptake by exponentially growing Neurospora crassa were studied to determine the nature of the differences in uptake activity associated with growth at different external phosphate concentrations. Conidia, grown in liquid medium containing either 10 mM or 50 ,AM phosphate, were harvested, and their phosphate uptake ability was measured. Initial experiments, where uptake was examined over a narrow concentration range near that of the growth medium, indicated the presence of a low-affinity (high Kmn) system in germlings from 10 mM phosphate and a high-affinity (low

Bacterial protoplasts, treated with fusidic acid, have been used to examine the modes of action of various other antibiotics in vivo. This system, in which ribosomal function is severely impeded, is particularly useful for studying the actions of drugs which do not inhibit protein synthesis potently in vim. One such drug is spectinomycin which is here shown to be an inhibitor of translocation ; similar results were obtained with lincomycin and celesticetin. Althiomycin, conversely, was found to inhibit the peptidyl transferase reaction. Supplementary evidence for these conclusions was obtained by examining the effects of the drugs upon the isolated peptidyl transferase reaction in vivo and by studying their effects upon polyribosome stability. We conclude that lincomycin and celesticetin inhibit translocation only on those ribosomes which bear nascent peptides not exceeding a critical, but short, chain length. Recently, we have described the effects upon protein synthesis resulting from the addition of fusidic acid to intact bacterial protoplasts [l, 21. We now wish to demonstrate how fusidic acid-treated protoplasts can be used as a novel system for studying the modes of action of other antibiotics against bacterial protein synthesis in vivo.Fusidic acid inhibits protein synthesis by sequestering elongation factor G (EF-G) and guanosine diphosphate (GDP) on ribosomes [3] and the primary consequence of this effect is to prevent the binding of aminoacyl-tRNA into trhe ribosomal A site [l]. This sequence of events can be rationalized by hypothesizing that a ribosome possesses a single guanosine triphosphatase site, located in or near the 50-5 moiety of the A site, which is utilised alternately by EF-G during translocation of peptidyl-tRNA from the A to the P site and by elongation factor Tu (EF-Tu) during the binding of aminoacyl-tRNA into the A site [4,5].Inhibition of binding into the ribosomal A sites causes peptidyl-tRNA to be held in the P sites from which the nascent peptides can be readily released by incubation with puromycin. Thus, immediately following the addition of fusidic acid to protoplasts, treatment with puromycin results in almost quantitative release of such peptides. Subsequently, however the proportion of nascent peptides which resist release by puromycin gradually increases to around one third Abbreviations. EF-G, elongation factor G; EF-Tu, elongation factor Tu. of the total, at which point a steady-state is reached in which the nascent peptides enter and leave both A and P sites. Thus a greatly-slowed ribosomal cycle is eventually established in the presence of fusidic acid and nascent peptides are held for considerable periods of time in both A and P sites [Z]. Escape of nascent peptides from P sites can be explained by postulating breakdown of ribosome -EF-G -GDP -fusidic acid complexes thereby permitting binding of aminoacyl-tRNA into the now-vacant A sites and subsequent transfer of peptide moieties. Since these peptides are then constrained to remain in the A sites for some time (at le...

We have examined the expression of actinidin, a cysteine protease found in kiwifruit, over the course of fruit development. Protease activity was first seen in fruit that had reached about half their final weight, and rose to high levels at harvest. The 5'-flanking region (nucleotides -1301 to +58) of a kiwifruit actinidin gene was fused to the beta-glucuronidase (GUS)-coding region, and the chimaeric gene was introduced into transgenic petunia plants. Induction of the GUS gene was observed during the later stages of seed pod development, closely resembling the pattern of actinidin induction in fruit tissues of kiwifruit. Some GUS expression was also detected in the vascular system of the receptacle, leaves, stems and roots. A shorter promoter fragment consisting of nucleotides -115 to +58 conferred similar spatial and temporal regulation in some of the transgenic plants.