Marine microalgae (152 species, 206 strains) from 12 classes were exam~ned for the presence of UVA-and UVB-absorbing compounds. Cultures were grown under white fluorescent light without supplementary UVA or UVB radiation and were extracted after harvest m tetrahydrofuran:methanol (20:80, v/v). Ratios of UV absorbance (280 to 390 nm) to chlorophyll a (chl a) (665 nm) obtained by spectrophotometry ranged from 0.18 to 6.75. Three groups of species were distinguished: those with low UV:chl a ratios (0.18 to 0.9, diatoms, green algae, cyanophytes, euglenophytes, eustlgmatophytes, rhodophytes, some dinoflagellates, some prymnesiophytes], those with intermed~ate ratlos (0.9 to 1.4, chrysophytes, some prasinophytes, some prymnesiophytes) and those with very high ratios (1.4 to 6.75, surface bloom-forming dinoflagellates, cryptoinonads, prymnesiophytes and raphidophytes). UV-absorbing pigments varied across species of the same algal class and strains of the same species. HPLC analysis of extracts of 5 species (1 diatom, 2 bloom-forming raphidophytes and 2 bloomforming dinoflagellates) showed suites of mycosporine-like amino acids in 4 of them, which included mycosporine-glycine, asterina-330, shinorme, porphyra-334 and palythine. The dinoflagellate Gymnodin~um catenatum also contained major quantities of unknown UV-absorbing compounds.

The control of rhythmic emission of floral volatiles emitted from Rosa damascena semperflorens cv. 'Quatre Saisons' throughout floral development under various light regimes was studied. 2-Phenylethanol was the major volatile emitted in addition to monoterpenols, oxidised monoterpenols, monoterpenes and aromatic compounds. All detected volatiles were emitted rhythmically, with maximum peaks coinciding 8-10 h into a 12-h photoperiod. For some compounds a secondary, nocturnal peak was apparent. The primary and secondary maxima both occurred at approximately 24-h intervals. Rhythms appeared to be regulated endogenously: rhythmic emission continued upon exposure to continuous light or continuous darkness, and a phase shift in emission was induced upon inversion of the photoperiod. Additionally, emission continued after flower excision. A similar profile of free volatiles was stored within the floral tissue, together with glycosidic forms of 2-phenylethanol (>99% beta-D-glucoside), benzyl alcohol, citronellol and geraniol. Regression analysis indicated a significant decrease in glycosylated 2-phenylethanol through the photoperiod. These results suggest that glycosylated volatiles stored within petals may be a source of rhythmically emitted volatiles.

This chapter selectively reviews research published since the preparation of Onions and Allied Crops [see Rabinowitch, H.D. and Brewster, J.L. Onions and Allied Crops, 3 Vols. CRC Press, Boca Raton, Florida. 1990, 273, 320 and 265 pp.], presenting significant advances in onion pre- and postharvest science.

To clarify the biosynthetic pathway to 2-phenylethanol (2), the deuterium-labeled putative precursor, [2H8]L-phenylalanine ([2H8-1]), was fed to the flowers of Rosa 'Hoh-Jun' and R. damascena Mill. throughout maturation, ceasing feeding at the commencement of petal unfurling and at full bloom. Based on GC-MS analyses, [2H8]-1 was incorporated into both 2 and 2-phenylethyl beta-D-glucopyranoside (3) when the flowers were fed until full bloom, whereas no such incorporation into 2 was apparent when feeding was ceased earlier. In both species of rose, the labeling pattern for 2 was almost identical to that for 3, and indicated the presence of [2H6]-, [2H7]- and [2H8]-2, and [2H6]-, [2H7]- and [2H8]-3. This may be ascribed to the equilibrium between 2 and 3. The labeling pattern for 2 and 3 also indicated that these compounds were produced from 1 via several routes, the route involving phenylpyruvic acid being the major one.