Various applications of biotechnological methods for the production of volatile compounds useful to the food and pharmaceutical industries are discussed. The yields obtained from intact or genetically modified plants are compared to those achieved by microbial methods. Plant yields are too low for the products to compete commercially to those synthesized chemically. Still lower yields are obtained with in vitro-cultured plant tissues. Trangenic plants with altered methylerythritol path gave 50% more essential oil in the best case. The 100-fold increases in shikimate-derived volatiles, obtained with overexpressed alcohol dehydrogenase and five-fold more C6 volatle aldehydes and 2-phenylethanol, were produced with overexpressed lipoxygenase and 2-phenylethanol dehydrogenase, respectively. However, the most spectacular yields were observed with biotransformations catalysed by microorganisms. Kluyveromyces marxianus, produces over 26 g/l 2-phenylethanol from phenyalanine, whereas Candida sorbophila, Mucor circillenoides or Yarrowia lipolytica can produce 5-40 g/l g-decalactone from ricinoleic acid. Vanillin production from ferulic acid is in the range 12-60 g/l with Amycolatopsis and Streptomyces species. Vanillin can be produced at 5 g/l by Escherichia coli and amorphadiene yields of 37 g/l have been observed with Saccharomyces cerevisiae, both with the genetically overexpressed methyl-erythritol path. Genetically engineered b-oxidation genes result in yields of 10 g/l g-decalactone byYarrowia lipolytica and up to 80 g/l dicaboxylic acids by various yeasts. These results far exceed the theoretical limit of about 1 g/l required for consideration of a procedure as a commercially interesting process, alternative to chemical sythesis.

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Low temperatures induce the accumulation of soluble sugars in plant cells. An attempt is made to identify the primary site of action of low temperatures and the sequence of physiological and biochemical events leading to sugar accumulation. The integration of all the available information points to a central role of increased intracellular calcium ion concentration generated by the inhibition of ATPases concerned with its homeostasis. A positive role of a cold-induced dysfunction of mitochondrial and chloroplast electron flow is also proposed. The biological significance of an explanation of this physiological response to a stress factor relies on its categorization into the major family of those employing alternative energy-producing pathways under stress conditions. More specifically, a connection of sugar mobilization to the needs of the cold-stressed cell to employ fermentative energy-producing mechanisms is made. From this ankle of view, new ways of genetically modifying the ability of plant cells to accumulate sugars become obvious.

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Isolation of genes controlling apomixis would be useful to plant breeders for fixing hybrid vigor. A single gene codes for aposporous apomixis in buffelgrass [Pennisetum ciliare (L.) Link]. This study was undertaken to assess the feasibility of using isozyme, protein, and random amplified polymorphic DNA (RAPD) markers to detect apospory‐linked sequences within a segregating half‐sib population. Sexual plant B‐2s, five sexual and three aposporous progeny of sexual B‐2s, and cultivar Higgins were studied. Floret and leaf proteins were separated by starch gel electrophoresis, and enzymes in the gel were stained to detect isozyme polymorphisms. Of 22 isozyme systems tested, 12 showed polymorphisms but none cosegregated with apomixis. Two‐dimensional polyacrylamide gel electrophoresis was used to separate steady state proteins of pistils at meiotic and post‐meiotic stages. This technique revealed ≈12% polymorphism within 308 spots, but none of the spots cosegregated with reproductive mode. Genomic DNA was screened for RAPD markers with 111 10‐mer random primers and polymerase chain reaction. Of 569 markers identified, 87% were polymorphic. One marker cosegregated with sexual lines, but none cosegregated with aposporous lines. Analysis of molecular variance examination of the B‐2s parent and the eight half‐sib progeny (Higgins excluded) showed that on the basis of 404 RAPD markers, the aposporous and sexual groups were not significantly different. No RAPD markers were tightly linked with apospory. Additional screening of new primers will allow identification of markers for the gene in full‐sib families.