Two morphologically distinct phenotypes of Centella asiatica (Type-1 and Type-2) in South Africa were compared in relation to the levels of triterpenoid saponins with the aim of assessing their potential for biotechnological manipulation of triterpenoid synthesis. The metabolites investigated included madecassoside and asiaticoside and their sapogenins madecassic-and asiatic acid; produced in cultured undifferentiated cells (cell suspensions and calli) and leaves. Weight determination in plant cell suspensions and the accumulation of secondary metabolites after 16 days for Type-1 and 20 days for Type-2 were investigated since these secondary metabolites accumulate during the period that follows the active growth phase. The four triterpenoids of interest were analysed and quantified by HPLC in crude ethanolic extracts. A difference in bioactive triterpenoids was exhibited that was tissue specific and varied between the two phenotypes. The triterpenoids from leaf tissue were more easily quantifiable in each phenotype than in the case of the undifferentiated cells (callus and cell suspensions), which had lower, but still quantifiable, levels of these targeted secondary metabolites. Leaves contained the highest triterpenoid levels (ranging from 1.8 to 5% dry weight for the triterpenoid acids and their glycosides, respectively), with the free acids occurring in a ratio of approximately 1:2.5 in relation to the glycoside content.

Significant improvements to microdrop extractions of triazine pesticides are realized by the intentional incorporation of an air bubble into the solvent microdroplet used in this microextraction technique. The increase is attributed partly to greater droplet surface area resulting from the air bubble being incorporated into the solvent droplet as opposed to it sitting thereon and partly to thin film phenomena. The method is useful at nanogram/liter levels (LOD 0.002-0.012 μg/L, LOQ 0.007-0.039 μg/L), is precise (7-12% at 10 μg/L concentration level), and is validated against certified reference materials containing 0.5 and 5.0 μg/L analyte. It tolerates water and fruit juice as matrixes without serious matrix effects. This new development brings a simple, inexpensive, and efficient preconcentration technique to bear which rivals solid phase microextraction methods.

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Static headspace sampling with solid-phase microextraction has been used in combination with GC-FID and GC-MS for the specific enrichment, identification and quantification of volatile methyl jasmonate secreted by wounded leaves of Arabidopsis thaliana. The microsample method of analysis was found to be precise, accurate, sensitive and rapid. The detection limit of the procedure is 1.5 ppb (approximately 1.3 ng) per injection, which is of adequate sensitivity to detect the natural baseline levels of methyl jasmonate (approximately 10-100 ng/g) present in plant tissues. The method can be applied to most plants, requires a minimum of sample material, and shows the additional advantage that it is suitable for automation and could thus be used for high-throughput screening.

Extracts from apple fruit (cultivar "Granny Smith") inhibited the cell-wall degrading polygalacturonase (PG) activity of Colletotrichum lupini, the causal agent of anthracnose on lupins, as well as Aspergillus niger PG. Southern blot analysis indicated that this cultivar of apple has a small gene family of polygalacturonase inhibiting proteins (pgips), and therefore heterologous expression in transgenic tobacco was used to identify the specific gene product responsible for the inhibitory activity. A previously isolated pgip gene, termed Mdpgip1, was introduced into tobacco (Nicotiana tabacum) by Agrobacterium-mediated transformation. The mature MdPGIP1 protein was purified to apparent homogeneity from tobacco leaves by high salt extraction, clarification by DEAE-Sepharose and cation exchange HPLC. Purified MdPGIP1 inhibited PGs from C. lupini and PGs from two economically important pathogens of apple trees, Botryosphaeria obtusa and Diaporthe ambigua. It did not inhibit the A. niger PG, which was in contrast to the apple fruit extract used in this study. We conclude that there are at least two active PGIPs expressed in apple, which differ in their charge properties and ability to inhibit A. niger PG. Graphical abstractBiochemical characterization of the apple polygalacturonase inhibiting protein1 was carried out by expression in a heterologous plant host, thus defining the activity of the product of this specific apple pgip gene. Article Outline