Simultaneous measurements of H+ and O2 fluxes in Zostera marina and its physiological implications.

Zostera marina (eelgrass) is an important ecological component of many shallow, temperate lagoons. Evidence suggests that Z. marina has a high bicarbonate utilization capability, which could be promoted by possible proton extrusion and the consequent formation of an 'acid zone' in the apoplastic space (unstirred layer) of its leaves. It has been found that 50 mM of the buffer Tris significantly inhibited the photosynthetic O(2) evolution of Z. marina and it was proposed that this was because of Tris's ability to bond with protons outside the cell wall. To investigate if H(+) played an important role in the photosynthetic carbon utilization of Z. marina, it is very important to simultaneously monitor the photosynthesis status and possible H(+) fluxes. However, probably because of the lack of suitable techniques, this has never been attempted. In this study, experiments were undertaken on Z. marina by monitoring H(+) and O(2) fluxes and the relative electron transport rates during light-dark transition. During stable photosynthesis, in addition to an obvious O(2) outflow, there was a significant net H(+) influx connected to Z. marina photosynthesis. The inhibitory effects of both Tris and respiration inhibitors on apparent O(2) evolution of Z. marina were confirmed. However, evidence did not support the proposed Tris inhibition mechanism.

Synthesis of apiose-containing oligosaccharide fragments of the plant cell wall: fragments of rhamnogalacturonan-II side chains A and B, and apiogalacturonan.

Fragments of pectic polysaccharides rhamnogalacturonan-II (RG-II) and apiogalacturonan were synthesised using p-tolylthio apiofuranoside derivatives as key building blocks. Apiofuranose thioglycosides can be conveniently prepared by cyclization of the corresponding dithioacetals possessing a 2,3-O-isopropylidene group, which is required for preservation of the correct (3R) configuration of the apiofuranose ring. The remarkable stability of this protecting group in apiofuranose derivatives requires its replacement with a more reactive protecting group, such as a benzylidene acetal which was used in the synthesis of trisaccharide ß-Rhap-(1→3')-ß-Apif-(1→2)-α-GalAp-OMe. The X-ray crystal structure of the protected precursor of this trisaccharide has been elucidated.