Extraction of Galactolipids from Waste By-Products: The Feasibility of Green Chemistry Methods

Galactolipids are a class of lipids present, inter alia, in the plastid membranes of plant cells. Apart from their biological significance, they are recognized as an important group of bioactive agents, especially in the treatment of osteoarthritis. The aim of this research was to evaluate the usefulness of the green chemistry approach in the extraction of these compounds. Waste products of food processing were selected as a raw material to improve the sustainability of the process even further, and their galactolipid content was investigated using an LC-MS analysis. The rosehip pomace, which was recognized as the most promising amongst materials used in this study, was subjected to supercritical fluid extraction (SFE) and ultrasound-assisted extraction (UAE). It transpired that SFE using pure CO2 was not an effective method for the extraction of galactolipids, although the use of ethanol as a cosolvent favored the separation. The results of UAE were also very promising—the improvement of the extraction yield up to 74% was observed. The green chemistry approaches used for galactolipid isolation were compared with a conventional processing method and proved to be an interesting alternative.

Phosphate deprivation induces transfer of DGDG galactolipid from chloroplast to mitochondria

In many soils plants have to grow in a shortage of phosphate, leading to development of phosphate-saving mechanisms. At the cellular level, these mechanisms include conversion of phospholipids into glycolipids, mainly digalactosyldiacylglycerol (DGDG). The lipid changes are not restricted to plastid membranes where DGDG is synthesized and resides under normal conditions. In plant cells deprived of phosphate, mitochondria contain a high concentration of DGDG, whereas mitochondria have no glycolipids in control cells. Mitochondria do not synthesize this pool of DGDG, which structure is shown to be characteristic of a DGD type enzyme present in plastid envelope. The transfer of DGDG between plastid and mitochondria is investigated and detected between mitochondria-closely associated envelope vesicles and mitochondria. This transfer does not apparently involve the endomembrane system and would rather be dependent upon contacts between plastids and mitochondria. Contacts sites are favored at early stages of phosphate deprivation when DGDG cell content is just starting to respond to phosphate deprivation.

705 PB 347 MEMBRANE LIPID COMPOSITION DURING RIPENING OF CALCIUM-INFILTRATED APPLE FRUIT

Postharvest Ca infiltration delays senescence and improves storage quality of apple fruit, but the consequences on membrane lipid composition have received little evaluation. We studied changes in galactolipids (mono- and digalactosyl-diacylglycerol; MGDG and DGDG) and sterol conjugates (sterol glycosides and acylated sterol glycosides; SG and ASG) in `Golden Delicious' cortical tissue. Fruit were pressure-infiltrated with CaCl, at harvest (0, 2, or 4% w/v), stored for 6 months at 0C, and evaluated during subsequent exposure to 20C. MGDG, SG and ASG concentrations were greater in Ca-infiltrated fruit (CIF) than in control fruit. A 35-37% increase in ASG occurred during the first 7 days at 20C in CIF, when ASG decreased by 19% in control fruit. Ca infiltration may delay degradation of plastid membranes and increase sterol conjugation during apple fruit ripening.

A Non-Metabolic Model of Acifluorfen Activity

The para-nitro substituted diphenyl ether herbicides which cause rapid plant pigment photo-bleaching can be divided into two categories: 1. those that have a photosynthetic requirement for activity (e.g. oxyfluorfen) and 2. those that have no apparent metabolic requirement for activity (e.g. acifluorfen). A model is presented for the latter category, in which the diphenyl ether herbicide interacts with carotenoids and/or chlorophyllide in plastid membranes to form a complex which photochemically generates singlet oxygen or lipid-peroxidizing radicals.

A Non-Metabolic Model of Acifluorfen Activity

The para-nitro substituted diphenyl ether herbicides which cause rapid plant pigment photo- bleaching can be divided into two categories: 1. those that have a photosynthetic requirement for activity (e.g. oxyfluorfen) and 2. those that have no apparent metabolic requirement for activity (e.g. acifluorfen). A model is presented for the latter category, in which the diphenyl ether herbicide interacts with carotenoids and/or chlorophyllide in plastid membranes to form a complex which photochemically generates singlet oxygen or lipid-peroxidizing radicals.

Preservation and separation of endomembrane marker enzyme activity in potato leaf homogenates

To minimize rapid browning and membrane degradation of crude microsomes, leaves of Solanum tuberosum (cv. Kennebec and cv. Katahdin) were initially homogenized in the presence of various inhibitors of polyphenol oxidase, phospholipase, and protease activity. To obtain and maintain marker enzyme activities used to identify plasma membranes, Golgi membranes, and endoplasmic reticulum, it was necessary to homogenize young leaves in the presence of sulfhydryls at pH 7.8. Further separation of these membranes, as determined by distribution of total activities of marker enzymes in linear sucrose density gradients, indicated a relatively pure plasma membrane fraction (1.15 g/cm3) free from contamination by thylakoids (1.19 g/cm3) and other endomembrane components. However, the distribution of specific activities across the gradient revealed that plasma membranes isolated from green tissue may be contaminated by Golgi membranes and not necessarily by plastid membranes.