Characterization and Measurement of Anthocyanins by UV-Visible Spectroscopy

Water deficits cause a reduction in the rate of photosynthesis. Exposure to mild water deficits, when relative water content (RWC) remains above 70%, primarily causes limitation to carbon dioxide uptake because of stomatal closure. With greater water deficits, direct inhibition of photosynthesis occurs. In both cases limitation of carbon dioxide fixation results in exposure of chloroplasts to excess excitation energy. Much of this can be dissipated by various photoprotective mechanisms. These include dissipation as heat via carotenoids, photorespiration, CAM idling and, in some species, leaf movements and other morphological features which minimize light absorption. The active oxygen species superoxide and singlet oxygen are produced in chloroplasts by photoreduction of Oxygen and energy transfer from triplet excited chlorophyll to oxygen, respectively. Hydrogen peroxide and hydroxyl radicals can form as a result of the reactions of superoxide. All these species are reactive and potentially damaging, causing lipid peroxidation and inactivation of enzymes. They are normally scavenged by a range of antioxidants and enzymes which are present in the chloroplast and other subcellular compartments. When carbon dioxide fixation is limited by water deficit, the rate of active oxygen formation increases in chloroplasts as excess excitation energy, not dissipated fay the photoprotective mechanisms, is used to form superoxide and singlet oxygen. However, photorespiratory hydrogen peroxide production in peroxisomes decreases. Increased superoxide can be detected by EPR (electron paramagnetic resonance) in chloroplasts from droughted plants. Stiperoxide formation leads to changes suggestive of oxidative damage including lipid peroxidation and a decrease in ascorbate. These changes are not, however, apparent until severe water deficits develop, and they could also be interpreted as secondary effects of water deficit-induced senescence or wounding. Non-lethal water deficits often result in increased activity of superoxide dismutase, glutathione reductase and monodehydroascorbate reductase. Increased capacity of these protective enzymes may be part of a general antioxidative response in plants involving regulation of protein synthesis or gene expression. Since the capacity of these enzymes is also increased by other treatments which cause oxidative damage, and which alter the balance between excitation energy input and carbon dioxide fixation such as low temperature and high irradiance, it is suggested that water deficit has the same effect. Light levels that are not normally excessive do become excessive and photoprotective/antioxidative systems are activated. Some of the photoprotective mechanisms themselves could result in active oxygen formation. Photoinhibitory damage also includes a component of oxidative damage. During normally-encountered degrees of water deficit the capacity of the antioxidant systems and their ability to respond to increased active oxygen generation may be sufficient to prevent overt expression of damage. Desiccation-tolerant tissues such as bryophytes, lichens, spores, seeds, some algae and a few vascular plant leaves can survive desiccation to below 30-40% RWC, A component of desiccation damage in seeds and bacteria is oxygen-dependent. Desiccation causes oxidation of glutathione, a major antioxidant, and appearance of a free radical signal detected by EPR in a number of tissues suggesting that oxidative damage has occurred. In photosynthetic cells damage may arise from photooxidation. Disruption of membrane-bound electron tranport systems in partially hydrated tissue could lead to reduction of oxygen to superoxide. Oxidation of lipids and sulphydryl groups may also occur in dry tissue. Tolerant cells recover upon rehydration and arc able to reduce their glutathione pool. Non-tolerant species go on to show further oxidative damage including lipid peroxidation. It is difficult to attribute this subsequent damage to the cause or effect of death. Embryos in seeds lose desiccation tolerance soon after imbibition. This is associated with membrane damage that has been attributed to superoxide-mediated deesterification of phospholipids and loss of lipophilic antioxidants. These effects are discussed in relation to other mechanisms involved in desiccation tolerance. Contents Summary 27 I. Introduction 28 II. Generation of active oxygen and defence mechanisms in plant cells 29 III. The effect of water deficit on photosynthesis 31 IV. Mechanisms for active oxygen generation during water deficit 36 V. Evidence for oxidative damage during water deficit 39 VI. Desiccation 47 VII. Conclusions 52 Acknowledgements 53 References 53.

The role of active oxygen in the response of plants to water deficit and desiccation.

Volatile Fatty Acid Analyses of Blood and Rumen Fluid by Gas Chromatography

The isotopic composition of reduced organic carbon

Pectin is an important polysaccharide with applications in foods, Pharmaceuticals, and a number of other industries. Its importance in the food sector lies in its ability to form gel in the presence of Ca2+ ions or a solute at low pH. Although the exact mechanism of gel formation is not clear, significant progress has been made in this direction. Depending on the pectin, coordinate bonding with Ca2+ ions or hydrogen bonding and hydrophobic interactions are involved in gel formation. In low‐methoxyl pectin, gelation results from ionic linkage via calcium bridges between two carboxyl groups belonging to two different chains in close contact with each other. In high‐methoxyl pectin, the cross‐linking of pectin molecules involves a combination of hydrogen bonds and hydrophobic interactions between the molecules. A number of factors—pH, presence of other solutes, molecular size, degree of methoxylation, number and arrangement of side chains, and charge density on the molecule— influence the gelation o...

Chemistry and uses of pectin--a review.

Some of the most important physiological and biochemical processes that occur during the development and maturation of de Chaunac grape berries have been investigated. The studies included monitoring changes in the pH, in total and individual major acids, cations, sugars, anthocyanins and their biosynthetic enzymes. Brix, pH, K+, sugars and anthocyanins showed a sharp rise during and immediately after veraison. There was a concomitant rise in the activity of anthocyanin biosynthetic enzymes. Total acidity and malic acid content increased during the first four weeks and declined thereafter, reaching a steady level approximately five weeks later. The concentration of phosphoric acid showed a rise during the maturation process, while tartaric acid levels declined continuously. On the per gram basis, the levels of Na+ showed no consistent changes, while Ca++, Cu++, Mg++, and Mn++ showed sharp declines during the expansion period of the berries and steady, low levels during the maturation process. The data suggest that the majority of metabolic events in the berries come to a steady state approximately eight weeks after veraison under the climatic conditions of the northeastern United States.

Physiological and biochemical events during development and maturation of grape berries.

SEEDS usually exhibit their maximum germination potential soon after harvest, and as storage time increases, they lose vigour and eventually die. The rate of physiological ageing generally increases with increased moisture content and temperature1. In addition, certain xerophytic storage fungi (primarily Aspergillus spp.) can attack seeds in storage when seed moisture content is in equilibrium with relative humidities greater than 65% (ref. 1), and cause changes that mimic physiological ageing. Physiological changes accompanying physiological ageing1–5 and attack by storage fungi5 have been catalogued, but the basic biochemical events leading to these changes are not known. Harrington1 and Pammenter et al.6, however, have suggested that oxidation of unsaturated lipids may lead to free-radical formation. Free radicals may then damage cellular membranes and react destructively with macromolecules. Similar suggestions have been presented to explain ageing in several other systems7, and the results of experiments reported here indicate that free-radical formation may be important in seed deterioration. Theories of mechanisms of lipid oxidation indicate that fatty acids with two or more unsaturated bonds should be more labile and prone to form free radicals than more highly saturated acids8,9. Thus, if fatty acid oxidation and free-radical formation are occurring, the highly unsaturated acids should decrease as seeds deteriorate, whereas the quantity of saturated fats should remain constant in the absence of beta oxidation.

Association of lipid oxidation with seed ageing and death

SUMMARY— Bovine intramuscular lipids extracted from the semitendinosus, triceps brachii and longissimus dorsi muscles were fractionated into phospholipids and neutral fats by silicic acid column chromatography. In spite of the wide range in total fat content at each location, phospholipids were present in all three muscles at a level of approximately 500 mg per 100 g of muscle tissue. This result, coupled with the lower total fat content of the semitendinosus as compared to the other two muscles, indicated a significantly higher percentage of phospholipid material in the total fat from the semitendinosus as compared to the triceps brachii or longissimus dorsi.



The fatty acids were identified in both lipid fractions using retention time data obtained on both a polar and a non-polar column. The identity of the unsaturated fatty acids was confirmed when their peaks did not appear on the chromatographs obtained from brominated samples. There was significantly more C14:0 in the longissimus dorsi neutral fat fractions than in the semitendinosus neutral fat fractions. In the phospholipids, there was significantly more C16:0 and significantly less C18:0 in the longissimus dorsi as compared to either the semitendinosus or triceps brachii. Although the two lipid fractions of the longissimus dorsi contained slightly higher percentages of total saturated fatty acids than the corresponding fractions in the other two muscles, the effects were not significant.

Composition of Bovine Muscle Lipids at Various Carcass Locations

SUMMARY
Changes in the lipids of soybeans brought about by Rhizopus orysae during the production of tempeh were studied. The mold possesses strong lipase activity and caused the hydrolysis of over one-third of the neutral fat of the soybean during the three-day fermentation. The fatty acid composition of soybean tempeh was compared with that of cooked soybeans by vapor-phase chromatography of the methylesters. The neutral fat was composed of palmitic, stearic, oleic, linoleic, and linolenic acids, with linoleic acid predominating. These acids were liberated during fermentation in roughly the same proportions found in soybeans after heating 90 min at 100°C. During the most active mold growth, proportionately higher levels of palmitic acid were found, and the level of linoleic acid was somewhat lower. Except for the depletion of some 40% of the linolenic acid in the later stages of the fermentation, there apparently was no preferential utilization of any fatty acid.

Leonard R. Mattick

Papers

Physiological and biochemical events during development and maturation of grape berries.

Association of lipid oxidation with seed ageing and death

Composition of Bovine Muscle Lipids at Various Carcass Locations

Changes in Soybean Lipids During Tempeh Fermentationa,b

Anthocyanin composition of Brassica oleracea cv. Red Danish