Pigments are present in all living matter and provide attractive colors and play basic roles in the development of organisms. Human beings, like most animals, come in contact with their surroundings through color, and things can or cannot be acceptable based on their color characteristics. This review presents the basic information about pigments focusing attention on the natural ones; it emphasizes the principal plant pigments: carotenoids, anthocyanins, and betalains. Special considerations are given to their salient characteristics; to their biosynthesis, taking into account the biochemical and molecular biology information generated in their elucidation; and to the processing and stability properties of these compounds as food colorants.

Natural Pigments: Carotenoids, Anthocyanins, and Betalains — Characteristics, Biosynthesis, Processing, and Stability

Carotenoids are integral and essential components of the photosynthetic membranes in all plants. Within the past few years, genes encoding nearly all of the enzymes required for the biosynthesis of these indispensable pigments have been identified. This review focuses on recent findings as to the structure and function of these genes and the enzymes they encode. Three topics of current interest are also discussed: the source of isopentenyl pyrophosphate for carotenoid biosynthesis, the progress and possibilities of metabolic engineering of plants to alter carotenoid content and composition, and the compartmentation and association of the carotenogenic enzymes. A speculative schematic model of carotenogenic enzyme complexes is presented to help frame and provoke insightful questions leading to future experimentation.

Genes and enzymes of carotenoid biosynthesis in plants

Carotenoid biosynthesis in flowering plants.

▪ Abstract The recent impressive progress in research on gibberellin (GA) biosynthesis has resulted primarily from cloning of genes encoding biosynthetic enzymes and studies with GA-deficient and GA-insensitive mutants. Highlights include the cloning of ent-copalyl diphosphate synthase and ent-kaurene synthase (formally ent-kaurene synthases A and B) and the demonstration that the former is targeted to the plastid; the finding that the Dwarf-3 gene of maize encodes a cytochrome P450, although of unknown function; and the cloning of GA 20-oxidase and 3β-hydroxylase genes. The availability of cDNA and genomic clones for these enzymes is enabling the mechanisms by which GA concentrations are regulated by environmental and endogenous factors to be studied at the molecular level. For example, it has been shown that transcript levels for GA 20-oxidase and 3β-hydroxylase are subject to feedback regulation by GA action and, in the case of the GA 20-oxidase, are regulated by light. Also discussed is other new info...

GIBBERELLIN BIOSYNTHESIS: Enzymes, Genes and Their Regulation.

Carotenoids form one of the most important classes of plant pigments and play a crucial role in defining the quality parameters of fruit and vegetables. Their role in the plant is to act as accessory pigments for light harvesting and in the prevention of photo-oxidative damage, as well as acting as attractants for pollinators. Their function as antioxidants in the plant shows interesting parallels with their potential role as antioxidants in foods and humans. Carotenoids are products of the isoprenoid biosynthetic pathway. The enzymes leading to carotenoid biosynthesis have all been characterised, and more recently the genes encoding these enzymes have been cloned from bacteria, fungi and plants. New information on enzyme activities and the factors leading to the regulation of the pathway is reviewed. Vitamin A deficiency is a widespread problem in the developing world, causing blindness, particularly in the young. This has driven research into finding ways of introducing provitamin A carotenoids into staple crops, and this has recently been achieved in rice and canola through genetic manipulation. The fact that carotenoids show protective activity in vitro and in vivo against a variety of degenerative disease end points has also give impetus to studying whether increasing intakes of the commonly consumed carotenoids would have public health benefits in the developed world. Human intervention studies have been undertaken using supplements of β-carotene rather than utilising foods with enhanced carotenoid levels, but no potential benefit has been shown. Indeed, there is evidence of an increased health risk from the consumption of β-carotene supplements. These observations suggest that the threshold between the beneficial and adverse effects of some carotenoids is low and provides a strong stimulus to further understanding the functional effects of specific carotenoids. Specific needs for future research are identified in the review.

© 2000 Society of Chemical Industry

The potential for the improvement of carotenoid levels in foods and the likely systemic effects

Geranylgeranyl pyrophosphate synthase is a key enzyme in plant terpenoid biosynthesis. Using specific antibodies, a cDNA encoding geranylgeranyl pyrophosphate synthase has been isolated from bell pepper (Capsicum annuum) ripening fruit. The cloned cDNA codes for a high molecular weight precursor of 369 amino acids which contains a transit peptide of approximately 60 amino acids. In-situ immunolocalization experiments have demonstrated that geranylgeranyl pyrophosphate synthase is located exclusively in the plastids. Expression of the cloned cDNA in E. coli has unambiguously demonstrated that the encoded polypeptide catalyzes the synthesis of geranylgeranyl pyrophosphate by the addition of isopentenyl pyrophosphate to an allylic pyrophosphate. Peptide sequence comparisons revealed significant similarity between the sequences of the C. annuum geranylgeranyl pyrophosphate synthase and those deduced from carotenoid biosynthesis (crtE) genes from photosynthetic and non-photosynthetic bacteria. In addition, four highly conserved regions, which are found in various prenyltransferases, were identified. Furthermore, evidence is provided suggesting that conserved and exposed carboxylates are directly involved in the catalytic mechanism. Finally, the expression of the geranylgeranyl pyrophosphate synthase gene is demonstrated to be strongly induced during the chloroplast to chromoplast transition which occurs in ripening fruits, and is correlated with an increase in enzyme activity.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-313X.1992.00025.x

Identification of a cDNA for the plastid‐located geranylgeranyl pyrophosphate synthase from Capsicum annuum: correlative increase in enzyme activity and transcript level during fruit ripening

C. Suire

Papers

Identification of a cDNA for the plastid‐located geranylgeranyl pyrophosphate synthase from Capsicum annuum: correlative increase in enzyme activity and transcript level during fruit ripening