Theoretically, each carbon-carbon double bond in the polyene chain of carotenoids may exhibit E-Z isomerization. However, the C-5,6 double bond in the acyclic lycopene is unhindered, and 5-Z-lycopene is increasingly detected, along with the 9-Z-, Z-, and the Z-isomers [ 41 ]. Although the presence of cis isomers is recognized due to the isomerization caused by heat or light sources, there are some carotenoids that can occur naturally.
Interestingly, they have different biological potency than their trans counterparts e. Phytoene and phytofluene, which have the Z configuration in most natural sources, are examples of carotenoids less thermodynamically stable [ 42 ].
Geometrical isomers. Zeaxanthin and astaxanthin are typical examples of carotenoids, in which this isomerization may occur.
Optical isomers. From this stage, the specific carotenoid biosynthetic pathway starts with condensation occurs of two molecules of GGPP, by phytoene synthase PSY to produce the first colorless carotenoid cis-phytoene C These precursors are produced by two independent pathways in photosynthetic beings: the mevalonate MVA pathway and the methylerythritol 4-phosphate MEP pathway [ 3 ]. Additionally, the carotenoids biosynthesized by different organisms are derived through a series of chemical and enzymatic modifications from the phytoene, such as reactions of desaturations, cyclizations, hydroxylations, glycosylation, oxidization, dehydrogenation, migration of double bonds, rearrangement, and epoxidations, as exemplified above [ 45 ].
These modifications are catalyzed by a number of enzymes which fall into few classes based on the type of transformation they catalyze such as geranylgeranyl pyrophosphate synthase, phytoene synthase, carotene desaturase, and lycopene cyclase. Thus, all of these modifications contribute to yield a family of more than compounds widely distributed in nature [ 4 , 46 ]. Of the total number of naturally occurring carotenoids, only eight are produced synthetically at industrial level.
For the chemical synthesis, several building concepts are possible. However, on industrial scale, only few of them have been applied successfully. All chemically synthesized C40 carotenoids have symmetric structures, and this is explained by the fact that all structures have identical end groups at their ends. Due to these characteristics, they are efficiently produced by double Wittig condensation of a symmetrical Cdialdehyde as the central Cbuilding block with two equivalents of an appropriate Cphosphonium salt.
Additionally, to use Grignard compounds, it is necessary to combine one diketone molecule and two methanol molecules, thereafter compound containing 40 carbon atoms is obtained [ 49 ].
Carotenoids industrial applications. In more recent times, the major commercial use of carotenoids has been as food and feed additives for coloration. They have also found some use in cosmetics and pharmaceutical products, but the most rapidly growing market now is health supplements, which in turn, provides a stimulus growing from production [ 1 ]. Carotenoids belong to the category of tetraterpenoids i. Structurally, carotenoids take the form of a polyene hydrocarbon chain which is sometimes terminated by rings, and may or may not have additional oxygen atoms attached.
Carotenoids with molecules containing oxygen, such as lutein and zeaxanthin , are known as xanthophylls. Carotenes typically contain only carbon and hydrogen i. Their color, ranging from pale yellow through bright orange to deep red, is directly linked to their structure. Xanthophylls are often yellow, hence their class name.
The double carbon-carbon bonds interact with each other in a process called conjugation , which allows electrons in the molecule to move freely across these areas of the molecule.
As the number of conjugated double bonds increases, electrons associated with conjugated systems have more room to move, and require less energy to change states. This causes the range of energies of light absorbed by the molecule to decrease.
A similar, although larger LH ring is found for the LH1 antenna that encloses the RC, although this LH complex requires no carotenoids for its assembly [5,8]. A recent spectroscopic study did however establish a clear functional role for carotenoids in the Rba. Carotenoids are synthesised by the sequential desaturation of the colourless pigment phytoene, which has three conjugated double bonds .
In Rba. Sometimes the pathway terminates prematurely; for example, Rps. The only difference between these bacteria appears to be the possession of a three- or four step phytoene desaturase; this was shown by an early carotenoid engineering study that swapped the native three-step phytoene desaturase for the four-step enzyme from Erwinia herbicola now Pantoea P.
This suggests the lemma and palea are mainly protective organs whereas the awn is primarily a photosynthetic structure. The seed was enriched with genes for the biosynthesis of starch, storage proteins, enzyme inhibitors, and cell proliferation. Carbohydrates for grain filling come from three sources: spike inflorescence photosynthates, flag leaf photosynthates, and reserve mobilization from the stem Tambussi et al. The contribution of each to the final seed dry weight varies between species, genotypes, and growth conditions.
In wheat Triticum aestivum L. Cereal spikes are composed of numerous spikelets, each consisting of multiple florets flowers. In barley, each floret contains a pair of glumes, a lemma, a palea, a pair of lodicules, three stamens and a pistil Briggs, The palea on the inside and the lemma on the outside, partially enclosing the palea cover the seed and become a husk when the seed is matured Fig.
The lemma has a long slender extension, the awn. The lemma, palea and awn are photosynthetic organs and supply the developing seed with carbohydrates Duffus and Cochrane, In addition, since the lemma and palea cover the seed, they are thought to play a protective role against pathogens and small insects.
Figure 1. Parts of the barley spike. A Spikes at pollination left , early grain filling middle , and dough stage right. B Components of a spikelet at the grain-filling stage. C Seed at the grain-filling stage showing an intact seed left , seed with epicarp partially peeled middle to show pericarp and seed with the pericarp partially removed to show the endosperm right.
Note that the pericarp contains chlorophyll and is capable of photosynthesis. The contribution of each spike organ to grain filling has not been fully elucidated. The lemma and palea are the second most prominent photosynthetic organs of the barley spike. Because the lemma and palea tightly adhere to the seed and also recycle respiratory CO2 released by the seed Jiang et al. Difficulties in measuring gas exchange in the spike organs can underestimate photosynthesis of the lemma and palea and inflate that of the awn.
Despite the vital role the lemma, palea, and awn play in the development of the seed, little information is available on gene expression to explain their specific functions. To our knowledge, the study presented here is the first detailed comparison of gene expression among the spike organs of barley. In an earlier study using cDNA macroarrays, we showed that the lemma and palea of barley preferentially express genes for photosynthesis, defense, nitrogen metabolism, and structural support when compared with the flag leaf Abebe et al.
This is consistent with the proposed role of the lemma and palea as sources of carbohydrate and protective organs for the developing seed. However, the awn was not included in that study and the lemma and palea were pooled together, making it difficult to determine gene expression in individual organs. Druka et al.Hoffmann La-Roche Ltd. Reddit Summary The Or gene of cauliflower Brassica oleracea var. This observation does not, however, preclude the possibility that additional uncolored proplastids exist in these cells. Quality of probe labeling and hybridization to the Barley1 GeneChips assessed by Expression Console v 1. However, most carotenoids found in nature are primarily in the more stable all-trans configurations; a small proportion of cis isomers is encountered [ 5 , 12 ]. In addition, it has five chiral centers, including an epoxide ring [ 19 ].
The only difference between these bacteria appears to be the possession of a three- or four step phytoene desaturase; this was shown by an early carotenoid engineering study that swapped the native three-step phytoene desaturase for the four-step enzyme from Erwinia herbicola now Pantoea P. Equal loading of mRNA was verified by ethidium bromide staining. Published by Elsevier B.
In an earlier study using cDNA macroarrays, we showed that the lemma and palea of barley preferentially express genes for photosynthesis, defense, nitrogen metabolism, and structural support when compared with the flag leaf Abebe et al. For each organ, three biological replications were collected on three different dates between a. Pfander spent most of his career at the University of Bern where his contributions include work in the field of organic synthesis of carotenoids, the characterization of naturally occurring carotenoids, and as an editor and founding member of the International Carotenoid Society. Functional Classification and Enrichment Analysis of Organ-Specific Genes Organ-specific genes were further categorized according to gene ontology GO terms to determine their biological roles. Epoxy carotenoids comprise a large group of xanthophylls and are widely encountered in foods [ 28 ]. Micron scale in a applies to d.