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Ecological Characterization of Vegetation Using Multisensor Remote Sensing in the Solar Reflective Spectrum
Published in Prasad S. Thenkabail, Land Resources Monitoring, Modeling, and Mapping with Remote Sensing, 2015
Conghe Song, Jing Ming Chen, Taehee Hwang, Alemu Gonsamo, Holly Croft, Quanfa Zhang, Matthew Dannenberg, Yulong Zhang, Christopher Hakkenberg, Juxiang Li
PAR absorbed by leaf pigments has three pathways within the chloroplast: photochemical quenching (i.e., used for photosynthesis), nonradiative quenching, and photoprotection through which excess energy is dissipated through the xanthophyll cycle and chlorophyll ¨uorescence (ChF) through which radiation is emitted at longer wavelength than the absorbed light (Coops et al. 2010). Energy directed toward nonradiative quenching and ChF reduces LUE in photosynthesis (Meroni et al. 2009; Coops et al. 2010). Remote sensing of LUE is based on
Photosynthesis
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Two other discoveries involving photosynthetic system adjustment to changing light levels should be mentioned. First, a primary role of carotenoids is believed to be photoprotection from high light levels, which can produce potentially damaging amounts of triplet excitations in the chlorophyll arrays. Yellow-colored carotenoid xanthophylls assist in photoprotection of green leaves. The plant and light intensity control enzymatic interconversion of two major xanthophyll forms, violaxanthin and zeaxanthin. Zeaxanthin’s triplet quenching protects lipids and the light-harvesting antennae (next section), and triggers reorganization of PSII antenna pigment-proteins. At high light levels, zeaxanthin production from violaxanthin is stimulated, reducing levels of triplets and excitations that reach the reaction centers, thus protecting the plant. Kromdijk et al. found a potentially important agricultural application of this xanthophyll cycle. The green plant response to changing light levels does not quite match the rate at which variable cloud cover typically changes the light intensity reaching plants in farm areas.14 See Figure 10.10. After production of higher levels of zeaxanthin and array reorganization to suppress high-light photodamage, plant leaves needed minutes to hours to readjust to reduced light caused by cloud cover. During this readjustment period, photosynthetic activity is corresponding reduced. Kromdijk bioengineered an accelerated interconversion and found that tobacco plant biomass production could be increased by about 15% under real field conditions. Though engineered plants would have to be produced in high quantity for this to be economically significant, the potential crop yield increase may justify the effort. The reader should notice the very biochemical/molecular-biological “flavor” of Figure 10.10: enzymes and genetic engineering are the focus; structures and mechanisms are not—a challenge for the next cadre of biophysicists. An issue deserving some thought relates to the genetic approach to this bioengineering of photosynthesis. If the new strain of crops survived, the modification would be a permanent addition to the (local) ecosystem, with its possible benefits and dangers. See miniproject 10.10. A final note on xanthophylls—readers with sensitive or aging eyes may have noticed zeaxanthin featured prominently on the labels of eye-vitamin supplements, where it purportedly supports eye health in humans.
Terpenoids Against Cardiovascular Diseases
Published in Dijendra Nath Roy, Terpenoids Against Human Diseases, 2019
Carotenoids form part of another class of vitamin precursors, a tetraterpenoid organic pigment that normally is found in the chromoplast and chloroplast of plants (Vasanthi et al. 2012). Xanthophylls and carotenes are the two classes of carotenoids. Lycopene, vitamin A–precursor β-carotene, zeaxanthin, α-carotene, lutein and β-cryptoxanthin are the most typical carotenoid derivatives of plants found in human food (Vasanthi et al. 2012). The anti-oxidant characteristics of carotenoids regarding free radicals and oxidising agents are due to their polyene chain (Britton, 1995). Jung Sook et al. (2004) proposed that by the dietary intake of β-carotene, diabetic vascular complication may be reduced via the decrease in the plasma TG level. Inhibition of atherosclerosis in hypercholesteraemic rabbits is due to the interaction of metabolites from trans-β-carotene and retinoic acid receptors in the arterial wall (Vasanthi et al. 2012). Consequently, endothelial injury and growth of foam cells lead to the genesis of arterial plaques when low-density lipids are oxidized (Vasanthi et al. 2012). Furthermore, nutritional carotenoids have a preventive effect on the occurrence and death rate following CHD, ischemic stroke and myocardial infarction (MI) (Knekt et al. 1994). Anti-oxidants reduce the cellular level of free radicals through the prevention of free-radical triggering enzymes (Vajragupta et al. 2004). Epidemiological studies have shown that carotenoids have a role in the protection of the lipoproteins and cellular membrane from oxidative damage by their lipophilicity and their scavenging of peroxy free radicals (Stahl and Sies, 2003). Another striking feature of carotenoids remains its redox properties, which are believed to influence the molecular pathway in apoptosis and cell proliferation (Upadhyaya et al. 2007). A large body of evidence stipulates that the oxidation of LDL-C plays a vital role in the prognosis of atherosclerosis (Wagner and Elmadfa, 2003). Consequently, the inhibition of peroxidation in LDL-C is thought to be the main role of carotenoids in the decrease of the risk of CVDs (Wagner and Elmadfa, 2003). Surprisingly, information on the effects of carotenoids on LDL-C oxidation are rather minimal and mostly concentrated on lycopene (Wagner and Elmadfa, 2003). Substantial documentation shows that lycopene, a carotenoid without provitamin A activity that is found in high concentrations in a small set of plant foods, has sufficiently great anti-oxidant potential in vitro and may play a role in the prevention of CVD in humans (Arab and Steck, 2000).
A simple and fast experimental protocol for the extraction of xanthophylls from microalga Chlorella luteoviridis
Published in Preparative Biochemistry & Biotechnology, 2021
Nourhane Ahmad, Jihane Rahbani Mounsef, Roger Lteif
Xanthophylls have considerable role as food colorants and antioxidants with beneficial effects on human health.[1] The presence of diverse sets of carotenoids with varied levels of polarity makes their simultaneous extraction difficult. Additionally, xanthophylls are susceptible to degradation when they are exposed to excess heat, light, acids, and long extraction times due to their oxidative property.[2] The sample pretreatment with physical and chemical approaches helps in the breakdown of the cell wall and other physical barriers, thus significantly improving the extraction yield. The choice of solvent is the most critical factor for efficient extraction of carotenoids, and mainly depends on the carotenoid composition of the microalgae.[3,4] Xanthophylls, being oxygenated molecules, can be extracted with polar solvents.[5] Nevertheless, there are also issues related to the use of toxic organic solvents that are generally required in high amounts to carry out the extraction step. On the basis of environmental and health and safety issues, ethanol and acetone are more ecofriendly and preferred polar solvents, compared to hexane, diethyl ether, and ethyl acetate which are generally used for extraction of Xanthophylls.[6] Nowadays, the use of innovative nonconventional extraction techniques, such as microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE), gained growing interest. These methods offer superior efficiency, selectivity, and a reduction in treatment time or solvent consumption.[5] Haque et al., Taucher et al. and Singh et al.[7–9] suggested that ethanol and acetone were effective solvents for the extraction of Astaxanthin from Haematococcus pluvialis and Zeaxanthin form Chlorella saccharophila, respectively, using ultrasound assisted extraction method. Zhao et al.[10] reported that microwave-assisted extraction is a fast disruption method for the extraction of Astaxanthin from Haematococcus pluvialis with 83 s of irradiation time. Moreover, a thorough optimization of MAE and UAE parameters is still required, with a focus on using environmentally friendly and economical solvents for increasing the yield of pigments with particular attention on the energy inputs.[11,12]
Production and purification of fucoxanthins and β-carotenes from Halopteris scoparia and their effects on digestive enzymes and harmful bacteria
Published in Environmental Technology, 2023
Farah Hadjkacem, Jihen Elleuch, Guillaume Pierre, Imen Fendri, Philippe Michaud, Slim Abdelkafi
Nowadays, chronic diabetes is becoming the most endocrine health problem in the world. The number of diabetic patients is likely to reach 300 million by 2025 according to the World Health Organization (WHO) [1]. Currently, North Africa has the second-highest rate of diabetes mellitus growth in the world [2]. This rapid development is projected to grow by 96.2% in 2035 [3]. One of the most significant public health issues in Tunisia is the diabetic syndrome [4]. It refers to the disturbance of carbohydrate, fat, and protein metabolism caused by abnormal glucose metabolism and difficulty in insulin secretion, which eventually leads to chronic hyperglycemia and various other complications such as damage to the nervous system, kidneys, eyes, heart, feet, and skin [2,5,6]. Diabetes may be classified into two groups based on etiology. Type 1 diabetes, known as insulin-dependent diabetes mellitus, is characterized by absolute insulin deficiency due to the destruction of pancreatic β-cells that normally secrete it. Type 2 diabetes is characterized insulin resistance and/or insulin deficiency leading to excessive glucose concentration in blood. It is often developed by patients with physical activity, and obesity. Administration of insulin or other oral hypoglycemic agents, are currents therapies for type 2 ineffective in some cases [7,8]. Therefore, there is an increasing demand for innovative alternatives based on the utilization of natural compounds with minimal or no adverse impact on patients. Plant-based resources are safety and effective in various applications [7]. To date, the WHO considers 119 plants as resources for therapeutic compounds, of which about 74% are used in modern medicine [9,10]. In contrast, the identification of natural ingredients and the isolation of active chemicals from underutilized marine organisms, especially macroalgae, is still poorly explored despite their potential. Brown seaweeds are rich in bioactive metabolites particularly soluble dietary fibers, sulfated polysaccharides, phlorotannins, peptides, sulfolipids, polyunsaturated fatty acids, vitamins, minerals, and pigments [11]. Carotenoids are a diverse group of natural pigments that play an important role in photosynthesis. They are defined as polyenes composed of 11 conjugated double bonds and two -ionone rings on each end [12]. The main groups of these hydrocarbons are carotenoids. Xanthophylls are polar oxygenated groups representing a subset carotenoid. Because of their conjugated double-bond structure, carotenoids are sensitive to isomerization and oxidation [13]. 700 carotenoids are found in nature, of which, zeaxanthin, violaxanthin, lutein, β-carotene, and fucoxanthin are the most common in seaweed [14].