The Water Permeability of Intact Subcellular Organelles
Gheorghe Benga in Water Transport in Biological Membranes, 1989
A second natural organelle that has been subjected to water permeability studies is the thylakoid membrane of chloroplasts. Thylakoid membranes form substructures of surpassing complexity within algal cells and within the chloroplasts of higher plants, where they contain the pigments and electron-transport apparatus of the light reactions of photosynthesis. The topology of these structures is still not completely understood, although the electron microscopic work in serial section of Paolillo and co-workers44–48 has provided considerable structural insight. Basically, the thylakoids are organized as layered stacks of flattened, osmotically tight vesicles (the grana stacks), in which are embedded the pigments and electron transport proteins which catalyze the following reactions:
Anatomy, Biochemistry and Physiology
Massimo Maffei in Vetiveria, 2002
Light microscopical observations of V. zizanioides leaves revealed the presence of Kranz BS cells common to the majority of C4 species (Laetsch, 1974). In V. zizanioides cross sections of minor veins the vascular BS appears surrounded by one layer of sheath cells, with chloroplasts in a centrifugal position (Figure 2.2a). No mestome sheath (MS) appears to be present between metaxylem vessel elements and laterally adjacent Kranz cells as in other grasses, e.g. Pooideae (Esau, 1977). According to ultrastructural studies V. zizanioides possesses a Kranz anatomy with dimorphic chloroplasts. The bundle sheath chloroplasts form larger and more numerous starch grains than the mesophyll chloroplasts and in contrast to the latter, they show a reduced grana development or none at all. In the BS, ultrastructural observations show a cell wall suberized lamella (Figure 2.2b) along with the presence of agranal chloroplasts. Sometimes these chloroplasts show an apparent distortion of the thylakoid system somewhere in the central part of the stroma (Figure 2.2b–c). Chloroplasts were observed to contain numerous starch grains (Figure 2.2b) and/or a developed peripheral reticulum, a system of anastomosing tubules contiguous with the inner membrane of the chloroplast envelope (Figure 2.2c). A few, small, and heavily cristated mitochondria were also observed. The mesophyll chloroplasts show most of the thylakoids staked in grana, the complete absence of starch grains, and the presence of several plastoglobules (Figure 2.2d–e) (Bertea et al., 2001).
Carotenoids
Ruth G. Alscher, John L. Hess in Antioxidants in Higher Plants, 2017
The bulk of the chloroplast carotenoids are associated with the light-harvesting complexes in the thylakoid membrane. The carotenoids present in these antenna complexes, the bulk of which are mainly xanthophylls, have the ability to absorb light in the wavelength range of 400 to 500 nm. Energy is transferred from the carotenoid-excited singlet state (1Car*) to S0 chlorophyll (1Chi) by singlet-singlet energy transfer (Reactions 1 to 3). This energy-transfer process is generally recognized to proceed with very high efficiency, itself suggesting a close proximity of carotenoid and chlorophyll molecules. In vitro studies using synthetic caroteno-porphyrin molecules have shown that high efficiencies can be achieved provided that a precise structural arrangement is maintained between the carotenoid and chlorophyll molecules.37 The possible role of carotenoid radical species in electron transfer processes in light harvesting has been discussed for a number of years, although there is still a lack of clear evidence for their involvement in anything but artificial systems.33
Current advances in the algae-made biopharmaceuticals field
Published in Expert Opinion on Biological Therapy, 2020
Sergio Rosales-Mendoza, Karla I. Solís-Andrade, Verónica A. Márquez-Escobar, Omar González-Ortega, Bernardo Bañuelos-Hernandez
The first step on the developmental path for the production of algae-made biopharmaceuticals comprises the design of the gene coding for the biopharmaceutical and its cloning to construct an expression vector that allows developing transformed algae clones. For these goals a detailed knowledge of the algae molecular biology (regulatory sequences such as promoters and terminators [36,37], signal peptides [38], genome insertion sites [39], etc.) is required to successfully express the functional biopharmaceuticals. Nuclear and chloroplast-based expression can be applied for the production of biopharmaceuticals and each alternative has its features and limitations that should be considered in a case by case scenario based on the characteristics of the biopharmaceutical of interest (i.e. requirements in terms of glycosylation, multimeric assembly, and protein secretion); each of these approaches leads to differential contexts in terms of protein processing. The chloroplast is an organelle present in photosynthetic eukaryotic algae where several biosynthetic pathways happen. For instance, the syntheses of fatty acids, amino acids, and isoprenoids occur in this organelle. The chloroplast possesses a circular genome (plastome) and the transcriptional and translational machineries to synthesize proteins. In fact, unlike bacterial hosts, the chloroplast from C. reinhardtii possesses chaperones [3], peptidyl propylisomerases (PPIases) [21], and protein disulfide isomerases (PDIs) [40] that allow proper synthesis of complex proteins requiring disulfide bonds for correct folding [41].
Trace elements concentration in soil and plant within the vicinity of abandoned tanning sites in Bangladesh: an integrated chemometric approach for health risk assessment
Published in Toxin Reviews, 2022
Md. Saiful Islam, Tapos Kormoker, Mohini Mazumder, Suraia Easnur Anika, Md. Towhidul Islam, Debolina Halder Hemy, Ummah Salma Mimi, Ram Proshad, Md. Humayun Kabir, Abubakr M. Idris
The concentrations of essential and toxic elements (mg/kg dw) in different plant parts are summarized in Table 2. A considerable variation of essential and toxic elements were observed among the plant parts and sampling locations. Leaves have been reported to have higher concentration of essential and toxic elements than tubers and stems (Zhao and Duo 2015), this is because the roots may act as a protective barrier for the movement (translocation) of elements into stem and leaves of plants (Liu et al. 2009). However, the present study reported a higher concentration of essential and toxic elements in leaves than tubers (roots) and stems. Generally, the concentration of essential and toxic elements among the plant parts decreased in the order of leaves > tubers > stem (Table 2). The average concentrations of essential and toxic elements in all vegetable samples were in the following decreasing order: Fe > Zn > Cu > Cr > Ni > Mn > Pb > As > Cd. All photosynthetic activities occur in the chloroplast of plants. Iron is an essential element in photosynthetic processes (Sulaiman and Hamzah 2018). The green part of leaves is usually made up of chloroplast which makes up a green pigment (chlorophyll), and as such high Fe accumulation is expected in plant leaves. Photosynthetic process such as photo-transpiration are said to accelerate the concentration of Fe in the leaves (Frossard et al. 2000).
Efficacy of nano-silicon in the control of chocolate spot disease of Vicia faba L. caused by Botrytis fabae
Published in Egyptian Journal of Basic and Applied Sciences, 2020
Khadiga A. Hasan, Hoda Soliman, Zakaria Baka, Yasser M. Shabana
TEM micrograph (Figure 6(a,b)) revealed that the leaves of untreated healthy V. faba had normal cell plasma membrane, normal mitochondria, big vacuole and thin cytoplasm. The cells contained typical ellipsoidal chloroplasts with normal organized membrane system of grana and inter-granal lamellae. The chloroplasts were arranged near the cell wall. However, infected V. faba leaf showed rounded chloroplasts with irregular membrane system, numerous plastoglobuli and grains of starch were very small (Figure 7(a,b)). Figures 8 and 9(a,b) revealed that NSi-treated plants (1.5 and 3 mM) had normal thick cell wall, plasma membrane, big vacuole and the chloroplasts were well normal and in close association to cell wall as those of the untreated control with few small starch grains. Furthermore, the chloroplasts contained regular structured grana and inter-granal lamellae.
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