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I P Yermakov - One of the best experts on this subject based on the ideXlab platform.
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antioxidant properties of the pollen Exine polymer matrix
Biophysics, 2012Co-Authors: A V Smirnova, K N Timofeyev, M A Breygina, N P Matveyeva, I P YermakovAbstract:The antioxidant properties of the polymer matrix of Exine, the outer layer of pollen grain wall, were studied. The main component of this matrix is sporopollenin, a unique biopolymer resistant to mechanical and chemical damage. Samples of isolated Exine purified from soluble compounds were studied with EPR using a stable nitroxyl radical TEMPO and a spin trap DMPO. At the same time, we analyzed changes in fluorescence of DCFH which detected ROS in the solution. It has been established that Exine effectively reduced TEMPO and eliminated the hydroxyl radical. Also, fluorimetric analysis demonstrated that Exine decomposed H2O2, and this ability significantly decreased after treatment of Exine with feruloyl esterase or mild alkaline hydrolysis (1 M NaOH), i.e. after hydrolysis of hydroxycinnamic acid esters. After harsh hydrolysis (4 M NaOH, 170°C) of ether bonds, a large amount of hydroxycinnamic acids was released, and the Exine almost completely lost its antioxidant capacity. The obtained results point to the ability of the extracellular polymer matrix of the Exine to eliminate free radicals and H2O2 during crucial periods of male gametophyte development. The participation of ferulic acid and, possibly, of other hydroxycinnamic acids of sporopollenin in these processes has been demonstrated.
John R Rowley - One of the best experts on this subject based on the ideXlab platform.
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Structure of the pollen Exine of Rhoiptelea chiliantha.
2009Co-Authors: Annie Skarby, Marta A. Morbelli, John R RowleyAbstract:The Exine of mature pollen grains of Rhoiptelea chiliantha was studied. The size of the pollen grains is about 23 by 27 μm. They are tricolporate with short colpi that are 1-2 μm wide and 10-12 long. The spinules of Rhoiptelea are similar in form and size to those of Gentianales. The spinules consist of rods of ca 70 nm in width. These rods are evident throughout the tectum and columellae. The columellae are of two distinct sizes. The smaller ones are ca 70 nm wide and join the tectum and the larger columellae. These larger ones appear to be composed of several 70 nm in width rods. They join the distal surface of the foot layer. The proximal surface of the foot layer is marked by a white line (referred to as a junction plane) where it joins the endExine. The endExine consists of a solid-appearing component adjacent to the foot layer (referred to as endExine-1) and laminar components (endExine-2) that are attached to and apparently become a part of endExine-1. There is no indication of an arcus. In well preserved grains the aperture is covered by an operculum or operculum-like component. In well-rehydrated pollen grains there is an oncus of considerable complexity under the aperture and over the intine. The Ubisch bodies have an Exine ornamented with widely-spaced spinules like the spinules on the pollen Exine.
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pollen wall ultrastructure and ontogeny in heliotropium europaeum l boraginaceae
Review of Palaeobotany and Palynology, 2005Co-Authors: Semia Ben Saadlimam, Mohamed Abdelhamid Nabli, John R RowleyAbstract:The pollen grains of Heliotropium europaeum are heterocolpate, with alternation of 3 colpori and 3 pseudocolpi. The Exine is characterized by a scabrate and thick tectum, massive columellae with a granular appearance and a thick nExine. The thickening of the intine at the apertural level makes the interpretation of this zone difficult. The ontogenetic study helped to understand the ultrastructure of the Exine and the apertures. The different steps are as follows. The primExine matrix is formed during the beginning of the tetrad stage; it consists of an outer thick and electron dense zone and an inner one, less dense to electrons. The tectum and the infratectum begin to form in the outer zone of the matrix, towards the middle of the tetrad stage. The infratectum consists of a network of columellae variable in thickness and oriented in different directions. The foot layer is lacking. The endExine is formed on a lamella system during the callose loss and microspore separation. The endExine becomes compact very early on its inner part. The apertures are initiated during the tetrad stage; a granulo-fibrillar oncus develops. At the free microspore stage, the oncus gets fibrillar and is bordered by endExine lamellae on its outer side and by endExine granulations on its inner one and laterally. The intine is set at the end of this stage. At the vacuolated microspore stage, the intine shows three layers: two thin, clear and homogeneous layers, one outside and the other inside, and a thick middle layer that forms the zwischenkorper, crossed by trabecula, in the apertural areas.
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transfer of material through the microspore Exine from the loculus into the cytoplasm
Botany, 2003Co-Authors: John R Rowley, John J. Skvarla, Gamal ElghazalyAbstract:Our results and those we review indicate that the Exine has a great capacity for modifications that enable nutrients to pass through from the anther loculus to the microspore cytoplasm. Avenues of passage include strands, some of which are viscin threads, from the tapetum to microspores in, for example, Betula, Fuchsia, and Epilobium. Micro channels in Lopezia, Gaura, and Gelsemium extend through the ectExine, endExine, and intine to the cytoplasm. The bulge regions in Epilobium represent portions of the endExine that become very greatly enlarged, forming conducting channels that transport materials into the microspore cytoplasm. Results with tracers such as colloidal iron and lanthanum have also shown that Exines of microspores are permeable across areas lacking obvious channels.Key words: Betula, Epilobium, Exine, Fuchsia, Gaura, Gelsemium, Lopezia, microchannels, pollen, tapetum, tufts, viscin threads.
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Structure of the Exine of Epilobium angustifolium (Onagraceae)
Grana, 1996Co-Authors: John R Rowley, Donald ClaugherAbstract:Abstract Exine units have a 40 nm wide hollow center in mature pollen grains of Epilobium angustifolium L. and other members of the Onagraceae. In Epilobium Exine units are rod-shaped and have an outside diameter of about 100 nm. Our interpretation of the hollow Exine units of mature pollen of this taxon is based on the sequence of early Exine development shown in transmission electron micrographs. At the beginning of the developmental sequence Exine units had a strongly stained core about 40 nm in diameter surrounded by weakly stained binder subunits. The transmission electron micrographs show the transition stages of stain reversal during which the core zone loses contrast. In both negatively stained sections (transmission electron microscopy) and in fractured Exines (scanning electron microscopy) the core zone of Exine units is evident as a fairly straight tube. Binder subunits wind about the core zone. The core contains 10–15 nm wide subunits which have both straight and looped portions. The looped po...
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Exine development in nymphaea colorata nymphaeaceae
Nordic Journal of Botany, 1994Co-Authors: Nina I Gabarayeva, John R RowleyAbstract:We show a sequence of developmental events in microspores and tapetal cells in Nymphaea colorata based upon transmission and scanning electron microscopic observations. There are parallel cytoplasmic processes and surface coatings in microspores and tapetal cells. Uptake is indicated by the passage of lanthanum as a tracer from anther locule into the microspore cytoplasm and by the condition of the cytoplasmic surface of microspores. The callose envelope is not a barrier to transfer of lanthanum. During formation of the proExine glycocalyx tiny spiral elements, components of the Exine substructural units, were oriented in different directions in the surface coating of microspores and tapetum. Lipoidal globules are associated with the spiral elements. After the uniform proExine stage, three regions of different Exine structure and their gradations become differentiated in the sporoderm: 1) a proximal region with thick tectum and foot layer, thin columellae and a compact layer of lamellated endExine; 2) a distal pole region with separately disposed endExine lamellae; and 3) an equatorial encircling-sulcate aperture region which consists of infratectal layer, foot layer, and endExine lamellae. Based upon the presence of structurally comparable surface coats in microspores and tapetal cells, experimental uptake of lanthanum nitrate, and the co-ordinated processes in tapetum and microspores, we conclude that there is probably a reciprocal controlling influence between the microspores and the tapetum and other sporophytic tissues.
A V Smirnova - One of the best experts on this subject based on the ideXlab platform.
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Antioxidant properties of the pollen Exine polymer matrix
Biofizika, 2020Co-Authors: A V Smirnova, K N Timoffev, M A Breĭgina, N P Matveeva, I P ErmakovAbstract:The antioxidant properties of Exine polymer matrix which forms the outer layer of pollen grain wall were studied. The main component of this matrix is sporopollenin - a unique biopolymer resistant to mechanical and chemical damage. The samples of isolated Exine, purified from soluble compounds, were studied with EPR using stable nitroxyl radical TEMPO and DMPO spin trap. At the same time, we analyzed changes in fluorescence of DCFH which detected ROS in the solution. It has been established that Exine effectively reduces TEMPO radical and eliminates hydroxyl radical. Also, the fluorometric analysis demonstrated that the Exine eliminated H2O2, and this ability significantly decreased after treatment of Exine with feruloyl esterase or mild alkaline hydrolysis (1M NaOH), i.e. after hydrolysis of hydroxycinnamic acid esters. After harsh hydrolysis (4M NaOH, 170 degrees C) of ethers bonds a large amount of hydroxycinnamic acids has been released, and Exines have lost their antioxidant capacity almost completely. The obtained results point to the ability of extracellular polymer matrix of the Exine to eliminate free radicals and H2O2 during crucial periods of male gametophyte development. The participation of ferulic acid and, possibly, of other hydroxycinnamic acids of sporopollenin in these processes has been demonstrated.
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antioxidant properties of the pollen Exine polymer matrix
Biophysics, 2012Co-Authors: A V Smirnova, K N Timofeyev, M A Breygina, N P Matveyeva, I P YermakovAbstract:The antioxidant properties of the polymer matrix of Exine, the outer layer of pollen grain wall, were studied. The main component of this matrix is sporopollenin, a unique biopolymer resistant to mechanical and chemical damage. Samples of isolated Exine purified from soluble compounds were studied with EPR using a stable nitroxyl radical TEMPO and a spin trap DMPO. At the same time, we analyzed changes in fluorescence of DCFH which detected ROS in the solution. It has been established that Exine effectively reduced TEMPO and eliminated the hydroxyl radical. Also, fluorimetric analysis demonstrated that Exine decomposed H2O2, and this ability significantly decreased after treatment of Exine with feruloyl esterase or mild alkaline hydrolysis (1 M NaOH), i.e. after hydrolysis of hydroxycinnamic acid esters. After harsh hydrolysis (4 M NaOH, 170°C) of ether bonds, a large amount of hydroxycinnamic acids was released, and the Exine almost completely lost its antioxidant capacity. The obtained results point to the ability of the extracellular polymer matrix of the Exine to eliminate free radicals and H2O2 during crucial periods of male gametophyte development. The participation of ferulic acid and, possibly, of other hydroxycinnamic acids of sporopollenin in these processes has been demonstrated.
Dabing Zhang - One of the best experts on this subject based on the ideXlab platform.
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the polyketide synthase ospks2 is essential for pollen Exine and ubisch body patterning in rice
Journal of Integrative Plant Biology, 2017Co-Authors: Jing Yu, Takayuki Tohge, Alisdair R Fernie, Sagit Meir, Asaph Aharoni, Dawei Xu, Dabing Zhang, Wanqi LiangAbstract:: Lipid and phenolic metabolism are important for pollen Exine formation. In Arabidopsis, polyketide synthases (PKSs) are essential for both sporopollenin biosynthesis and Exine formation. Here, we characterized the role of a polyketide synthase (OsPKS2) in male reproduction of rice (Oryza sativa). Recombinant OsPKS2 catalyzed the condensation of fatty acyl-CoA with malonyl-CoA to generate triketide and tetraketide α-pyrones, the main components of pollen Exine. Indeed, the ospks2 mutant had defective Exine patterning and was male sterile. However, the mutant showed no significant reduction in sporopollenin accumulation. Compared with the WT (wild type), ospks2 displayed unconfined and amorphous tectum and nExine layers in the Exine, and less organized Ubisch bodies. Like the pksb/lap5 mutant of the Arabidopsis ortholog, ospks2 showed broad alterations in the profiles of anther-related phenolic compounds. However, unlike pksb/lap5, in which most detected phenolics were substantially decreased, ospks2 accumulated higher levels of phenolics. Based on these results and our observation that OsPKS2 is unable to fully restore the Exine defects in the pksb/lap5, we propose that PKS proteins have functionally diversified during evolution. Collectively, our results suggest that PKSs represent a conserved and diversified biochemical pathway for anther and pollen development in higher plants.
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Exine export in pollen
2014Co-Authors: Dabing Zhang, Hui LiAbstract:Pollen as a sperm cell carrier is mainly protected by outer pollen wall (called Exine) from physical and biological stresses. The major composition of Exine is the highly resistant biopolymer sporopollenin, which mainly consists of hydrophobic lipids, phenylpropanoids, and aromatic compounds. The biosynthesis of these constituents has been shown to be catalyzed by enzymes preferentially expressed in the sporophytic tapetal layer, a nutritive tissue supporting pollen development. How the synthesized sporopollenin precursors are exported from tapetal cells onto the surface of microspore for pollen Exine formation remains largely unknown. Here, we review the structure of tapetal cella and pollen Exine in the model monocot rice (Oryza sativa) and the model dicot Arabidopsis thaliana. In addition, we highlight the update understanding on the role of ATP-binding cassette (ABC), lipid transfer protein (LTP), and multidrug and toxic efflux (MATE) transporters in trafficking of sporopollenin precursors across tapetal cells for Exine development in rice and Arabidopsis. We also discuss the future research focus on the transport of sporopollenin precursors for Exine synthesis.
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biosynthesis of anther cuticle and pollen Exine in rice
Plant Signaling & Behavior, 2010Co-Authors: Hui Li, Dabing ZhangAbstract:The lipidic structures, anther cuticle (outer anther surface) and pollen Exine (outer pollen wall), play a key protective role for the male gametophyte and pollen grain development. We recently identified ancient cytochrome P450 family member CYP704B2 in rice, and proposed a common fatty acid ω-hydroxylation pathway for synthesizing anther cuticle and pollen Exine during plant male reproductive development. Furthermore, we propose developmental model of pollen Exine formation and discuss key genes required for pollen Exine synthesis in the important crop plant rice.
R. B. Knox - One of the best experts on this subject based on the ideXlab platform.
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Exine formation in the pollinium ofDendrobium
Protoplasma, 1994Co-Authors: M. A. Fitzgerald, S. H. Barnes, S. Blackmore, D. M. Calder, R. B. KnoxAbstract:The position of the callose wall is related to the position of the primExine matrix that forms around the peripheral tetrads during microspore development of the compound unit, the pollinium. We report a combined freeze-fracture and freeze-substitution study of the events associated with early Exine development. Stage one of Exine development is deposition of protosporopollenin that is probably synthesised by the microspore and secreted to the primExine matrix where it is polymerised. Enzymes for the polymerisation of the protosporopollenin may be synthesised by the microspores and then transported, via the endoplasmic reticulum, to the plasma membrane. Stage two of Exine development follows callose dissolution and deposition of tapetally derived sporopollenin. Hence Exine form and Exine deposition in Dendrobium appear to be the result of intimate cooperation between the microspore, the plasma membrane, the callose and the tapetum.
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Exine formation in the pollinium of Dendrobium
Protoplasma, 1994Co-Authors: M. A. Fitzgerald, S. H. Barnes, S. Blackmore, D. M. Calder, R. B. KnoxAbstract:The position of the callose wall is related to the position of the primExine matrix that forms around the peripheral tetrads during microspore development of the compound unit, the pollinium. We report a combined freeze-fracture and freeze-substitution study of the events associated with early Exine development. Stage one of Exine development is deposition of protosporopollenin that is probably synthesised by the microspore and secreted to the primExine matrix where it is polymerised. Enzymes for the polymerisation of the protosporopollenin may be synthesised by the microspores and then transported, via the endoplasmic reticulum, to the plasma membrane. Stage two of Exine development follows callose dissolution and deposition of tapetally derived sporopollenin. Hence Exine form and Exine deposition inDendrobium appear to be the result of intimate cooperation between the microspore, the plasma membrane, the callose and the tapetum.