Pectins: structure, biosynthesis, and oligogalacturonide-related signaling.

Plant compounds that are perceived by humans to have color are generally referred to as 'pigments'. Their varied structures and colors have long fascinated chemists and biologists, who have examined their chemical and physical properties, their mode of synthesis, and their physiological and ecological roles. Plant pigments also have a long history of use by humans. The major classes of plant pigments, with the exception of the chlorophylls, are reviewed here. Anthocyanins, a class of flavonoids derived ultimately from phenylalanine, are water-soluble, synthesized in the cytosol, and localized in vacuoles. They provide a wide range of colors ranging from orange/red to violet/blue. In addition to various modifications to their structures, their specific color also depends on co-pigments, metal ions and pH. They are widely distributed in the plant kingdom. The lipid-soluble, yellow-to-red carotenoids, a subclass of terpenoids, are also distributed ubiquitously in plants. They are synthesized in chloroplasts and are essential to the integrity of the photosynthetic apparatus. Betalains, also conferring yellow-to-red colors, are nitrogen-containing water-soluble compounds derived from tyrosine that are found only in a limited number of plant lineages. In contrast to anthocyanins and carotenoids, the biosynthetic pathway of betalains is only partially understood. All three classes of pigments act as visible signals to attract insects, birds and animals for pollination and seed dispersal. They also protect plants from damage caused by UV and visible light.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1365-313X.2008.03447.x

Biosynthesis of plant pigments: anthocyanins, betalains and carotenoids

Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept

One of the defining features of plants is a body plan based on the physical properties of cell walls. Structural analyses of the polysaccharide components, combined with high-resolution imaging, have provided the basis for much of the current understanding of cell walls. The application of genetic methods has begun to provide new insights into how walls are made, how they are controlled, and how they function. However, progress in integrating biophysical, developmental, and genetic information into a useful model will require a system-based approach.

/pdf/toward-a-systems-approach-to-understanding-plant-cell-walls-375h7arxvl.pdf

Toward a Systems Approach to Understanding Plant Cell Walls

Living cells need to be more or less saturated with water to function normally, but they are usually incomplete in this desirable condition. The two basic parameters which describe the degree of unsaturation, i.e. the plant water deficit are (i) the water content and (ii) the energy status of the water in the cell. The water content is usually expressed as relative to that at full saturation, i.e. the relative water content or water saturation deficit, and the energy status of the water is usually expressed as the total water protential. Although the two parameters are linked in such a way that the total water potential decreases as the water content decreases, the relationship between the two, variously known as the moisture release curve, water potential isotherm or water retention characteristic, is not unique but varies with species, growth conditions and stress history (Slatyer, 1960; Jarvis and Jarvis, 1963; Altmann and Dittmer, 1966; Noy Meir and Ginzburg, 1969; Ludlow, 1976; Jones and Turner, 1978). Thus for completeness, both the water content and energy status of the water in plant tissue need to be measured. The total water potential (7') at any point in the plant can be partitioned into its components: the osmotic potential (re), turgor pressure (P), matric potential (z) and gravitational potential. As the gravitational component of the total water potential is only 0.01 MPa m- 1 (0.1 MPa = 1 bar), it can be neglected, except in very tall trees (Conner et al., 1977). For cells in equilibrium with their surroundings the total water potential is the same throughout the system, i.e. in the wall, cytoplasm, organelles and vacuole. However, the components of the total water potential may be quite different: in the vacuole the total water potential arises largely from osmotic and turgor forces, whereas in the wall, it arises largely from matric forces and to a small degree from osmotic forces. Thus the total water potential of a plant cell is given

Techniques and experimental approaches for the measurement of plant water status

Structure and solution properties of tamarind-seed polysaccharide.

Galactomannan biosynthesis in vitro is catalysed by membrane preparations from developing fenugreek seed endosperms. Two enzymes interact: a GDP-mannose dependent (1→4)-β-d-mannan synthase and a UDP-galactose dependent (1→6)-α-d-galactosyltransferase. The statistical distribution of galactosyl substituents along the mannan backbone, and the degree of galactose substitution of the primary product of galactomannan biosynthesis appear to be regulated by the specificity of the galactosyltransferase. We now report the detergent solubilisation of the fenugreek galactosyltransferase with retention of activity, the identification on gels of a putative 51 kDa galactosyltransferase protein, and the isolation, cloning and sequencing of the corresponding cDNA. The solubilised galactosyltransferase has an absolute requirement for added acceptor substrates. Beta-(1→4)-linked d-manno-oligosaccharides with chain lengths greater than or equal to 5 acted as acceptors, as did galactomannans of low to medium galactose-substitution. The putative galactosyltransferase cDNA encodes a 51282 Da protein, with a single transmembrane alpha helix near the N terminus. We have also confirmed the identity of the galactosyltransferase by inserting the cDNA in frame into the genome of the methylotrophic yeast Pichia pastoris under the control of an AOX promoter and the yeast alpha secretion factor and observing the secretion of galactomannan α-galactosyltransferase activity. Particularly high activities were observed when a truncated sequence, lacking the membrane-spanning helix, was expressed.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-313x.1999.00566.x

Molecular characterisation of a membrane-bound galactosyltransferase of plant cell wall matrix polysaccharide biosynthesis.

http://www.jbc.org/content/261/20/9489.full.pdf

Purification and properties of a novel xyloglucan-specific endo-(1----4)-beta-D-glucanase from germinated nasturtium seeds (Tropaeolum majus L.).

The levels of cell-wall xyloglucan (amyloid) in nasturtium (Tropaeolum majus L.) cotyledons were monitored during a 28-d period covering seed imbibition, germination and early seedling development. The activities of the following enzymes capable of hydrolysing the glycosidic linkages in the xyloglucan were assayed in cotyledon extracts over the same period: endo-(1→4)-β-glucanase (EC 3.2.1.4), β-glucosidase (EC 3.2.1.21), α-xylosidase and β-galactosidase (EC 3.2.1.23). The endo-β-glucanase was assayed viscometrically using xyloglucan as substrate, and the three glycosidases using appropriate p-nitrophenylglycosides. Alpha xylosidase and β-galactosidase, the enzymes which would be expected to hydrolyse the side-chains from the xyloglucan molecule, were also assyed using xyloglucan as substrate. Under our culture conditions, xyloglucan levels remained constant at 30 mg per cotyledon pair for 7 d, that is until 3 d after germination: thereafter, the amount of xyloglucan diminished to zero in a 12-d period. The most rapid period of depletion was between days 9 and 13. The mobilisation of all reserve substances from the cotyledons resulted in a weight-loss of 92 mg: xyloglucan, therefore, is an important storage substance, representing 33% by weight of the seed's substrate reserves. It is a cell-wall storage polysaccharide. Xyloglucan mobilisation was accompanied by a 17-fold increase in endo-β-glucanase activity, a 7-fold increase in β-galactosidase and an 8-fold increase in α-xylosidase activities, all determined using xyloglucan as substrate. All three activities began to increase at day 5, peaked at days 12–14 when the most rapid phase of xyloglucan breakdown was over, and had declined to zero by days 22–25. The levels of theses enzymes have been shown to be consistent with their being responsible for xyloglucan hydrolysis in vivo. Nitrophenyl-β-galactosidase activity increased up to day 3, remained constant and then increased again 2.5-fold from day 5, peaking at day 11. Nitrophenyl-β-glucosidase remained relatively constant up to day 16 and then decreased to zero by day 25. Nitrophenyl-α-xylosidase activity was not detected.

Xyloglucan (amyloid) mobilisation in the cotyledons of Tropaeolum majus L. seeds following germination.

A beta-D-galactosidase from nasturtium (Tropaeolum majus L.) cotyledons. Purification, properties, and demonstration that xyloglucan is the natural substrate.

Mary Edwards

Papers

Structure and solution properties of tamarind-seed polysaccharide.

Molecular characterisation of a membrane-bound galactosyltransferase of plant cell wall matrix polysaccharide biosynthesis.

Purification and properties of a novel xyloglucan-specific endo-(1----4)-beta-D-glucanase from germinated nasturtium seeds (Tropaeolum majus L.).

Xyloglucan (amyloid) mobilisation in the cotyledons of Tropaeolum majus L. seeds following germination.

A beta-D-galactosidase from nasturtium (Tropaeolum majus L.) cotyledons. Purification, properties, and demonstration that xyloglucan is the natural substrate.