Plant Cell and Plant tissues
plastids Cell wall Primary wall composition and architecture
Primary walls isolated form higher plant tissues and cells are
composed predominantly of polysaccharides together with lesser
amounts of structural glycoproteins (hydroxyproline-rich
extensins), phenolic esters (ferulic and coumaric acids), ionically
and covalently bound minerals (e.g. calcium and boron), and
enzymes. In addition walls contain proteins (expansins) that are
believed to have a role in regulating wall expansion Cellulose - a
polysaccharide composed of 1,4-linked -D-glucose
residuesHemicellulose - branched polysaccharides that are
structurally homolgous to cellulose because they have a backbone
composed of 1,4-linked -D-hexosyl residues. The predominant
hemicellulose in many primary walls is xyloglucan. Other
hemicelluloses found in primary and secondary walls include
glucuronoxylan, arabinoxylan, glucomannan, and galactomannan.Pectin
- a family of complex polysaccharides that all contain 1,4-linked
-D-galacturonic acid. To date three classes of pectic
polysaccharides have been characterized: Homogalacturonans,
rhamnogalacturonans, and substituted galacturonans.
Microcrystalline cellulose is embedded in a hydrated matrix
consisting of coextensive networks of complex heteropolysaccharides
and sometimes glycoproteins. Cell walls also constitute renewable
resources and are often present in by-products of industrial
production. Genetic engineering of crop plant cell walls can
identify biopolymers with novel functional properties, as well as
simplify their extraction, thus increasing the value of these
"waste-products." Cell walls will become more important in the
future, as they are an abundant resource that can contribute to our
biofuel needs. Chitin is a polymer of 14-linked GlcNAc, which
occurs in chains that typically exceed 1000 residues. These chains
self-associate to form microfibrils and are deposited primarily at
the bud neck of yeast or at septa in filamentous fungi. The
cell-wall polysaccharides that have been described so far are
composed of polymers of mannose, glucose, galactose,
N-acetylglucosamine, and/or rhamnose, and these include mannans,
glucans, chitin, galactomannans, glucomannans, rhamnomannans, and
phosphomannans. Secondary cell walls of specialized plant cells
sclerenchymatic cell walls
tannins Chloroplasts Chromoplasts Plastids amyloplasts Leucoplasts
/ protein bodies All plant seeds that store triglycerides as future
energy sources, eg
All plant seeds that store triglycerides as future energy sources,
eg. safflower, sunflower, canola, cottonseed, etc, sequester these
oils in specialized organelles called Oleosomes
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