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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 β-D-glucose residues
Hemicellulose - branched polysaccharides that are structurally homolgous to
cellulose because they have a backbone composed of 1,4-linked β-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 α-Dgalacturonic 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 β1–4-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. safflower,
sunflower, canola, cottonseed, etc,
sequester these oils in specialized
organelles called Oleosomes