Only found in eukaryotic plants = specialized organells – uinque to plants Come in several forms Fx = involved in metabolism PLASTIDS
Have a x2 (envelope) membrane 2 internal phases Membrane system Stroma/matrix Why are they called plastids? PLASTIDS: Structure
Contain ribosomes Fx mRNA translation in protein synthesis Also contain a small amount of DNA 3 main types of plastids Chloroplasts Chromoplasts Leukoplasts PLASTID: Function
Chloroplasts contain chlorophyll Fx = photosynthesis THE CHLOROPLAST
CHLOROPLAST: Structure • highly developed membrane system • Tiny, flattened membrane-bound sacs Thylakoids • Form grana • grana are rather important: as all the photosynthetic pigments are found within the grana. • Grana are connected to each other by fibres called • Stroma lamella
= the colour pigments which determines plant colour (green, yellow, red, orange, blue, etc) THE CHROMOPLAST
Chromoplast plastids Capsicum annum
Chromoplasts • Chromoplasts develop from mature chloroplasts. • Why don’t all chloroplast change into chromoplasts? • Fx = store pigment. • Pigment is formed when thylakoids and the stroma lamella break down.
Leucoplasts are colourless plastids Found: roots non – photosynthesising tissue May become specialized for bulk storage of starch, lipid or protein. Called amyloplasts (starch) elaioplasts (fat storage) proteinoplasts (protein storage) Can change into chloroplasts/chromoplasts LEUCOPLASTS
CELL INCLUSIONS = Any non-living mass, found within the cell • Can be - floating around in the cytoplasm - stored in an organelle like a plastid or vacuole - secreted by a cell, either outside the cell, or secreted into the cell wall. • E.g: starches, waxes,, crystals, alkaloids, tannins, etc. • Fx = pharmacological & medicinal value
Lily Parenchyma Cross Section . • Note the large nucleus and nucleolus in the centre of the cell, mitochondria and plastids in the cytoplasm.
Tonoplast = differentially permiable Fx – stores salts Recycles materials in plants Play an important role in plant turgor Vacuoles
Encloses the whole cell Freely permeable Cellulose fibrils – NB component. Functions of the cell wall? THE CELL WALL
Cell Wall Cell wall and nucleus – Allium cepa
Cellulose • Cellulose is a linear polymer, made of millions of sugar (glucose) molecules. • The older the cell or the plant (herb) the more cellulose it’s going to contain. • WHY?
Plant Matrix = Ground substance/substance in which something else originates/develops or is contained. • Responsible for the attributes of plant dietary fibre. • Made up of hemi-cellulose (not glucose, mostly Xylose – wood sugar) – malabsorbtion • Hemi-cellulose provides little strength (unlike cellulose). • Mucilages = hemi-cellulose
made up of pectinic acid (made up of polymeres of galacturonic acid) Pectin is mainly found in the middle lamella. Pectin
Processes occurring in the plant • Photosynthesis • Respiration • Ligninification • Cutinisation • Suberization • Mineralization
Lignins = propane polymeres Lignins – Latin ‘Lignas’ = woody Deposited in the cellulose network & are embedded in the cellulose fibres of woody plants Liginins & Lignification
Lignin Fx = added rigidity to cell walls Fills the spaces in the cell walls between cellulose, hemicellulose and pectin Fx = decreases xylem permeability (NB role in the transport of H20 & nutrients) Fx = plant defence: protects against destructive environmental enzymes Ligninification
LIGININ Cross Section of Angiosperm Stem. After staining, G-type lignins are stained in brown and G+S lignins are red.
H, G & S lignin monomers G-type lignins = brown H+S lignins = red.
Cuticle = Ester of saturated fatty acids & oxyacids. Has an outer layer of wax Fx = Reduce plant H20 loss Cutinisation = process of cuticle formation THE CUTICLE
= Formation of cork (phellem) Fx – protection from excessive H20 loss - added protection Suberins making up cork are similar to cutins making up cutins (unsaturated fatty acids instead of saturated fatty acids) Suberins – impermeable to gasses & water Cork = non-living, water-resistant, protective tissue that displaces the stem epidermis as the plant undergoes an increase in diameter during the secondary growth phase.. SUBERIZATION
Periderm (from cortex) Red – cork Yellow – cork cambium Red - phelloderm CORK CELLS
MINERALISATION = inorganic salts are deposited into the cell wall stronger cell wall stronger plant. E.g. Silica formation in Equisetum. Medicinal uses of Equisetum Pre-historic uses of Equisetum
Silica moleucle isolated from Equisetum arvense MINERALISATION
LESSON TAKE-AWAY • Plastids • Processes involved in Plantae