Summary 
The Protoplast consists of the Plasmalemma & everything Inside of it.
Individual Protoplasts are interconnected via Plasmodesmata & comprise the Symplast.
The Cell Wall is outside of the Protoplast and is thus part of the Apoplast.
Intercellular Air Spaces are part of the Apoplast.
Aqueous Solutions can move in the Apolast and the Symplast.
Cellulose Fibrils have high tensile strength. They are insoluble, chemically inert and resist enzymatic attack!
Cellulose Fibril deposition during Interpase occurs in the Plasmalemma and is directed by Microtubules in the Cytoplasm.
Cell Wall
synthesis after Telophase
involves Golgi Vesicles which are
directed by Microtubules. This forms the
Cell Plate, otherwise known as the Middle Lamella.
Thereafter, Cellulose Fibrils
are synthesized as above for Interphase.
The Cell Wall is necessary for the development of Turgor Pressure.
Turgor Pressure is the "driving force" for cell expansion!
Primary Cell Walls are formed during cell expansion.
Secondary Cell Walls are formed inside the Primary Wall after cell expansion has ceased.
The Principal
Components of Primary Cell Walls are
Polysaccharides.
These include Cellulose, Hemicellulose
& Pectin.
Lignin can replace Pectin, especially in Secondary Cell Walls.
Lignin makes cell walls "water-proof" and incredibly strong and rigid.
Lignification can encompass the Primary Wall and the Middle Lamella as well as Secondary Walls. This completely blocks the Apoplast.
Structural proteins and Enzymes also contribute to cell wall rigidity & loosening.
Cellulose Fibrils are disorganized in Primary Walls.
Cellulose Fibrils are highly organized in Secondary Walls.
Secondary
Walls have discrete layers of Cellulose Fibrils which have
opposing patterns of deposition.
Cellulose in Primary Walls is stabilized by Hydrogen Bonds.
Cells can secrete Cutin & Waxes which are barriers to Water Loss and Pathogen attack.
Suberin has properties that are similar to Cutin.
Waxes can be reflective and can protect leaves from excess sunlight.
Most of the Carbon in terrestrial ecosystems is located in plant cell walls.
The properties of cell walls have an important bearing on soil structure and water holding capacity.
Root Hairs and Pollen Tubes exhibit Tip Growth.
Most plant cells grow by Diffuse Growth.
Cell Shape depends on the orientation and loosening of Cellulose Fibrils in cell walls.
Cellulose Fibril Orientation is controlled by Microtubules.
Most plant cells are elongated.
The current concept which accounts for cell expansion is called the Stress Relaxation & Acid Growth Hypothesis. How does this work?????
Polarity means that an entity displays regional differences.
Polarity exists at the Molecular, Cellular and Organismal levels of development.
Polarity has been extensively studied with Fucus Zygotes.
These are Apolar at Fertilization.
Light and other external factors can establish Polarity in Zygotes.
This causes a redistribution of Membrane Proteins which leads to the establishment of + & - Poles at opposite ends of the Zygote.
Actin Microfilaments direct Golgi Vesicles so that one end of the Zygote begins to grow.
An Unequal Cell Division occurs.
The smaller cell produces a Rhizoid which becomes the non-photosynthetic Holdfast.
The larger cell produces the Photosynthetic Thallus.
Unequal Cell Divisions frequently lead to the production of specialized structures.
Examples include the development of Pollen Grains, Root Hairs, Stomata & Embryos of Flowering Plants. The latter affects the fundamental organization of the entire organism.
Microtubules may control the symmetry of Cell Divisions.
Asymmetric divisions need to have organized Microtubules present. Otherwise the result is an equal cell division.
Formative Divisions send Daughter Cells along Different Developmental Paths.
Proliferative Divisions increase the Number of Cells in One Path.
Unequal Divisions are usually Formative Divisions.
The Embryos of Flowering Plants go through a series of stages (Globular - Heart-Torpedo) which are characterized by differential patterns of Cell Division and Cell Enlargement.
The Shoot Apical Meristem & the Root Apical Meristem are established during Embryogenesis. This defines the Axial Polarity of the Organism.
The Radial Organization of the Primary Meristems (Protoderm, Ground Meristem & Procambium) and Primary Tissues (Epidermis, Ground, Xylem & Phloem) are also established in Embryogenesis.
The Embryonic Root & Shoot Apical Meristems can be called Primary Apical Meristems.
Branches have Secondary Apical Meristems.
Secondary Roots have an internal origin near the Vascular Tissues.
Secondary Shoots (Branches) have a superficial origin near the leaf-stem junction (Leaf Axil).
Non-seed plants usually have Apical Cells as Apical Meristems.
Seed Plants have Multicellular Apical Meristems which may contain a few "Initials".
Initials are found in many Root Apical Meristems but are not generally found in Shoot Apical Meristems.
A Quiescent Center (QC) is typically found in the Root and Shoot Apical Meristems of Flowering Plants. The QC encompasses any Initials.
The QC is a structural manifestation of the meristem's Physiology and is NOT a permanent structural entity.
The QC has a regenerative function.
It may also protect cells from excessive mutations.
The Root has two fundamental parts (Root Cap & Root Body)
Root Caps protect the RAM from physical damage.
They also secrete a mucilage which lubricates the root as it grows through the soil.
It prevents the desiccation of Aerial Root Tips.
Root Caps can also perceive Gravity.
Roots primarily increase in length which helps them penetrate soil.
The Root has four Zones (Root Cap, Meristematic, Absorption/Maturation) .
Periclinal Divisions would be oriented such that the New Cell Walls lie Parallel to the surface. This increases the number of Cell Layers.
Anticlinal Divisions are characterized by having their New Walls oriented Perpendicular to the Surface. Anticlinal Divisions produce long Cell Files that can be traced to their origins which surround the Quiescent Center.
Shoot Apical Meristems produce superficial Leaf Primordia in a specific pattern.
Leaves define Nodes.
The stem segments between Nodes are called Internodes.
The Shoot Apex includes the Promeristem (Meristem Proper) and its associated Leaf Primordia.
Initials like those seen in some roots are not apparent in Shoot Apical Meristems.
Most Shoot Apical Meristems have at least one Tunica Layer which is characterized by Anticlinal Divisions.
The outermost Tunica layer produces the Protoderm which forms the Epidermis.
The Corpus is an area with cell divisions in several planes that subtends the Tunica.
Leaf and Branch Primordia originate in the outer 2-3 layers of cells. The Corpus may NOT always contribute to the initiation of these primordia.
The Shoot Apical Meristems of Gymnosperms have a central group of cells that are not Meristematic. These are called the Central Mother Cells or Central Cells.
Cytohistological Zonation is the term used to describe this situation.
The Central Cells correspond with the Quiescent Center.
The cells just below the Central Cells divide rapidly and are called the Peripheral Zone.
Similar patterns of cell division have been observed in Angiosperms which have pronounced Quiescent Centers.
Vegetative Meristems produce Leaves and Axillary Shoots.
They are Indeterminate.
Floral Meristems produce Flowers directly. They produce primordia which become flower parts rather than Leaves.
They are Determinate.
Inflorescence Meristems produce modified leaves called Bracts. They also produce Axillary Flowers.
Inflorescence Meristems can become Vegetative and are potentially Indeterminate.
Leaf and Flower Primordia are produced in precise geometric patterns.
This is called Phyllotaxy.
The disposition of leaves and flower parts have important ecological implications.
Cells Communicate via the Apoplast and Symplast.
The Size Exclusion Limit of Plasmodesmata limits the size of Macromolecules that can be transported Symplastically.
The Size Exclusion Limit of the Apoplast is several times greater than that of Plasmodesmata (Symplast).
Auxin is a small molecule that regulates the growth and differentiation of tissues over long distances.
Auxin can move in the Apoplast.
Xylem Differentiation is a good example of Auxin mediated Growth & Differentiation.
Auxin is produced in the Shoot Tip and travels Basipetally in Stems.
Stems have higher Auxin levels than Roots.
Consequently, it is one source of Polarity in Plants.
Xylem Differentiation involves the production of elaborate Secondary Walls & programmed Cell Death (Apotopsis).
This is a positive adaptation for water transport in the Tracheary Elements because cytoplasm would impede water flow through the Tracheary Elements & severely limit growth.
