WHAT SORT OF MATERIALS DO PLANTS NEED TO STORE?
WATER
I. Parenchyma in close association with chlorenchyma
A. Central vacuole
B. Mucilage within cytoplasm
1. Cortex and pith regions
2. Water reserve associated with seed coats
ELABORATED RESERVES
I. Products of photosynthesis and other anabolic processes that are not immediately used in growth
II. Products used after a period of dormancy to support new growth
III. Products used to attract animals that facilitate seed dispersal
IV. Accumulated as
A. Crystals
1. Starch
2. Aleurone grains
B. Amorphous globule
C. Dispersed in cytoplasm
1. Sugars
2. Fatty oils
D. Extracellular matrix components
1. Cellulose
VI. Specialized parenchyma
A. Fruits
B. Seeds
1. Endosperm
2. Aleurone layer
3. Cotyledons
4. Caruncle (Castor Bean Seed)
C. Asexual reproductive structures
1. Bulbs
2. Corms
3. Tubers
4.
Storage Roots
D. Primary Plant Body
1. Meristems
2. Pith
3. Cortex
1. Axial
2. Ray
SECRETORY SYSTEMS
STRICTLY SPEAKING:
SECRETION = Act of seperation of a substance from the protoplasm (eg. hormones, enzymes)
EXCRETION = Seperation of products eliminated from metabolism which are apparently nonutilizable or toxic (eg. terpenes, essential oils, carotenoids, saponins, rubber, tannins, crystals)
NO SHARP DISTINCTION MADE IN LITERATURE BECAUSE
1. Role of by-products not known
2. Secreted and excreted compounds can accumulate in same cells or tissues
I. Secretory/Excretory structures vary with regard to
A. Degree of cellular complexity
B. Location within plant organs
C. Relation between secreted substances and the cytoplasm doing the secreting
1. Internal Secretory Structures
a. Remains within cytoplasm
b. Enters intercellular spaces
2. External Secretory Structures
a. Exits to surface of plant
II. External Secretory Structures derived from protoderm
2. Unicellular or multicellular
B. Glands
1. Areas of epidermal cells involved in secretion having
a. Little vacuolation
b. Cytoplasm rich in proteinaceous substances
c. Large nuclei that are frequently polyploid
d. Amplified mitochondria, golgi, and endoplasmic reticulum
e. Cell wall ingrowths = transfer cells
C. Secretion is usually released between cell wall and cuticle, which eventually bursts
1. Cells may die
a. Colleters secrete sticky mixture of terpenes and mucilage on bud scales
2. Cuticle may regenerate
3. Continual production of head cells, like conidia
4. Silicified tips of pointed hairs may break, injecting cytoplasm into offending animal epidermis
a. Urtica stinging hairs inject histamine, acetyl choline and other unknowns
D. Same structures sometimes secrete and absorb at different time
1. Trichomaceous hydathodes secrete water in young leaves, but absorb water in older leaves
2. Trichomes and glands of insectivorous plants secrete nectar, mucilages, and digestive enzymes, then absorb dissolved elements from trapped insects
E. Nectaries
1. Trichomes or glands that secrete sugar solution to attract pollinators
a. Floral = on sepals, petals, stamens, or pistils
b. Extrafloral = on leaves or stem in close association with flowers
2. Sugar transported into secretory cells from closely associated terminal vasculature which often consists only of phloem tissue
F. Osmophors
1. Glands, often several cell layers thick in perianth, that secrete volatile essential oils
2. Secrete large amounts of stored products in very short time for short duration of time
3. Attraction of pollinators
4. Big bucks in the perfume industry
G. Salt glands
1. Typical of halophytes
2. Secrete salt which would otherwise inhibit growth
H. Hydathodes
1. Actively discharge water during guttation
a. Requires metabolism since poisoned plants don't guttate
b. Sometimes damages plants because of high salt content of guttation
fluid
2. Trichomes
3. Complex tissue areas (Brassica)
a. Terminal vascular bundle, often only consisting of tracheids in
contact with
b. Epithem consisting of parenchyma deficient in chloroplasts but
with abundant intercellar space, surrounded by
c. Cells with suberized cell walls or casparian strips
d. Guard cells are incompletely differentiated with permanently open
pores
III. Internal Secretory Structures
A. Individual secretory cells (idioblasts) containing balsams, resins, oils, tannins, mucilages, gums, crystals
B. Secretory spaces termed canals or ducts that arise
1. Schizogenously = increase in intracellular spaces
2. Lysigenously = cell death
3. Both schizogenously and lysigenously
4. Volatile terpenes, balsams, resins, gums, latex, mucilage either come from
a. Surrounding Epithelial cells
b. cells that will ultimately lyse to create the space
C. Laticifers
1. Conclusive information on function of laticifers is lacking
a. Food conduction? - no apparent internal movement
b. Food storage? - doesn't appear to be readily mobilized
c. Regulation of water balance in surrounding tissue?
d. Transport of oxygen in plant?
e. Protection against herbivory?
f. Excretion? - most widely accepted since latex appears to
be useless metabolic by products
2. Rubber, resins, gums, hydrocarbons of laticifers have economic
importance to humans
