BIO 201: Botany
PLANT DEVELOPMENT

ORGANS AND TISSUES

Overall, vascular plants are less complex than vertebrate animals

Plants lack the organ system level of organization

Plant Organs = group of tissues with a common organismal function

• Root - support plant (anchor), absorb nutrients & water
• Stem - support plant for vertical growth
• Leaf - photosynthetic (obtain energy)
• Flower - reproductive, sexual

Plant Tissues = group of cells with common physiological function

• Vascular - transport of nutrients & water and support
     xylem for water;  phloem for nutrients
• Mesophyll - chloroplast containing cells of leaves
     sometimes in stems too
• Epidermal - surface cells for protection
     on trees tissue develops into bark
• Ground - nonspecialized (morphologically) cells mostly for storage
     example: potato
     generic term for cell type = parenchyma

Also need to remeber that some cells able to divide:

• Reproductive - cells which will go through meiosis
• Meristematic -- non specialized tissue, programmed to dividing further by mitosis

SEED STRUCTURE

Seeds contain several structural components:
     1) seed coat – sometimes this is fused to pericarp (fruit)
     2) embryo – tissue as beginning of next generation

Embryo of three distinct structures

     1) epicotyl – embryonic shoot

     2) hypocotyl – embryonic root (technically it is the shoot + root)

     3) cotyledon – embryonic leaves
            important for energy storage in a number of seeds

Development constant in all species following fertilization
    1) endosperm develops quickly takes up much of the volume
            initially noncellular, eventually becomes cellular
            ex.: coconut
    2) embryo slow to develop

Patterns differ between species
    1) the extent of development by the time seed released
    2) amount of development while seed appears dormant
    3) proportion of embryo and endosperm present by the time of seed germination

Seeds structure at time of germination
    1) very large endosperm, well over 50% of volume
    2) endosperm small or non existent, cotyledons large

SEED GERMINATION

A number of processes must occur before germination can occur
    1) embryo needs to mature
            some species develop after falling off parent
    2) dormancy needs to be broken
            typically the result of chemical changes
            may mean seed coat must decompose
    3) external environment needs to be right
            water, light, temperature

Early process upon seed germination
    1) a primary root elongates
            hypocotyl elongates to push cotyledons & epicotyl
            ex.: beans
    2) epicotyl elongates to push bud above ground
            cotyledon and hypocotyl remains underground
            ex.: peas, corn

PLANT GROWTH

MERISTEM = zone of active cell division
    1) root tip (new root tissue, length)
    2) stem tip or buds (new stem tissue, length)
    3) trunk margins (growth in diameter of stem & root on trees ... develops in area between bark and wood)

ZONES OF CELL AND TISSUE DEVELOPMENT --
    1) Zone of Cell Division (mitosis) -- buds
    2) Zone of Cell Growth -- some cells enlarge, some elongate
    3) Zone of Cell Specialization -- become specific cell types
            tissues produced

As stems and roots mature into specialized tissues, we can see the development of:
1) Protoderm - surface layer cells
            * epidermis, including hairs
            * bark
2) Procambium - beginning of vascular tissue
            * primary xylem & phloem
            * cambium (for continued growth in diameter)
3) Ground meristem - other nonspecific cells
            distinguished by location
            * cortex (outside vascular tissue)
            * pith (in center of stem from vascular tissue)
            * leaf