EVIDENCES FROM PALYNOLOGY
Palynology has numerous applications:
Biostratigraphy - correlation of rock sections.Proper indentification of indicative palynomorphs could lead to the discovery of oil, coal, and gas deposits.
Geochronology - dating of rocks. Paleoecology - past environments. Non-geological uses - archeaological palynology, forensic palynology, aeroallergy.
Pollen wall structure
Sporoderm1. Exine (sporopollenin + glycocalyx) a) sexine- supratactal + tectum + columella b) nexine- foot layer + endexine 2. Intine (cellulose)
TEM of crosssection of Arabidopsis pollen. P- pollen grain cytoplasm, i- intine, ebacula of exine, pc- pollen coat.
Function of exine
Protects protoplasm from impacts & abrasion Allows expansion & reduction of grain size with changing humidity Provides the pollen tube at the time of fertilization Yields identifying characteristics
Pollen varies in size, exine ornamentation, and number and arrangement of apertures.
Section of pollen wall showing structure and some features
Types of apertures in pollen
Pores- usually isodiametric; can be slightlyelongated but have rounded ends.
Colpi (fissures)- elongated, withpointed ends; more primitive
Monoaperturate- Describing a pollen grainor spore with a single aperture. Examples: monocolpate , monoporate, monosulcate (Erdtman, 1952).
Tricolpate- Describing pollen grainswith three ectocolpi, three compound apertures or three pores.
SULCUS- An elongated latitudinal ectoaperture situated at the distal or proximal pole of a pollen grain. It has the same shape as a colpus, but differs in orientation. Sulci are essentially latitudinal apertures whereas colpi are essentially longitudinal apertures.
Equatorial view, NasturtumPolar view, Nasturtum, with 3 colpi equidistantly arranged along the equator (trizonocolpate); triangle in polar view
There are 6 pori arranged equidistantly around the axis of the pollen grain and therefore this pollen grain is hexazonoporate.
This image shows the isodiametric apertures, pori
Camellia japonica, equatorial view; elliptic; granulate
Polar view of the pollen grains: Three of the very long and pointed apertures equidistantly arranged along the equator of the pollen grain. This type of grain is therefore a trizonocolpate.
Golden Rod (echinate), Oak pollen(colpi) and Birch pollen (pores). SEM images ofpollen.
Porus with clear annulus and operculum (lid), Plantago
SEM image of pollen grains from : sunflower (Helianthus annuus), morning glory (Ipomoea purpurea), prairie hollyhock (Sidalcea malviflora), oriental lily (Lilium auratum), evening primrose (Oenothera fruticosa), and castor bean (Ricinus communis).
Lilium auratum Oenothera fruticosa
Scanning electron micrograph of pollen of Meliosma pinnata (Sabiaceae). Polar view showing three colporate apertures. Scale bar = 5m.
POLLEN SHAPESPROLATE- the polar axis is larger than the equatorial diameter (1.33-2.0) PROLATE-SPHEROIDAL: the ratio between the polar axis and the equatorial diameter is 1.00-1.14.
OBLATE- the polar axis is shorter than the equatorial diameter.
OBLATE-SPHEROIDAL- the ratio between the polar axis and the equatorial diameter is 0.88-1.00
SUBOBLATE- the ratio between the polar axis and the equatorial diameter is 0.75-0.88
Echinate- pollen and spores with anornamentation comprising spines longer than 1m.
Transmission electron micrograph showing the point of contact between a pollen grain (P) and a stigma papillus (S).
Two basic kinds of pollen in angiosperms: monosulcate and tricolpateMONOSULCATE: boat-shaped, with one long germinal furrow and aperture; characteristic of primitive dicots, most monocots, cycads & pteridosperms TRICOLPATE: globosesymmetrical, typically have 3 germinal apertures; characteristic of advanced dicots
a) Convallaria (monosulcate); b) and c) Aizoaceae (tricolpate)
A typical pollen of Asteraceae with a spiky (echinate) surface; tricolpate (g- polar view; h- equatorial view))