Presentation on theme: "Division: Coniferophyta / Pinophyta I. Coniferophyta / Pinophyta The conifers are assigned to the –Division: Pinophyta / Coniferophyta –Class: Pinopsida."— Presentation transcript:
Coniferophyta / Pinophyta The conifers are assigned to the –Division: Pinophyta / Coniferophyta –Class: Pinopsida / Coniferopsida –Order: Pinales / Coniferales Termed conifers because most members bear their seeds in cones –Cones protect ovule and seed and facilitate pollination and dispersal They are the largest and most ecologically & economically important of the gymnosperms
Coniferophyta - Uses –Forest vegetation –Watershed protection –Habitat for variety of animals –Seed as food source esp. for birds & mammals –Aesthetic appeal –Ornamentals –Paper production –Construction –Resin extraction –Medicinals
Coniferophyta / Pinophyta The division includes the –Pines- Spruces –Cedars- Cypresses –Redwoods- Giant sequoias –Junipers - Firs –Hemlocks Evolved over 300 mya. Present-day genera appeared approx. 170 mya. Oldest living and largest trees
Pinus longaeva (Pinaceae) is the oldest known living thing.
Strong trees Emit strong odour from bark &/or leaves –Resin canals throughout stem & leaves Branches whorled or opposite –Consist of long and short shoots Simple leaves –Linear / Needle-shaped –Clustered in fascicles of 2-5 needles –Sessile or short petioled on long shoots –Tightly clustered on short shoots –Persistent (evergreen)
Coniferaceae / Pinaceae Usually have straight trunks with horizontal branches varying more or less regularly in length from bottom to top, so that the trees are conical in outline Members are monecious Reproduce through micro- & megasporangiate (staminate and ovulate) cones Wood is very hard and pycnoxylic
Pinaceae – Young Stem Concentric arrangement of primary tissue Pith is small Thick vascular cylinder, comprised of a ring of separate collateral and open vascular bundles Cortex & epidermis relatively thin Epidermal outline is wavy due to the presence of scale leaves.
Pinaceae – Older Stem The edges of cambia for each VB grow closer and eventually meet complete ring of cambium Secondary growth occurs with the laying down of vascular tissue on either side of cambial ring: –Inside: new xylem (secondary xylem) laid between primary xylem and cambium –Outside: new phloem (secondary phloem) laid between cambium and primary phloem
Pinaceae - Roots Very similar to angiosperm roots. –There is an embryonic root which develops into a tap root system from which lateral branching occurs. Mycorrhizae are typically associated with conifer roots and play an important role in seedling growth. The root apical meristem is multicellular with a prominent root cap. The primary tissues are arranged concentrically with diarch – tetrarch xylem at the center, surrounded by phloem, and the pericycle. The endodermis and the rest of the Cortex are typical. The dermal layer, however, is somewhat ambiguous as the epidermis is indistinct.
Pinaceae - Reproduction Microsporangiate cones –Terminally at the stem/branch apex –Spirally arranged, bilaterally symetrical microsporophylls –Derived from modified branch with modified leaves –Two microsporangia on abaxial surface of the microsprophyll –Pollen grains bear 2 saccae Pollination is by wind Pollen grains possess two saccae for extended ‘flight’ and for buoyancy & orientation in the pollination droplet Pollination droplet catches pollen
Microgamete Development in Conifers First Pathway: In Pinaceae, Podocarpaceae & Araucariaceae the microspore nucleus divides in the following way: –The microspore nucleus (Androspore) divides twice by periclinal (parallel to the other surface) walls to cut off two primary Prothallial cells –The prothallial cells soon degenerate and the large remaining cell is called the Antheridal initial/cell. –The primary prothalial cells may divide further to form secondary prothallial cells. –The antheridal initial divides to form a tube cell and a generative cell. –The generative cell may divide periclinally to form a sterile (stalk cell) and a spermatogenous cell (body cell). –The spermatagenous cell divides ultimately into two male gametes (or male cells).
Microgamete Development in Conifers In other conifers, such as the Taxaceae, Cuppressaceae, Cephalotaxaceae the prothallial cells are not formed & the androspore cell acts directly as an antheridal initial, that is, the prothalial cell and antheridal cell stages are eliminated.
Microgamete Development in Conifers The pollen grains do not immediately start germinating on reaching the nucellus. In Pinaceae it rests for about a year after the migration of the tube nucleus into the pollen tube (soon after pollination). It is during the next spring that the generative cell divides into sterile (stalk) cell and spermatogenous (body) cell, which then migrate into the tube. No motile sperm. Pollen tube delivers sperm nuclei into the archegonium
Pinaceae – Reproduction (cont’d) Megasporangiate/ovulate cones –Larger than the male cones –Borne on stem (intercalary) –Spirally arranged, flattened bract/ovuliferous-scale complex Woody (ovuliferous) scale (megasporophyll) envelops the 2 ovules on adaxial surface. Papery bract / carpellary scale Micropyles of ovules directed toward the axis of the cone Few archegonia/ovule –Derived from modified branch bearing lateral branches (with seeds) borne in the axils of leaves
Pinaceae - Embryogeny After fertilization the zygote develops. The zygote divides twice to give four free nuclei –They are arranged horizontally at the bottom of the zygote (or it can be said that they migrate to the chalazal end of the archegonium). –The four nuclei divide once more to form an eight celled structure and –Arrange themselves in two tiers of four nuclei each. –The lower one is enclosed by walls all around whereas the upper one is free from walls at their distal end
Pinaceae - Embryogeny These two tiers divide again to form a 16 celled proembryo, four tiered structure with four cells each. These are from below upwards: –embryonal tier –suspensor tier –rosette tier –Upper/open tier.
Pinaceae - Embryogeny The cells of the upper tier have no walls towards their upper side and are also called open cells. Their nuclei slowly degenerate. The rosette tier of Pinaceae is unique to this group as usually no rosette tier is formed in the other groups. The rosette tier behaves as suspensor tier in other coniferous families. The cells of the suspensor tier elongate considerably and push the terminal embryonal cells out of the archegonium and Deep into the tissue of the female prothallus, at the expense of which they grow.
Pinaceae - Embryogeny The four embryonal cells divide transversely into: –upper four cells that act as secondary suspensor cells and –lower four cells. The primary and secondary suspensor cells elongate considerably and ultimately split apart longitudinally into four parts each carrying an embryonal cell at its tip. As division continues in the embryonal cell, it passes through the quadrant and then an octant stage. Rosette embryos
Pinaceae - Embryogeny Each of the octants is a potential embryo. It is formed from one embryonal cell only. There are thus four potential embryos formed from one fertilized egg. This feature of embryogeny is termed as cleavage polyembryony which is a characteristic feature of Pinaceae. In the course of further development of the potential embryos, one takes the lead and grows more rapidly than the others.
Pinaceae - Embryogeny The actively growing potential embryo by cell division, cell growth and differentiation becomes the embryo of the seed while the others die off. Only one embryo reaches maturity in one seed. Sometimes the cells of the rosette tier also develop into embryos and this is called rosette polyembryony. In Pinus, Cedrus, Tsuga and Pseudolarix members of the family Pinaceae, all the four tiers are present: the upper, rosette, embryo & suspensor tiers. In Abies, Picea, Larix the rosette tier disappears later.
Pinaceae – Seed Adaptations The seed has many obvious functional adaptations Has winged appendage to aid wind dispersal (developed from lining of ovuliferous scale). The seed is nutritive and is eaten by animals who act as dispersal agents. The strong seed coat allows seeds to be dispersed by abiotic agents without damage. The seed coat prevents the entry of pathogens and protects it from physical damage.
Pinaceae – Seed Adaptations The seed contains a mature embryo which is ready to germinate (endosporic development). –Polycotyledonous: 2-18 –Maturing in 2-3 yrs –The megagametophyte is a readily available food source to the embryo during germination. The seed is viable for long periods in the soil. Thus, its germination can be stretched over many years or can be triggered by specific environmental stimuli, like heat.
Pinaceae - Germination Germiation is epigeal The first sign of germination is the fracturing of the seed coat and the emergence of the Radicle The hypocotyl elongates and lifts the remainder of the seed above the substrate. The cotyledons enlarge and absorb nutrients from female gametophyte (now endosperm), further growth of the cotyledons results in their separation from the megagametophyte. The cotyledons complete their development and act as photosynthetic leaves.
Pinaceae - Germination The embryonic shoot (Epicotyl) emerges and produces the first leafy stem. This overtakes the cotyledons as the source of photosynthate.