Development in the Meristem
The meristem is the growth area of a plant. In the meristem the cells divide very rapidly. After the division of one cell into two cells, one stays in the meristem and one becomes part if the plant body with specialized tissue.
Types of Meristem Tissue
One type of meristem tissue is apical meristem which is found in the roots and shoots of plants. Division of the apical meristem results in growth of the roots, leaves and flowers. In the roots the apical meristem is protected by the root cap. In the stem it is protected in the terminal bud. Terminal buds stop growing in the winter. Another type of meristem tissue is lateral meristem. This is the growth of tissue beneath the bark of tree stems. Lateral meristem thickens the cylinders of tissue. In woody plants, there is vascular cambium lateral and cork cambium lateral. The vascular cambium protects the xylem and phloem cells in the roots and stems. The cork cambium produces the outer bark.
Hormones
Hormones enhance plant growth. There are plant growth hormones which are promoter hormones and inhibitor hormones that block the growth.
Classes of Hormones
Auxins
-Stimulate and inhibit
-promote plant elongation
-apical bud growth and growth/ripening of fruit
-lateral bud growth inhibited
-regulates cell division in vascular cambium, dropping of fruit and leaves
-present in low quantities but exert strong influence
-synthetic auxins can cause unwanted plants to grow so fast that they exhaust carbohydrate reserves then die
Gibberellins
-promote cell division and elongation in shoots
-can cause stem to elongate just before flowering -Called bolting which raises flower to pollinators and wind (most successful)
-dwarf plants have mutated genes which block synthesis of gibberellins. If gibberellin is applied artificially to stem it will grow normally
Cytokinins
-stimulate cell division and leaf mesophyll growth
-mostly concentrated in endosperm tissue of young fruit
Etheylene
-fruit ripening- produces etheylene gas before rise in cellular respiration which corresponds to mass of conservation of starch into sugar (sugar increases sweetness of fruit)
-related to softening and colour change in ripening fruit
Abscisic Acid
-growth regulator
-usually acts as inhibitor
-promotes stomata closure, inducing seed and bud dormancy providing resistance to water stree
-Stimulate and inhibit
-promote plant elongation
-apical bud growth and growth/ripening of fruit
-lateral bud growth inhibited
-regulates cell division in vascular cambium, dropping of fruit and leaves
-present in low quantities but exert strong influence
-synthetic auxins can cause unwanted plants to grow so fast that they exhaust carbohydrate reserves then die
Gibberellins
-promote cell division and elongation in shoots
-can cause stem to elongate just before flowering -Called bolting which raises flower to pollinators and wind (most successful)
-dwarf plants have mutated genes which block synthesis of gibberellins. If gibberellin is applied artificially to stem it will grow normally
Cytokinins
-stimulate cell division and leaf mesophyll growth
-mostly concentrated in endosperm tissue of young fruit
Etheylene
-fruit ripening- produces etheylene gas before rise in cellular respiration which corresponds to mass of conservation of starch into sugar (sugar increases sweetness of fruit)
-related to softening and colour change in ripening fruit
Abscisic Acid
-growth regulator
-usually acts as inhibitor
-promotes stomata closure, inducing seed and bud dormancy providing resistance to water stree
Plant Tropisms
Phototropism
-growth of plant is affected by light
-grow towards sun- growth caused by different amounts of auxins prouced on the light and dark side of the stem. Dark side grows faster because auxins accumulate on shaded side which elongates cells on shaded side and bends toward sun
Gravitropism
-Growth of plant is affected by gravity
-roots grow down (positive gravitropism)
-stem grows up (negative gravitropism)
Thigmotropism
-response to touch
-specialized cells in epidermis
-vining plants are strong positive thigmotropism- grow towards object and coils around
Nastic response
-Caused by stimulus- not directional or permanent
-leaves close at touch
-result of change in turgor pressure in cells- drop in pressure= cells become limp (leaves fold down)
once stimulus is ceased, turgor pressure restores= leaves open
-growth of plant is affected by light
-grow towards sun- growth caused by different amounts of auxins prouced on the light and dark side of the stem. Dark side grows faster because auxins accumulate on shaded side which elongates cells on shaded side and bends toward sun
Gravitropism
-Growth of plant is affected by gravity
-roots grow down (positive gravitropism)
-stem grows up (negative gravitropism)
Thigmotropism
-response to touch
-specialized cells in epidermis
-vining plants are strong positive thigmotropism- grow towards object and coils around
Nastic response
-Caused by stimulus- not directional or permanent
-leaves close at touch
-result of change in turgor pressure in cells- drop in pressure= cells become limp (leaves fold down)
once stimulus is ceased, turgor pressure restores= leaves open