Plant Growth and Development

As growth regulators control the growth of plants, pesticides control the pests and fertilizers enhance productivity of the soil, hence all of these are regarded as agricultural chemicals.

Day neutral plants do not need a specific photoperiod to produce flowers. They are also called intermediates or photoneutrals. Their photoperiod varies from a few hours to 24 hours of uninterrupted light e.g. tomato, cucumber, sunflower, Helianthus annuus, maize and cotton etc.

Due to continued formation of secondary tissues in the older stem and roots however the epidermis gets stressed and ultimately tends to rupture and followed by death of epidermal cells and outer tissues, and a new protective layer is developed called periderm. Structurally it consists of three parts Phellogen or Cork cambium, phellem or cork and phelloderm. Usually in the periderm of most plants, certain areas with loosely arranged cells have been found, which possess more or less raised and corky spots where the underneath tissues break through the epidermis. Such areas are universally found in the stems of woody plants. These broken areas are called lenticels, which perform the function of exchange of gases in the absence of stomata.

“It has been known since the 1930s that the plant hormone auxin is released by the plant’s actively growing tip and is transported down the main stem where it has an indirect effect on buds to inhibit branching. There are a number of ways in which the hormone exerts this effect and we have discovered a new path by which it works.”

The research suggests that for a shoot tip to be active, it must be able to export auxin into the main stem. But if substantial amounts of auxin already exist in the main stem, export from an additional shoot tip cannot be established

2, 4-D is a selective weed killer. It kills broad-leaved plants (dicots) but do not affect mature monocot plants.

Auxins induce cell elongation. IAA is true auxin hormone. Auxins are generally acidic in nature.

Ethylene is responsible for ripening of fruits.

Cytokinin is the hormone responsible for cell division as it stimulates the metabolism and the formation of flowers on side shoots.

Vernalization is the induction of a plant's flowering process by exposing it to low temperature. It shortens the juvenile or vegetative phase of the plant. This term was coined by Lysenko in 1928.

Cryobiology is the branch of biology that studies the effects of low temperature on living things within Earth's cryosphere or in science.

Phototropism is the orientation of a plant or other organism in response to light, either towards the source of light or away from it.

Pruning is a horticultural and silvicultural practice involving the selective removal of certain parts of a plant, such as branches, buds or roots.

Cork is impervious to water because it has deposition of suberin. The thin walls of those cells are saturated with fatty waxy substance, called suberin which makes cork almost impervious to water and air.

The ABA inhibits gibberellin induced growth activities on account of this antagonistic behaviour, it is also called antigibberellin.

The bud dormancy is induced by adantscissic acid (ABA). The level of endogenous ABA increases with the onset of dormant period and decreases when it is broken.