Question

Autumn colouration of leaves appear only in

• A. Tropical regions
• B. Evergreen plants
• C. Temperate deciduous plants
• D. Deserts

Answer 1

The correct option is C Temperate deciduous plants

Autumn leaf colour is a phenomenon, that affects the normally green leaves of many deciduous trees and shrubs. They take on various shades of red, yellow, purple, black, orange, pink, magenta, blue and brown during a few weeks in the autumn season. During the growing season, hormone auxin prevents the growth of a special layer of corky cells called as the abscission layer.

In late summer or early fall, days start to shorten and nights become longer. Plants are sensitive to the length of darkness each day and when nights reach a particular threshold value, an end to auxin production is triggered. This decline in auxin allows the abscission layer to form at the base of each leaf stem, which cuts off the supply of water and nutrients to the leaves. It also prevents the transport of carbohydrates from the leaves to the rest of the plant. When this happens, leaves stop replenishing chlorophyll as it is degraded and it disappears from the leaves relatively quickly. This is when we start to see colour transitions in leaves.