5. Other Growth Regulators and Seasonal Responses


Vernalization is the low-temperature stimulation of flowering. Vernalization is important for fall-sown grain crops, such as winter wheat, barley, and rye. For example, wheat seeds are sown in the fall and survive the winter as small seedlings. Exposure to cold weather causes the plants to flower in the early spring, and an early crop is produced. If the same wheat is sown in the spring, it will take about two months longer to produce a crop. Thus, cold temperatures are not absolutely required for most crops, but they do expedite flowering. Farmers often use vernalization to grow and harvest their crops before a summer drought sets in and stunts growth.

A biennial plant is a plant that lives for two years, usually producing flowers and seeds during the second year. Biennial plants, such as carrots, beets, celery, and foxglove, survive their first winter as short plants. In the spring their flowering stem elongates rapidly, a process called bolting. Most biennials must receive cold weather to vernalize before they flower during the second year. They will then die after flowering. Treating a biennial with gibberellin is sometimes a substitute for cold temperatures in vernalization, and will stimulate the plant to grow.

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