Why a seed can wait for years, how a plant knows the length of the night, and why some plants need a cold winter before they flower. With the classic experiments and how to read them.
3 lessons, about 1 h 30 min3 simulations10 problems3 practice questionsPython in every lesson
Created by StemPy LabA dormant seed is alive but does not germinate, even when water, air and warmth are given. Dormancy helps a plant survive bad seasons and spread its germination over time. The causes are a hard seed coat, an embryo that is not ready, chemical inhibitors such as abscisic acid, and a need for cold or light. Scarification, stratification, gibberellic acid, nitrate and light end it.
Photoperiodism is the response of a plant to the relative lengths of day and night. Short-day plants flower when the dark period is longer than a critical length, long-day plants when it is shorter, and day-neutral plants whatever the length. The dark period is what counts, and a flash of light in the night breaks it. The leaf perceives it, and a flowering signal moves to the shoot tip.
Vernalisation is the promotion of flowering by a period of low temperature. Winter varieties of wheat, barley and rye, and biennials such as sugar beet, cabbage and carrot, need it. The cold is sensed by the shoot apex, where cells divide. It stops a plant from flowering in autumn, and it can be undone by a warm spell. Gibberellic acid can take the place of cold in some biennials.
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