Question

One set of a plant was grown at 12 hours a day and 12 hours a night period cycles and it flowered. While in the other set, the night phase was interrupted by a flash of light and it did not flower. Under which one of the following categories will you place this plant?
A. Short day
B. Long day
C. Darkness neutral
D. Day neutral

Answer 1

Hint: The flowering in the angiosperm plant depends on certain factors like sunlight intensity, sunlight duration, time of exposure. Thus every plant is flowering at different times like some flower at day time while some at night time.

Complete Answer:
the response of the flowering plants to periods of day or night is termed as photoperiodism. Based on the duration of exposure, plants are classified into 3 types. These are:
- Long day plants: plants that require a long period of exposure to light, exceeding a well-defined critical duration are called long day plants. Example: hibiscus, lettuce, spinach, radish, potato.
- Short day plants: plants that require a short period of exposure to light, less than a well-defined critical duration and initiated flowering before that critical duration are called as short day plants. Example: rice, soybean, onion, poinsettia.
- Day neutral plants: the plants having no correlation between the duration of light exposure and induction of flowering response is called day neutral plants. Example: cucumber, corn, tomato, pea, dandelion.
- For flowering not only light period is important, dark period also equally important for flowering.
- Therefore, if 12 hours a day and 12 hours a night period cycles of light are provided optimum condition for flowering but it is interrupted then it does not flowered because the plant is short day plant.

The correct option is A i.e. short day.

Note: It is noted that when shoot apices modify themselves into flowering apices prior to flowering then the shoot apices of plants by themselves cannot perceive photoperiods. The site of perception of exposure to light or dark duration is the leaf. Thus it has been hypothesized that there is a hormonal substance i.e. responsible for flowering by migrating from leaves to shoot apices for inducting flowering only when the plants are exposed to the necessary inductive photoperiods.