Induction of Flowering in Short Day Plants

Short day plants are those plants which require a photoperiod below a critical length to induce flowering. The critical length varies for different plant species. For example, chrysanthemum requires a photoperiod of 11 hours or less, while soybean requires a photoperiod of 12 hours or less.

The induction of flowering in short day plants is controlled by phytochrome, a pigment that is sensitive to red and far-red light. The phytochrome exists in two forms: the Pr form and the Pfr form. The Pr form absorbs red light and is converted into the Pfr form, which absorbs far-red light.

Induction of Flowering in Short Day Plants by Uninterrupted Long Night

When a short day plant is exposed to a photoperiod below the critical length, the Pr form of phytochrome accumulates in the plant cells. When the Pr form absorbs red light, it is converted into the Pfr form, which promotes flowering. However, during the dark period, the Pfr form is slowly converted back into the Pr form.

In short day plants, uninterrupted long nights promote flowering because they prevent the conversion of the Pfr form into the Pr form. When a short day plant is exposed to uninterrupted long nights, the Pfr form of phytochrome accumulates in the plant cells, promoting flowering.

Induction of Flowering in Short Day Plants by Interrupted Long Night

Short day plants can also be induced to flower by a short photoperiod and an interrupted long night. When a short day plant is exposed to a short photoperiod, the Pr form of phytochrome accumulates in the plant cells. When the Pr form absorbs red light, it is converted into the Pfr form, which promotes flowering.

However, when the dark period is interrupted by a brief exposure to light, the Pfr form of phytochrome is converted back into the Pr form, which inhibits flowering. This is because the interruption of the dark period prevents the accumulation of the Pfr form of phytochrome, which is necessary for flowering.

Conclusion

In short day plants, flowering is induced by a photoperiod below a critical length and uninterrupted long nights. This is because uninterrupted long nights prevent the conversion of the Pfr form of phytochrome into the Pr form, which promotes flowering. Short day plants can also be induced to flower by a short photoperiod and an interrupted long night, but the interruption of the dark period inhibits flowering by converting the Pfr form of phytochrome back into the Pr form.