PHOTOPERIODISM and VERNALISATION

/ NCERT LINE BY LINE, Plant Growth and Development / By Prof. Siddharth Sanghvi

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Photoperiodism: Key Details

Aspect	Details
Definition	The response of plants to periods of day and night, influencing flowering based on light and dark duration.
Requirement for Flowering	Some plants require specific light exposure to induce flowering and can measure the duration of light exposure.
Categories of Plants	Long Day Plants (SNP): Require light exposure exceeding a critical duration. Short Day Plants (LNP): Require light exposure less than a critical duration. Day-Neutral Plants: Flowering is independent of light exposure duration.
Critical Duration	Varies between plant species and determines flowering based on light exposure.
Importance of Dark Period	The duration of dark periods is equally significant in influencing flowering.
Photoperiod Perception	Leaves are the site of light and dark duration perception. Hormonal substances migrate from leaves to shoot apices to induce flowering under suitable conditions.
Role of Phytochrome	Phytochrome is a light-sensitive pigment that helps in perceiving light and dark periods. Exists in two forms: Pr (absorbs red light) and Pfr (absorbs far-red light). Pfr is the biologically active form and plays a role in signaling flowering in response to photoperiods.
Additional Notes	Shoot apices modify into flowering apices but cannot perceive photoperiods directly. Flowering depends on a combination of light and dark exposures. Short Day Plants are now referred to as Long Night Plants (LNP), and Long Day Plants as Short Night Plants (SNP).

Vernalisation: Key Details

Aspect	Details
Definition	The promotion of flowering in plants due to exposure to a period of low temperature.
Purpose	Prevents premature reproductive development late in the growing season. Allows plants sufficient time to reach maturity.
Effect on Food Crops	Spring Varieties: Planted in spring, they flower and produce grain within the growing season. Winter Varieties: Planted in autumn, they germinate, overwinter as seedlings, grow in spring, and are harvested mid-summer.
Examples of Food Crops	Wheat, barley, rye (having winter and spring varieties).
Effect on Biennials	Biennial plants are monocarpic (flower once and die). They usually flower in the second growing season. Examples include sugarbeet, cabbages, and carrots. Cold treatment during the first growing season stimulates flowering in response to subsequent photoperiods.
Role of Cold Treatment	Vernalisation involves exposing seeds or plants to temperatures between 0°C and 4°C. Cold treatment is typically applied to seeds or young plants before planting. Ensures synchronized flowering and better yield in crops like winter wheat.
Improving Winter Wheat Quality	Expose seeds or seedlings to cold conditions (0°C to 4°C) for a specific duration before planting. This process simulates overwintering, accelerating the flowering and maturity process. Leads to improved grain quality and higher yields in a single growing season. Proper soil preparation and post-vernalisation care enhance crop output further.