Photoperiodism & Vernalization

Photoperiodism –

      Effect of sunlight on plant’s flowering is called photoperidism. It is studied by Garner & Allard in Maryland & Soybean.

Plants are mainly divided in 3 types on the basis of photoperiodism –

1.SDP (Short Day Plants) –

In this type we include such plants which needs less sunlight than critical photo period. SDPs need critical photo period or less than it for flowering. So dark phase is very important for SDPs. So these plants are also called LNP (Long Night Plants).

If dark phase is replaced by red light, the flowering can’t be done in such plants.

Examples – Tobacco, Soya bean, Viola, Xanthium, Chrysanthemum, Cannabis, Chenopodium, Mustard, Dahlia, Rice, Sugarcane.

2.LDP (Long Day Plants) –

 Which plants need sunlight more than critical photo period, is called LDPs. These plants also called SNP (Short Night Plants), because Light phase is more important than dark phase for these plants.

Examples – Barley, Avena, Potato, Radish, Carrot, Spinach.

3.DNP (Day Neutral Plants) –

Such plants which doesn’t depends on sunlight or photo-period.

Examples – Maize, Sunflower, Cotton, Cucumber, Tomato etc.

Some other types of plants on the basis of photoperiodism –

1.Short LDPs –

 These plants are LDP but in the earlier growth phase it needs less photo-period, is called Short LDPs.

Examples – Wheat

2.Long SDPs –

These plants are SDPs but in the earlier phase of growth it needs more photo-period, is called Long SDPs.

Examples – Bryophyllum

Vernalization / Yarovization –

Discovery & word given – by Lysenko

Inducing flowering in plants by cold treatment is called vernalization. Cold treatment’s stimuli are gained by apical shoot (leaves). Water and oxygen is important for vernalization.

Vernalin hormone is responsible for vernalization. This hormone is discovered by Melchers.

Devernalization – reducing vernalization’s effect at high temperature, is called devernalization.

Some important points –

1.Study of plant senescence is called phytogerontology.

2.Discovery of phytochrome – Barth wick & Hendrik discovered phytochrome. Butter isolated it and named phytochrome. Phytochrome is an open tetra pyloric porphyrin chrome.

3.Plasticity – According to atmospheric conditions or different life stages plant develops different types of structures, this character of plant is called Plasticity.

Example- Heterophylly in larkspur & Butter cup.

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