VERNALIZATION

Vernalization Vernalization is the effect of cold temperature on flowering. It prevents precocious reproductive development late in the growing season and enables the plant to have sufficient time to reach maturity. These plants remain vegetative during the warm season, receive low temperature during winter, grow further & then bear flower …

PHOTOPERIODISM

Photoperiodism Photoperiodism is the effect of light on flowering. Garner & Allard 1st reported the effect of light on flowering in Maryland Mammoth (variety of tobacco) & Glycine max. On the basis of photoperiodic requirements, plants are divided into 3 types: Short day plants: in these plants, the dark period …

Abscisic acid

Abscisic acid: Abscisic acid (ABA) is a growth inhibitor. Discovered by 3 independent researchers as inhibitor-B, abscission II & dormin.They were chemically identical. Addicott isolated it from cotton balls. Later renamed as abscisic acid. Site of synthesis:  chloroplast in leaves. Translocated through phloem. Formed by oxidation of carotenoids.

Ethylene

Ethylene: Ethylene is a volatile gaseous compound that stimulates transverse growth but retards longitudinal growth. Cousins confirmed its presence in ripened oranges, that hastened the ripening of stored unripe bananas. Formed in all parts of the plant i.e., roots, leaves, flowers, seeds. Maximum synthesis occurs in ripening fruits & tissues …

CYTOKININ

Cytokinin: Skoog & co-workers showed that callus formation occurred when internodal segments of tobacco are cultured. In the nutrient medium in addition to auxin, they provided extracts of yeast, vascular tissues, coconut milk or DNA. Miller first discovered it from autoclaved Herring sperm DNA. He named it as kinetin. Letham first obtained natural …

Gibberellins

Gibberellins A Japanese farmer in his rice field found a seedling that is extremely tall, he named it as Bakanae means ‘foolish seedling’. Kurosawa showed that it was due to an infection by fungus Gibberella fujikorai (Fusarium monoliforme). Yabuta & Sumuki isolated it & named it as Gibberellins. Chemically it …

Auxins

Auxins: Term ‘auxein’ means to grow. Weak organic acid Found in the root & shoot tip. Shows polar movements: i.e., shoot tip downwards & root tip upwards. Charles Darwin & his son Francis Darwin: 1st reported the presence of auxin in the coleoptile of canary grass (Phalaris). They showed that …