The movement of a plant part in response at an external stimulus in which the direction of response is not determined by direction of stimulus is called nastic movement.
- Thigmonastic movement is that non-directional movement of a plant part in response to the touch of an object is called T.M. such as movement of leaves of mimosa pudica plant in response to touch (Non- directional).
- Photonastic Movement is that non-directional movement of plant in response of light called photonastic movement. Such as opening and closing of petals dandelion flowers in response to intensity of light is an example of N. Movement in which stimulus is light.
Tropism (Tropic movements)
A growth movement of a plant part in response to an external stimulus in which direction of stimulus determines the direction of response is called tropism. It directional movement.
- Phototropism is the movement of a plant part in response to light. Stem of growing plant bend towards light show +ve while roots shows –ve movement.
- Geotropism is the movement of plant part in response to gravity. Movement of roots towards it shows +ve while of stem shows-ve geotropism.
- Movement of plant part in response to a chemical stimulus is called chemotropism. Growth of pollen tube towards ovules during fertilization is +ve movement.
- Movement of a plant part in response to water is called hydrotropism. Movements of roots always towards water i.e. +ve movement. Other parts which move away from water shows –ve movement.
Movement of plant part in response to touch of an object is called Thigmotropism. Climbing part of plants such as tendrils grow towards any support which they happen to touch & wind around that support.
Auxin: Naturally occurring auxin is indole 3-acetic acid.
- It promotes cell enlargement & differentiation.
- It promotes stem & fruit growth.
- It induces parthenocarpy (formation of seedless fruits without fertilisation).
effect of gibberellin has been known in Japan where certain rice plants were found to suffer from disease foolish seedling they were sterile. disease was found by Kurosava and Hori. Mevolonic is a precursor for it
- It stimulates internodes growth in rosette plant just before reproduction.
- Also induce parthenocarpy.
it is basic in nature that promotes the cell division either alone or in conjugation of Auxin. first isolate by Letham et al in 1964. it is known as Zeatin
- It promotes cell division in plants.
- It helps in breaking the dormancy of seed & buds.
- It delays ageing in leaves.
- Promote opening of stomata.
it is also called as stress hormone because stimulated in adverse condition of environment. it is also called dormin. it was first isolated by Adicott et. al in 1963 in cotton bolls.
- It promotes dormancy in seeds and buds and inhibits growth.
- It promotes closing of stomata.
- excess of its prevent RNA & protein synthesis in leaves.
- It promotes falling of leaves
it is a gaseous hormone which stimulate transverse growth but retard longitudinal growth. it was first isolated by cracker et al in 1935. its precursor is methionine. it is formed in all part of plant body.
- Promote ripening of fruits.
- Promote yellowing of leaves.