The dormancy of seed is regulated by
Dormancy is a mechanism to prevent germination during unsuitable ecological conditions, when the probability of seedling survival is low. It is mainly regulated by ABA (Absicsic acid).
Ageing is retarded by
Cytokinins are a class of plant growth substances (phytohormones) that promote cell division or cytokinesis, in plant roots and shoots. They are also involved in cell growth and differentiation but also affect apical dominance, axillary bud growth and leaf senescence.
Eg, degradation of protein and chlorophyll was delayed in the detached leaves of Xanthium, if cytokinin was used in a medium.
Which hormone is responsible for mobilization of storage food during seed germination ?
Gibberellin is responsible for mobilization of storage food during seed germination. After getting moisture, the embryo of seed releases gibberellins. It induces the alemone layer of endosperm to produce enzymes (e.g. -amylase). These enzymes digest stored starch to mobilize sugars for germination.
Gibberellin was first extracted from
roots of higher plants
Yabuta and Hayashi (1939) isolated an active substance from a fungus, Gibberella fujikuroi and called it gibberellin-A. It causes backane disease in rice seedlings.
Avena curvature test is a bioassay for examining the activity of
Bioassay is a testing of biological activity like growth response of a substance by employing plant part. Avena curvature test is a bioassay for examining the activity of auxins. It is based upon experiments of Went. 10° curvature is produced by auxin concentration of150 g/lit at 250C and 90% relative humidity. It can measure auxin upto 300g/litre. Auxin from shoot tip or any other plant organ is allowed to diffuse in a standard size agar block. 15- 30 mm long oat coleoptile grown in dark is held vertically over water. 1 mm tip of colcoptile is removed without injuring the primary leaf. After 3 hours a second decapitation is carried out for 4mm distance. Primary leaf is now pulled loose and agar block supported against it at the tip of decapitated coleoptile. After 90- 100 mm the coleoptile is found to have bent. The curvature is measured
The plants respond to photoperiods due to the presence of :
Photoperiodism is the response of an organism to seasonal changes in day length.
It is regulated by the photoreversible pigment called phytochrome. Phytochrome is a photoreceptor chromoprotein.
Pencils are prepared from the wood of
Juniperus virginiana wood is used for making pencils.
Pinus vinaster wood is used for carpentry items such as furniture, window frames, floors, roofing etc.
Chamaecyparis piscifera is used as a material for builiding palaces,temples, shrines and baths.
Abies pindrow is used for curing Respiratory ailments like Asthma.
Gibberellins can promote seed germination because of their influence on
rate of cell division
production of hydrolyzing enzymes
synthesis of abscisic acid
absorption of water through hard seed coat
production of hydrolyzing enzymes
Gibberellins induces the hydrolyzing enzymes in the endosperm of germinating seeds. It stimulates the production of digestive enzymes like proteases, amylase, lipase which help to mobilise stored nutrients.
The wavelength of light absorbed by Pr form of phytochrome is
When Pr absorbs red light (660- 665 nm) it is converted into Pfr form and when Pfr absorbs far red light (730-735 nm) it is converted into Pr form
First natural cytokinin was discovered by :
Skoog and Miller
Benson and Calvin
Thimann and Went
First natural cytokinin was obtained from unripe maize grains or Kernels. It is known as zeatin or 6- hydroxy 3- methyl trans butenyl amino purine.