Tag: plant growth

ABA, abscisic acid was discovered for its role in regulating abscission and dormancy. It acts as a general plant growth inhibitor and an inhibitor of plant metabolism. It inhibits seed germination, stimulates the closure of stomata in the epidermis and increases the tolerance of the plant to various kind of stresses. 

Only hormone which  induce and maintain seed dormancy is ABA (abscisic acid).

Gibberellin are involved in seed germination in certain plants. They break seed dormancy by promoting mobilisation of reserve food material. In a classic experiment involving barley seed germination, researchers showed that the release of gibberellin from the embryo triggers the synthesis of $\alpha$-amylase, an enzyme that digests starch in the endosperm. As a result, glucose becomes available for absorption by the embryo. Although enzymes mobilize starch reserves in many types of seeds, gibberellin control of seed enzymes appears restricted to cereals and other grasses. 

The conditions present outside the embryo causes Exogenous dormancy and are grouped into physiological, morphological and mechanical dormancy.

Seed dormancy is an adaptation to ensure its germination during favourable period. One important function of most seeds is delayed germination, which allows time for dispersal and prevents germination of all the seeds at the same time. The staggering of germination safeguards some seeds and seedlings from suffering damage or death from short periods of bad weather or from transient herbivores; it also allows some seeds to germinate when competition from other plants for light and water might be less intense. Seed dormancy can be caused by all the factors mentioned. A dormant seed is one that is unable to germinate in a specified period of time under a combination of environmental factors that are normally suitable for the germination of the non-dormant seed. Dormancy is a mechanism to prevent germination during unsuitable ecological conditions, when the probability of seedling survival is low. 
Thus, the correct answer is option B.

Dormancy is the condition of a seed when it fails to germinate even when environmental conditions considered necessary for germination are available. The following are some main causes of seed dormancy:

Stratification involves the treatment of seeds at low temperature (5-10 degree C) under sufficiently moist conditions to break its dormancy and to induce germination.

Dormancy is defined as the condition of seed when it fails to germinate even though the envoirnment condtions, usually considered favourable for active growth, are present.

A. Ethylene serves as a hormone in plants. It acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves.

B. Cytokinins are plant hormones that cause increased celldivision by stimulating the process of mitosis. 

C. Abscisic acid owes its names to its role in the abscission of plant leaves. In preparation for winter, ABA is produced in terminal buds. This slows plant growth and directs leaf primordia to develop scales to protect the dormant buds during the cold season.

So, the correct answer is 'Abscisic acid'.

A. The storage function  of Lecythis and (Brazil nut) Bertholletia is neither endosperm nor cotyledon, but hypocotyl.

B. Nymphae- Food stored in perisperm.

C. Cotton- Food stored in cotyledons.

D. Rice- Food stored in endosperm.

So, the correct answer is 'Bertholettia'.