Plant Growth and Hormones

Lemon juice helps keep the apple from browning, because it is full of ascorbic acid (Vitamin C) and it has a low (acidic) pH level. Ascorbic acid works because oxygen will react with it before it will react with the polyphenol oxidase. However, once the ascorbic acid gets used up, the oxygen will start reacting with the enzyme and browning will occur. Lemon juice's low pH level also helps prevent browning. Polyphenol oxidase works best when the pH level is between 5.0 and 7.0. However, below a pH level of 3.0, the enzyme becomes inactivated. The pH of lemon juice is in the 2.0 range, making it very effective against browning.

Abscissic acid regulates abscission (the shedding of leaves, flowers and fruits from the living plant) and dormancy. It acts as general plant growth inhibitor and also inhibit plant metabolism. It inhibits closure of stomata in epidermis, and increase tolerance of plant to various kinds of stresses, and therefore called as stress hormone.
ABA plays an important role in seed development, maturation and dormancy. By inducing dormancy, ABA helps seeds to withstand dessication and other factors favourable for growth.

Abscisic acid is the hormones also called as stress hormones as they function in stress conditions. They are also known as dormant as they induce dormancy in buds. It mostly induced bud dormancy at the start of the winter season. They are generally growth hormone which inhibits growth normally.

Abscisic acid inhibits seed germination and stimulates the closure of stomata in the epidermis and increases the tolerance of plants to various kinds of stresses. Therefore, it is also called the stress hormone.

A plant will abscise apart either to discard a membrane that is no longer necessary, such as a leaf during autumn or a flower following fertilization or for the purpose of reproduction. Most deciduous plants drop their leaves by abscission before winter, whereas evergreen plants continuously abscise their leaves.

Application of GA can induce flowering in long day plants. It has no favourable effect on size of flower and fruit in certain plants. The genetically dwarf plants can be made tall by application of GA.

Crown gall disease involves the transfer of T-DNA into the plant genome, which causes the plant cells to produce auxins and cytokinins, leading to excessive meristematic activity and tumor growth.

The Pr form absorbs light between $660$ to $680 nm$ and absorbs at a peak of $666 nm$. It is the form synthesized in dark-grown seedlings. When Pr absorbs red light, it is converted to the $Pfr$ form.

 Vernalization is the process of induction of flower by prolonged exposure to cold temperature. It is an adaptation shown by plants which are exposed to harsh winter followed by relatively short growing seasons. Vernalization is practiced artificially too.

In many plants, the temperature has a profound effect on flowering. Some plants do not flower under the inductive photoperiod conditions but flower when a cold temperature treatment is given to them. This acquisition or acceleration of the ability to flower by a chilling treatment is said to be vernalization. It is the method of inducing early flowering in plants by pretreatments of their seeds at a very low temperature. Thus option C is the correct answer. 

Vernalization is the process by which plant can be induced to flower by exposing it to the prolonged cold of winter. The term was coined by Lysenko in 1928. He stated that certain plants can be made to flower by providing low temperature treatment to young plants or moistened seeds. Other terms like jarovization, springification were also coined for the same phenomenon. However, today the most accepted term is vernalization.

Vernalization is the process by which plant can be induced to flower by exposing it to the prolonged cold of winter. Plants can be made to flower by providing low temperature treatment to young plants or moistened seeds. Vernalin is a plant hormone that is produced on vernalization. It induces flowering in plants.

Vernalization is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional seasonal cues or weeks of growth before they will actually flower. Vernalization is sometimes used to refer to herbal (non-woody) plants requiring a cold dormancy to produce new shoots and leaves but this usage is discouraged. Many plants grown in temperate climates require vernalization and must experience a period of low winter temperature to initiate or accelerate the flowering process. This ensures that reproductive development and seed production occurs in spring and winters, rather than in autumn. The needed cold is often expressed in chill hours. Typical vernalization temperatures are between 5 and 10 degrees Celsius (40 and 50 degrees Fahrenheit).

Vernalization is the process by which plant can be induced to flower by exposing it to the prolonged period of low temperature or cold. After this, plants show quicker flowering. Gibberellic acid is a plant hormone which helps in growth of stem. It also brings about the rapid flowering in plants.