Question

One hormone hastens the maturity period in juvenile conifers, a second hormone controls xylem differentiation while the third increases the tolerance of plants to various stresses. They are respectively
A. Auxin, gibberellin, and cytokinin
B. Gibberellin , auxin, cytokinin
C. Gibberellin , auxin, ethylene
D. Gibberellin , auxin, ABA
E. Auxin, gibberellin, ABA

Answer 1

Hint: Production of hormones in plants results in regulation of different activities such as activation of different signaling pathways, cell cycling, plant water behavior, plant response to stress, etc.

Complete answer:
Plant hormones are a gaggle of unrelated chemical substances that affect plant morphogenesis. Five major plant hormones are traditionally described: auxins, cytokinins, gibberellins, ethylene, and abscisic acid. Additionally, other nutrients and environmental conditions are going to be characterized as growth factors. Plant hormones affect all aspects of flora, from flowering to fruit setting and maturation, and from phototropism to leaf fall. Potentially, every cell can produce plant hormones. The hormones can act in their cell of origin or be transported to other portions of the plant body.
> Auxins: Auxins are the foremost hormones accountable for cell elongation in phototropism and gravitropism. They control the differentiation of meristem into plant structure and promote leaf development and arrangement. While many manmade auxins are used as herbicides, indole acetic acid (IAA) is that the sole naturally-occurring auxin that shows physiological activity. Flowering, fruit setting and ripening, and inhibition of abscission (leaf falling) are other plant responses under the direct or indirect control of auxins. Auxins also act as a relay for the results of the blue light and red/far-red responses.
> Cytokinins: Cytokinins are most abundant in growing tissues, like roots, embryos, and fruits, where cell division goes on. Cytokinins are known to delay senescence in leaf tissues, promote mitosis, and stimulate differentiation of the meristem in shoots and roots. Many effects on plant development are under the influence of cytokinins, either in conjunction with auxin or another hormone.
> Gibberellins: Gibberellins stimulate shoot elongation, seed germination, and fruit and flower maturation. These are synthesized within the foundation and stem apical meristems, young leaves, and seed embryos. GAs break dormancy within the seeds of plants that require exposure to cold or light to germinate. Gas also affects gender expression, seedless fruit development, and thus the delay of senescence in leaves and fruit.
> ABA: ABA is chemically related to the cytokinins. It is universally distributed in higher plants and has a variety of actions such as, it promotes abscission (leaf fall), the development of dormancy in buds, and the formation of potato tubers. The mode of action of abscisic acid involves the direct inhibition of the synthesis of RNA and protein.

Therefore, the correct option is D, gibberellin, auxin, ABA.

Note:
Plant hormones are part of a signal-transduction pathway. They stimulate reactions that are signal and/or causative agents for stress responses. They determine the formation of root, stem, leaf, flower, and also facilitate shedding leaves and the development and ripening of fruits. Hormones shape the plant and affect which tissues grow upward and which grow downward and even plant death. Hormones are vital to plant growth and lacking them, plants would be mostly a mass of undifferentiated cells.