Cytokinins, Gibberellins and Nitric Oxide

Plant growth and development are found to be affected by the presence of multiple signaling molecules. These molecules are present in the low concentration in plants and mediate the regulation of the growth ranging from embryogenesis to reproductive development. 

The signaling molecules are termed plant hormones or phytohormones as they are related to plants. The presence of these plant hormones is found in almost all the members of the plant kingdom following algae, bacteria, and fungi, with the role of a secondary metabolite. Phytochromes and Phytohormones with their cumulative response to the light dependence and the accumulation of compounds such as betacyanin aids the plants’ growth.

Types of Plant Hormones

The plant hormones are found to be moving in the plants and with their chemical structure are involved in the formation of the varying response. The major types of plant hormones found includes:

Ethylene

It is found as a gas and has movement in the plants through the air. The primary function of the hormone involves the ripening of the fruits and the process of abscission with the dropping of ripened leaves, flowers, and fruits.

Gibberellins

It is found to be involved in the growth of plants. The primary function of the hormone involves the breaking of the dormant stage in the seeds and buds and allowing them to grow to aid the development of plants.

Cytokinins

The hormone is found to be responsible for adding age to plants by avoiding senescence. The hormone is found to have its function in the promotion of cell division and thereby contributes to the delay in aging.

Abscisic Acid

The hormone has its function in the stress condition. With the unavailability of the water, there is the closing of stomata to allow the formation of the dormant stage. The abscisic acid functions in allowing the plant to enter the dormant stage with the closing of stomata.

Auxins

The plant’s apical growth is mediated by the presence of auxin as the signaling messenger, The hormone has the function in the development of the response of the plant towards stimuli with the apical dominance.

Nitric Oxide

Another signaling molecule that is found to be involved in the development of the plant is Nitric Oxide. It is a gaseous compound with function in the morphogenesis and being formed as the reactive oxygen species it also engages in post-translational modifications. It is evident from the plant hormones that ethylene, abscisic acid, and auxins are involved in the aging process, and gibberellins, cytokinins, and nitric oxide are involved in plant growth.

Signaling properties of plant growth hormones

The hormones act as the chemical messenger and thereby interact with the receptors for the formation of the change in the development process. The signaling for the following hormones is given as:

Cytokinin signaling

The cytokines are given as the N-6 substituted purines derivative molecules. The class of the cytokinins has its role in the development by allowing the delay in the aging of leaves, the stimulation of cell division with the differentiation of plastids, and the activation of the metabolic inflow.

The signaling of Cytokinin in plants is given in the studies that evaluate the presence of a two-component system in the cytokine signaling.

The system comprises Histidine kinases with CHASE, histidine kinase, and receiver domain. The other component in the system is the regulator protein that mediates the development of the transcription to present the development of plant growth.

The signaling of cytokinin can be given as:

• Binding of Cytokinin to the CHASE domain of histidine kinase

• Autophosphorylation of the Histidine molecule in the kinase

• Transfer for phosphate to the aspartate molecule of the receiver domain.

• Regulator of the response in the regulator domain with the transfer of phosphate from receiver domain of histidine kinase

• Binding of the phosphate to the DNA binding domain 

• The activation of the glutamine-rich domain with the initiation of the transcription process.

Gibberellin Signaling

Gibberellin molecules in plants are found to be involved in the process of flower development, cell proliferation, phosphate cell response, as well as with oxidative stress response.  

The hormone is found to be involved in breaking the dormant stage and mediating plant growth. The signaling for the process is followed by the Gibberellin acid receptor molecules, and the DELLA protein. The DELLA protein is the negative regulator of the hormone, and with its binding, it regulates degradation with the ubiquitin-proteasome pathway.

The basic Gibberellin acid signaling is given as:

• The Gibberellin acid binds to the Gibberellin acid receptor, G1D1

• The binding of the acid mediates the polyubiquitination of the DELLA protein

• The degradation of the protein allows the response to break the dormant stage

Nitric Oxide Signaling

The presence of the gaseous nitric oxide compound in plants mediates its development in the stress response. The compound allows the growth with the senescence of flowers and the root nodule formation in the leguminous plants and many more.

The synthesis of the compound in the plants is mediated by the various processes as the product and the byproduct. There was the synthesis of the compound that forms the formation of the various signaling with the receptor and adds to the development of the plants.

The targets of Nitric oxide are the metalloenzyme and the metal complexes. The Fenton chemistry is suppressed with the interaction of nitric oxide through the cGMP and cADPR pathway releasing calcium ions and suppressing the formation of free radicals. This helps the plants to deal with the stress conditions. 

Conclusion

The plant hormones or phytohormones have their role in the development and growth of plants, these molecules or the compounds have their role in the abscission, aging, and various other developmental processes. Abscisic acid, ethylene, gibberellin, auxins, and nitric oxide are some classes of the compounds that are considered to be involved in plant signaling. The signaling mechanism for different classes of hormones follows different mechanisms. The basic cytokinin signaling mechanism involves the binding with histidine kinase and the transcription through the regulation domain. The gibberellic acid signaling follows the degradation of the DELLA protein, while nitric oxide signaling was mediated with the metalloenzymes.