PGR (Plant growth regulators) are substances based on plant hormones (phytohormones) with the capacity to regulate or modify the physiological processes of plants, affecting their development, growth
, or maturation, among other aspects.
The history of plant plant growth regulators goes back to before Christ, when it was a common practice in the Middle East to place a drop of olive oil on figs to promote their development. It is now when it is known that the heat and time caused the decomposition of the oil, releasing ethylene, which in turn affected the ripening of the fig.
As early as the 19th century, studies by Julius Von Sachs and Charles Darwin demonstrated that various plant growth processes were regulated by substances that were transported from one part of the plant to another.
In the year 1893 when a carpenter working in a greenhouse in the Azores accidentally set fire to some wood shavings. Surprisingly, instead of being damaged, the plants flourished earlier. Later in the 1930s, it was discovered that smoke generated by combustion was the cause of accelerated blooming and that the active constituents were unsaturated gases such as ethylene. Thereafter, acetylene gas was soon used commercially in Hawaii to force the start of flowering.
Of natural or synthetic origin, they all have one thing in common: they are small chemical molecules that, at very low concentrations and doses, have the capacity to bring great benefits to the normal functioning of the crop. It is this fact in which lies the great antagonism of these substances. On the one hand, its great potential, with good handling; and on the other, the risk of misusing them, which could cause unwanted effects on the crop.
Different types of plant growth regulators
Within the phytoregulators we can differentiate 5 types of phytohormones: auxins, cytokinins, gibberellins, ethylene and abscisic acid.
Auxins are plant growth hormones, due to their ability to stimulate differential growth in response to light stimuli. They are the phytohormones that play the most important role in the development of plants. They regulate cell division and expansion, vascular differentiation, lateral root development, and apical dominance. Induce the development of auxiliary shoots, flowers and fruits
At a practical level, auxins, used as phytoregulators, have very important uses such as fruit fattening or as fall inhibitors. Among the most important are 2.4D, Triclopyr, ANA or MCPA.
This class of phytohormones, used at a higher concentration, and at a higher dose, are also commonly used as herbicides.
Cytokines are adenine derivatives identified for their ability to promote cytokinesis. They are mainly synthesized in the roots. It also synthesizes in the aerial meristems and in the young leaves. Cytokines directly activate the cell division process and can interact with auxins. They promote lateral shoot growth and leaf expansion. They delay the senescence of the leaf, promote the synthesis of chlorophyll.
In agriculture, we can use these hormones to stimulate the formation of lateral buds and the growth of tubers, increase the caliber, or the quantity and quality of the fruits. The main cytokine used in agriculture is 6-benzyladenine.
Gibberellins are diterpenoid compounds that promote germination, stem elongation and induction of flowering, among other functions.
In agriculture, they have multiple uses, since they get used to inducing flowering, increase fruit set, improve the skin, advance maturation, etc. Mainly represented by gibberellic acid (GA3) they are the most versatile phytohormones with the greatest amount of practical use.
Ethylene gas promotes root and shoot development and regulates fruit ripening, senescence, responses to pathogens, and abiotic stress.
In agriculture, they are used to promote the ripening or color of different fruits, both climacteric and non-climacteric.
Abscisic acid (ABA) promotes seed dormancy and participates in development and growth processes, as well as in the adaptive response to both biotic and abiotic stress.
In agriculture, it is used to promote coloration and pigmentation of fruits.
In conclusion, plant hormones are molecules with enormous development potential within the agriculture of the future, since they are small molecules, with low environmental impact that, used under correct management, have the capacity to bring great benefits to our productions. It is the task of companies to rigorously investigate, develop and transmit all the performance that we can obtain from them.