Hormones and Growth Regulators in Plants One of the internal factors that influence plant growth and development is growth hormones. Auxin and gibberellin directly influence cell elongation. Cytokinin is active in stimulating cell division and abscinin has the effect of inhibiting growth. Enthylene is the only growth hormone that is in gas form, which plays a role in stimulating fruit ripening and leaf loss. Apart from these hormones, there are several phenolic compounds that can influence plant growth, for example coumarin and caffeine. However, because this compound has an effect at high levels, it cannot be included in hormones. Plant hormones are compounds that are synthesized in one part of the plant and translocated to other parts; in low concentrations (often effective at an internal concentration of around 1 uM) can cause physiological responses. Responses in target organs are not always promotive because processes such as growth and differentiation are sometimes inhibited by hormones, especially ABA. Because there are many synthetic compounds that have hormone-like activity, the term is usedgrowing substancesorplant growth regulatorfor compounds made synthetically. Basically there are five types of hormone groups that play a role in plants, namely auxin, cytokinin, gibberellin, abscisin and ethylene. Growth is not only influenced by one hormone, but is the result of cooperation between the five groups of hormones. Below we can see an outline of the role of each hormone separately in various growth processes. Auxin Auxin is a growth regulator that plays a role in cell enlargement, stimulates cell division in initiating the formation of adventitious roots and also plays a role in cell division in the cambium. At a certain concentration, auxin can promote the developmental phase but will inhibit it if the concentration is increased, and a concentration that promotes cell enlargement in shoots may inhibit cell enlargement in the roots of the same plant. The nature of this "dual" auxin action depends on the sensitivity of the tissue, the concentration of endogenous auxin in the tissue or other physiological conditions of the tissue. Cytokinins Cytokinin is a growth regulator that is found in many young organs, especially root tips. Cytokinins function in stimulating cell division, delaying leaf aging and increasing the activity of nutrient storage containers. Apart from that, cytokinins also stimulate the development of chloroplasts and chlorophyll synthesis so that the aging process can be delayed. Gibberellins Like auxin, the role of gibberellins at the cellular level is by influencing a number of physiological processes that cannot yet be clearly explained. In several cases, the role of gibberellin is to stimulate RNA and protein synthesis. In this case, the formation of hydrolase enzymes is the greatest effect of gibberellin, so that in contrast to auxin, gibberellin is able to stimulate the decomposition of reserve organic material, for example in seeds that germinate or dormant buds that grow again. The role of gibberellins is clearly visible when present together with other hormones, for example the formation of the amylase enzyme in seed germination is a collaboration between gibberellins and cytokinins. Abscisine (Abscisic Acid) Abscisin inhibits RNA synthesis due to its allosteric effect. Abscisine also stimulates the production of carbohydrate compounds which will be stored as food reserves. Abscisin inhibits the work of ATPase, so that the transport of nutrients across the membrane is hampered. This includes barriers to K's entry+ into the stoma guard cells, causing the stomata to close. Abscisine is a hormone that causes plants to be able to defend themselves against drought. In old tissue abscisin stimulates ethylene synthesis. Ethylene Gas The lipophilic nature of ethylene does not have a direct influence on enzymes or structural and chromosomal proteins. It is suspected that only the lipid part of the plasma membrane is where it works so that the transport of nutrients and organic materials in this membrane changes. Ethylene is able to inhibit auxin transport in the parenchyma. This process causes the shedding of leaves and fruit. The influence of ethylene is thought to also be related to its competition with CO2to obtain the same binding point, so that ethylene is able to influence the enzyme indirectly. This can be seen, for example, in the occurrence of ethylene racing against the activity of the enzymes phenylalaninammoniumlyase and cellulase in the shedding zone of the leaf petiole. The effect of giving ethylene is greatly reduced if CO is given at the same time2.