ABA has its uses in agriculture and is mostly applied to crops as an anti-drought measure, acting to reduce transpiration and photosynthesis to delay wilting and keep plants alive during brief periods of intense dryness. It can be used to prolong dormancy in seeds and plants, and is also used to enhance colour development in red table grapes by stimulating anthocyanin biosynthesis.
Gibberellins are growth-promoting phytohormones that act as general plant growth stimulants, playing an important role in many of the metabolic functions of vascular plants. Gibberellins promote germination by breaking seed dormancy, they are key to flower initiation and also promote bud and trichome development, stem elongation and root development. Gibberellins also help plants to respond to stress caused by environmental factors. They are present in the growing parts of plants, the apical bud, flower stamens, young leaves and the root system.
The balance between auxin and ethylene has an important role to play in leaf abscission at the end of the growing season when the cold weather triggers ethylene production at the same time as auxin levels are reducing within the ageing leaf.
Strigolactones – Works to inhibit branching through its control of auxin secretion. It is also linked to the synthesis of Abscisic Acid. Strigolactones are crucial to the relationship between plants and symbiotic fungi, stimulating the germination of mycorrhizal spores, and are essential to the exchange of nutrients between roots and fungi, and vice-versa. They also play a key role in the germination of parasitic plants of the genus Striga, which parasitise the root zone of host plants, causing serious losses in crops such as maize, rice, legumes, sugarcane among others.
Hormones can be defined as natural organic chemical messengers or signals that are produced by an organism to control the way its cells function. These hormones are normally synthesised in very small amounts by specialist cells in one part of the organism, before being transported to the part where they take effect. Humans and other animals do this by means of an endocrine system, a network of glands that have evolved to produce and store hormones which are then moved to their target site through the body’s circulatory system. Plants, however, do not possess an endocrine system. Instead, all plant cells have the potential to synthesise hormones, which are then either transported via vascular tissue as well as cell-to-cell through a process known as plasmodesmata or on occasion used locally.
Indeed, it is the balance between auxins and cytokinins that means plants are generally wider and more bushy at the bottom than at the top. In 1957, Skoog & Miller showed that the ratio of cytokinin to auxin was responsible for the differentiation in cell development, with high auxin concentrations promoting roots and high cytokinin levels promoting shoots. When the ratio is equal, simple cell division without differentiation is promoted, a function which has become very useful to produce callus material as part of the tissue culture process.
Young willow branches and shoots are high in salicylic acid, ideal for rooting clones.
Plants produce abscisic acid in their terminal buds as winter approaches, which works to halt growth in preparation for the coming cold weather. In drought conditions, ABA is produced in the roots and then transported to the leaves, where it stimulates the closing of stomata, temporarily halting transpiration and reducing water demand in times of scarcity.
Maize is a great source of cytokinins and perfect for a seed sprout tea to apply in flower and veg
In this blog post, we take a look at the complex world of plant hormones, talking about the wide range of effects they have, and how they control and