Plant vs Animal Hormones
The form and function of multi cellular organisms requires efficient communication between cells, tissues, organs etc. In these organisms, almost all the processes depend on the chemical signals from one part of the organism to another.
Plants too produce signalling molecules called hormones. Plant growth regulators are organic compounds, which are either natural or synthetic. They can modify or control certain specific physiological processes within the plant. Those are called hormones if they are produced within the plant. Plant hormones are a group of naturally occurring organic substances, which influence physiological processes at low concentrations. The effects of plant hormones are more often localized to the target tissues. When a hormone binds to a specific receptor, it stimulates the activation of chemical and transport steps. This in turn generates second messengers. They can trigger various responses of the cell to the original signal. Auxins, gibberellins, cytokinins, ethylene and abscisic acid are the commonly known types of plant growth regulators. Auxins are synthesized in shoot apices and young leaves. These are transmitted downwards by diffusion and through phloem. They enhance root elongation, induce roots on shoot cuttings, control phototropic movements, maintain apical dominance etc. Gibberellins are synthesized in young leaves, buds, seeds and root tips. They move upwards and downwards by diffusion or in phloem or xylem. They promote cell elongation and cell enlargement. Also, they can break seed dormancy and induce seed germination by mobilizing stored food. Cytokinins are synthesized in tissues where fast cell division is taking place. They move upwards in the xylem. Cytokinins interact with auxins and promoting cell division. Also, they keep flowers as fresh. Abscisic acid is synthesized in leaves, stems, fruits and seeds. Transportation is by diffusion and through phloem. It is an inhibitor antagonistic to auxins, gibberellins and cytokinins. It maintains bud dormancy and seed dormancy and promotes closure of stomata.
Long-term coordination of activities in animals including humans is carried out by the endocrine system. It consists of several ductless glands. Endocrine glands secrete specific chemical substances known as hormones, which are carried by the blood stream and passed to a distant part or tissue where they bring about a specific physiological function in an organism. They are produced in small quantities. Therefore, a hormone can be described as a chemical substance produced in small quantities in one part of an organism to another part and bring about a physiological change.
What is the difference between Plant Hormones and Animal Hormones?
• Plant hormones are simple organic substances and animal hormones are complex organic substances.
• Plant hormones are transported through xylem, phloem or by diffusion and animal hormones are transported in the blood.
• There are no specific organs involved in the synthesis of the plant hormones, whereas animal hormones are always synthesized in endocrine glands.