Guttation

The survival of all plants depends on their abilities to obtain, retain and transport a variety of substances into, through, and out of their bodies. Guttation is one of these abilities to exude fluids out of leaves in the form of droplets through special structures called “hydathodes.” These hydathodes are principally located at the tips and margins or edges of the leaves. Guttation is a biophysicochemical and physiological phenomenon in plants which is often noticed in the early morning in a wide range of plant species including angiosperms, gymnosperms, algae, and fungi. The water droplets exuded by guttation contain both the organic and inorganic substances including microorganisms and trickle down from the exuding sites bathing the soil surface and plant residues lying underneath. The main physiological roles of guttation consisting of essentially xylem and phloem saps driven by root pressure involve the transport of water, nutrients, metabolites, hormones, enzymes, transport proteins, pathogenesis-related proteins, etc. within the plants impacting their growth, development, biological, and economic yield. Thus, it serves a variety of purposes in plants. It may also serve as valve for release of excess hydrostatic pressure. Guttation has been shown to play a crucial role in controlling leaf senescence and photosynthesis. Its intensity has been found to be an indicator of root activity. The role of hydathodes has been suggested to be crucial in maintaining water status of plants enabling them survive and grow under water-limited situations. The guttation fluids have tendency to enrich soil fertility and improve its biochemistry by adding and activating certain enzymes such as peroxidases which catalyze the oxidative cross-linking and polymerization of certain organic compounds by hydrogen peroxide and other organic peroxides. The exudation of certain compounds having natural herbicidal effect on other plants helps exercise control over ecological balance among plant communities. Further, it may also serve as a noninvasive assessment test for pesticide residues in plants facilitating proper plant protection measures. It is of great significance that guttation is a means of excreting excess of harmful elements such as Ni, Se, etc. from metal-enriched soils thereby promoting plant growth on such inhospitable soils. Of particular interest is the fact that the variation in color of guttation fluids caused by the presence of different species of fungi therein provides a useful tool for taxonomic classification of certain fungi. Though guttation fluids are considered to be an ideal habitat for pathogen development causing some diseases however, they also contain antimicrobial phylloplane proteins that not only protect plants from certain diseases, they rather elevate disease resistance of certain field crops as well. Guttation fluids may also be used for the production of pharmaceuticals by transgenic plants. However, nutrient losses through guttation at times may be of sufficient magnitude to alter markedly the behavior of the plant. Taken all together, it may be summarized that guttation may be viewed as an efficient barometer for gauging internal chemical strategies translating into increased plant growth, development, and productivity.