Plant Hormones- Classification, Function and Detection Methods
Online InquiryWhat Are the Plant Hormones?
Plant hormones are organic substances that are metabolically synthesized in specific plant tissues by plant cells receiving certain signal induction and regulate plant growth and development by binding to specific protein receptors in trace amounts.
Plant endogenous hormones include auxins, gibberenllins, cytokinins, ethylene, abscisic acid, and brassinosteroids (BRs). Among them, growth hormone, gibberellin, cytokinin and brassinosteroids belong to growth promoters, while abscisic acid and ethylene belong to growth inhibitors. In addition to the six major hormones, in recent years, scientists have discovered a variety of other substances that have regulatory effects on plant growth and development, such as polyamine (PAs), jasmonic acid (JAS), salicylates (SA), plant polypeptide hormone hormone, zearalenone, oligosaccharin, 1-triacontanol, etc.
Functions of Plant Hormones
Auxins are among the first discovered and most physiologically important substances. Auxins are mostly concentrated in the tissues of plants with high division and growth metabolism, such as root tips, stem tips, young leaves, developing seeds and fruits, etc. Auxins can only be transported from the top to the base of the plant body. This unidirectional form of transport is called polar transport. Auxins in leaves can also be transported non-polarly through the bast to other parts of the plant.
The main physiological roles of auxins are:
- Promoting the formation of lateral roots and adventitious roots
- Promoting the growth of shoot sheaths and stems, inhibiting root growth and maintaining apical dominance
- Delaying leaf senescence and abscission
- Inducing female flower differentiation and unisexual fruit development
- Promoting fruit development and delaying fruit ripening
- Promoting leaf expansion
- Inducing vascular cell differentiation. Low concentration induces phloem differentiation, high concentration induces xylem differentiation, etc.
Although erythromycin is the most diverse of the plant hormones found, only a few of them are physiologically active in plants. GAs are synthesized mainly in tissues such as embryos, stem tips, root tips, growing seeds and fruits. The transport of GAs is not polarized. GA synthesized in the root tip can be transported upward through the xylem. The GA synthesized in the upper stem and leaves can be transported downward through the bast.
The main physiological roles of gibberellin are:
- Promoting stem elongation
- Inducing flowering in plants. Induces plants without vernalization and long day plants to flowering with significant effect
- Breaking dormancy and promoting seed germination. Gibberellins initiate the synthesis of various hydrolytic enzymes, thus effectively providing nutrients for seedling growth
- Promoting male flower differentiation (most effective for Cucurbitaceae)
- Inducing unisexual fruit set in some plants and increasing fruit set rate
- Inhibiting maturation and organ senescence
- Delaying leaf senescence
- Promoting tuber formation
- Increasing growth hormone content in plants and promoting vascular bundle differentiation
Cytokinins (CTK) are a class of adenine derivatives. The natural CTK is divided into free state cytokinins and bound state cytokinins. The natural free state cytokinins in plants include zeatin (ZT), zeatin riboside (ZR), dihydrozeatin (DHZ), dihydrozeatin riboside (DHZR), and isopentenyl adenine (IP). The bound state cytokinins include methionyl zeatin, methionyl isopentenyl adenosine, isopentenyl adenosine (iPA), etc.
Above-ground and below-ground actions of cytokinin in regulating plant development (Werner et al., 2009)
In embryonic plants, cytokinins are mainly synthesized in tissues such as root tips, stem ends, developing fruits and germinating seeds.
The main physiological effects of cytokinins are:
(1) Promoting cell division. Cytokinins promote cytoplasmic division, which leads to cell size expansion. Growth hormone, gibberellin and cytokinin have different mechanisms in cell division. Cytokinins are used for tissue expansion and thickening through cytoplasmic division. Growth hormone is primarily responsible for tissue elongation through division of the nucleus. Gibberellins are mainly used for stem elongation by shortening the G1 and S phases of the cell division cycle.
(2) Delaying plant senescence. Zeaxanthin nucleosides and dihydrozeaxanthin nucleosides are most effective in slowing down the rate of protein and chlorophyll degradation and inhibiting the activity of some hydrolytic enzymes associated with plant tissue senescence.
(3) Inducing the differentiation of shoots.
(4) Eliminating apical dominance and promoting the growth of lateral shoots. Cytokinin and growth hormone have antagonistic effects, and CTK accelerates the rate of differentiation of lateral buds into transporting tissues.
(5) Break seed dormancy. Cytokinin can break the dormancy of some plant seeds and promote their germination.
ABA is synthesized mainly in organs that are dormant and about to be shed. The content of ABA in plants increases rapidly under stress conditions. ABA is mainly transported in free form, and the transport is not polar.
Current model for the major abscisic acid (ABA) signaling pathways in response to cellular dehydration (Miyakawa et al., 2013)
Abscisic acid, as a growth inhibiting substance regulating dormancy, abscisic acid and plant stress response, has the following main physiological functions:
(1) Inhibiting plant growth. Abscisic acid inhibits the secretion of cell H and prevents cell wall acidification and cell elongation, which in turn inhibits the elongation growth process of organs such as the germinal sheath, embryonic axis, shoot and root.
(2) Causes stomatal closure. ABA promotes the outflow of potassium ions and chloride ions from guard cells, causing higher water potential in guard cells than in surrounding cells, thus causing cellular water loss causing organ closure.
(3) Increase resistance to stress. Drought, cold, high temperature, salinity and water-logging all cause an increase in ABA content in the plant, which induces the resynthesis of certain enzymes related to plant resistance in the plant and increases the plant's resistance to stress.
(4) Affect sexual differentiation. For example, gibberellin treatment can make the female plants of cannabis form male flowers, but the spraying of abscisic acid has the opposite effect and cannot make the male plants form female flowers.
(5) Promoting dormancy and inhibiting germination. For example, the presence of abscisic acid in the seed coat of many dormant seeds, and the ABA content in the leaves of plants in autumn is significantly more than in other seasons.
(6) Promoting abscission. ABA can promote the formation of isolated layer of organs, thus accelerating organ abscission.
Plant Hormone Analysis Methods
Ultra-trace endogenous plant hormone determination is an important tool for studying the molecular mechanism of plant hormone action. However, the low levels of phytohormones in plants and the complexity of plant matrices pose difficulties for their accurate quantitative analysis.
Creative Proteomics' LC-MS-based analytical platform enables the qualitative and quantitative analysis of a wide range of plant hormones.
Advantages of our plant hormone analysis platform:
- High specificity and accuracy: precise characterization and absolute quantification using MRM technology
- Advanced platform: 5500 Q-trap mass spectrometry with wide linear range
- Strict quality control: double quality control of internal standard + external standard
- High acquisition rate for reliable quantification of more analytes
- Excellent durability for reproducible detection of low levels of analytes in complex matrices
References
- Werner, T., & Schmülling, T. (2009). Cytokinin action in plant development. Current opinion in plant biology, 12(5), 527-538.
- Miyakawa, T., Fujita, Y., Yamaguchi-Shinozaki, K., & Tanokura, M. (2013). Structure and function of abscisic acid receptors. Trends in plant science, 18(5), 259-266.
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