The efficacy and function of brassinolide

1. Promote cell elongation and division

Brassinolide at the nM to μM level can cause significant elongation of the hypocotyl, epicotyl and monocot floral axis, coleoptile and mesocotyl of dicotyledonous plants. Treating the second internode of bean seedlings with 10 ng of brassinolide can cause the internode to elongate and bend significantly, accelerate cell division, expand and even crack the internode. Brassinolide can increase the activity of plant DNA polymerase and RNA polymerase, and increase the content of DNA and protein. Brassinolide can also stimulate the ATPase activity on the plasma membrane of the cell, prompt the plasma membrane to secrete H+ to the cell wall, relax the cell wall, promote cell elongation, accelerate plant growth, and increase yield.

2. Promote photosynthesis

Brassinolide can increase the activity of RuBP carboxylase, accelerate the rate of CO2 fixation, increase the photosynthetic efficiency, and the plants will show darker leaf color, larger leaf area, thicker leaves, neat growth, and improved leaf surface quality. The product of photosynthesis is the fundamental source of organic matter accumulation in plants, so brassinolide can improve crop yield.

3. Conducive to pollen fertilization, increase fruit setting rate and seed setting rate

In the early stage of pollen development, brassinolides in pollen cells are in a bound state and stored in starch granules. When the pollen completes development, the starch granule absorbs fluid and releases brassinolide, which greatly increases the content of free brassinolide, which shows the important role of brassinolide in the fertilization process. Exogenous brassinolides stimulate pollen tube elongation, opening the way for fertilization. In addition, exogenous brassinolides can stimulate some plants to form bisexual flowers, increase the number of male flowers, and have obvious effects on sex differentiation and sperm formation.

4. Enhance the stress resistance of plants

Brassinolide can improve the stress resistance of plants, relieve various stresses, and greatly reduce the damage of adversity to plant growth.

(1) Low temperature stress: Spraying brassinolide can increase the seed setting rate of rice varieties by 40.1% at low temperature. The physiological function of improving the cold tolerance of rice is mainly manifested in improving the physiological metabolism of rice and promoting the growth and development of rice organs. Plants treated with 24-epibrassinolide, under the experimental conditions of 1-5°C, had electroosmotic effect (decreased), superoxide dismutase activity (decreased), ATP and proline (content increased), etc. There were obvious changes in the physiological indexes of cold tolerance.

(2) High temperature stress: application of brassinolide can significantly increase leaf chlorophyll and protein content, superoxide dismutase (SOD) and peroxidase (POD) activities of heat-sensitive rice varieties, and reduce leaf malondialdehyde content and electrolyte extravasation rate, but the effect on heat-tolerant rice varieties is relatively small.

(3) Saline-alkali stress: After treating the seeds of Eucalyptus redus with 10 μmol of 24-epibrassinolide, the seeds can still maintain a high germination rate in the environment of 150 mmol of NaCl. Ultramicroscopic examination of brassinolide-treated barley plants soaked in 500 mmol NaCl for 24 h revealed that the structure of barley leaves was preserved.

(4) Drought stress: The growth of sugar beet and other crops treated with brassinolide was better than that of the control group in a drought environment.

(5) Disease resistance: Brassinolide can also reduce the damage of certain plant diseases, such as rice sheath blight, cucumber gray mold and tomato late blight. Wu Xiaoliang et al. studied the control effect of brassinolide on tobacco mosaic disease. The research results show that the application of brassinolide can not only promote the growth of tobacco, but also achieve 70% control effect on tobacco mosaic disease. An ideal agent for tobacco mosaic disease. The disease resistance of plants is controlled by the genes of the plant itself. However, brassinolide can fully regulate the physiological and biochemical processes of plants, thereby reducing the disease. At the same time, as a plant hormone, brassinolide may induce some The expression of disease resistance genes enhances the disease resistance of plants.

5. Mitigate the impact of phytotoxicity on plants

Brassinolides have significant effects in alleviating herbicide damage. Studies by Zhou Xiaomao et al. have shown that a certain concentration of brassinolide can alleviate the phytotoxicity of ethametsulfuron on rice and corn, but attention should be paid to the concentration of brassinolide, because the concentration of brassinolide may aggravate the phytotoxicity . Mu Xingwu et al. reported that brassinolide can promote the metabolism of metsulfuron-methyl in rice, reduce the inhibition of metsulfuron-methyl on photosynthesis, and thus alleviate the phytotoxicity of the herbicide metsulfuron-methyl on rice. In addition, there are also reports about brassinolide as a safener to alleviate the phytotoxicity of herbicides sizazone and butachlor.