Physiological effects of brassinolide
Promote cell elongation and division
The most salient physiological effect of brassinolide is to promote the elongation and division of plant cell. The reason why it can promote cell elongation and division: first, it enhances the DNA polymerase and RNA polymerase activity, and promote the synthesis of nucleic acids and proteins; second, it stimulates the plasma membrane ATP enzyme activity to promote the secretion of H + into the cell wall membrane and promote cell elongation. Studies have shown that, the reason why brassinolide promotes cell division is due to its activation reaction on transcription factor, CycD3, as cytokinin promotes cell division through this gene. Some researchers believe that brassinolide promotes cell elongation by inducing its division and elongation, prompting its wall expansion, increasing water absorption and adjusting the direction of microtubule distribution.
Improve the photosynthesis of plants
On one hand, brassinolide can maintain higher chlorophyll content and increase the net photosynthetic rate of leaves; on the other hand, it also can promote the transport of photosynthetic products, maintain a high content of soluble protein and can be lifted light on the growth inhibition. Thereby enhancing photosynthetic rate, and promote plant photosynthesis, so as to promote plant growth. Tests showed that with 0.1 mg/L brassins cucumber leaves after treatment can significantly improve the net photosynthetic rate, and its effects can last for one week. The researchers used brassinolide to treat cucumbers results show, it can promote cucumber palisade cells become larger, the layers increases, the accumulation of starch grains, which is beneficial nutrient absorption and translocation, increased CO2 assimilation and its assimilation to the library transit, improve the K+ absorption rate. This shows brassinolide can promote the transport of photosynthetic products, regulating the distribution of nutrients, thereby promoting photosynthesis, and promote plant growth.
Improve plant disease resistance
Catalase(CAT) and peroxidase(POD) in plants is a kind of important antioxidant enzymes, and plays an important role in clear the oxygen free radicals and peroxides which induced by the pathogen, inhibit lipid peroxidation, protecting cells from damage and other aspects. After sprayed brassinolide, the content of H2O2 in crops is increased, the content of malondialdehyde (MDA) is decreased, CAT activity is increased, and POD activity decreased slowly at first and then increased. Brassinolide makes the plant has more efficient disease resistance for it has adjusted the metabolic balance of oxygen in plants, thereby reduce oxidative stress.
Promoting the production and induction of callus
The concentration of brassinolide has a significant effect on the growth of leaf callus. Suitable concentration of brassinolide can promote callus growth. When the concentration is too high, the conductivity in callus will rise, and the peroxidase and superoxide dismutase (SOD) activity will also increase, which have an inhibitory effect on callus growth. Research shows that, with different concentrations of brassinolide in MS medium, respectively on the germination of new Cactus buds, stems and leaves for tissue culture. It shows brassinolide promote new germination cactus buds, stems, leaves endures Callus induction and bud proliferation. The researchers used Lilium Lancifolium which belonging to Liliaceae Lilium as materials to study the effects of brassinolide on the callus growth and differentiation. The results showed that after treatment of the crop by brassinolide, its growth rate of callus fresh weight and callus rates have improved significantly. The content of chlorophyll and protein in callus on the treatment group have varying degrees of improvement compared with the control group, and the peroxidase activity of callus in treatment group were slightly lower compared with the control group, but the difference was not significant.