Resist Low Temperature, Resist Drought, Keep Flowers and Fruits Setting, Improve Quality The Broad Prospect of Application of Natural Brassinosteroid

1. The current situation of global agriculture

1.1 Global extreme weather events are more frequent, and agricultural production is facing challenges

Under the circumstance of global warming, extreme natural disasters caused by global climate change increase the instability of agricultural production [1]. Agricultural production is a production activity in which natural reproduction and economic reproduction are intertwined. Climate change is an important challenge in the agricultural production. At present, high temperature weather is frequent in many areas in the northern hemisphere, which has brought various adverse effects on global agricultural production. Firstly, there is a greater risk of grain crop yield reduction. Secondly, agricultural production costs may rise. Thirdly, uncertainty in the global grain market will increase [2]. The World Meteorological Organization believes that due to climate change, extreme high temperatures are expected to occur more frequently and more intensely in the future. How to deal with the significant negative impact of extreme high temperature on agricultural production is an unavoidable issue [3].

1.2 The pursuit of quality and yield stability of agricultural products has become one of the main goals of agriculture

Improving the yield and quality of crops has always been one of the main goals of global agriculture [4]. This goal can be roughly achieved via the following researches: firstly, to improve the production capacity of crops and agricultural sideline products. Secondly, to improve the ability of crops to resist virus, pests, and fungi. Thirdly, to improve the ability of crops to resist drought and cold [5]. The use of phytochemical control technology and plant growth regulators is an important way to increase crop yield and improve crop quality, and it is of great significance to deeply tap the potential of crop yield [6].

2. Plant growth regulators play a significant role in agriculture

Plant growth regulators are a type of product that control plant growth and development, including synthetic analogs of the natural phytohormones and the hormones that are extracted from plants. The plant growth regulators are products that are developed when people understand the structures and mode of actions of natural plant hormones, understand microanalysis, organic synthesis, plant physiology and biochemistry, and master science and technology including modern agriculture, horticultural cultivation and etc. [7]. The application of plant growth regulators is one of the five new technologies in agriculture. It has the advantages of small investment, quick effects, small dosage in ppm level (parts per million), significant results, and high input-output ratio. With the development of agricultural production technology, the role of plant growth regulators is becoming more and more important. On the one hand, it can further improve crop yields. On the other hand, the plant growth regulators can improve plant immunity, promote plant health, reduce the use of pesticides and damage caused by adverse weather conditions to crops. The research on plant growth regulators and their application in agricultural production is one of the major advances in modern plant physiology and agricultural science. Agricultural scientists from all over the world have attached great importance to this field. The application of plant growth regulators has become an important symbol of the development level of agricultural science and technology [8].

Fig. 1: Main functions of plant growth regulators (from Science of Crop Protection)

3. Research status of plant growth regulator-Brassinosteroids

3.1 The discovery of brassinosteroids

Since the researches on auxin started in the 1930s, plant growth regulators were developed rapidly, followed by the discovery of gibberellin (GA), abscisic acid (ABA), cytokinin (CTK), ethylene (ETH) and brassinosteroids (BRs). Among the different plant growth regulators, brassinosteroids have become a hot topic among scientists since its discovery. Brassinosteroids are a class of plant hormones that play multiple roles in plant growth and development, which were firstly extracted from rapeseed pollen by J.W. Mitchell and others in 1970 [10]. In 1979, Grove et al. isolated 4mg biologically active substance from rapeseed bee pollen, and determined its chemical structure by crystal diffraction analysis. The compound was named brassinolide (BL) [11]. In 1982, Japanese scientists Yokota et al. Isolated another biologically active substance - castasterone (CS) - similar to BL from the galls of chestnut, and proved that CS is the direct precursor of BL. After that, scientists isolated more than seventy analogs of brassinolide from various organs of different plants, and named this group of compounds brassinosteroids (BRs) [12]. In 1998, brassinosteroids were officially recognized as the sixth class of plant hormones at the 16th Annual Conference of International Plant Growth Substances Association [13].

Fig. 2: Chemical structures of brassinolide and castasterone [12]

3.2 Mode of actions of brassinosteroids

In vivo synthesis of BRs occurs in the endoplasmic reticulum of the synthesis site, and is then secreted outside the cell through the Golgi apparatus and bound by receptors on the cell membrane of the effector site, thereby activating a series of intracellular signal transduction pathways. The BRs receptor protein BRI1 and the receptor complex protein BAK1 exist on the cell membrane [14]. In the absence of BRs, BRI1 and BAK1 interact with their inhibitory proteins BKI1 and BIR3 respectively, inhibiting the formation of the BRs receptor complex and keeping the BRs signaling pathway closed. Cytoplasmic protein kinase BIN2 is a negative regulatory factor of BR signaling, which can phosphorylate the BRs transcription factors BES1 and BZR1 and keep them stay in the cytoplasm and cannot enter the cell nucleus to perform transcriptional activation functions. In the presence of BRs, the extracellular structure of the receptor protein BRI1 can bind to BRs and cause changes in the intracellular molecular structure. At the same time, the receptor complex protein BAK1 on the cell membrane is recruited to form the BRI1-BR-BAK1 receptor complex and activate the intracellular signal transduction pathways [15, 16].

Fig. 3: Diagram of BRs receptor and bound with BRs

Fig. 4 Intracellular BR Signal Transduction Pathway [16]

4. Discovery and advantages of Natural Brassinosteroids

4.1 Source and industrialization of Natural Brassinosteroids

It has been reported that the production of ″Brassinosteroids″ are divided into two distinct processes: natural extraction and artificial synthesis. The research on the extraction technology of natural brassinosteroids in China began in the early 1980s. In the beginning, the active ingredient of natural brassinosteroids was extracted and obtained from beewax. After that, new technologies such as enzymatic hydrolysis and directional extraction were successively developed. According to China Pesticide Information Network, natural brassinosteroids from natural extraction, represented by 14-hydroxylated brassinosteroid (trade name: Shuofeng 481) was firstly registered by Chengdu Newsun Crop Science Co., Ltd. at the Ministry of Agriculture and Rural Affairs of China in 2017. The researches on the artificial synthesis of brassinolide analogs began in 1982. Different countries in the world were committed to the artificial synthesis of brassinolide, making low-cost, large-scale and industrialized production of brassinolide a reality. According to Europe and China pesticide registration information, the synthetic brassinolide analogs that have obtained pesticide registration include: 24-epibrassinolide, 28-homobrassinolide, 28-epihomobrassinolide, 22, 23, 24-trisepibrassinolide, and propionyl-brassinolide. Among them, the chemical structures of the first four brassinolide analogs are based on BL. Their biological activities are different according to their structural differences. While propionyl-brassinolide is a propionylated brassinolide analog, which does not have biological activity, and functions only after absorbed and metabolized in plants.

4.2 Functions and advantages of Natural Brassinosteroid

Natural sourced brassinosteroid widely exists in nature and plants and have higher affinity for plants and is more widely used in crops. It is more suitable for the regulation of plant hormone levels. It has multiple functions, high activity and good safety. It is the most dominant active component in different brassinolide products. In recent years, with the frequent occurrence of extreme weather, the agricultural production and food security are impacted and threatened more and more seriously. How to deal with the problems caused by climate change, so that farmers can adapt to these extreme weather; at the same time, how to avoid traditional chemical hormones’ impacts to the fruit shape and size externally and the quality and taste internally, and significantly improve the safety and quality of agricultural products. Natural brassinosteroid can solve the problems of extreme weather, promote healthy seed growth, and improve agricultural yield and quality.

4.2.1 Higher efficacy than other structural brassinolides

The dosage with 0.01ppm of different brassinolides in the market were used to carry out the wheat hydroponic culture test. After 5 days test, the results showed that 14-hydroxylated Brassinosteroid had 3%-168% more on root length, 8%-49% more on root weight, 5%-29% more on plant height and 44%-127% more on plant weight than other structural brassinolide products. In addition, the roots of wheat treated with other brassinolide product showed curling. So under stress conditions, the efficacy of natural brassinosteroid (14-hydroxylated Brassinosteroid) are more significant than other brassinolide products.

Fig. 5: The efficacy of different kinds of Brassinolide under normal condition (from Science of Crop Protection)

Fig. 6: The efficacy of different kinds of Brassinolide under stress condition (from Science of Crop Protection)

4.2.2 The key functions of natural brassinosteroid on fruits

1) More flowers, stronger flowers, much better effect on keeping fruits

For the citrus, apple, jujube and other fruit trees, there is the problem of flowers and fruit dropping. The natural fruit setting rate of fruit trees is generally very low, like citrus, with only 2 to 3%. It is of great significance to increase the yield of fruit trees through increasing the number of fruits per unit area by protecting flowers and fruits [17]. For Shatang tangerine in Guangxi, China, use natural brassinosteroid + gibberellic acid before flowering, 2/3 of the flower faded, and 5 to 7 days before the second physiological fruit dropping, the fruit setting rate was increased by 20% compared with the conventional treatment; young fruit and fruit stem turn green 3 days earlier. Therefore, use natural brassinosteroid in citrus, apple and other fruit trees, there will be more flowers and strong flowers, reduce deformed flowers and fruits; keep flowers and fruits, improve fruit setting rate, and turn green quickly; reduce flowers and fruits dropping, and accelerate fruit development. It has a significant effect on improving fruit quality and yield.

 Fig. 7: The efficacy of natural brassinosteroid for keeping flowers and fruits setting on citrus and jujube

 (From Science of Crop Protection) 

2) Improve fruit quality, significantly increase fruit yields

For citrus, apple, cherries and greenhouse fruits, use natural brassinosteroid 2000-3000 dilutions times + high potassium foliar fertilizer can accelerate nutrient absorption and utilization, promote cell division and fruit expansion, regulate endogenous hormone levels, and promote delicate peels, better fruit shape.

Fig. 8: Natural brassinosteroid promoted delicate peels, better fruit shape (from Science of Crop Protection)

At early fruit coloring stage, continuously use natural brassinosteroid + high potassium foliar fertilizer for 2-3 times, it can accelerate pigment accumulation, promote uniform coloring, bright color, delicate peel, increase photosynthesis and promote sugar accumulation.

Fig. 9: Natural brassinosteroid increased sugar content of fruits (from Science of Crop Protection)

4.2.3 The key functions of natural brassinosteroid on field crops

1) Break seed dormancy, improve seed vigor, promote uniform and strong seedlings

Natural brassinosteroid can enhance DNA and RNA polymerase activities, thereby activating the expression of related genes and the synthesis of related proteins, and can activate some ATPases, promote the generation of H+ in the plasma membrane and transfer to the cell wall, resulting in cell wall relaxation, cell elongation and accelerates tissue growth, thereby increasing crop growth rate and effectively promoting seed germination [18].

Fig. 10: I. Germination of rice seeds with different treatments; II. Effects of different treatments on the germination rate of rice seeds; III. Effects of different treatments on germination potential of rice seeds

A: seed soaking treatment with 0.01 g•L-1 brassinolide (BL); 

B: germination treatment with 0.01 g•L-1 brassinolide (BL); C: water control

For seed dressing on wheat, rice, corn, soybean, etc., mix 30-50ml natural brassinosteroid with fungicides and insecticides to treat for 100kg seeds. For seed soaking, use 1000-2000 times dilution of natural brassinosteroid to soak the appropriate quantity of seeds until the seeds germinated. It can significantly break the seed dormancy, promote uniform and strong seedlings, and grow the strong root system to better absorb nutrients.

Fig. 11: Natural brassinosteroid promoted seed germination, strong roots, uniform and strong seedlings 

(From Science of Crop Protection)

2) Promote plant growth, increase crop yields

Natural brassinosteroid is also widely used in Turkey. According to the customer feedback, add 5% Natural brassinosteroid TC into water soluble fertilizer 18-18-18 + TE with dose 120g/mt, then 200 gram/ha for foliar spray can significantly promote the growth of corn. The field results show the corn plants are taller, the leaves are greener and thicker, and corn plants grow stronger.

Fig. 12: The field results of natural brassinosteroid in Turkey 

(Left: Control; Right: natural brassinosteroid treatment)

The greening period after winter is one of the key stages of wheat growth management. During this period, use 0.01% Natural brassinosteroid AS 75-150 ml/ha + foliar nutrition quickly regulates the physiological state of wheat and supply foliar nutrients to wheat, promotes strong stems, and effectively increases the number of tillers. According to the field data, spray natural brassinosteroid at tillering stage, the number of tillers per plant can reach 4-5, while the control is 3.5-4. The average yield is increased by 11 to 14%.

Fig. 13: Natural brassinosteroid promoted tillering of wheat and increased yield 

(from Science of Crop Protection)

At booting stage of rice and wheat/soybean podding stage/peanut flowering to pod filling stage, use Natural brassinosteroid 120-240ml/ha + foliar nutrition K-Power 300-600ml/ha by foliar spray to reduce empty shells/grains and increase 1000-grain weight, the average yield increased by 15%.

Fig. 14 Natural brassinosteroid increased crop yields by 15.28% in China

4.2.4 The key functions of natural brassinosteroid for crops in greenhouse

The products of plant photosynthesis are the basic source of organic compound accumulation in plants. Natural brassinosteroid can promote the activity of RuBP (ribulose 1,5-bisphosphate) carboxylase, increase the CO2 fixation rate, and enhance the photosynthetic efficiency, increase crop yields and farmers’ income [19].

1) Promote seedlings recover after transplant

After the vegetable seedlings are transplanted and survived, use 0.0075% Natural brassinosteroid AS 1.2L/ha by drip irrigation or soil drench to promote root growth, improve seedling survival rate, reduce died and rotten seedlings, accelerate nutrient absorption and promote rapid growth in seedling stage.

Fig. 15: Left: Control; Right: Treated by Natural brassinosteroid 

(from Science of Crop Protection)

2) Promote seedling growth and more flowering

In the seedling or flowering stage, use 0.0075% Natural brassinosteroid AS 2000-3000 times + foliar nutrition N-Power 1000 times + Plant VC 1000 times, which can promote thick and green leaves, improve nutrient absorption, promote seedlings growth and strong, stimulate the differentiation of flower buds of solanaceous plants, and reduce deformed and weak flowers.

4.2.5 The key functions of natural brassinosteroid in stress resistance and increase yields

Natural brassinosteroid can enhance the stress resistance of crops such as wheat, corn, rice, and fruit trees under abiotic stresses like drought, high temperature, and low temperature. At 2-4 days before frost or cold comes, 3 days after frost or cold and 10-15 days after frost or cold respectively, use 8-15ml 0.0075% natural brassinosteroid AS + monopotassium phosphate/amino acid foliar fertilizer with 15-30L water to spray on cherry trees at flowering stage, it can enhance the ability of crops to resist cold damage and freezing damage, reduce the impact of freezing damage by more than 30%, and the frozen damaged crops can quickly recover for growth (Fig. 16).

Fig. 16: The effects of Natural brassinosteroid on cherry flowers to resist low temperature

Natural brassinosteroid can regulate hormone levels in plants, reduce the opening of stomata on leaves, inhibit transpiration, decrease water loss, and improve the ability of wheat plants to resist drought and dry hot wind. It is recommended to use 0.0075% Natural brassinosteroid AS 2000 times + Pollen polysaccharide foliar nutrition K-Power 1000 times by foliar spray during the heading and flowering stages of wheat, the 1000-grain weight will increase by 2-6%, and the yield will increase by 17-22%. At the same time, before the wheat grains mature (from soft dough to hard dough stages), according to the weather conditions and soil moisture, apple soil irrigation one time before the dry hot wind comes to improve the microclimate conditions in the field and reduce the harm of the dry hot wind.

Fig. 17 The effects of Natural brassinosteroid on wheats to resist dry hot wind (from Science of Crop Protection)

5. Future and Prospects

In the face of the pressures of unprecedented population and extreme climate and environment, current threats and long-term challenges to the food security are attracting global attention. Plant growth regulators play an significant role in regulating crop growth and development, enhancing crops’ stress resistance ability, and improving yield and quality, and have gradually formed a set of mature and effective crop chemical control technologies. These technological achievements play an active role in overcoming environmental and genetic limitations, improving quality and storage conditions. At present, the global pesticide market is basically stable at about 65 billion US dollars, of which the plant growth regulators account for about 3%. From a global perspective, in recent years, in the market environment where other pesticides are developing slowly, the plant growth regulator market has maintained a sustained and stable growth trend. In 1975, the global sales of plant growth regulators was 200 million US dollars, and reached 900 million US dollars in 1990. At present, the global sales of plant growth regulators are about 1.5 billion US dollars.

As a broad-spectrum and highly active plant growth regulator, 14-hydroxylated brassinosteroid has become a bio-product with high market popularity in the market of plant growth regulator, because of its unique physiological activity, wide application range, ultra-low dosage, high safety, and significant effects of yield and profit increase. At the same time, 14-hydroxylated brassinosteroid is the only natural brassinosteroid product that has realized industrialization in the world, and has obtained the organic certification in European Union and the United States, and is widely used in the organic and green agricultural production. With the frequent occurrence of extreme weather in the world and the increasing demand for high quality agricultural products, natural brassinosteroids will play an increasingly important role in enhancing crop stress resistance, improving food security, increasing yield and quality, and promoting the green development of global agriculture.

Newsun Crop Science's website: http://www.cdxzy.com/en/

E-mail: newsunagro@cdxzy.com

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