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Introduction of Soybean

Introduction to Soybean Biology

Soybean is an annual herb that can self-pollinate. Wild soybeans are different from the soybeans we eat every day. In fact, soybeans evolved from wild soybeans. The following table shows the biological classification of these two soybeans: 

Soybean Biology


Soybean has a high intraspecific diversity. According to the color of the seed coat, it can be divided into yellow, cyan, black, brown, and two-color varieties. Among them, the yellow soybean is the most common. Next, the structure of soybean will be introduced in detail. 

Seed structure

Seed structure


Soybean seeds consist of seed coat and embryo. 

  • The seed coat is developed from the outer bead and has a protective effect on the seeds. 

  • Hypocotyls support cotyledons in the early stages of seed germination and will subsequently develop into stems 

  • The radicle develops into the root of the plant 

  • The seed navel is the channel through which the plant supplies nutrients to the seed during the formation of the seed. It is also the trace left on the seed coat after the seed is free from the bead stalk. 

  • Endosperm stores nutrients for seed germination. 

Soybean growth


Reproductive Stage

Soybean root and Rhizobium

Soybean root and Rhizobium

Nitrogen is an essential nutrient for plant growth, and plants need nitrogen for protein, DNA, and chlorophyll production. Although there is a large amount of gaseous nitrogen in the atmosphere, plants cannot directly absorb it. Therefore, in the environment where the soil lacks nitrogen, the legumes will secrete betaine, flavonoids and isoflavones, these substances can attract rhizobia. Once Rhizobium grows on the roots of legumes, it will become the plant's "nitrogen-fixing plant", transforming atmospheric nitrogen into nitrogen compounds that can be used by plants. On the other hand, plants will also provide nutrients for the survival of rhizobia in return, which is a typical mutually beneficial symbiotic relationship. 


  • What are rhizobia and rhizobia? 
    Rhizobium bacteria, also known as "nitrogen-fixing bacteria", are mostly parasitic in legumes, converting atmospheric nitrogen into nitrogen compounds. When soybeans germinate and grow root hairs, rhizobia gather on the roots. After the root hair contacts the rhizobia, the rhizobia invade the root hair until the root cortex stimulates the root cortical cells, causing a large amount of growth of these cells to form nodules.  


  • What is the relationship between soybeans and rhizobia?  
    Rhizobium grows on the roots of soybeans and converts atmospheric nitrogen into nitrogen compounds available for soybeans. On the other hand, plants will also provide nutrients for the survival of rhizobia in return, which is a typical symbiotic relationship: soybeans will supply part of the organic matter produced by photosynthesis to rhizobia; rhizobia produce ammonia to supply soybeans. This conversion process is called nitrogen fixation. 


  • The nitrogen-fixing 
    rhizobia can absorb nitrogen in the air and convert it into nitrogen compounds, which are released in the soil. Plants can then absorb more nitrogen compounds for growth. The following is a flow chart describing nitrogen fixation: 

nitrogen fixing.PNG

Cultivated soybean and wild soybean

Cultivated soybean and wild soybean

Regardless of plant morphological characteristics, growth environment requirements, and nutritional content, artificially cultivated soybeans and wild soybeans are significantly different. For example, wild soybeans may have better disease resistance and cold resistance. Artificial breeding can combine the advantages of different varieties and cultivate more valuable soybeans. 


The following table shows the differences in appearance of one of the artificially cultivated soybean varieties and wild soybean varieties: 

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