As the world population grows, so does the need for food, raw materials and energy. This increases the burden on the environment and the climate. One strategy for reducing greenhouse gas emissions is the cultivation of so-called C4 plants. These operate photosynthesis particularly efficiently, thus binding carbon dioxide (CO2) more effectively and building more biomass than other plants. Usually they are native to sunny and warm places. One of the C4 plants is sorghum, also known as large millet, a species of the sorghum genus in the sweet grass family. The particularly high-sugar varieties are called sweet millet (Sorghum bicolor L. Moench). Other varieties include grain orghum, which is used as animal feed. Sorghum can be grown on so-called interfaces, which are difficult to cultivate and therefore do not compete with other food or forage crops.
A new sweet sorghum variety called KIT1 was developed by Dr. Adnan Kanbar in the Molecular Cell Biology working group under the direction of Professor Peter Nick at the Botanical Institute of KIT. KIT1 enriches a lot of sugar and thrives particularly well under moderate climatic conditions. It can be used both energetically, i.e. for the production of biogas and biofuels, and as a raw material for the production of new types of polymers. The estimated sugar yield per hectare is over 4.4 tons, which would correspond to almost 3,000 liters of bioethanol. In addition, the fermentation residues from biogas production can be used as fertilizer to replace the phosphate fertilizer, which will soon become scarce.
It all depends on the anatomy of the plant stem
Researchers from Nick’s laboratory, which is part of the Institute for Applied Biosciences, and their colleagues from the KIT Institute for Technical Chemistry and ARCUS Greencycling Technology in Ludwigsburg compared the KIT1 sweet millet and Razinieh corn millet varieties in order to investigate the different types of sugar accumulation behavior in the plant stem. For the study, published in Industrial plants & products Journal, the team examined the stem anatomy. These include the thickened areas (nodes) and the narrow areas or spaces between the nodes (internodes), but also transcripts of important sucrose transporter genes and stress reactions of plants to high salt concentrations in the soil. Sugar accumulation was highest in the central internodes of both genotypes. However, a connection has been found between sugar accumulation and the structure of the vessels that are used to transport water, dissolved substances and organic substances. The vessels are combined into vascular bundles. These consist of the phloem (bast part) and the xylem (wooden part). The phloem mainly transports sugars and amino acids, while the main function of the xylem is to transport water and inorganic salts; In addition, the xylem has a support function. The study found that in KIT1 and five other sorghum varieties, the phloem cross-sectional area in the stem is much larger than the xylem cross-sectional area – the difference is much more pronounced than in the Razinieh grain sorghum variety. “Our study is the first to examine the relationship between the structure of the vascular bundles and the accumulation of sugar in the trunk,” says Nick.
Sweet sorghum copes better with salt stress
As the study further showed, the salinity stress in KIT1 led to a higher sugar accumulation than in Razinieh. The expression of sucrose transporter genes was higher in KIT1 leaves under normal conditions and significantly increased under salt stress. “In addition to anatomical factors, there are also some molecular factors that could help regulate the accumulation of sugar in the stem,” explains Kanbar. “In any case, KIT1 reacts better to salt stress.”
Reference: Kanbar A, Shakeri E, Alhajturki D, et al. Sweet versus grain millet: Different sugar transport and accumulation are associated with the vascular structure. Ind Crops Prod. 2021; 167: 113550. do: 10.1016 / j.indcrop.2021.113550
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