Abstract
Chitin, an N-acetylglucosamine polymer, is well-known to have unique biological functions, such as growth promotion and disease resistance induction in plants. Chitin has been expectedly used for improving crop yield using its functions; however, chitin derivatives, such as chitin oligosaccharide (CO) and chitosan, are widely used instead since chitin is difficult to handle because of its insolubility. Chitin nanofiber (CNF), produced from chitin through nanofibrillation, retains its polymeric structure and can be dispersed uniformly even in water. Here, the effects of CO and CNF on plant responses were directly compared in soybeans (Glycine max) to define the most effective method to produce chitin derivatives for plant response induction. The growth promotion of aerial parts was observed only in CNF-treated plants. The transcriptome analysis showed that the number of differentially expressed genes (DEGs) in CNF-treated soybeans was higher than in CO-treated soybeans. Notably, the expression patterns of DEGs were mostly similar but were strongly induced by CNF treatment as compared with the CO group. These results reveal that CNF can induce stronger plant response to chitin than CO in soybeans, suggesting nanofibrillation, rather than oligomerization, as a more effective method to produce chitin derivatives for plant response induction.
Highlights
Chitin is a natural polymer with an N-acetylglucosamine-repeating structure, which is a highly abundant polysaccharide occurring mainly in the exoskeletons of arthropods, including crustaceans and insects, and in the cell walls of yeast and fungi [1,2]
We showed that chitin nanofiber (CNF) supplementation to soils, rather than chitin oligosaccharide (CO), promoted the growth of aerial parts and induced a stronger plant response to chitin
In a previous study [10], both CO and CNF showed growth-promoting action on the aerial parts of tomato by improving nitrogen uptake efficiency, which is inconsistent with the results of promoting effects on soybean growth found in this study
Summary
Chitin is a natural polymer with an N-acetylglucosamine-repeating structure, which is a highly abundant polysaccharide occurring mainly in the exoskeletons of arthropods, including crustaceans and insects, and in the cell walls of yeast and fungi [1,2]. Chitin and its deacetylated derivative chitosan are well-known to have various kinds of unique functions that can contribute to the crop yield improvement. Chitin derivatives directly induce defense responses and affect plant growth, as well as stimulate beneficial microbe activity in soils, promoting plant growth and disease resistance [1]. These highly sophisticated functions that increase the crop yield have been expectedly used for chitin-derived materials widely as an ecofriendly promising agent instead of chemicals, such as fertilizers and pesticides, in agriculture. Original polymeric chitin generally produced from crab or shrimp shell wastes is difficult to be insoluble in most solvents mainly because of the highly extended hydrogen-bonded semi-crystalline structure [3]. The water- or Plants 2020, 9, 810; doi:10.3390/plants9070810 www.mdpi.com/journal/plants
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