Abstract
Coumestrol is a natural organic compound synthesized in soy leaves and functions as a phytoalexin. The coumestrol levels in plants are reported to increase upon insect attack. This study investigates the correlation between coumestrol, senescence, and the effect of phytohormones on the coumestrol levels in soybean leaves. Our analysis involving high-performance liquid chromatography and 2-D gel electrophoresis indicated a significant difference in the biochemical composition of soybean leaves at various young and mature growth stages. Eight chemical compounds were specifically detected in young leaves (V1) only, whereas three different coumestans isotrifoliol, coumestrol, and phaseol were detected only in mature, yellow leaves of the R6 and R7 growth stage. MALDI-TOF-MS analysis was used to identify two proteins 3,9 -dihydroxypterocarpan 6A-monooxygenase (CYP93A1) and isoflavone reductase homolog 2 (IFR2) only in mature leaves, which are key components of the coumestrol biosynthetic pathway. This indicates that senescence in soybean is linked to the accumulation of coumestrol. Following the external application of coumestrol, the detached V1-stage young leaves turned yellow and showed an interesting development of roots at the base of the midrib. Additionally, the application of phytohormones, including SA, methyl jasmonate (MeJA), and ethephon alone and in various combinations induced yellowing within 5 days of the application with a concomitant significant increase in endogenous coumestrol accumulation. This was also accompanied by a significant increase in the expression of genes CYP81E28 (Gm08G089500), CYP81E22 (Gm16G149300), GmIFS1, and GmIFS2. These results indicate that various coumestans, especially coumestrol, accumulate during leaf maturity, or senescence in soybean.
Highlights
MATERIALS AND METHODSSoybean [Glycine max (L.) Merr.] is an important crop
Yuk et al (2011b) described the α-glucosidase inhibition activity of soybean leaf extracts. They found that coumestrol was the most abundant polyphenol, indicating the importance of coumestrol and other coumestans in the armada of secondary soybean metabolites
This study further highlights the role of coumestans, especially coumestrol in soybean senescence
Summary
MATERIALS AND METHODSSoybean [Glycine max (L.) Merr.] is an important crop. It is one of the most economical and valuable agricultural commodities because of its unique chemical composition. Plant secondary metabolites are used as medicines, flavorings, and recreational drugs (Saxena et al, 2014) They play vital roles and perform essential functions in plants (Seigler, 1998). It was reported that the coumestrol levels in soybean leaves increase during the mature stage (R7) (Ha et al, 2019). The level of coumestrol in soybean leaves appears to increase as the plant ages. An increase in coumestrol levels upon insect attack in some plants has been reported (Kain and Biggs, 1980). The changes in the chemical and protein composition of young and mature soybean leaves was analyzed with respect to aging and in response to phytohormone application using 2-dimensional gel electrophoresis (2-DE) and high-performance liquid chromatography (HPLC). The young leaves were selected at the vegetative growth stages V1, V3, and V5, whereas mature leaves were selected at the reproductive stages R1, R2, R4, R6, and R7
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