A Potential Role of Coumestrol in Soybean Leaf Senescence and Its Interaction With Phytohormones

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.

Mass Biosynthesis of Coumestrol Derivatives and Their Isomers via Soybean Adventitious Root Cultivation in Bioreactors

“…Nevertheless, the periodic movement of AR in the bioreactor via aeration might have triggered the synthesis of phytoalexins, following light stress. It is well-known that the synthesis of CMSN can be facilitated by environmental factors and periodic changes in the plant growth cycle (Song et al, 2014 ; Mun et al, 2021 ). To date, only Romani et al ( 2003 ) have detected M-CMSN in soybean roots via a tentative assignment by the UV spectra and mass fragmentation only.…”

“…Malonyl isoflavones, which are produced when symbiotic organisms in the rhizosphere secrete isoflavones in the form of aglycones or glycosides, account for most soybean polyphenols (Sugiyama et al, 2017 ). The metabolic responses to the synthesis of polyphenols in soybean plants can be altered by endogenous and exogenous factors, such as leaf maturation at the late-growth stage and defense pressure due to biological infections in the rhizosphere (Mun et al, 2021 ; Ling et al, 2022 ). Accordingly, other polyphenols can be generated from existing isoflavones via different endogenous enzymatic pathways (Ha et al, 2019 ).…”

“…Moreover, compared with the large quantities of glyceollins produced in the seeds and leaves of soybean, low quantities of coumestan, the oxidation product of pterocarpans, have also been reported ( Figure 1 ). Although coumestan derivatives were first identified in soybean roots 40 years ago (Le-Van, 1984 ), their studies only began a decade ago (Yuk et al, 2011a ; Jeon et al, 2012 ; Yun et al, 2020 , 2021 ; Cox et al, 2021 ; Mun et al, 2021 ). Considering that plant-derived coumestan exhibits a wide range of pharmacological activities (Tu et al, 2021 ), researchers have attempted to mass-produce coumestrol (CMS), a coumestan exhibiting phytoestrogenic activity, from soybean adventitious root (AR) (Lee et al, 2020 ).…”

The PGPR Bacillus aryabhattai promotes soybean growth via nutrient and chlorophyll maintenance and the production of butanoic acid

“…For the “tissue plate” assay ( Mun et al., 2021 ), at least three leaves from soybean plants (V3 stage) were detached and surface sterilized. Next, sterilized tissue papers were kept in 12cm square petri plates covering the bottom half of the plate.…”

Changes in secondary metabolites in soybean (Glycine max L.) roots by salicylic acid treatment and their anti-LDL oxidation effects

“…Coumestrol is a phytoalexin in the soybean plant and is associated with insect attacks and senescence to which SA as a phytohormone connects ( Morandi et al, 1984 ; Boué et al, 2000 ; Mun et al, 2021 ). In addition, coumestrol is considered as a valuable phytochemical with diverse biological activities such as its anti-low density lipoprotein (anti-LDL) oxidation ( Jin et al, 2006 ), anti-inflammation ( Yuk et al, 2017 ), anti-cancer ( Zafar et al, 2017 ), anti-obesity ( Kim et al, 2020b ), and skin protection ( Park et al, 2015 ) benefits.…”