Effects of Light Orientation and Mechanical Damage to Leaves on Isoflavone Accumulation in Soybean Seeds

Giuseppe Barion,Andrea Aloia,Teofilo Vamerali,Anna Panozzo,Mohamed Hewidy

doi:10.3390/agronomy11030589

Giuseppe Barion, Andrea Aloia + Show 3 more

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https://doi.org/10.3390/agronomy11030589

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Abstract

Soybean is largely cultivated worldwide providing high amounts of proteins and oil for food and feed, and isoflavones for nutraceutical uses. The increasing interest in agroforestry practices for improving carbon sequestration and mitigating climate changes suggests the need to assess soybean response to variations of light availability and direction. A two-year pot trial was carried out at Legnaro (NE Italy) in order to mimic the response of the soybean var. Sponsor to contrasting light orientation (east or west) by artificial shading, associated or not with mechanical leaf damage, in terms of protein accumulation, total cotyledon isoflavone concentration (TCIC) and isoflavone profile. Here, we demonstrate that a different intensity of the isoflavone metabolism exists in response to lighting conditions, with higher TCIC and slightly increased seed crude proteins in plants lighted from the east (morning time) and after mechanical leaf damage. The isoflavone profile was not changed, but low temperatures and high rainfall during seed filling (1st year) were associated with increased accumulation of medium-high molecular weight (MW) forms (i.e., glycosyls and malonyls), while high temperatures and low rainfall (2nd year) with increased accumulation of medium-low MW forms (i.e., glycosyls and aglycones). It is concluded that within agroforestry systems, there is possibly a large scope for maximizing isoflavone accumulation by selecting the harvesting area in the neighboring of the east side of the tree alleys, with further improvements if a mild shoot stripping is applied before flowering.

Highlights

Soybean is a staple crop for human nutrition and animal feed worldwide and for nutraceutical/cosmetic uses, being one of the largest sources of proteins and isoflavones, respectively
The decreased intensity of the infrared radiation, due to low clouds and morning mist, was likely to play a role in slightly reducing the average temperature of the plants mainly lighted from the east, favoring the isoflavones accumulation. This trial carried out under controlled conditions provided illuminating results on the morphological and physiological response of soybean under modified lighting conditions that are typical of agroforestry alley cropping systems
It is expected that designs with north–south oriented alley trees create growing conditions that modify growth, yield and quality of the intercropped soybean, depending on the selected side of the tree alley, which is related to a prevailing light orientation

Summary

Introduction

Soybean is a staple crop for human nutrition and animal feed worldwide and for nutraceutical/cosmetic uses, being one of the largest sources of proteins and isoflavones, respectively. Twelve different isoflavones are synthesized in soybean seeds, classified into three families, which are distinguished by the different aglycone groups daidzein, genistein and glycitein, the latter found only in the embryo. The effects of the environmental light on isoflavone synthesis are poorly studied, solar radiation may have an impact due to its essential role in anthocyanin production [8]. The metabolic pathway of isoflavones synthesis shares naringenin as an intermediate compound with the biosynthesis of anthocyanins. In this way, it is hypothesized that light might have an effect on isoflavones synthesis as well

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