Background Isoflavones first accumulate in the embryo axis. Once a plateau is reached, isoflavones begin to accumulate in the cotyledons, where they are found in lower concentrations, but in greater quantities. This shift is associated with a difference in composition, with mainly conjugated forms of Daidzein and Glycitein in the embryo axis, and only conjugated forms of Dadzein and Genistein in the cotyledons. Isoflavone accumulation in the 2 seed compartments is independently regulated. The quantity of isoflavone in the seed is subject to strong genetic and environmental determinism. From one genotype to another or from one year to the next, concentrations can triple. The effect of location is also significant, with concentrations varying by as much as a factor of two. Among the environmental factors studied in the literature, cold stress4 and irrigation are the most significant. The stimulating effect of potassium fertilization has also been noted.

 Aims : Characterize interactions between abiotic stress and phenological phases on isoflavones content in cotyledons and embryo axis

Methods For this investigation, the seeds were obtained from field experiments conducted at INRAE Auzeville, southwestern France for SOJAMIP project. Two sowing modalities (conventional and early or late sowing) and two hydric modalities (rainfed and irrigated) were used to cultivate two early cultivars (Shouna and Sultana, 000 maturity group) and two late cultivars (Ecudor and Isidor, II and I maturity group) in 2017 and 2018. There were 4 plots in the experiment. On the cotyledons and embryo axis, the isoflavone content (mg aglycone equivalent per gram of dry mass) of each sample was determined by HPLC. ANOVA was used to statistically test the impact of the experimental setup. Stress scores by day, 3 for temperature (degree day, low and high temperature), and 2 for water (stomatal and turgor stress), were calculated using the STICS growth crop model7. These scores were averaged across four phenological periods : the vegetative period from sowing to R1, the flowering period from R1 to R5, the pod development from R5 to R6, and the maturation phase from R6 to harvest. Isoflavone content variability in cotyledons and embryonic axis was predicted by PLS regression of these ecoclimatic indicators and genotypes.

Results Most of the variability of the cotyledons and embryo axis isoflavone content were explained by ANOVAs from various experimental modalities. The amount of isoflavone in the two compartment of the seed were significantly influenced by genotype, year, irrigation, and sowing date, but several interacting effects made difficult to interpret the results. All genotypes were affected by irrigation’s stimulation of isoflavone accumulation in cotyledons in 2017, while only late genotypes were affected in 2018. In 2017, early sowing increased isoflavone accumulation in the cotyledons of late genotypes while having the opposite impact on early genotypes. In 2018, only Ecudor had significantly reduced cotyledon levels with late sowing. In the embryo axis, early sowing reduced the quantity of isoflavone for early genotypes in 2017 while late sowing decreased the content of late genotypes in 2018. Although explaining less variability (R²=0.3), PLSR by ecoclimatic indicators demonstrate a stimulating effect of temperature from the vegetative stage onwards, and in particular on isoflavones in the embryonic axis, as well as water stress. Cotyledons and the embryo axis continue to be affected by these effects during flowering. At the development of the pod for embryo axis and with a higher effect on cotyledons at the maturation stage, cold stress becomes very stimulating and hot stress limiting on isoflavone accumulation. Finally, during maturation, the accumulation in the two seed’s compartment is limited by water stress.

Conclusion : This study confirms the differences and lag between cotyledons and embryo axis in isoflavone accumulation, as well as the effect of cold and irrigation on the maturation phase. It highlights the importance of the vegetative phase in those dynamics. The ecoclimatic approach provides a better description of genotype-environment interactions, and could provide a relevant approach for varietal evaluation of isoflavone content.

• Unregistered authors: Monique Berger
• Publishing organisation: LIDEA
• Year of publication: 2023
• Brief introduction:

  Isoflavones first accumulate in the embryo axis. Once a plateau is reached, isoflavones begin to accumulate in the cotyledons, where they are found in lower concentrations, but in greater quantities. This shift is associated with a difference in composition, with mainly conjugated forms of Daidzein and Glycitein in the embryo axis, and only conjugated forms of Dadzein and Genistein in the cotyledons. Isoflavone accumulation in the 2 seed compartments is independently regulated. The quantity of isoflavone in the seed is subject to strong genetic and environmental determinism. From one genotype to another or from one year to the next, concentrations can triple. The effect of location is also significant, with concentrations varying by as much as a factor of two. Among the environmental factors studied in the literature, cold stress and irrigation5 are the most significant. The stimulating effect of potassium fertilization has also been noted.

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  References
  1. Berger et al., 2008. DOI : 10.2135/cropsci2007.08.0431
  2. Hoeck et al., 2000. DOI : 10.2135/cropsci2000.40148x
  3. Lee et al., 2003. DOI : 10.1016/S0378-4290(02)00220-4
  4. Rasolohery et al., 2008. DOI : 10.1002/jsfa.3075
  5. Lozovaya et al., 2005. DOI : 10.2135/cropsci2004.0567
  6. Vyn et al., 2002. DOI : 10.1021/jf0200671
  7. Schoving et al., 2022. DOI : 10.1016/j.eja.2021.126439

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• Citation:

  Brustel Jean, MAURY Pierre, Debaeke Philippe, Monique Berger , 2023. Explaining environmental influence on isoflavone accumulation in soybean cotyledons and embryo axis. Legume Hub. https://www.legumehub.eu

• Alternative citation:

  Brustel Jean, Monique Berger , MAURY Pierre, Debaeke Philippe, 2023. Explaining environmental influence on isoflavone accumulation in soybean cotyledons and embryo axis. Legume Hub. https://www.legumehub.eu