Effect of heat stress on seed protein composition and ultrastructure of protein storage vacuoles in the cotyledonary parenchyma cells of soybean genotypes that are either tolerant or sensitive to elevated temperatures

Authors: Krishnan, Hari; KIM, WON-SEOK - University Of Missouri; Oehrle, Nathan; Smith, James - Rusty; Gillman, Jason

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/4/2020
Publication Date: 7/5/2020
Citation: Krishnan, H.B., Kim, W., Oehrle, N.W., Smith, J.R., Gillman, J.D. 2020. Effect of heat stress on seed protein composition and ultrastructure of protein storage vacuoles in the cotyledonary parenchyma cells of soybean genotypes that are either tolerant or sensitive to elevated temperatures. International Journal of Molecular Sciences. 21(13). Article 4775. https://doi.org/10.3390/ijms21134775.
DOI: https://doi.org/10.3390/ijms21134775

Interpretive Summary: Soybean seed development is sensitive to elevated temperatures. Seeds grown under high temperatures are impaired in seed quality causing economic loss for soybean farmers. In order to minimize the economic loss, soybean breeders have been attempting to develop heat stress tolerant soybean cultivars. DS25-1 (04025) is the first elevated temperature tolerant public released soybean line. In an attempt to identify and characterize heat stress tolerance mechanisms we have conducted a biochemical and ultrastructural analyses of soybean genotypes that is either susceptible or tolerant to high growth temperatures. Our study demonstrate that accumulation of certain seed storage proteins is negatively impacted by extreme heat stress and heat stress disrupted the structure and the membrane integrity of protein storage vacuoles, organelles that accumulate seed storage proteins. Interestingly, these negative effects were less pronounced in the heat-tolerant genotype. Results obtained from this study will assist soybean farmers to minimize economic loss imposed by high growth temperatures encountered in Mid-South United states.

Technical Abstract: High growth temperatures negatively affect soybean (Glycine max (L.) Merr) yields and seed quality. Soybean plants, heat stressed during seed development, produce seed that exhibit wrinkling, discoloration, poor seed germination, and have an increased potential for incidence of pathogen infection and an overall decrease in economic value. Soybean breeders have identified a heat stress tolerant exotic landrace genotype, which has been used in traditional hybridization to generate experimental genotypes, with improved seed yield and heat tolerance. Here, we have investigated the seed protein composition and ultrastructure of cotyledonary parenchyma cells of soybean genotypes that are either susceptible or tolerant to high growth temperatures. Biochemical analyses of seed proteins isolated from heat-tolerant and heat-sensitive genotypes produced under 28/22 °C (control), 36/24 °C (moderate), and 42/26 °C (extreme) day/night temperatures revealed that the accumulation in soybean seeds of lipoxygenase, the ß-subunit of ß-conglycinin, sucrose binding protein and Bowman-Birk protease inhibitor were negatively impacted by extreme heat stress in both genotypes, but these effects were less pronounced in the heat-tolerant genotype. Western blot analysis showed elevated accumulation of heat shock proteins (HSP70 and HSP17.6) in both lines in response to elevated temperatures during seed fill. Transmission electron microscopy showed that heat stress caused dramatic structural changes in the storage parenchyma cells. Extreme heat stress disrupted the structure and the membrane integrity of protein storage vacuoles, organelles that accumulate seed storage proteins. The detachment of the plasma membrane from the cell wall (plasmolysis) was commonly observed in the cells of the sensitive line. In contrast, these structural changes were less pronounced in the tolerant genotype, even under extreme heat stress, cells, for the most part, retained their structural integrity. The results of our study demonstrate the contrasting effects of heat stress on the seed protein composition and ultrastructural alterations that contribute to the tolerant genotype’s ability to tolerate high temperatures during seed development.