Characterization of photosynthetic phenotypes and chloroplast ultrastructural changes of soybean (Glycine max) in response to elevated air temperatures

Authors: Herritt, Matthew; FRITSCHI, FELIX - University Of Missouri

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2020
Publication Date: 3/3/2020
Citation: Herritt, M.T., Fritschi, F.B. 2020. Characterization of photosynthetic phenotypes and chloroplast ultrastructural changes of soybean (Glycine max) in response to elevated air temperatures. Frontiers in Plant Science. 11:153.

Interpretive Summary: Increased ambient temperatures (heat stress) are known to negatively affect photosynthesis in crop plants including soybeans (Glycine max). Exposure of four soybean genotypes to elevated air temperatures showed similar trends in net photosynthesis over a simulated seven-day heat wave. Analysis of the chloroplast ultrastructure from two soybean genotypes, exposed to control and increased air temperatures, revealed contrasts in the percentage of the total chloroplast area taken up by starch grains. This study serves to improve the understanding of how soybean responds to heat stress and provide contrasting phenotypes for improving soybean production. However, additional physiological and genetic studies are required to determine the underlying cause for targeting crop improvement in heat stress environments.

Technical Abstract: Heat stress negatively affects photosynthesis in crop plants. Chlorophyll fluorescence provides information about the efficiency of the light-dependent reactions of photosynthesis and can be measured non-destructively and in a high throughput manner. Chlorophyll fluorescence can provide useful insights into the effects of heat stress on the efficiency of the light-dependent reactions. Four soybean (Glycine max) genotypes were grown in controlled environments at 28/20 °C (control), followed by imposition of control, 38/28 °C, and 45/28 °C day/night temperature regimes for seven days. Coordinated chlorophyll fluorescence, gas exchange measurements, and analysis of chloroplast ultrastructure over the course of the seven-day temperature treatments revealed contrasting responses among different soybean genotypes. In more heat tolerant genotypes, photosynthetic rates at elevated temperature were more similar to those at control temperature. Reduced photoinhibition in the heat tolerant genotypes was coordinated with reduction in starch accumulation. These changes were associated with differences in the percent area of chloroplasts that were occupied by starch grains. The starch dynamics were coordinated with alterations in chlorophyll fluorescence and gas exchange phenotypes. The genotypic differences evident in photosynthetic and chloroplast ultrastructure responses to high temperatures are of interest for the development of more tolerant soybean cultivars and to facilitate the dissection of molecular mechanisms underpinning heat stress tolerance of soybean photosynthesis.