|Grennan, Aleel - UNIVERSITY OF ILLINOIS|
|Sivaguru, Mayandi - UNIVERSITY OF ILLINOIS|
|Sozzani, Rosangela - NORTH CAROLINA STATE UNIVERSITY|
Submitted to: Journal of Experimental Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2016
Publication Date: 6/20/2016
Citation: Slattery, R.A., Grennan, A.K., Sivaguru, M., Sozzani, R., Ort, D.R. 2016. Light sheet microscopy reveals more gradual light attenuation in light green versus dark green soybean leaves. Journal of Experimental Biology. 67:4697-4709.
Interpretive Summary: The primary focus of this study was to compare light absorption profiles within dark and light green soybean leaves grown in chamber and field settings using light sheet microscopy. Reducing chl was expected to reduce the disparity of light availability between the upper and lower chloroplasts of the leaf, reduce the modeled gradient of A across the leaf, and therefore explain the increases in light green soybean mutant photosynthetic efficiency at the leaf level. Light sheet microscopy demonstrated the same patterns in leaf light attenuation in blue, red, and green light. As expected, greater light absorption occurred in deeper leaf layers of the light green mutant leaf with the most noticeable differences in blue light. In addition, modeled leaf A profiles based on chl profiles and Beer’s Law were also more gradual in the mutants. However, while photosynthetic light use efficiency was greater in the field-grown mutant, it was lower in the mutant when grown in chambers, which may be due to confounding pleiotropic effects of the mutation.
Technical Abstract: Light wavelengths preferentially absorbed by chlorophyll (chl) often display steep absorption gradients. This oversaturates photosynthesis in upper chloroplasts and deprives lower chloroplasts of blue and red light, causing a steep gradient in carbon fixation. Reducing chl content could create a more even leaf light distribution and thereby increase leaf light use efficiency and overall canopy photosynthesis. This was tested on soybean cultivar “Clark” (WT) and a near-isogenic chl b deficient mutant, Y11y11, grown in controlled environment chambers and in the field. Light attenuation, measured as relative chl fluorescence profiles, was quantified using a novel approach involving light sheet microscopy in which leaf adaxial and abaxial surfaces were illuminated with blue, red, and green wavelengths. Relative fluorescence was significantly greater in deeper layers of the Y11y11 mesophyll than in WT with the greatest differences in blue, then red, and finally green light when illuminated from the adaxial surface. Modeled relative photosynthesis based on chlorophyll profiles and Beer’s Law predicted less steep gradients in mutant relative photosynthesis rates compared to WT. Despite more gradual light attenuation and predicted CO2 fixation profiles in the mutant in both experiments, photosynthetic parameters were only similar or greater in the mutant when chl was reduced by ~50% in the field but were reduced by approximately 20-25% compared to WT with ~80% reductions in chl in the growth chamber experiment. The inconsistency was most likely due to the pleiotropic effects of the mutation and may warrant further testing in other low chl lines.