*4.2. Chl Contents, Net Photosynthetic Rate and Photochemical E*ffi*ciency Analysis*

The third true leaves from the top of five-week-old soybean plants were used to estimate Chl contents, net photosynthetic rate and photochemical efficiency. The total Chl, Chl *a* and Chl *b* contents were determined as previously described [46]. Fresh leaves (200 mg) were immersed into 10 mL of 95% ethanol for pigments extraction under dark conditions. Then the absorbance of supernatant was quantified spectrophotometrically at 665 and 649 nm. Chlorophyll contents were calculated using the following formulas [46]: Chl *a* (mg/g) = [(13.95OD665 − 6.88OD649) × 10]/(tissue fresh weight (g) × 1000); Chl *b* (mg/g) = [(24.96OD649 − 7.32OD665) × 10]/(tissue fresh weight (g) × 1000); Total Chl (mg/g) = Chl *a* (mg/g) + Chl *b* (mg/g). Net photosynthetic rate was measured using an Li-6400 instrument (LI-COR, Lincoln, NE, USA) under a CO2 concentration of 250 μmol mol−<sup>1</sup> and 1000 μmol m<sup>−</sup>2s−<sup>1</sup> photosynthetically active radiation (PAR) between 9:00 and 11:00 in the morning. The maximum photochemical efficiency of photosystem II was measured as the Fv/Fm using an IMAGING-PAM Chlorophyll Fluorometer (Heinz Walz, Effeltrich, Germany).

Three to eight individual plants were examined for each material and the examination were repeated at least three times. The experimental data for each material are reported as mean ± standard deviation (SD). Statistical significance of differences between *yl* mutant and wildtype plants were tested using independent sample Student's t test algorithm. All statistical analysis were performed in SPSS Statistics 17.0.
