*4.2. Transmission Electron Microscopy (TEM)*

TEM analysis was performed as described by Shih et al. [3]. Green and yellow sectors of leaves were cut into small cubes in the field and placed in a fixation solution containing 2.5% glutaraldehyde and 4% paraformaldehyde in 0.1 M sodium phosphate buffer (pH 7.0). Samples underwent 20 min of rinsing three times and were post-fixed in 1% osmium tetroxide for 2 h. After being dehydrated through an ethanol series, samples were infiltrated and embedded in Spurr's resin and then polymerized at 70 ◦C for 8 h. Ultrathin sections (~70–90 nm) were collected and stained with ethanol uranyl acetate and lead citrate. The morphology of plastids was observed with Tecnai F20S TEM (The Thermo Scientific™, Waltham, MA, USA) at 200 kV.

#### *4.3. Measurement of Physio-Biochemical Parameters*

A total of 50 mg fresh leaves were used to extract chlorophyll. The total chlorophyll content (ChlT, mg g−1FW) and carotenoids content (Ca, mg g−<sup>1</sup> FW) were determined as described by Wellburn [77]. The net photosynthetic rate (*Pn*, µmol m−<sup>2</sup> s −1 ), intercellular CO<sup>2</sup> concentration (*Ci*/ppm) and transpiration rate (*Tr*, mmol.m−<sup>2</sup> s −1 ) were determined with a portable L-6400XT (LI-COR, Lincoln, NB, USA). The measurements of photosynthetic parameters were taken at the

saturation irradiance with an incident photosynthetic photo flux density (PPFD) of 1200 µmo m−<sup>2</sup> s −1 and an airflow rate at 500 µmol s−<sup>1</sup> . The enzymatic activities of superoxide dismutase (SOD, U g−<sup>1</sup> ), catalase (CAT, U g−<sup>1</sup> .min−<sup>1</sup> ), peroxidase (POD, U g−<sup>1</sup> .min−<sup>1</sup> ) and the content of malonaldehyde (MDA, µmol g−<sup>1</sup> ) were calculated by following the manufacturer's instructions (Biological Engineering Institute of Nanjing Jiancheng, China). Means from three replicates were used for statistical analysis.
