*2.5. Protein Extraction and Western Blotting*

Protein extraction was conducted following the method described elsewhere [16], with slight modifications. An extraction buffer was used to homogenize approximately 500 mg tomato leaves. The buffer contained 100 mM Tris-HCl (pH 8.0), 0.5 mM EDTA·Na2, 1% (v/v) polyvinylpyrrolidone, 10 mM β-mercaptoethanol, and 200 mM sucrose. At 4 ◦C, the mixture was centrifuged at 12,000 rpm for 10 min. Subsequent to determination of protein concentrations, the supernatant (10 μL) was mixed together with protein loading buffer and then separated on 12% SDS-PAGE gel. After that, proteins were moved to a polyvinylidene fluoride (PVDF) blotting membrane (Type specification: Millipore, Bedford, MA, USA) using an electrotransfer instrument (Type specification: Bio-Rad, Hercules, CA, USA). Following electrotransfer, the PVDF blotting membrane was transferred into 5% nonfat skimmed milk, dissolved in tris buffered saline tween (TBST) overnight at 4 ◦C to prevent nonspecific adsorption, washed with TBST, and incubated by using the following polyclonal primary antibodies: 1:3000 dilution of anti-PsaA (Specification: Agrisera AS06 172, Vännäs, Sweden) for PsaA, 1:10,000 dilution of anti-PsbA (Specification: Agrisera AS05 084, Vännäs, Sweden) for PsbA, and 1:10,000 dilution of anti-RbcL (Specification: Agrisera AS03 037, Vännäs, Sweden) for loading control overnight at 4 ◦C, respectively. After that, PVDF blotting membranes were incubated in 1:10,000 dilution of HRP (horseradish peroxidase)-linked anti-rabbit 1gG (Bethyl A120 101P, Montgomery, TX, USA) for 1 h at ambient temperature as a secondary antibody before visualization of immunoreactive proteins using Clarity™ Western ECL Substrate (#6883, Bio-Rad, Hercules, CA, USA) on an iBright™ Imaging Systems (Type specification: Thermo Fisher Scientific, Waltham, MA, USA).

### *2.6. Data Collection and Analysis*

After supplemental lighting treatments for 10 d, this study measured the following parameters: lengths of scion and root, diameters of scions, number of leaves, leaf length, leaf width, leaf area and thickness, chlorophyll (SPAD), fresh weight of root, dry weight of root, specific weight of leaf, and dry weight to height ratio of scion.

The experiment was carried out in three replicates with a design of randomized complete block, using 9 seedlings in each replication. Locations of replications were randomly mixed to eliminate position effect within a controlled environment. One-way analysis of variance ANOVA by SAS program Statistical Analysis System (V.9.1, Cary, NC, USA), was applied to statistically analyze the collected data. Duncan's multiple range test was adopted to test significant differences between different means.
