High-Light-Induced Degradation of Photosystem II Subunits' Involvement in the Albino Phenotype in Tea Plants

Abstract

The light-sensitive (LS) albino tea plant grows albinic shoots lacking chlorophylls (Chls) under high-light (HL) conditions, and the albinic shoots re-green under low light (LL) conditions. The albinic shoots contain a high level of amino acids and are preferential materials for processing quality green tea. The young plants of the albino tea cultivars are difficult to be cultivated owing to lacking Chls. The mechanisms of the tea leaf bleaching and re-greening are unknown. We detected the activity and composition of photosystem II (PSII) subunits in LS albino tea cultivar "Huangjinya" (HJY), with a normal green-leaf cultivar "Jinxuan" (JX) as control so as to find the relationship of PSII impairment to the albino phenotype in tea. The PSII of HJY is more vulnerable to HL-stress than JX. HL-induced degradation of PSII subunits CP43, CP47, PsbP, PsbR. and light-harvest chlorophyll-protein complexes led to the exposure and degradation of D1 and D2, in which partial fragments of the degraded subunits were crosslinked to form larger aggregates. Two copies of subunits PsbO, psbN, and Lhcb1 were expressed in response to HL stress. The cDNA sequencing of CP43 shows that there is no difference in sequences of PsbC cDNA and putative amino acids of CP43 between HJY and JX. The de novo synthesis and/or repair of PSII subunits is considered to be involved in the impairment of PSII complexes, and the latter played a predominant role in the albino phenotype in the LS albino tea plant.

Keywords: Camellia sinensis; albino tea; photodamage; photosystem II; thylakoid.

Figure 1

(A–K) Immunoblotting of PSII subunits during shading treatment. Thylakoids were extracted from the 4th leaf beneath apex bud on tea shoots, and 1 µg of chlorophyll was used each lane. The blots were probed with specific antibodies: anti-CP43, anti-CP47, anti-D1, anti-D2, anti-PsbE, anti-PsbH, anti-PsbI, anti-PsbN, anti-PsbO, anti-PsbP, and anti-PsbR. CLP, crosslinking product. The data 0, 6, 15, and 30 refer to the days of shading treatment. The bars are expressed as mean ± standard deviation (n = 3).

Figure 2

(A–I) Immunoblotting of LHC proteins during shading treatment. Thylakoids were extracted from the 4th leaf beneath apex bud on tea shoots, and 1 µg of chlorophyll was used each lane. The blots were probed with specific antibodies: anti-Lhca1, anti-Lhca2, anti-Lhca3, anti-Lhca4, anti-Lhcb1, anti-Lhcb2, anti-Lhcb4, anti-Lhcb5, and anti-Lhcb6. CLP, crosslinking product. The data 0, 6, 15, and 30 refer to the days of shading treatment. The bars are expressed as mean ± standard deviation (n = 3).

Figure 3

(A–G) Immunoblotting of partial subunits of electronic transport complexes. Thylakoids were extracted from the 4th leaf beneath apex bud on tea shoots, and 1 µg of chlorophyll was used each lane. The blots were probed with the following specific antibodies: anti-PsaA, anti-PsaD, anti-PetB, anti-PetA, anti-AtpB, anti-AtpC, and anti-AtpH. CLP, crosslinking product; DF, degradation fragment. The data 0, 6, 15, and 30 refer to the days of shading treatment. The bars are expressed as mean ± standard deviation (n = 3).

Figure 4

Changes in Fv/Fm during shading treatment period. The Fv/Fm was determined on the 4th leaf beneath apex bud, and 10 leaves were tested each treatment. HJY, cultivar “Huangjinya”; JX, cultivar “Jinxuan”.

Figure 5

Effects of lincomycin on Fv/Fm in leaves of HJY and JX. Fv/Fm was measured for detached leaves (the 4th leaf beneath apex bud on bush under 30-day shading treatment) in the absence (–) or presence (+) of lincomycin during exposure to an irradiance of 1500 μmol m⁻² s⁻¹. The leaves were collected on 30th August 2018 at dusk and immersed in water before photoinhibition. Time 0 represents the dark-adapted samples before light exposure. For lincomycin treatment, the leaves were kept in darkness with the petioles in 1 mM lincomycin solution for 12 h before light exposure. The values are the mean ± standard deviation from at least six replicated experiments. HJY, cultivar “Huangjinya”; JX, cultivar “Jinxuan”.

Figure 6

HL-induced disassembly of PSII–LHCII SC and its reassembly under LL conditions in LS albino tea plant.