The major light-harvesting chlorophyll (Chl) a/b complexes of photosystem II (LHCIIb) play important roles in energy balance of thylakoid membrane. They harvest solar energy, transfer the energy to the reaction center under normal light condition and dissipate excess excitation energy under strong light condition. Many bamboo species could grow very fast even under extremely changing light conditions. In order to explain whether LHCIIb in bamboo contributes to this specific characteristic, the spectroscopic features, the capacity of forming homotrimers and structural stabilities of different isoforms (Lhcb1-3) were investigated. The apoproteins of the three isoforms of LHCIIb in bamboo are overexpressed in vitro and successfully refolded with thylakoid pigments. The sequences of Lhcb1 and Lhcb2 are similar and they are capable of forming homotrimer, while Lhcb3 lacks 10 residues in the N terminus and can not form the homotrimeric structure. The pigment stoichiometries, spectroscopic characteristics, thermo- and photostabilities of different reconstituted Lhcbs reveal that Lhcb3 differs strongly from Lhcb1 and Lhcb2. Lhcb3 possesses the lowest Qy transition energy and the highest thermostability. Lhcb2 is the most stable monomer under strong illumination among all the isoforms. These results suggest that in spite of small differences, different Lhcb isoforms in bamboo possess similar characteristics as those in other higher plants., Z. H. Jiang ... [et al.]., and Obsahuje bibliografii
Exposure of two-month-old seedlings of Bruguiera parviflora to NaCl stress (0 to 400 mM) for 45 d under hydroponic culture caused notable disorganisation of the thylakoid structure of chloroplasts in NaCl-treated leaves as revealed from transmission electron microscopy. The absorption spectra of treated and control thylakoid samples were similar having a red peak at 680 nm and Soret peaks at 439 and 471 nm in the blue region of the spectrum. The spectra of treated samples differed from control samples by gradual decrease in absorbance of 100, 200, and 400 mM NaCl treated samples at 471 and 439 nm, which could be due to scattering of radiation in these samples. Thus, absorption characteristics of thylakoid membranes indicated no major alterations in the structural integrity of the photosynthetic membranes during salt stress in B. parviflora. Analysis of pigment protein complexes of thylakoids on non-denaturing gel showed that CP1 complex consisting of photosystem (PS) 1 reaction centre decreased marginally by 19% and the CP47 constituting the core antenna of PS2 declined significantly by 30% in 400 mM NaCl treated samples in respect to control. This decrease in structural core antenna might cause inefficient photon harvesting capacity. However, CP43 content did not alter. An increase in CP2/CP1 ratio from 3.2 in control to 4.0 in 400 mM NaCl treated samples indicated significant structural changes in the thylakoids of salt treated plants. Haem staining of thylakoids revealed significant losses in cytochrome (Cyt)f and Cyt b 6 contents by NaCl stress. However, Cyt b 559 content remained nearly constant in both control and NaCl treated samples. SDS-PAGE of thylakoid proteins showed that the intensity of many of Coomassie stained polypeptide bands ranging from 15-22 and 28-66 kDa regions decreased significantly in NaCl treated samples as compared to control. Electron transport activity of thylakoids, measured in terms of DCPIP photoreduction, was 22% lower in 400 mM NaCl treated plants than in the control ones. Hence, NaCl induces oxidative stress in chloroplasts causing structural alterations in thylakoids. These structural alterations might be responsible for declined efficiency of photosystems and reduced electron transport activity. and A. K. Parida, A. B. Das, B. Mittra.
We studied the development of chloroplasts from etioplasts in the cotyledonary leaves of 4-d-old dark-grown cucumber (Cucumis sativus) seedlings after irradiation (20 μmol m-2 s-1). Upon irradiation, the triggering of chlorophyll (Chl) synthesis and accumulation showed a relatively short lag phase. The irradiation of etiolated seedlings initiated the synthesis of apoproteins of pigment-protein complexes. While Chl-protein 2 (CP2) was detected at 6 h after irradiation, CP1 only after 29 h. The appearance and accumulation of some of the apoproteins were monitored by Western-blotting. LHC2 apoprotein was detected after a 6 h-irradiation. The amounts of D1 protein of photosystem (PS) 2 and PsaA/B protein of PS1 were quantitated by ELISA. Further, the thylakoid membrane function during this time period in terms of PS1- and PS2-mediated electron transfer activity and intersystem electron pool size were analyzed. While PS1 activity was detected after 4 h, PS2-mediated O2 evolution was detected only after a 17 h-irradiation. Fv/Fm value of Chl a fluorescence measurements indicated that the photochemical efficiency of these leaves reached its maximum after 29 h of irradiation. The intersystem pool size of cotyledonary leaves was equivalent to that of the control cotyledonary leaves grown for 25 h under continuous irradiation. Thus etioplasts develop into fully functional chloroplasts after approximately 25 h when 4 d-dark grown cucumber seedlings are continuously moderately irradiated. The development of photosynthetic electron transport chain seems to be limited in time at the level of PS2, possibly at the donor side. and K. Bala Krishna ... [et al.].