Amount Of Light-harvesting Complexes Research Articles

Cellular response of Parachlorella kessleri to a solid surface culture environment.

Attached culture allows high biomass productivity and is a promising biomass cultivating system because neither a huge facility area nor a large volume of culture medium are needed. This study investigates photosynthetic and transcriptomic behaviors in Parachlorella kessleri cells on a solid surface after their transfer from liquid culture to elucidate the physiological and gene-expression regulatory mechanisms that underlie their vigorous proliferation. The chlorophyll content shows a decrease at 12h after the transfer; however, it has fully recovered at 24h, suggesting temporary decreases in the amounts of light harvesting complexes. On PAM analysis, it is demonstrated that the effective quantum yield of PSII decreases at 0h right after the transfer, followed by its recovery in the next 24h. A similar changing pattern is observed for the photochemical quenching, with the PSII maximum quantum yield remaining at an almost unaltered level. Non-photochemical quenching was increased at both 0h and 12h after the transfer. These observations suggest that electron transfer downstream of PSII but not PSII itself is only temporarily damaged in solid-surface cells just after the transfer, with light energy in excess being dissipated as heat for PSII protection. It thus seems that the photosynthetic machinery acclimates to high-light and/or dehydration stresses through its temporal size-down and functional regulation that start right after the transfer. Meanwhile, transcriptomic analysis by RNA-Seq demonstrates temporary upregulation at 12h after the transfer as to the expression levels of many genes for photosynthesis, amino acid synthesis, general stress response, and ribosomal subunit proteins. These findings suggest that cells transferred to a solid surface become stressed immediately after transfer but can recover their high photosynthetic activity through adaptation of photosynthetic machinery and metabolic flow as well as induction of general stress response mechanisms within 24h.

Loss of Albino3 leads to the specific depletion of the light-harvesting system.

The chloroplast Albino3 (Alb3) protein is a chloroplast homolog of the mitochondrial Oxa1p and YidC proteins of Escherichia coli, which are essential components for integrating membrane proteins. In vitro studies in vascular plants have revealed that Alb3 is required for the integration of the light-harvesting complex protein into the thylakoid membrane. Here, we show that the gene affected in the ac29 mutant of Chlamydomonas reinhardtii is Alb3.1. The availability of the ac29 mutant has allowed us to examine the function of Alb3.1 in vivo. The loss of Alb3.1 has two major effects. First, the amount of light-harvesting complex from photosystem II (LHCII) and photosystem I (LHCI) is reduced >10-fold, and total chlorophyll represents only 30% of wild-type levels. Second, the amount of photosystem II is diminished 2-fold in light-grown cells and nearly 10-fold in dark-grown cells. The accumulation of photosystem I, the cytochrome b(6)f complex, and ATP synthase is not affected in the ac29 mutant. Mild solubilization of thylakoid membranes reveals that Alb3 forms two distinct complexes, a lower molecular mass complex of a size similar to LHC and a high molecular mass complex. A homolog of Alb3.1, Alb3.2, is present in Chlamydomonas, with 37% sequence identity and 57% sequence similarity. Based on the phenotype of ac29, these two genes appear to have mostly nonredundant functions.

Correlation of iron content, spectral forms of chlorophyll and chlorophyll‐proteins in iron deficient cucumber (Cucumis sativus)

Leaves and chloroplast suspensions of severely and slightly iron deficient cucumber (Cucumis sativus L.) plants were characterized by low‐temperature fluorescence emission spectroscopy and Deriphat polyacrylamide gel electrophoresis. The emission spectra of the chloroplast suspensions were resolved into Gaussian components and those changes induced by iron deficiency were related to the variations in the chlorophyll‐protein pattern. The symptoms described with these methods were also correlated with the iron content of the leaves. It was concluded that the lack of physiologically active iron caused a relative decrease of photosystem I (PSI) and light harvesting complex I (LHCI), together with the long wavelength fluorescence, especially the 740 nm Gaussian component, and. to a much lesser extent, of the photosystem II (PSII) core complexes (relative increase of 685, 695 nm components). However, the relative decrease in the amount of light harvesting complex II (LHCII) was followed by a relative increase in its fluorescence band at 680 nm, showing that energy transfer from LHCII to core complex II (CCII) was partly disturbed. Thus iron deficiency affected the photosynthetic apparatus in a complex way: it decreased the synthesis of chlorophylls (Chls) and influenced the expression and assembly of Chl‐binding proteins.

Enhanced Thermal Tolerance of Photosynthesis and Altered Chloroplast Ultrastructure in a Mutant of Arabidopsis Deficient in Lipid Desaturation

A mutant of Arabidopsis thaliana, deficient in activity of the chloroplast n-6 desaturase, accumulated high levels of C(16:1) and C(18:1) lipids and had correspondingly reduced levels of polyunsaturated lipids. The altered lipid composition of the mutant had pronounced effects on chloroplast ultrastructure, thylakoid membrane protein and chlorophyll content, electron transport rates, and the thermal stability of the photosynthetic membranes. The change in chloroplast ultrastructure was due to a 48% decrease in the amount of appressed membranes that was not compensated for by an increased amount of nonappressed membrane. This resulted in a net loss of 36% of the thylakoid membrane per chloroplast and a corresponding reduction in chlorophyll and protein content. Electrophoretic analysis of the chlorophyll-protein complexes further revealed a small decrease in the amount of light-harvesting complex. Relative levels of whole chain and protosystem II electron transport rates were also reduced in the mutant. In addition, the mutation resulted in enhanced thermal stability of photosynthetic electron transport. These observations suggest a central role of polyunsaturated lipids in determining chloroplast structure and maintaining normal photosynthetic function and demonstrate that lipid unsaturation directly affects the thermal stability of photosynthetic membranes.

Chlorophyll-protein and polypeptide composition of Mn-deficient sugar beet thylakoids

The chlorophyll-protein and polypeptide composition of manganese deficient and control sugar beet thylakoids was examined using three different detergent-electrophoresis systems. On a per chlorophyll basis, manganese deficiency reduced the amounts of CPa complex (separated by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis), and CP 47 and CP 43 complexes (separated by octylglucoside/SDS-polyacrylamide gel electrophoresis) without decreasing the amounts of light harvesting complexes. Lithium dodecylsulfate/Triton X-100 polyacrylamide gel electrophoresis showed that manganese deficiency decreased several thylakoid polypeptides, including a chlorophyll b containing 30 kilodalton chlorophyll-protein complex, but did not decrease the amounts of 28 and 29 kilodalton light-harvesting chlorophyll b-containing polypeptides.

Oxygen‐quenched chlorophyll a fluorescence and electron transport in barley during greening

Seedlings of barley (Hordeum vulgare L. cv. Conquest) were dark‐grown for 7 days and then transferred to light. The time courses of chlorophyll a fluorescence induction underwent changes during greening periods of from 3 to 48 h. Yields of variable fluorescence during greening correlated with electron transport capacity via photosystem II (PS II) except at the early stage from 3 to 6 h. The discrepancy may result from there being only a small amount of light harvesting complex associated with PSII for 3 to 6 h greening. Oxygen quenching effects were interpreted as indicating the development of the electron transport system and the organization of light harvesting complex associated with PSII. The most intensive O2 quenching of relative fluorescence is found during the early stage of greening when the ratio of the primary quinone electron acceptor (Q) to chlorophyll is high.