CHLOROPHYLL b: AN INTEGRAL COMPONENT OF PHOTOSYSTEM I OF HIGHER PLANT CHLOROPLASTS

Remembering Jeanette Snyder Brown (1925-2014)

Jeanette Snyder Brown (universally called Jan) was associated with the Department of Plant Biology, Carnegie Institution for Science (until recently Carnegie Institution of Washington) over a period of 37 years. Jan has left a scientific legacy of extensive publications concerned with photosynthetic pigments and their organization, and a historic collection of portraits of scientists who were prominent during her long tenure in the Department of Plant Biology. This legacy will stand for many years to come.

Lateral heterogeneity of plant thylakoid protein complexes: early reminiscences

The concept that the two photosystems of photosynthesis cooperate in series, immortalized in Hill and Bendall's Z scheme, was still a black box that defined neither the structural nor the molecular organization of the thylakoid membrane network into grana and stroma thylakoids. The differentiation of the continuous thylakoid membrane into stacked grana thylakoids interconnected by single stroma thylakoids is a morphological reflection of the non-random distribution of photosystem II/light-harvesting complex of photosystem II, photosystem I and ATP synthase, which became known as lateral heterogeneity.

The chlorophyll-protein complexes of higher plant photosynthetic membranes or Just what green band is that?

Higher plant thylakoid membranes can be fractionated into a bewildering array of macrocomplexes, chlorophyll-protein complexes and chlorophyll-proteins with various deteregents and separations techniques. The chemical nature of each of these entities depends on the particular methods used to obtain them. This review summarizes the current status of the biochemical identification and characterization of individual chlorophyll-proteins and chlorophyll-protein complexes, and attempts to clarify the relationships among them.

Characterization of a full-length petunia cDNA encoding a polypeptide of the light-harvesting complex associated with photosystem I

We have isolated and characterized a full-length cDNA clone (LHCI-15) which specifies a new chlorophyll-binding protein. This protein is associated with the light-harvesting complex of photosystem I (LHCI). The DNA sequence predicts a precursor protein of 270 amino acids, which shares significant homology with the amino acid sequence of another chlorophyll-binding protein; the chlorophyll a/b-binding (Cab) protein of the photosystem II light-harvesting complex (LHCII). There are two extensive regions of homology (at least 45 residues each) which have approximately 50% amino acid sequence identity. These regions coincide with two of the proposed membrane-spanning alpha helices in the Cab proteins of the LHCII and probably include conserved chlorophyll-binding sites. The LHCI-15 cDNA hybridizes to at least 7 genomic EcoRI DNA fragments, which are very closely related at the nucleotide sequence level.

Organization of the photosynthetic apparatus of the chlorina-f2 mutant of barley using chlorophyll fluorescence decay kinetics

The time-resolved chlorophyll fluorescence emission of higher plant chloroplasts monitors the primary processes of photosynthesis and reflects photosynthetic membrane organization. In the present study we compare measurements of the chlorophyll fluorescence decay kinetics of the chlorophyll-b-less chlorina-f2 barley mutant and wild-type barley to investigate the effect of alterations in thylakoid membrane composition on chlorophyll fluorescence. Our analysis characterizes the fluorescence decay of chlorina-f2 barley chloroplasts by three exponential components with lifetimes of approx. 100 ps, 400 ps and 2 ns. The majority of the chlorophyll fluorescence originates in the two faster decay components. Although photo-induced and cation-induced effects on fluorescence yields are evident, the fluorescence lifetimes are independent of the state of the Photosystem-II reaction centers and the degree of grana stacking. Wild-type barley chloroplasts also exhibit three kinetic fluorescence components, but they are distinguished from those of the chlorina-f2 chloroplasts by a slow decay component which displays cation- and photo-induced yield and lifetime changes. A comparison is presented of the kinetic analysis of the chlorina-f2 barley fluorescence to the decay kinetics previously measured for intermittent-light-grown peas (Karukstis, K. and Sauer, K. (1983) Biochim. Biophys. Acta 725, 384-393). We propose that similarities in the fluorescence decay kinetics of both species are a consequence of analogous rearrangements of the thylakoid membrane organization due to the deficiencies present in the light-harvesting chlorophyll a/b complex.

Adaptation of the thylakoid membranes of pea chloroplasts to light intensities. I. Study on the distribution of chlorophyll-protein complexes

The effect of light intensity (16 h white light and 8 h dark) during growth of pea plants at 20°C on the chlorophyll composition and on the relative distribution of chlorophyll amongst the various chlorophyll-protein of pea thylakoids was studied. The chl a/chl b ratios increased from 2.1 to 3.2 as light intensity during growth varied from 10 to 840 μEm(-2) s(-1). This function can be described by two straight lines intersecting at a transition point of approximately 200 μEm(-2) s(-1). Similar discontinuities in the responses were observed in the changes in the relative distribution of chlorophyll amongst the various chlorophyll-protein complexes. This demonstrates that the chl a/chl b ratio of the various thylakoids is a good indicator of changes in the relative distribution of chlorophyll. As the chl a/chl b ratio decreased, the amount of chlorophyll associated with photosystem I complexes decreased, that with photosystem II core reaction centre complex was halved, and that with the main chl a/b-proteins of the light-harvesting complex was markedly increased.