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The photosynthetic efficiency of leaves under low light is considered to be a major determinant of crop photosynthetic performance. The aim of this study was to identify chromosome effects on some parameters associated with photosynthetic efficiency under low light. Photosynthetic activity was analyzed using a pulse-amplitude modulation fluorometer for the measurement of the photochemical quenching (Q(sub p)) and of the quantum efficiency of Photosystem II electron transport (phi(sub PSII)) under an actinic light of 45 micron mol m to the -2 s to the -1 on wheat (Triticum aestivum L.) plants grow in pots under natural conditions. Reciprocal sets of chromosome substitution lines between the hard red winter wheat cultivars Wichita and Cheyenne were used to identify the chromosomes involved in the expression of these traits. The two parental cultivars were significantly different for Q(sub p) and phi(sub PSII). Chromosome 3D affected Phi(sub PSII) at various stages of development when plants were exposed to low light intensities. Relationships between yield and photosynthetic efficiency under nonsaturating light have been postulated. Thus, chromosome 3D probably influences bread wheat productivity.

A study was conducted to show that the inactivation of each of Rhodopseudomonas palustris strain CGA009 ppsR genes results in an elevated level of formation of the photosystem under dark aerobic conditions. The findings show that both the PpsR1 and PpsR2 proteins from R. palustris strain CGA009 function as oxygen-responsive transcriptional repressors.

Diversity in photosynthetic pathways in the angiosperm family Chenopodiaceae is expressed in both biochemical and anatomical characters. To understand the evolution of photosynthetic diversity, we reconstructed the phylogeny of representative species of tribe Salsoleae of subfamily Salsoloideae, a group that exhibits in microcosm the patterns of photosynthetic variation present in the family as a whole, and examined the distribution of photosynthetic characters on the resulting phylogenetic tree. Pylogenetic relationships were inferred from parsimony analysis of nucleotide sequences of the internal transcribed spacer regions (ITS) of the 18S-26S nuclear ribosomal DNA of 34 species of Salsola and related genera (Halothamnus, Climacoptera, Girgensohnia, Halocharis, and Haloxylon) and representative outgroups from tribes Camphorosmeae (Camphorosma lessingii, Kochia prostrata, and K. scoparia) and Atripliceae (Atriplex spongiosa). A highly resolved strict consensus tree largely agrees with photosynthetic type and anatomy of leaves and cotyledons. The sequence data provide strong support for the origin and evolution of two main lineages of plants in tribe Salsoleae, with NAD-ME and NADP-ME [C.sub.4] photosynthesis, respectively. These groups have different [C.sub.4] photosynthetic types in leaves and different structural and photosynthetic characteristics in cotyledons. Phylogenetic relationships inferred from ITS sequences generally agree with classifications based on morphological data, but deviations from the existing taxonomy were also observed. The NAD-ME [C.sub.4] lineage contains species classified in sections Caroxylon, Malpigipila, Cardiandra, Belanthera, and Coccosalsola, and the NADPME lineage comprises species from sections Coccosalsola and Salsola. Reconstruction of photosynthetic characters on the ITS phylogeny indicates separate NAD-ME and NADP-ME lineages and suggests two reversions to [C.sub.3] photosynthesis. Reconstruction of geographic distributions suggests Salsoleae originated and diversified in central Asia and subsequently dispersed to Africa, Europe, and Mongolia. Inferred patterns and processes of photosynthetic evolution in Saisoleae should further our understanding of biochemical and anatomical evolution in Chenopodiaceae as a whole. Key words: [C.sup.3] and [C.sub.4] photosynthesis; Chenopodiaceae; evolution; ITS sequences; leaf anatomy; phylogeny; Salsola.

A plastid-derived signal plays an important role in the coordinated expression of both nuclear- and chloroplast-localized genes that encode photosynthesis-related proteins. Arabidopsis GUN (genomes uncoupled) loci have been identified as components of plastid-to-nucleus signal transduction. Unlike wild-type plants, gun mutants have nuclear Lhcb1 expression in the absence of chloroplast development. We observed a synergistic phenotype in some gun double-mutant combinations, suggesting there are at least two independent pathways in plastid-to-nucleus signal transduction. There is a reduction of chlorophyll accumulation in gun4 and gun5 mutant plants, and a gun4gun5 double mutant shows an albino phenotype. We cloned the GUN5 gene, which encodes the ChlH subunit of Mg-chelatase. We also show that gun2 and gun3 are alleles of the known photomorphogenic mutants, hy1 and hy2, which are required for phytochromobilin synthesis from heme. These findings suggest that certain perturbations of the tetrapyr-role biosynthetic pathway generate a signal from chloroplasts that causes transcriptional repression of nuclear genes encoding plastid-localized proteins. The comparison of mutant phenotypes of gun5 and another Mg-chelatase subunit (ChlI) mutant suggests a specific function for ChlH protein in the plastid-signaling pathway.

Most effects of atmospheric CO2 increase arise indirectly as a result of photosynthetic stimulation, inhibition of respiration, or improved water use efficiency. Only the guard cells that control stomatal function are known to directly sense variation in CO2 and transduce it into a regulated response. High CO2 reduces stomatal aperture, while low CO2 increases it. The mechanism of this signal-transduction response remains unclear. At the level of the internal leaf biochemistry, the expression of only a few enzymes may be directly regulated by CO2 level. For example, carbonic anhydrase expression is reduced by high CO2, but the mechanism for this control is also unclear. Increasing CO2 promotes photosynthesis through its effect as a substrate in carbon fixation and as an inhibitor of photorespiration. Long-term (weeks to years) exposure to high CO2 increases leaf carbohydrate status, which in turn reduces photosynthetic gene expression, causing a decline in photosynthetic capacity. This reduction in photosynthetic capacity is the main acclimation response to high CO2, and is similar to acclimation responses to other environmental agents that promote carbohydrate accumulation. Factors that affect carbohydrate accumulation following transfer to high CO2 modulate the strength of the acclimation response. For example, low sink capacity and low nutrient status promote carbohydrate accumulation and a strong CO2 acclimation response. Carbohydrates status alone does not drive CO2 acclimation. Instead, it appears leaves must be primed to respond to high levels of carbohydrate, probably by long-distance signals such as ABA and cytokinins that are sent from the roots and other sinks. Identifying the mechanisms of interaction between carbohydrate status, plant hormones and other developmental signals is a major requirement for understanding how plants will respond to atmospheric CO2 enrichment.

ASSESSING PHOTOSYNTHETIC POTENTIAL IN A HOLOPARASITIC PLANT WITH A CONSERVED PHOTOSYNTHETIC GENE. Carol J. Baskauf, W. G. Eickmeier, and C. W. dePamphilis, Austin Peay State University, Clarksville, Tennessee, Vanderbilt University, [...]

Fulvimarina pelagi is a Mn(II)-oxidizing marine heterotrophic bacterium in the order Rhizobiales. Here we announce the draft genome sequence of F. pelagi [HTCC2506.sup.T], which was isolated from the Sargasso Sea by using dilution-to-extinction culturing. The genome sequence contained a xanthorhodopsin gene as well as a photosynthetic gene cluster, which suggests the coexistence of two different phototrophic mechanisms in a single microorganism. doi: 10.1128/JB.00761-10

As part of an intensive study of heritable differences among the progeny of Pinus ponderosa parents from two contrasting habitats (coastal vs. interior, continental), we examined the potential for differences in photosynthesis rate, stomatal conductance, and photosynthetic wateruse efficiency. Plants from a cross between two coastal parents (ponderosa x ponderosa) exhibited lower photosynthetic water-use efficiencies, relative to plants from a coastal x interior cross (ponderosa X scopulorum). The lower water-use efficiencies in the ponderosa X ponderosa plants were evident as a lower ratio of external to intercellular CO[sub.2] concentrations and higher stomatal conductances at any given rate of photosynthesis. The ponderosa X scopulorum plants exhibited lower stomatal conductances over a rangee of leaf-to-air water vapor concentration differences, which was partially explained by lower stomatal densities. The ponderosa X scopulorum plants also exhibited lower maximum photosynthesis rates and loweer needle nitrogen concentrations. Taken together, the results suggest that in adapting to drier habitats, P. ponderosa has acquired improved water-use efficiencies and lower transpiration rates, but at the expense of reduced maximum photosynthesis rates.