Species divergence and relationships in Stephanomeria (Compositae): PgiC phylogeny compared to prior biosystematic studies.

We present a maximum likelihood tree of 41 PgiC sequences for the monophyletic Stephanomeria, with 10 perennial and six annual species, widely distributed in western North America and exemplary of different speciation processes. The phylogenetic analysis represents the first use of PgiC sequences for Compositae. The annual species were originally delimited by biosystematic studies that provided evidence of their reproductive compatibility and chromosome structural homology. The perennial species are highly distinctive in morphology and have not been examined similarly. The PgiC tree provides more resolution than our previous ITS/ETS tree and reflects both past and ongoing hybridization and/or incomplete lineage sorting. Two major PgiC clades were resolved in Stephanomeria. One clade contains the genes from the annual species plus the perennial, insular endemic S. guadalupensis, which appears closely related to a monophyletic S. virgata. Stephanomeria exigua is not monophyletic. The second clade includes the genes from all other sampled perennial species and a monophyletic subclade of four genes from two annual species. The results are compared to previous studies, also using PgiC, of Clarkia (Onagraceae). Both molecular systematic and biosystematic approaches are essential to discern the very different courses of evolution in these two, well-studied genera of western North America.

Reassessment of phylogenetic relationships in Clarkia sect. Sympherica.

Clarkia (Onagraceae) is a genus of 42 annual species, mostly native to California, that has served as a model for many studies of plant evolutionary biology, particularly morphological, cytological, and genetic divergence; reproductive isolation; and speciation. Section Sympherica is the largest section with eight diploid and one allotetraploid species. Species in the section have provided important evidence about the evolution of reproductive isolation (C. lingulata derived from C. biloba) and large morphological change (C. dudleyana thought to be sister to the morphologically distinct C. heterandra, recently transferred into Clarkia from the monotypic Heterogaura). Clarkia epilobioides, another diploid species in the section, was previously shown to be one parent of the allotetraploid C. delicata, the other parent being C. unguiculata from sect. Phaeostoma. Lewis and Lewis (1955) interpreted the parentage of C. delicata and other evidence of intersectional hybridization to mean that the diploid sections of the genus, though highly diverse, were closely related and should be maintained in the single genus Clarkia. Here we assess phylogenetic relationships among the species of sect. Sympherica and related species by analyzing the nucleotide sequences of PgiC1 and PgiC2, a pair of paralogous genes that encode the cytosolic isozyme of phosphoglucose isomerase (EC 5.3.1.9). The major results were the following: (1) C. unguiculata and both genomes of C. delicata are within a well-defined "Sympherica" clade; thus, C. delicata should not be considered an intersectional hybrid; (2) C. heterandra belongs in the clade and is closely related to C. unguiculata; and (3) on the evidence of PgiC1, C. dudleyana is not in the clade and is not closely related to C. heterandra.

The 5' leader of plant PgiC has an intron: the leader shows both the loss and maintenance of constraints compared with introns and exons in the coding region.

PgiC, a complex gene with 23 coding exons and 22 intervening introns, encodes the cytosolic isozyme of phosphoglucose isomerase (EC 5.3.1.9) in higher plants. Here, we report RNA ligase-mediated rapid amplification of cDNA ends experiments that showed that PgiC in Clarkia (Onagraceae) and Arabidopsis thaliana has an intron in the 5' leader. Comparison of the EMBL accessions of the cDNA and genomic sequences showed that this is also the case in rice (Oryza sativa), suggesting that a leader intron is generally present in higher plant PgiC. The intron is bounded by consensus 5'-GT and AG-3' splice sites but showed alternative splicing in Clarkia, resulting in mature transcripts that differ by 8-19 nt in length. The intron is located 18 or 10 nt upstream of the start codon in Clarkia, 2 nt upstream in Arabidopsis, and 9 nt in rice. PgiC in Clarkia was duplicated before the divergence of the extant species, many of which have two expressed genes PgiC1 and PgiC2. Full-length transcripts of both genes identified the transcription start and made it possible to identify the leader intron and leader exon (between the transcription start and leader intron) from previously obtained genomic sequences of both genes in other Clarkia species. These data permit the comparison of evolution in the leader exon and intron with the exons and introns of the coding region, a topic that has not been studied previously. Both the leader exon and the leader intron resemble introns of the coding region in base substitution rate and accumulation of gaps. But the leader intron splice junctions are not strictly conserved in position as are those of the coding region introns. Also, in base composition, the leader intron resembles the other introns, whereas the leader exon more nearly resembles the coding exons. A difference in base composition between coding exons and flanking introns is known to be important for the recognition of splice sites. Thus, the marked difference in base composition between the leader exon and leader intron is probably maintained by selection despite a high rate of sequence divergence.

Single mutations silence PGiC2 genes in two very recent allotetraploid species of Clarkia.

Our understanding of how polyploidy influences gene evolution is limited by the fact there have been few molecular descriptions of particular genes and their expression in polyploid plants and their diploid progenitors. Here we use evidence from sequencing of genomic DNA and cDNA obtained by reverse transcriptase-polymerase chain reaction and 3' rapid amplification of cDNA ends to describe PgiC genes and their expression in two allotetraploid species of the wildflower genus Clarkia, C. delicata and C. similis. PgiC encodes the cytosolic isozyme of phosphoglucose isomerase (EC 5.3.1.9) and was duplicated in the ancestral stock of Clarkia, giving rise to paralogous genes PgiC1 and PgiC2. The active form of the PGIC enzyme is a dimer of like subunits. The electrophoretic patterns in the parent species show three bands of activity, representing two homodimers and a heterodimer of intermediate mobility, and are encoded by two genes. The electrophoretic patterns in the tetraploids also show three bands, but the tetraploids were expected to have multiple PGIC isozymes encoded by four genes. Our molecular studies demonstrated that each tetraploid has two PgiC1 and two PgiC2 genes, as predicted. One gene in each of them has been silenced by a single mutation, and a functional protein is no longer produced. In C. similis, PgiC2(mod) was silenced by a mutation of a single nucleotide in exon 5 that created a stop codon. In C. delicata, a polymorphism exists between a normal allele and a defective allele of PgiC2(epi) that has a deletion of a splice junction in intron 19 that results in the synthesis of a transcript lacking an entire exon, an example of exon skipping. The three-banded PGIC electrophoretic pattern of both tetraploid species arises because isozymes encoded by two or three of the genes comigrate. A very recent origin for both tetraploids is suggested by the near identity of several of their PgiC genes to their corresponding diploid orthologues and the absence of any acceleration in mutation rates. The problem of assessing genetic redundancy in tetraploids is discussed.

Phylogeny of Stephanomeria and related genera (compositae-lactuceae) based on analysis of 18S-26S nuclear rDNA ITS and ETS sequences.

A phylogenetic analysis of DNA sequences from the internal transcribed spacer (ITS), the external transcribed spacer (ETS), and the 5.8S regions of 18S-26S nuclear rDNA from all diploid species of Stephanomeria and related genera shows that Stephanomeria does not include either Munzothamnus blairii (previously S. blairii) or Pleiacanthus spinosus (previously S. spinosa). Without these two taxa, Stephanomeria is a well-supported (100% bootstrap), monophyletic group of ten perennial and six annual species. Munzothamnus blairii and Pleiacanthus spinosus, both now considered members of monotypic genera, had been placed in Stephanomeria primarily because they have the same chromosome number as Stephanomeria and similar pollen surface features, but many disparities were ignored in previous classifications. Within Stephanomeria, an unsuspected sister relationship was detected between the montane S. lactucina and coastal S. cichoriacea. A second clade contained all the annual taxa and five of the perennial species. Among the annuals, strong bootstrap support was obtained for the previously recognized relationships between S. diegensis and S. exigua (98%) and between S. malheurensis and its progenitor, S. exigua subsp. coronaria (96%). Among the five perennial species that constitute a clade with the annuals, the recently described S. fluminea was shown to be sister to S. runcinata, and both of them were closely allied to S. tenuifolia and S. thurberi. The clade including the annuals (and five of the perennial species) was subtended by perennial lineages and pairwise divergence values among the annual taxa were much lower than among the perennial taxa as a group (though not too different than among the perennials in the same clade). The annuals probably originated recently within the genus.

The status of Clarkia australis (Onagraceae).

Clarkia australis and C. virgata grow on the western slope of the central Sierra Nevada of California. Clarkia australis was established to accommodate populations of C. virgata from south of the Tuolumne River that could not be successfully hybridized to populations north of the river. Although the species is maintained in the new Jepson Manual, its validity has been questioned because only two populations were originally tested, and they had no useful morphological traits that distinguished them from C. virgata. We report here the results of a large program of interpopulation hybridizations that show that C. australis is distinct and that its reproductive isolation from C. virgata is complete and absolute and reflects a compatibility block that apparently causes abortion of hybrid seeds in early development. Both species include populations north and south of the Tuolumne River and, in general, those of C. australis occupy higher elevations. Morphologically, the species are extremely similar though the mean values of several dimensions of the petals are different. However, significant variation among their populations has the consequence that, at present, the only certain way to assign particular populations to species is to test their compatibility with previously tested populations.

MOLECULAR CHARACTERIZATION OF PgiC IN A TETRAPLOID PLANT AND ITS DIPLOID RELATIVES.

Allotetraploid plant species combine the genomes of related diploid species, but little is known about whether homologous genes from the diploid genomes are expressed, how they interact, or whether they evolve differently when in a common tetraploid nucleus. Polyploidy may lead to gene silencing, but few molecular characterizations of silenced genes encoding enzymes in polyploids and related diploids have been reported. Here we describe the PgiC genes in the tetraploid Clarkia gracilis and related diploid species, which are native from California to southern Washington. PgiC encodes the cytosolic isozyme of phosphoglucose isomerase (PGIC; EC 5.3.1.9). The gene was duplicated in the basal stock of Clarkia and now both genes, PgiC1 and PgiC2, are active in about half of the diploid species, whereas only PgiC1 is active in the others. Clarkia gracilis was found to have three PgiC genes: two PgiC1s and a PgiC2. Reverse-transcriptase-polymerase chain reaction (RT-PCR) experiments, starting with mRNAs prepared from seedling leaves of C. gracilis, showed that the three genes are expressed. Analysis of their sequences showed they are evolving at similar rates to their homologues and that they have the same intron-exon structure. The presence of an expressed PgiC2 in C. gracilis was unexpected because all related diploid species, including one identified as a parent, have only active PgiC1s. The donor of the PgiC2 is now presumed extinct, but parsimony analysis identified its phylogenetic position. None of the PgiC genes that were active when C. gracilis arose were silenced. A possible example of gene conversion involving a 300-nuclectide region of one PgiC1 and PgiC2 was identified, but it probably occurred in the diploid parental species rather than in C. gracilis. PgiC2 is the first known example of an active locus in a tetraploid plant species that is no longer expressed in its diploid relatives.

A collaborative project in Connecticut to improve the care of patients with acute myocardial infarction.

BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstracters who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.

A recently silenced, duplicate PgiC locus in Clarkia.

Previous electrophoretic analysis showed that 17 diploid species of the wildflower Clarkia (Onagraceae) have two cytosolic isozymes of phosphoglucose isomerase (PGIC; EC 5.3.1.9), whereas 15 other diploid species have a single PGIC. Molecular studies revealed that the two isozymes in the former species are encoded by duplicate genes, PgiC1 and PgiC2, whereas the single isozyme in the latter is always encoded by PgiC1. Phylogenetic analysis of the nucleotide sequences implied that PgiC2 was silenced four times independently in the genus. Here we describe a psi PgiC2 from C. mildrediae, a species in which only PgiC1 is expressed. The discovery of the psi PgiC2 is significant because it confirms a formal prediction of the phylogenetic analysis. The psi PgiC2 includes 5,039 nucleotides corresponding to 18 of the 23 exons of PgiC, as well as the intervening introns and 3' nontranslated region. The absence of an increase of nucleotide substitutions in its "exons" suggests that the gene was silenced recently. The present study appears to be the first to establish that a specific duplicate gene locus regularly expressed in a group of related plant species has been silenced in one of them. The multiple independent silencings of PgiC2 suggest that it remained functional but inessential in ancestral lineages. We discuss the possibility that PgiC2 may have been preserved in these lineages by selection against mutants causing defective PGIC1-PGIC2 heterodimers.

A collaborative project in Connecticut to improve the care of patients with acute myocardial infarction.

BACKGROUND: State-based peer review organizations (PROs) and individual hospitals are challenged to achieve their quality improvement (QI) goals with shrinking resources. In 1993-1994 the Connecticut PRO and 15 local hospitals generated a comparative QI database on acute myocardial infarction (AMI) care for 1,202 Medicare and non-Medicare patients discharged in 1992 and 1993. METHODS: A steering committee composed of hospital and PRO representatives was assembled to provide oversight. PRO staff developed a chart abstraction tool and trained hospital abstractors who collected and submitted data to the PRO for comparative analyses. Written feedback was provided to all hospitals and supplemented with onsite presentations when requested. Each hospital prepared a written QI plan based on its unique data profile. RESULTS: Opportunities for improvement were identified at all hospitals. The most commonly targeted areas for improvement included the use of thrombolytics at presentation, aspirin at presentation and at discharge, and beta blockers at discharge. Improvement interventions included staff education sessions, development of AMI critical paths and standing orders, and storage of appropriate medications in emergency departments. Self-report data from the hospitals indicate improvements in care. DISCUSSION: PROs and hospitals can augment their individual QI activities by working together to share data, resources, and lessons learned. Twenty-three hospitals are now collaborating with the Connecticut PRO on a similarly designed QI project aimed at improving the care of patients hospitalized with atrial fibrillation. This project includes a more formal means of communicating QI interventions.

Clinical pathway for pneumonia: development, implementation, and initial experience.

BACKGROUND: As part of a large multidisciplinary project to reduce cost, decrease hospital length of stay, and improve efficiency of patient care at Saint Mary's Hospital, a clinical pathway for pneumonia was developed and implemented. METHODS: After using analysis of severity-adjusted data to determine which conditions would be best targets for improvement, a utilization management steering committee created a multidisciplinary group to develop a clinical pathway for pneumonia. This group was led by physician champions and consisted of representatives from nursing, respiratory therapy, pharmacy, and home healthcare. With information gained from chart abstraction, which identified "best practice" patterns, guidance from the medical literature, and local expertise, this group developed a clinical pathway that included an auxiliary protocol for respiratory care and a detailed educational brochure for patients. Before implementing the clinical pathway, extensive educational activities were undertaken involving the medical staff, house staff, nurses, and other staff. Data collected on consecutive patients discharged after implementation of the pathway were compared with data collected on patients discharged before the pathway in 1994. RESULTS: For DRG 89, the patients who were on the pathway in comparison to the control patients from 1994 had a lower average length of stay by 1.45 days (5.84 vs. 7.29 days) and a lower average total charge by $1,453 ($9,511 vs. $10,964). For DRG 90, the patients who were on the pathway in comparison to the control patients from 1994 had a lower average length of stay by 1.83 days (3.45 vs. 5.28 days) and a lower average total charge by $1319 ($5450 vs. $6769). CONCLUSIONS: The pneumonia clinical pathway that was implemented was associated with reductions in the length of stay and total charges. These reductions were seen in relationship to historical controls and to patients cared for concurrently who were not placed on the pathway. Although not fully used on all pneumonia patients, the presence of the pathway probably had some positive effects even on patients not formally on the pathway, through systems changes and educational influences. The pathway also positively influenced other conditions by the use of ancillary algorithms for conditions other than pneumonia, and the more rapid administration of antibiotics for other infectious diseases. Also, lessons learned in the creation of this first pathway have been helpful in streamlining the process of future pathway development.

Random amplified polymorphic DNA variation in the eggplant, Solanum melongena L. (Solanaceae).

RAPD analysis was carried out on 52 accessions of Solanum melongena (eggplant) and related weedy forms known as "insanum". Twenty-two primers amplified 130 fragments. Solanum melongena exhibited 117 of the fragments, all of which were also present in insanum. Insanum displayed an additional 13 fragments not found in S. melongena. Overall, the insanum accessions were more diverse than those of S. melongena. The calculated similarity between them was 0.947. The RAPD results were closely concordant with the results of an electrophoretic isozyme survey performed on the same accessions. The concordance of the results shows that even though S. melongena and insanum are highly diverse morphologically, it is no longer appropriate to distinguish them taxonomically.

Allozyme variation in the eggplant, Solanum melongena L. (Solanaceae).

Enzyme electrophoretic studies were made in cultivated Solanum melongena L. (eggplant) and similar wild and weedy forms, several of which have been thought to be different species/taxa. Twenty-nine accessions of S. melongena, 33 accessions of weedy forms (referred to as "insanum") and 2 accessions of wild forms (referred to as "incanum") were surveyed for 29 isozyme loci. In S. melongena, 22 of the 29 loci were monomorphic, and nearly all of its genes were either also monomorphic or in similar frequencies in insanum and incanum. The results demonstrate that the three taxa have a very close genetic relationship. The high genetic identities between them (0.913-0.967) suggests that they are conspecific even though they include extensive morphological diversity.

Randomized controlled trial in alcohol relapse prevention: role of atenolol, alcohol craving, and treatment adherence.

Previous studies suggest that beta-adrenergic blockers reduce craving levels during acute alcohol withdrawal. We conducted a new study to assess whether the daily use of atenolol by the abstinent alcoholic could maintain a blunted craving for alcohol and result in a decreased rate of relapse for alcohol abuse. The study was designed as a randomized, controlled, double-blind clinical trial. Among all 100 patients (50 atenolol, 50 placebo), only 15 stayed in the trial and remained fully abstinent for 1 year (7 atenolol, 8 placebo). Of the remaining 85 patients, 30 withdrew early while still abstinent (17 atenolol, 13 placebo). In the 57 high-risk patients who reported craving for alcohol at baseline, the treatment failure rates were 90% for patients receiving placebo, and was reduced to 65% in those who received atenolol (risk reduction = 28%, 95% confidence interval, -3% to 49%). The data from this trial also support the observation that poorer levels of treatment adherence are strongly associated with adverse outcomes for alcoholics during follow-up. This relationship was present both for patients who received atenolol and for those who received placebo.

Molecular characterization of duplicate cytosolic phosphoglucose isomerase genes in Clarkia and comparison to the single gene in Arabidopsis.

The nucleotide sequence of PgiC1-a which encodes a cytosolic isozymes of phosphoglucose isomerase (PGIC; EC 5.3.1.9) in Clarkia lewisii, a wildflower native to California, is described and compared to the previously published sequence of the duplicate PgiC2-a from the same genome. Both genes have the same structure of 23 exons and 22 introns located in identical positions, and they encode proteins of 569 amino acids. Exon and inferred protein sequences of the two genes are 96.4% and 97.2% identical, respectively. Intron sequences are 88.2% identical. The high nucleotide similarity of the two genes is consistent with previous genetic and biosystematic findings that suggest the duplication arose within Clarkia. A partial sequence of PgiC2-b was also obtained. It is 99.5% identical to PgiC2-a in exons and 99.7% in introns. The nucleotide sequence of the single PgiC from Arabidopsis thaliana was also determined for comparison to the Clarkia genes. The A. thaliana PgiC has 21 introns located at positions identical to those in Clarkia PgiC1 and PgiC2, but lacks the intron that divides Clarkia exons 21 and 22. The A. thaliana PGIC protein is shorter, with 560 amino acids, and differs by about 17% from the Clarkia PGICs. The PgiC in A. thaliana was mapped to a site 20 cM from restriction fragment length polymorphism marker 331 on chromosome 5.

The impact of gender on clinical characteristics and outcome in alcohol withdrawal.

Few studies have compared the social and clinical features of alcoholism for women and men, and none has focused on patients entering treatment for withdrawal. We investigated the role of gender by analyzing the data for 179 patients (34 women, 145 men) who underwent outpatient withdrawal. Our analysis focused on two questions: 1) How do women and men compare in terms of baseline social and clinical features? and 2) Do women and men have similar treatment outcomes in alcohol withdrawal? Baseline sociodemographic features revealed that women were more likely to be poor (90% vs. 71%, p = .03) but less likely to be uninsured (32% vs. 51%, p = .05), homeless (6% vs. 20%, p = .05), or have legal problems (29% vs. 54%, p = .02). Surprisingly, women and men reported a similar mean daily alcohol intake (240 g vs. 243 g). Women reported a shorter duration of alcohol abuse prior to entering treatment (16.1 y vs. 19.1 y). Although women experienced a higher treatment failure rate (53% vs. 43%), this difference is not significant. Our analysis highlights gender similarities and differences among patients entering treatment for withdrawal. We conclude that women and men have similar treatment outcomes in the management of alcohol withdrawal.

Molecular analysis of the plant gene encoding cytosolic phosphoglucose isomerase.

The gene encoding a cytosolic isozyme of phosphoglucose isomerase (PGI, EC 5.3.1.9) was isolated from Clarkia lewisii, a wild flower native to California, and the structure and sequence of the entire coding region determined. PGI catalyzes an essential step in glycolysis and carbohydrate biosynthesis in plants. Spanning about 6 kb, the gene has 23 exons and 22 introns, the highest number yet reported in plants. The exons range in size from 43 to 156 nt and encode a protein of 569 amino acids. The protein is about 44-46% identical to the inferred protein sequences of pig, Escherichia coli and Saccharomyces cerevisiae. All of the introns are bordered with the consensus 5'-GT...AG-3' dinucleotides. The longest intron includes a large stem-loop structure bounded by a perfect 9 nt direct repeat. We cloned the PGI gene from a genomic library prepared from a single plant of known PGI genotype. The locus and allele of the clone were identified by matching restriction fragments to fragments from genetically defined genomic DNAs by Southern hybridization.

Social and clinical features as predictors of outcome in outpatient alcohol withdrawal.

OBJECTIVE: To identify patient features--both social and clinical--that may be associated with treatment failure in outpatient alcohol withdrawal. DESIGN: A prospective observational cohort study of patients who underwent outpatient management of the alcohol withdrawal syndrome. SETTING: Community hospital-based outpatient alcohol treatment program. PATIENTS: The 179 patients who were eligible for and participated in a clinical trial of drug therapy for outpatient management of the alcohol withdrawal syndrome. MAIN RESULTS: Treatment failure occurred for 45% (80/179) of the patients. Failure rating did not vary according to diverse sociodemographic features such as age, level of education, income, medical insurance status, and marital status. Persons who were homeless did as well as those who were not. In contrast, two clinical features of withdrawal were associated with significantly higher rates of treatment failure: craving and withdrawal symptom severity. High cravers had a treatment failure rate of 56% (22/39), compared with 36% (41/115) for those with lower scores (p less than 0.03). Among those with moderate-to-high withdrawal symptom severity, 49% (74/151) represented treatment failures, compared with 22% (6/27) of those in the low-symptom group (p less than 0.01). CONCLUSIONS: While these data do not confirm that socially disadvantaged persons are at increased risk for withdrawal treatment failure, two clinical features--craving and withdrawal symptom severity--may help identify high-risk patients.

Decreased-activity mutants of phosphoglucose isomerase in the cytosol and chloroplast of Clarkia xantiana. Impact on mass-action ratios and fluxes to sucrose and starch, and estimation of Flux Control Coefficients and Elasticity Coefficients.

1. Subcellular-compartment-specific decreased-activity mutants of phosphoglucose isomerase in Clarkia xantiana were used to analyse the control of sucrose and starch synthesis during photosynthesis. Mutants were available in which the plastid phosphoglucose isomerase complement is decreased to 75% or 50% of the wild-type level, and the cytosol complement to 64%, 36% or 18% of the wild-type level. 2. The effects on the [product]/[substrate] ratio and on fluxes to sucrose or starch and the rate of photosynthesis were studied with the use of saturating or limiting light intensity to impose a high or low flux through these pathways. 3. Removal of a small fraction of either phosphoglucose isomerase leads to a significant shift of the [product]/[substrate] ratio away, from equilibrium. We conclude that there is no 'excess' of enzyme over that needed to maintain its reactants reasonably close to equilibrium. 4. Decreased phosphoglucose isomerase activity can also alter the fluxes to starch or sucrose. However, the effect on flux does not correlate with the extent of disequilibrium, and also varies depending on the subcellular compartment and on the conditions. 5. The results were used to estimate Flux Control Coefficients for the chloroplast and cytosolic phosphoglucose isomerases. The chloroplast isoenzyme exerts control on the rate of starch synthesis and on photosynthesis in saturating light intensity and CO2, but not at low light intensity. The cytosolic enzyme only exerts significant control when its complement is decreased 3-5-fold, and differs from the plastid isoenzyme in exerting more control in low light intensity. It has a positive Control Coefficient for sucrose synthesis, and a negative Control Coefficient for starch synthesis. 6. The Elasticity Coefficients in vivo of the cytosolic phosphoglucose isomerase were estimated to lie between 5 and 8 in the wild-type. They decrease in mutants with a lowered complement of cytosolic phosphoglucose isomerase. 7. The implications of these results for regulation and for evolution are discussed.