Chloroplast Fe(III) chelate reductase activity is essential for seedling viability under iron limiting conditions

Photosynthesis, heme biosynthesis, and Fe-S cluster assembly all take place in the chloroplast, and all require iron. Reduction of iron via a membrane-bound Fe(III) chelate reductase is required before iron transport across membranes in a variety of systems, but to date there has been no definitive genetic proof that chloroplasts have such a reduction system. Here we report that one of the eight members of the Arabidopsis ferric reductase oxidase (FRO) family, FRO7, localizes to the chloroplast. Chloroplasts prepared from fro7 loss-of-function mutants have 75% less Fe(III) chelate reductase activity and contain 33% less iron per microgram of chlorophyll than wild-type chloroplasts. This decreased iron content is presumably responsible for the observed defects in photosynthetic electron transport. When germinated in alkaline soil, fro7 seedlings show severe chlorosis and die without setting seed unless watered with high levels of soluble iron. Overall, our results provide molecular evidence that FRO7 plays a role in chloroplast iron acquisition and is required for efficient photosynthesis in young seedlings and for survival under iron-limiting conditions.     

Thrombocytopenia in the critically ill: prevalence, incidence, risk factors, and clinical outcomes

Purpose

The aim of this cohort study was to describe the prevalence, incidence, and risk factors for thrombocytopenia in the intensive care unit (ICU) and to evaluate the impact of thrombocytopenia on mortality with further comparisons amongst major diagnostic categories.

Methods

Patients admitted to the ICU from 1997-2011 for cardiac, medical, surgical, and trauma conditions were included. The presence of a platelet count < 100 × 10⁹·L^?1 on admission day or its appearance during ICU stay were considered as prevalent and incident thrombocytopenia, respectively. Risk factors for thrombocytopenia and the influence of thrombocytopenia on mortality were also analyzed.

Results

This study included 20,696 patients. Prevalent and incident thrombocytopenia occurred in 13.3% and 7.8% of patients, respectively, with associated mortality rates of 14.3% and 24.7%, respectively, compared with 10.2% in the group with normal platelet count (P < 0.001). After adjustments, thrombocytopenia remained associated with an increased risk of mortality (odds ratio 1.25; 95% confidence interval 1.20 to 1.31; P < 0.001). The greatest impact of thrombocytopenia on mortality was observed in the cancer, respiratory, digestive, genitourinary, and infectious diagnostic categories. Independent risk factors included age, female sex, admission platelet counts and hemoglobin, mechanical ventilation, days of hospitalization prior to ICU admission, liver cirrhosis, hypersplenism, coronary bypass grafting, intra-aortic balloon pump placement, acute hepatitis, septic shock, and pulmonary embolism or deep vein thrombosis.

Conclusions

Thrombocytopenia in the ICU is associated with an independent risk of mortality that varies greatly depending on diagnostic admission category.