Can hypodermal passage cell distribution limit root penetration by mycorrhizal fungi?

* The basis for significant interspecific variability in colonization by arbuscular mycorrhizal fungi is poorly understood. Limited evidence suggests that, for species with a dimorphic hypodermis, colonization of the root cortex occurs only through hypodermal passage cells. Therefore, the hypothesis that interspecific variability in mycorrhizal colonization is accounted for by interspecific variation in passage cell distribution was tested. * The arbuscular mycorrhizal colonization and distribution of fungal penetration points and hypodermal passage cells in the root systems of eight species (seven plant families) possessing a dimorphic hypodermis were characterized. * Mycorrhizal fungal penetration of the hypodermis occurred exclusively through passage cells. Moreover, the proportion of root length with passage cells explained nearly 99% of the variability among the eight plant species in the proportion of root length with penetration points. * In dimorphic hypodermal species, passage cells appear to be key determinants of mycorrhizal colonization because they are the cells through which fungal penetration of the hypodermis occurs. Variation among such species in mycorrhizal colonization may be at least partly determined by variation in the proportion of root length with passage cells.

Spontaneous pneumothorax in common pulmonary vein atresia.

Common pulmonary vein atresia is a rare congenital anomaly that is rapidly fatal unless immediately recognized and corrected by surgical intervention. This article describes three neonates who died with the diagnosis soon after birth. In the constellation of presenting clinical features in each case, the occurrence of early spontaneous pneumothorax was particularly noteworthy. This sign may well be a helpful physiologic marker within the context of suspected congenital heart disease associated with severe pulmonary venous obstruction.

Myopathy and fatal cardiopathy due to cytochrome c oxidase deficiency.

A 3-day-old girl had a syndrome of lethargy and lactic acidosis. Pregnancy and delivery had been normal; there was no consanguinity or family history of neuromuscular disease. At age 4 1/2 months, she had generalized weakness, hypotonia, areflexia, and macroglossia. She developed cyanosis and respiratory failure, and marked cardiomegaly was noted. She died at age 8 1/2 months of cardiac arrest. Results from a muscle biopsy specimen obtained at age 4 1/2 months showed ragged-red fibers and increased glycogen and lipid droplets. With the cytochrome c oxidase reaction, only 5% of the fibers stained positively in the biopsy specimen. Cytochrome c oxidase activity was 7.3% of normal in muscle mitochondria and 12.2% of normal in heart mitochondria. Reduced-minus-oxidized cytochrome spectra showed lack of the cytochrome aa3 peak. Immunotitration using antibodies against purified human heart cytochrome c oxidase showed normal amount of cross-reacting material in both heart and muscle. The genetic error could have involved a cytochrome c oxidase isozyme common to heart and muscle.

Frontonasal "dysplasia," cerebral anomalies, and polydactyly: report of a new syndrome and discussion from a developmental field perspective.

We describe a boy with frontonasal "dysplasia"; cerebral anomalies, including agenesis of corpus callosum and probable Dandy-Walker malformation (absent superior vermis, hypoplastic cerebellum and brain stem, and possible posterior fossa cyst in this case); short neck, relatively long trunk with short limbs; cryptorchidism; and polydactyly of hands and feet. We suspect he has a previously undescribed syndrome of presently unknown cause. We also discuss this case from a developmental field perspective, in view of the unusual combination of cerebral and facial defects.

Autosomal recessive syndrome of sacral and conotruncal developmental field defects (Kousseff syndrome).

Kousseff [1984] reported on three sibs with an autosomal recessive syndrome of sacral meningocele, conotruncal heart defects, and minor anomalies of head and neck. We report on a fourth case and discuss the findings from a developmental field perspective and the ramifications for genetic counseling.