Robert Dirks

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Protoplast fusion studies between various auxotrophic mutants of Nicotiana plumbaginifolia were performed to optimize conditions for PEG-mediated fusion and to identify factors influencing the plant protoplast fusion process. Numerous parameters in the isolation, culture, and fusion of protoplasts were tested, and established fusion protocols were compared.(More)
Petiole protoplasts from in vitro-grown carrot plants are a very good alternative to traditionally obtained protoplasts from suspension cultures. High plating and regeneration efficiencies were obtained in most of the breeding lines that were tested. The embedding of the protoplasts in alginate was crucial for initiating cell division and further(More)
The relation of left ventricular (LV) diastolic filling with the clinical outcome in patients with idiopathic dilated cardiomyopathy (IDC) was examined. LV diastolic filling was assessed by Doppler echocardiography in 57 patients with IDC at the time that the diagnosis was established by angiocardiography. Patients were followed for 29 +/- 16 months.(More)
Fusion complementation experiments between nitrate reductase (NR) deficient lines CNX 20, 27, 82 and 103 of Nicotiana plumbaginifolia were performed with the already characterized N. plumbaginifolia mutants nx 1, 24 and 21, belonging respectively to the complementation groups cnx A, B and C. CNX 20 and 82 were identified as belonging to the group of cnx A.(More)
Protoplast-derived colonies of haploid N. plumbaginifolia were selected for by chlorate resistance in media supplemented with casamino acids. Eighty resistant lines were confirmed by a second passage on a higher concentration of chlorate. Frequency of spontaneous mutation ranged from 10−5 to 10−6. Fifty of the resistant lines could be regenerated into(More)
Several amino acid requiring auxotrophs have been isolated from unsupplemented protoplast cultures of haploid Nicotiana plumbaginifolia following incubation with BUdR (1-5x10-5, 2 days) and recovery on complete medium. The auxotrophic lines required the following amino acid(s) for growth: his, ile, leu, ile+val, met or try. Met− is a new type isolated in(More)
Lung epithelial permeability was measured in five normal, five asthmatic, and five smoking subjects by quantifying removal from the lung and accumulation in the blood of an inhaled radiolabeled low-molecular-weight substance, technetium-99m-labeled diethyleneaminepentaacetate (99mTc-DTPA). Measurements on 2 control days were highly reproducible. Nonspecific(More)
In idiopathic dilated cardiomyopathy (IDC), an impaired left ventricular filling as assessed by the Doppler echocardiographic mitral flow pattern is closely related to the severity of congestive heart failure. This study examined the relation of left ventricular filling and the clinical course of the disease in patients with a recent diagnostic procedure(More)
There is mounting evidence of an association between chronic neck pain and impaired cervical flexor muscle performance. It is likely that the deep cervical flexors demonstrate changes very early after the onset of pain, but evidence is currently lacking. This study investigated the effect of experimental neck muscle pain on the activation of the cervical(More)
Early field studies in human nutrition documented the eating habits of African Americans living in a variety of circumstances. We compare the results of these investigations. Our analysis shows systematic differences along a continuum reaching from remote, rural communities in the South toward increasingly metropolitan locations. On the latter end of the(More)