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A M Hirsch

Publications and source records attributed to A M Hirsch.

9 recordsLinked to original sources
PubMed1992

An alfalfa (Medicago sativa L.) cDNA encoding an acidic leghemoglobin (MsLb3).

We have found an alfalfa cDNA clone that encodes an acidic leghemoglobin. To date, 14 alfalfa leghemoglobin clones have been identified. Five different leghemoglobin 'components' have been biochemically defined on the basis of their pI. A higher-resolution comparison, provided by sequence data analysis, identifies six leghemoglobin 'classes'. All 14 leghemoglobins are assigned to the six 'classes', which can be distributed among the five leghemoglobin 'components'. The newly identified leghemoglobin is the only member of a sixth 'class' of leghemoglobins, and it also is the only member of one of the acidic leghemoglobin 'components' IV or V.

Amino Acid Sequence↗
PubMed1988

Interaction of nod and exo Rhizobium meliloti in alfalfa nodulation.

Among the genes of Rhizobium meliloti SU47 that affect nitrogen-fixing symbiosis with alfalfa are nod genes, in which mutations block nodule induction, and exo genes, in which mutations allow nodule formation but block rhizobial exopolysaccharide production as well as nodule invasion and nitrogen fixation. To investigate whether an exo+ bacterium can "help" (that is, reverse the symbiotic defect of) an exo mutant in trans, we have coinoculated alfalfa with pairs of rhizobia of different genotypes. Coinoculant genotypes were chosen so that the exo+ helper strain was nif while the exo "indicator" strain was nif+, and thus any fixation observed was carried out by the exo coinoculant. We find that a nod exo+ coinoculant can help an exo mutant both to invade nodules and to fix nitrogen. However, a nod+ exo+ coinoculant cannot help an exo mutant: Few exo bacteria are recovered from nodules, some bacteroids differentiate into bizarre aberrant forms, and the nodules fail to fix nitrogen. In a triple coinoculation, the effect of nod+ helper supersedes that of nod helper. Implications of these results for interaction of nod and exo gene products are discussed.

Genes, Bacterial↗
PubMed1987

Rhizobium meliloti mutants that fail to succinylate their calcofluor-binding exopolysaccharide are defective in nodule invasion.

We have identified a set of Tn5-generated mutants of Rhizobium meliloti on the basis of their failure to form a fluorescent halo under UV light when grown on agar medium containing Calcofluor. These mutations define a new genetic locus we have termed exoH. Alfalfa seedlings inoculated with exoH mutants form ineffective nodules that do not contain intracellular bacteria or bacteroids. Root hair curling is significantly delayed and infection threads abort in the nodule cortex. Analyses of exopolysaccharide secreted by exoH mutants have shown that it is identical to the Calcofluor-binding exopolysaccharide secreted by the exoH+ parental strain except for the fact that it completely lacks the succinyl modification. In vitro translation of total RNA isolated from nodules induced by an exoH mutant has shown that only one of the plant-encoded nodulins is induced, as compared with the 17 nodulins induced by wild-type strains. These observations suggest that succinylation of the bacterial polysaccharide is important for its role(s) in nodule invasion and possibly nodule development.

DNA Transposable Elements↗
PubMed1987

Effects of Rhizobium meliloti nif and fix mutants on alfalfa root nodule development.

Ineffective alfalfa nodules were examined at the light and electron microscope level after inoculation with Rhizobium meliloti strains with mutations in nif and fix genes. All the mutant strains induced nodules that contained elongated bacteroids within the host cells, but the bacteroids quickly senesced. The nodules were small and numerous, and the host cells also exhibited symptoms of an ineffective symbiosis. nifB, fixA, and fixB bacteroids appeared to be completely differentiated (by ultrastructural criteria), i.e., as bacteroids developed, they increased in diameter and length and their cytoplasm underwent a change from homogeneous and electron dense to heterogeneous and electron transparent after enlargement. In contrast, nifA bacteroids rarely matured to this state. The bacteroids degenerated at an earlier stage of development and did not become electron transparent.

Medicago sativa↗
PubMed1985

Symbiotic mutants of Rhizobium meliloti that uncouple plant from bacterial differentiation.

Spontaneous mutants at a new symbiotic locus in Rhizobium meliloti SU47 are resistant to several phages and are conditionally insensitive to a monoclonal antibody to the bacterial surface, apparently because they are deficient in a wild-type exopolysaccharide. On alfalfa, the mutants do not curl root hairs, but penetrate the epidermis directly, forming nodules that contain no visible infection threads or "bacteroids," have a few bacteria in superficial intercellular spaces only and not within the nodule cells, and fail to fix nitrogen (Fix-). Evidently, infection threads are not essential for cell proliferation and nodule formation, which are here induced by a bacterial signal at a distance and uncoupled from the bacterial differentiation that normally goes on as well.

Antibodies, Monoclonal↗
PubMed1985

Nodules are induced on alfalfa roots by Agrobacterium tumefaciens and Rhizobium trifolii containing small segments of the Rhizobium meliloti nodulation region.

Regions of the Rhizobium meliloti nodulation genes from the symbiotic plasmid were transferred to Agrobacterium tumefaciens and Rhizobium trifolii by conjugation. The A. tumefaciens and R. trifolii transconjugants were unable to elicit curling of alfalfa root hairs, but were able to induce nodule development at a low frequency. These were judged to be genuine nodules on the basis of cytological and developmental criteria. Like genuine alfalfa nodules, the nodules were initiated from divisions of the inner root cortical cells. They developed a distally positioned meristem and several peripheral vascular bundles. An endodermis separated the inner tissues of the nodule from the surrounding cortex. No infection threads were found to penetrate either root hairs or the nodule cells. Bacteria were found only in intercellular spaces. Thus, alfalfa nodules induced by A. tumefaciens and R. trifolii transconjugants carrying small nodulation clones of R. meliloti were completely devoid of intracellular bacteria. When these strains were inoculated onto white clover roots, small nodule-like protrusions developed that, when examined cytologically, were found to more closely resemble roots than nodules. Although the meristem was broadened and lacked a root cap, the protrusions had a central vascular bundle and other rootlike features. Our results suggest that morphogenesis of alfalfa root nodules can be uncoupled from infection thread formation. The genes encoded in the 8.7-kilobase nodulation fragment are sufficient in A. tumefaciens or R. trifolii backgrounds for nodule morphogenesis.

Conjugation, Genetic↗
PubMedDate not supplied

The effect of infertility on marriage and self-concept.

Two groups of subjects (couples seeking medical treatment for infertility and couples not yet attempting to conceive) completed questionnaires assessing the impact of infertility on their marriages and self-concept. Infertile individuals experienced greater dissatisfaction with themselves and their marriages. Females experienced greater discontent over time and had greater emotional investment than males. Infertile couples, labeled noncommunicators, were found to be affected even more by infertility. Nurses can play vital roles in counseling infertile couples.

Adult↗