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PubMed1995

Molecular characterization and expression of alfalfa (Medicago sativa L.) flavanone-3-hydroxylase and dihydroflavonol-4-reductase encoding genes.

Flavonoids are plant phenolic compounds involved in leguminous plant-microbe interactions. Genes implied in the central branch (chalcone synthase (CHS), chalcone isomerase (CHI)) or in the isoflavonoid branch of the flavonoid biosynthesis pathway have been characterized in Medicago sativa. No information is available to date, however, on genes whose products are involved in the synthesis of other types of flavonoids. In this paper we present the genomic organization as well as the nucleotide sequence of one flavanone-3-hydroxylase (F3H) encoding gene of M. sativa, containing two introns and exhibiting 82-89% similarity at the amino acid level to other F3H proteins. This is the first report on the genomic organization of a f3h gene so far. We present also the sequence of a partial dihydroflavonol-4-reductase (DFR) M. sativa cDNA clone. Southern blot experiments indicated that f3h and dfr genes are each represented by a single gene within the tetraploid genome of M. sativa. By a combination of Northern blot and RT-PCR analysis, we showed that both f3h and dfr genes are expressed in flowers, nodules and roots, with a pattern distinct from chs expression. Finally, we show that dfr is expressed in M. sativa leaves whereas f3h is not. The role played by these two genes in organs other than flowers remains to be determined.

Alcohol Oxidoreductases↗
PubMed1977

Regulation of symbiotic nitrogen fixation in root nodules of alfalfa (Medicago sativa) infected with Rhizobium meliloti.

Symbiotic nitrogen fixation of Rhizobium meliloti bacteroids in Medicago sativa root nodules was suppressed by several inorganic nitrogen sources. Amino acids like glutamine, glutamic acid and aspartic acid, which can serve as sole nitrogen sources for the unnodulated plant did not influence nitrogenase activity of effective nodules, even at high concetrations. Ammonia and nitrate suppressed symbiotic nitrogen fixation in vivo only at concentrations much higher than those needed for suppression of nitrogenase activity in free living nitrogen fixing bacteria. The kinetics of suppression were slow compared with that of free living nitrogen fixing bacteria. On the other hand, nitrite, which acts as a direct inhibitor of nitrogenase, suppressed very quickly and at low concentrations. Glutamic acid and glutamine enhanced the effect of ammonia dramatically, while the suppression by nitrate was enhanced only slightly.

Ammonia↗
PubMed1980

Pesticides and honey bees: nectar and pollen contamination in alfalfa treated with dimethoate.

Medicago sativa L. (Leguminosae) sprayed with O,O-dimethyl S-(N-methylcarbamoylmethyl) phosphorodithioate (dimethoate) had only 0.5 ppm of dimethoate in pollen one day later, but 3 ppm in nectar one week later, and 1 ppm in nectar two weeks later. As little as 1 ppm added to syrup fed to caged workers of Apis mellifera L. (Apidae) inhibited cholinesterase and reduced survival. Bees given a choice between treated and untreated syrups showed no preference; this suggests that the levels of dimethoate found in nectar are toxic and not repellent.

Animals↗