Radiation induced developmental instability in Arabidopsis thaliana.

In a study on the nature of induced genetic variations in quantitative characters using the selfpollinated plant Arabidopsis thaliana, it was observed that not only quantitative performance but also intraline variability, or developmental instability, was affected by induced mutations. Emphasis was placed on the latter.Seeds of Landsberg strain were used.

Evidence for ammonia as an inhibitor of heterocyst and nitrogenase formation in the cyanobacterium Anabaena cycadeae.

Growth and regulation of heterocyst and nitrogenase by fixed nitrogen sources were studied comparatively in parent and glutamine auxotrophic mutant of Anabaena cycadeae. The parent strain grew well on N2, NH+4 or glutamine while the mutant strain grew on glutamine but not on N2 or NH+4. The total lack of active glutamine synthetase in the mutant strain thus appears to be the reason for its observed lack of growth in N2 or NH+4, which explains why it is a glutamine auxotroph and at the same time shows glutamine synthetase to be the sole primary ammonia assimilating enzyme.

Release of synaptosomal dopamine formed from tyrosine and L-DOPA.

The present report compares the synaptosomal release of [3H]dopamine, continuously forming from [3H]DOPA, with that of [14C]dopamine, forming from [14C]tyrosine as a marker of dopaminergic nerve endings. For the purpose of the comparison, synaptosomal (P2) preparations from rat caudate nuclei were incubated with L-[3H]DOPA and [14C]tyrosine for 10 min and the particulates were rapidly separated from the medium postincubation. The separated fractions were analyzed for the level of double labelled (14C/3H) dopamine and the synaptosomal content of the labelled substrates.

Synaptosomal dopamine from phenylalanine in brain: effects of some dopaminergic agents.

This report demonstrates for the first time that the synthesis and release responses to some dopaminergic agents may be elicited from that synaptosomal dopamine which may be formed by the hydroxylations of phenylalanine. Amphetamine and Cogentin increased the release of dopamine formed from 14C-phenylalanine in rat caudate nucleus synaptosomal preparation and concomitantly stimulated the synthesis. Amfonelic acid also caused a net release of that dopamine.

Dopamine formation from phenylalanine: independent existence in caudate nucleus synaptosomes.

Dopa and dopamine formations from phenylalanine and tyrosine in rat caudate nucleus synaptosomal preparation were studied. Phenylalanine and tyrosine, labelled with either 14C or 3H, were employed as cosubstrates leading to the formations of double labelled Dopa and dopamine. The ratio of the two isotopes in dopamine was found to be significantly different from that in Dopa.

Decarboxylation of newly formed DOPA by caudate nucleus synaptosomal particles.

The present study compares dopamine formation from two different sources of DOPA: preformed and added to the medium and that newly formed by the hydroxylations of phenylalanine or tyrosine. Synaptosomal preparations from rat brain caudate nucleus were incubated with 3H-labeled DOPA mixed as cosubstrate with either [14C]phenylalanine or [14C]tyrosine. Following the incubation, DOPA and dopamine were separated and their isotope ratios (isotope in phenylalanine (tyrosine) X 100/isotope in DOPA cosubstrate) were determined and compared.