Light differentially regulates lateral and longitudinal auxin transport in the mesocotyl of etiolated maize seedlings

The uptake of IAA into excised mesocotyls of non-irradiated maize seedlings was linear up to a concentration of about 4×M and in this range there was a tight coupling between the IAA in the stele and the cortex. Prior irradiation with white light of intact seedlings unbalanced this coupling. Lateral and longitudinal transport were affected differently. In the stele, the effect of prior irradiation on longitudinal transport was multiphasic, with an initial stimulatory effect followed by a negative effect at longer prior irradiation times. The lateral transport from the stele to the cortex showed no stimulatory effect and appeared to be inhibited within at least 15 min. The effect of the prior irradiation on longitudinal transport in the stele appeared to be a high intensity effect. In contrast, the effect of the prior irradiation on the lateral transport from the stele to the cortex was saturated at much lower intensities. The data suggest that the light induced change in the lateral transport of IAA between the two tissues may be due to changes either in the number of open lateral transport channels/carriers or in the conductivity of these channels/carriers.     

Multifrequency EPR analysis of the dimanganese cluster of the putative sulfate thiohydrolase SoxB of Paracoccus pantotrophus

A detailed analysis of the EPR signatures at X-band and Q-band of an enzyme (SoxB) involved in sulfur oxidation from Paracoccus pantotrophus is presented. EPR spectra are attributed to an exchange-coupled dimanganese Mn₂(II,II) complex. An antiferromagnetic exchange interaction of J=?7.0 (±1) cm^?1 (H=?2JS ₁ S ₂ ) is evidenced by a careful examination of the temperature dependence of the EPR spectra. The spin Hamiltonian parameters for a total spin of S ^T =1, 2 and 3 are obtained and an inter-manganese distance of 3.4 (±0.1) Å is estimated. The comparison with exchange coupling and inter-manganese distance data of other dimanganese proteins and model compounds leads to a tentative assignment of the Mn bridging ligands to bis(μ-hydroxo) (μ-carboxylato).     

An analysis of the partial metabolic derepression of sea urchin eggs by ammonia: the existence of independent pathways

Incubation of unfertilized eggs in ammonia has been reported to initiate such late responses to fertilization as K⁺-conductance, DNA synthesis, chromosome condensation and cytoplasmic mRNA polyadenylation. It does not initiate such early responses as Na⁺-influx and the cortical reactions. We have further analyzed this metabolic derepression and find that ammonia activation does not result in the early respiratory burst and also does not initiate the late activation of Na⁺-dependent amino acid transport. Protein synthesis is increased, similar to that following normal fertilization. This indicates that augmentation of protein synthesis is causally linked neither to the earlier Na⁺-influx, cortical reactions, and respiratory burst nor to the later activation of amino acid transport. The temporal correlation between activation of transport and increased protein synthesis is therefore coincidental. The association between increased protein synthesis and establishment of K⁺-conductance was analyzed by abolishing K⁺-conductance through acidification of the sea water. This did not affect protein synthesis, indicating that K⁺-conductance and protein synthesis are also not causally linked.There is also no obligate link between protein synthesis and chromosome condensation. Incubation in low concentrations of ammonia results in increased protein synthesis but not chromosome condensation. Higher ammonia concentrations cause chromosome condensation but with no further increase in rate of protein synthesis. This suggests a concentration-dependent hierarchy of activation.These results are consistent with the concept that the late fertilization changes are not causally linked and proceed independently of each other. As we have not been able to disassociate the early changes, they may be obligately linked and dependent on each other.