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The root exudates of 24 pea (Pisum sativum L.) non-nodulating mutants, originating from cv. ′Finale′, were tested for Rhizobium nodulation ( nod) gene-inducing activity to reveal potential differences from the wild type. The interaction with flavonoid receptor NodD of R. leguminosarum bv. viciae strain 248 was monitored as the activity of the regulated operon nodABC fused to the reporter gene lacZ. In the uninoculated plants, the only decreased exudate activity was found in the line Risnod17 and ascribed to the impaired root growth in this line. Consequently, constitutive deficiency in the flavonoid nod gene inducers is not a cause of the asymbiotic phenotypes in the studied set. On the other hand, line Risnod5 had constitutively higher nod gene-inducing activity which might be responsible for its conditional nodulation and Fix– phenotype when the nodules are present. Monitoring of the response of wild-type plants to inoculation revealed an increase in nod gene-inducing activity (Ini response) starting first day after inoculation. The chosen mutant lines Risnod22 (putative locus sym9) and Risnod25 (putatively sym8) showed Ini as well indicating that the flavonoid burst can be mutationally dissociated from nodule initiation. On the other hand, absence of Ini in Risnod20 (assumed sym19) suggests branching of the signal transduction pathway downstream of this mutation and places it upstream of the two former mutations in the transduction of the bacterial Nod factor signal. More intense Ini response observed in the supernodulating mutant RisfixC, included in the study for its contrasting symbiotic phenotype, suggests common regulation of nodulation and Ini response via systemic shoot factor. The time shift in the exudation of isoflavonoid phytoalexin pisatin compared to Ini, its increased level in Risnod25 and lowered level in RisfixC are consistent with the regulatory role of plant defence in nodule initiation, which might be mediated directly by isoflavonoids as negative regulators. [ABSTRACT FROM AUTHOR]

The effects of exogenous sucrose, lactose. ᴅ-glucose, ᴅ(-)fructose, ᴅ-galactose, ᴅ-mannose, ւ-sorbose, ւ-arabinose and ᴅ-xylose on nitrate reductase (NR), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) levels, on anaerobic nitrite production and on respiratory O2 consumption were studied in excised roots of pea (Pisum sativum L. cv. Raman). Sucrose, glucose and fructose increase NR and GS levels and decrease GDH level (when compared with roots cultures without any sugar) at all concentrations used, but the extent of this effect varies. NR induction is enhanced by all sugars within the concentration range studied. Precultivation of roots with mannose and galactose results in an increase in anaerobic nitrite production in a medium consisting of phosphate buffer and KNO3. GS reaches its maximum at lower sugar concentrations, this fact being especially clear-cut with galactose. The decrease in GS level observed in roots cultured without sucrose is enhanced by higher sorbose concentrations. The increase in GDH level occurring in roots cultured without sucrose is depressed by low galactose and mannose concentrations but enhanced by high galactose, mannose, xylose and a wide range of sorbose concentrations. Lactose exerts only slight influence on the enzymes. The effects of sugars are in no case consistent with their effect on respiratory O2 consumption which is most pronounced with NR. The above results show that the effects of sugars on NR, GS and GDH are not mediated by one universal mechanism. [ABSTRACT FROM AUTHOR]