Pisum sativum nodule

One feature of the rhizobium-legume symbiosis is the high degree of specificity that many legumes and their symbiotic partners exhibit. For example, Sinorhizobium meliloti, the well-characterized bacterial symbiont of alflalfa and related Medicago species, is unable to nodule its close relative Pisum sativum (Mendel s pea), and conversely pea symbionts do not nodulate Medicago species. It is now clear that there are multiple molecular determinants... 

Pig. 1.—Bacteroids from a very young nodule of pea (Pisum sativum), showing swannere among the bacteroide. X 1080. 

Pernet JJ, Pilet PE (1976) Indoleacetic acid movement in the root cap. Planta 128 183-184 Philipson JJ, Hillman JR, Wilkins MB (1973) Studies on the action of abscisic acid on lAA-induced rapid growth of Avena coleoptile segments. Planta 114 87-93 Phillips DA (1971) Abscisic acid inhibition of root nodule initiation in Pisum sativum. Planta 100 181-190... 

Pisum sativum L. 15 Naturally occurring and EMS mutagenesis condition nonnodula-tion, ineffective, and supemodulation, and nodulation in presence of NOs". Some traits temperature sensitive Engvild (1987) Holl and LaRue(1976) Jacobsen and Feenstra (1984) Kneeneta/. (1987) LaRue et al. (1985) Lie (1984) Postma et al. (1988)... 

Fig. 7. Roots and nodules of Pisum sativum L. (A) WUd-type and (B) supemodulating nod, mutant. Both plants were grown under identical conditions and inoculated with equal numbers of rhizobia. The supemodulating nod, mutant forms 50- to 100-fold more nodules than the wild type. The nod mutant also nodulates in the presence of nitrogen fertilizer while the wild type does not.

The oxidizing enzymes involved in the conversion of purines to ureides have been well studied and are described in the next subsection. Little attention has, however, been paid to the hydrolytic enzymes. Conversion of nucleotides to ureides by nodule tissue or cell-fiee extracts or organelle preparations thereof implies that an efficient hydrolytic system is present. A study by Christensen and Jochimsen (1983) identified a 50-fold excess in levels of 5 -nucleotidase in soybean nodules over nodules of Pisum sativum. Similar differences were found for levels of the enzyme in other organs of the two plants. Levels of purine nucleosidase were, however, not significantly different between the two species, although levels in soybean were somewhat higher in all organs. 

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