Anatomy, physiology and biochemistry of root nodules of Sprint-2 Fix-, a symbiotically defective mutant of pea (Pisum sativum L.) |
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Authors: | Romanov VI; Gordon AJ; Minchin FR; Witty JF; Skt L; James CL; Borisov AY; Tikhonovich IA |
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Abstract: | A plant-determined pea mutant Sprint-2 Fix and the parentalline Sprint-2 were compared for selected physiological and biochemicalparameters. The Fix mutation prevented differentiationof Rhizobium leguminosarum bacteria into bacteroids and producedlarge, white, non-fixing nodules. These lacked nitrogenase-linkedrespiration, but had a background rate of CO2 evolution similarto the normal Fix+ nodules. The cortical structure of the ineffectivenodules suggests the existence of an oxygen diffusion barrierand this was supported by a low oxygen concentration in thecentral region (0.53.0%), measured using an O2 sensitivemicro-electrode. Sucrose and starch contents were similar innormal and ineffective nodules while ononitol content was about15 times lower in the Fix nodules. The distribution ofstarch was also different in the two nodule types. The activitiesof glutamine synthetase (GS), sucrose synthase (SS), phosphoenolpyruvatecarboxylase (PEPC) and alanine pyruvate aminotransferase (APAT)were markedly higher in Fix+ nodules while the activities ofpyruvate decarboxylase (PDC), alcohol dehydrogenase (ADH) andglutamate dehydrogenase (GDH) were higher in Fix nodules.The data from immunodetection of host nodule proteins confirmedthe reduced levels of sucrose synthase and the almost completeabsence of glutamine synthetase and leghaemoglobin in mutantnodules. There was no significant difference in the amount ofnitrogenase component 1 extracted from the microsymbiont ofnormal and ineffective nodules, but component 2 was hardly detectablein the Fix mutant. Key words: Pisum sativum, Fix mutant, nodules |
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