Transactions of the 9th Nitrogen Workshop [antikvár]

-1-Nj Fixation in nodulated pea plants: optimization of boron requirementsEsteban E., Gárate A., Carpena Ruiz R.O.Dpto. Química Agrícola C-VII. Universidad Autónoma. 28049 Madrid. SPAIN.INTRODUCTIONBoron requirement for atmospheric nitrogen fixation has been demonstrated in cyanobacteria; it appears to be essential in the structure of heterocyst envelopes (Garcia González y col., 1991). Pea, as the rest of the leguminous plants, is also able to fix atmospheric nitrogen, in symbiosis with Rhizobium legwninosarum. Brenchley and Thornton (1925) reported that B was not essential for rhizobia growth; but in the abscense of B, nodule development in bean plants was hindered. Mulder (1948) did not observe nodule development in pea plants without added B. Both reports suggest that B is essential for plant and nodule development, but not during the infection process. Our previous work (Gárate y col., 1993) showed that B was necessary for N, fixation in pea plants, and that they grew properly with 0.1 mg.L"' B in nutrient solution. The aim of this work is trying to optimize boron requirements for the symbiosis pea-rhizobia, in order to improve Nj fixation efficiency.MATERIALS AND METHODSSterilized seeds of Pisum sativum cv. Argona were germinated in dark at 28°C for 3 days and then transferred to a 0.1 mM CaS04 solution for another 4 days. Afterwards, plants were transplanted to Riviera pots, 9 plants per pot, filled with 5 kg acid-washed quartz sand. The assay was conducted in a growth chamber under controlled conditions (25/15 °C and 60/63 % HR day/night, 16 hours of daylight). Nutrient solution without nitrogen was used (R): CaS04 0.5; K2SO4 0.5; MgS04 1; KHJPO4 2; CaClj 1.5; KCl 1; NaCl 0.1 (mM). Micronutrient concentrations in mg.L"' were: Fe 2.5; Mn 1.0; Zn 0.4; Cu 0.2; Mo 0.02; Co 0.001; Ni 0.001. The value of pH was adjusted to 6.0 in all nutrient solutions. Plants were inoculated -2 ml each- with a suspension of Rhizobium leguminosarum bv. viciae 3841. The assay lasted 5 weeks. B levels applied were 0.1, 0.2, 0.4 and 0.8 mg.L"' in B,, Bj, B3 and B4 treatments. Three replicates for each treatment were done, randomly distributed. Nutrient solutions were renewed weekly. Plants were sampled 3 times, 1, 3 and 5 weeks after the beginning of B treatments. B content was assesed using Azometine H as colorimetric reagent