POSSIBLE REASONS FOR RELATIVE SALT STRESS TOLERANCE IN NODULES OF WHITE LUPIN CV MULTOLUPA

The effects of different NaCl concentrations on the growth and nitroge n fixation activity of white lupin (Lupinus albus [L.]) was studied ov er a 6 d period. Plant growth parameters, photosynthesis and shoot res piration were unaffected by NaCl concentrations up to 150 mol m(-3). H owever, nitrogenase activity decreased with increased NaCl concentrati on up to 100 mol m(-3), whilst the O-2 diffusion resistance increased with 100 mol m(-3) NaCl, but showed no further change when 150 mol m(- 3) NaCl was applied for 6 d. Increases in NaCl concentration decreased nodular starch content while increasing sucrose content, suggesting a n osmotic regulation. These changes were associated with a 77% decreas e in sucrose synthase activity. The effect on the O-2 diffusion resist ance was paralleled by changes in glycoprotein content of the nodules, as determined by immunogold localization and ELISA. X-ray microanalys is studies of nodules showed that, following a 6 d exposure to 150 mol m(-3) NaCl, Na+ ions were largely excluded from the infected zone, wh ilst only low levels of Cl- ions penetrated into this region. Na+ entr y into roots and leaves was also at a low level. Leghaemoglobin conten t decreased with saline stress, as did superoxide dismutase; which dec reased by 36% following exposure to 100 mol m(-3) salt for 6 d. These results are discussed in relation to the relative salt tolerance of th e Multolupa/lSLU-16 symbiosis.