04373nam a2200301 a 450000100080000000500110000800800410001910000200006024500610008026000390014130000110018050000200019152036500021165000170386165000220387865000190390065000130391965000100393265000100394265000120395265000180396465000160398265000160399865000230401465000090403765000110404665300140405712046232006-01-16       1996    bl uuuu  m   00u1 u    #d1 aRAMOS, M. L. G.  aPhysiological responses of crop legumes to water stress.  aDundee: University of Dundeec1996  a228 p.  aTese Doutorado.  aThe effects of water on growth, photosynthesis and nitrogen fixation in two grain legumes, soybean (Glycine max) and common bean (Phaseolus vulgaris) were studied. Two soybean cultivars, one tolerant (BR-4) and one sensitive (Bragg) to water stress were compared. Stress affected shoot growth and nitrogenase activity of Bragg earlier than BR-4. Further, 24 h after rewatering, following 8d of stress, nitrogenase activity recovered in BR-4, but not in Bragg. Stressed plants of both cultivars had increased amino acid levels in leaves. The major amino acid was proline, representing up to 50% of the total amino acid detected. When water stress was maintained for longer (10 days), both cultivars had much lower amino acid contents in roots, leaves and nodules. However, the tolerant cultivar (BR-4) maintained higher levels of total amino acid in leaves and nodules, while the sensitive cultivar (Bragg) maintained higher levels only in roots. Bragg tended to have lower stomatal conductance and photosynthesis than BR-4, especially at high levels of water stress. BR-4 also had higher RNA content in leaves and  nodules, while the sensitive cultivar had higher RNA content in roots. Two Bradyrhizobium japonicum strains, one efficient (CB1809) and one less efficient (29W) were compared in water stressed soybeans. Plants inoculated with 29W produced more nodules, but accumulated less N than those with CB1809, especially in stressed plants. On the other hand, stressed nodules from CB1809 produced 5 times more ureides than those from 29W. Also, amino acid content, especially asparagine and aspartate in nodules were different between these strains. Asparagine was not detected in nodules of plants inoculated with CB1809, while aspartate increase from 5 umol g1 FW (watered) to 26 umol g1 FW in stressed plants. On the other hand, plants inoculated with 29W produced 6 umol g1 FW asparagine in watered nodules and 38 umol g1 FW in those stressed, while the levels of aspartate were similar (around 1 umol g1 FW), in either watered or stressed plants. Two common bean cultivars (carioca and EMGOPA-201) were also studied. Water stress decreased nodule fresh weight of carioca by up to 60%, accompanied by a very low nitrogenase activity, leading to very low nitrogen and carbon accumulation. EMGOPA-201 had unaltered nodule fresh weight and N and C accumulation. Nodules from both cultivars showed a flaccid cell cortex and after 8 days of stress, a rupture of membranes in the inner cortex of carioca was observed. Peribacteroid membranes were ruptured after 5 and 8 days of stress for both cultivars and a release of bacteroids in the intercellular spaces in nodules from carioca was observed following severe stress (8 days). In commom bean, the resistance of the nodule cortex to oxygen diffusion was measured at several levels of water stress. A sharp increase of cortex resistance to O2 was observed in plants kept at 30% `soil` field capacity (SFC); at this level of stress, nitrogenase linked respiration was also very low. Amino acid levels in the xylem sap were very low when plants were kept at the same level of stress for 10 days and no difference was observed among levels of water. With an increase of stress, the total amino acid content tended to be higher at 50 and 30% SFC, than in control plants. In general, common bean and soybean started decreasing growth after 4 days of water stress. Stomatal conductance was lower in stressed plants, leading to lower photosynthesis. Also, water stress increased the oxygen diffusion barrier in nodules, which could lead to lower nitrogen fixation and N accumulation in the plant.  akidney beans  anitrogen fixation  aphotosynthesis  asoybeans  awater  aÁgua  aFeijão  aFotossíntese  aGlycine Max  aNitrogênio  aPhaseolus Vulgaris  aSoja  aStress  aFixação