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Metal–silicon and silicide–silicon diodes were fabricated by depositing thin layers of the metals Hf, Zr, Mn, Ni, and Rh on 〈111〉 epilayers of silicon, and annealing to transform the metal–silicon junctions to silicide–silicon junctions. A formation of the silicides was followed, and the stoichiometries were determined by ion back‐scatter analysis. The compositions and approximate formation temperatures were (HfSi, 700 °C; HfSi2, 850 °C), (ZrSi2, 700 °C), (MnSi, ≈ 500 °C; MnSi1.7, 800 °C), (NiSi, ≈ 600 °C; NiSi2, 850 °C), (RhSi, 600 °C). These temperatures are below those of the liquid phase eutectica hence indicating that the silicide forms in solid–solid reactions. The barrier heights were measured by the photoelectric method, giving the values: (Hf, 0.81 eV; HfSi 0.73 eV), (Mn, 0.77 eV; MnSi, 0.76 eV; MnSi1.7, 0.72 eV), (Ni, 0.75 eV; NiSi2, 0.70 eV), (Rh, 0.80 eV; RhSi, 0.70 eV).

Tolerance to water stress was studied in plants of grey alder, Alnus incana (L.) Moench, grown in a climate chamber in pots of sand supplied with a nitrogen‐free nutrient solution. The plants were subjected to a single drying and recovery cycle, during which acetylene reduction, transpiration and stomatal resistance were measured. At different stress levels the plants were placed in a closed system to equilibrate the water potential in the plant‐soil system. The water potential of the plants was determined, after which they were watered and their recovery studied. Nitrogenase activity showed low tolerance to water deficit. At moderate stress (−0.6 to −0.8 MPa) acetylene reduction was reduced by half, and at more severe stress, (< −1 MPa) activity was near zero. There was a rapid decrease in nitrogenase activity coincident with stomatal closure, which indicates a continuous need for photoassimilates for nitrogenase activity. Nodules or nitrogenase activity seemed to be weak sinks for assimilates compared with root pressure bleeding. Measurements of nitrogenase activity in root nodule homogenates supplied with ATP and reductant suggested a loss of active nitrogenase in the nodules in response to water stress. The recovery from moderate stress or long dark treatment took several days, and recovery from severe stress took still longer. Shortage of assimilates and disturbances in oxygen and nitrogen balances in the nodules are discussed as reasons for the reduced nitrogenase activity in response to water stress.

K. 1995. Long-term drought stress alters nitrogenase activity and carbon translocation in split-root cultured Alnus incana. -Physiol. Plant. 94: 181-186.Split-root cultured grey alder, Ainus incana (L.) Moench., was grown in sand in cuvettes with a continuous supply of nutrient solution. During the drought treatment for up to 9 days the supply of solution was withheld from one of the split-root halves. After 2-3 days of treatment, soil water became depleted and the unwatered root halves were at a constant drought stress, water potential (W,^ui,J = -1.1 to -1.6 MPa. Nitrogenase activity in the drv' half decreased to about 70% of the initial value during the first 2-3 days and then stayed al this level. The water supply to the shoot from the wet root half was high and only a temporary slight decrease in photosynthesis and stomata! conductance was found in drought-stressed split-root plants. Labelling studies showed a reduced translocation of phoioassimilates to the dry nodules. The fixation of CO, in the nodules seemed to be more tolerant to drought than nitrogenase activity. During the drought treatment there was an osmotic adjustment from -0.9 to -1.7 MPa. but no change in the storage of starch in tbe nodules. In alders where parts of the root system is kept dry these roots acclimate and continue a persistent nitrogenase activity.

The tested strain of Exobasidium vaccinii (Fuck.) Woron. required thiamine or its two moieties, thiazole and pyrimidine, for good growth. When grown on pyrimidine medium, rapid growth or thiazole synthesis appears after 600–1000 hours. As methionine, a supposed precursor in the biosynthesis of thiazole, stimulates this inductive growth, the influence of methionine precursors or metabolites stimulating methionine synthesis were tested for their ability to shorten the lag phase of E. vaccinii cultured on a thiamine‐deficient synthetic medium. None of the tested methionine precursors replaced methionine or significantly stimulated the inductive growth. This result does not exclude acetylhomoserine as a central metabolite in methionine synthesis. Acetyl phosphate, alcohols and the fatty acids of Tween, possible deliverers of the active acetyl groups, induced growth in thiamine‐free media. This growth seems to be possible by utilization of the compounds through a metabolic pathway not requiring thiamine. No evidence for participation of the glyoxylate cycle was found.