Division of cortical cells in roots of leguminous plants is triggered by lipochitin oligosaccharides (LCOs) secreted by the rhizobial microsymbiont, Previously, we have shown that presence of pea... Show moreDivision of cortical cells in roots of leguminous plants is triggered by lipochitin oligosaccharides (LCOs) secreted by the rhizobial microsymbiont, Previously, we have shown that presence of pea lectin in transgenic white clover hairy roots renders these roots susceptible to induction of root nodule formation by pea-specific rhizobia (C, L, Diaz, L, S, Melchers, P. J, J, Hooykaas, B, J, J, Lugtenberg, and J, W, Kijne, Nature 338:579-581, 1989), Here, we report that pea lectin-transformed red clover hairy roots form nodule primordium-like structures after inoculation with pea-, alfalfa-, and Lotus-specific rhizobia, which normally do not nodulate red clover. External application of a broad range of purified LCOs showed all of them to be active in induction of cortical cell divisions and cell expansion in a radial direction, resulting in formation of structures that resemble nodule primordia induced by clover-specific rhizobia, This activity was obvious in about 50% of the red clover plants carrying hairy roots transformed with the pea lectin gene. Also, chitopentaose, chitotetraose, chitotriose, and chitobiose were able to induce cortical cell divisions and cell expansion in a radial direction in transgenic roots, but not in control roots. Sugar-binding activity of pea lectin was essential for its effect. These results show that transformation of red clover roots with pea lectin results in a broadened response of legume root cortical cells to externally applied potentially mitogenic oligochitin signals. Show less
The green Met121His mutant of the blue-copper protein azurin has been investigated by pulsed electron paramagnetic resonance (EPR) spectroscopy at 95 GHz on a single crystal. The axial histidine is... Show moreThe green Met121His mutant of the blue-copper protein azurin has been investigated by pulsed electron paramagnetic resonance (EPR) spectroscopy at 95 GHz on a single crystal. The axial histidine is more strongly bound to copper than the methionine for the wild-type protein. The g tensor of M121H is found to be virtually axial and the z principal axis perpendicular to the plane spanned by copper and the nitrogens of the ligating histidines 46 and 117. The direction of the x axis is close to the bond direction from copper to the nitrogen of histidine 46. Theoretical analysis of the axiality and the orientation of the principal axes shows that the wave function of the unpaired electron on copper, largely d(xy) for blue-copper proteins, acquires some d(yz) character for M121H. Comparison of these results with data for wild-type azurin and the mutant M121Q provides insight into the subtle relation between the electronic and the geometric structure of blue-copper sites. Show less
We report the spectroscopic observation of single pentacene molecules in the matrices n-tetradecane and n-hexadecane, using a confocal microscope operating at liquid-helium temperatures. A maximum... Show moreWe report the spectroscopic observation of single pentacene molecules in the matrices n-tetradecane and n-hexadecane, using a confocal microscope operating at liquid-helium temperatures. A maximum detected photon emission rate of only 30 counts per second (cps) is found for pentacene in n-hexadecane and 160 cps for pentacene in n-tetradecane. For the latter system, the low count rate is shown to be caused by a high S-1 --> T-1 intersystem crossing yield of about 40% in combination with a triplet lifetime of 33 +/- 3 mu s. Pentacene molecules in this polycrystalline host are found to show little spectral diffusion on a timescale of seconds. (C) 2000 Elsevier Science B.V. All rights reserved. Show less
