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An inhibitory effect of excess moisture on the early development of Sinapis alba L. seedlings 总被引:1,自引:1,他引:0
Abstract. Mustard seedlings in the early stages of growth are sensitive to the presence of excess moisture, growth of the radicle and anthocyanin synthesis being retarded by water at a suction of less than 3 cm water for seedlings growing on a plane surface. This inhibitory effect commences at about 12-15 h from wetting of the seed. It can be counteracted by increasing the partial pressure of oxygen in the atmosphere or by de-coating the seed, suggesting that the inhibition is caused by a restricted flow of oxygen through the mucilaginous seed coat. The positive effect of gravity on anthocyanin synthesis in the developing seedling can be wholly accounted for in terms of the removal of excess moisture. This explanation largely accounts for the improved growth of the root, but a tonic effect of gravity on root growth can also be discerned. 相似文献
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Group therapy for the husbands of hospitalized psychotic women relieved the anxiety and feeling of guilt of the husbands and led to better communication between husband and wife. It was particularly helpful just before and after the wife came home from the hospital. The group meetings saved various members of the hospital staff considerable time which they otherwise would have had to devote to the husbands individually. 相似文献
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H. BERALDI-CAMPESI H. E. HARTNETT A. ANBAR G. W. GORDON F. GARCIA-PICHEL 《Geobiology》2009,7(3):348-359
Biological soil crusts (BSCs) are topsoil biosedimentary structures built by photosynthetic microbes commonly found today on arid soils. They play a role in soil stabilization and the fertility of arid lands, and are considered modern analogues of ancient terrestrial microbial communities. We determined the concentrations of four biogenic and 21 other elements, mostly metals, in surface soils that hosted BSCs, in the soils underneath those crusts, and in proximate but non-crusted surface soils. The samples were from six sites in the Colorado Plateau highlands and the Sonoran Desert lowlands. In spite of the variability in climate and geologic setting, we found statistically significant overall trends of enrichment in biogenic elements and depletion in non-biogenic elements when BSCs were compared with non-crusted soils. The differences between crusted and non-crusted soils were statistically significant at ∼95% confidence for C, N (enrichments) and for Ca, Cr, Mn, Cu, Zn, As, and Zr (depletions). These trends are best explained by the activity of microbes. As expected, no differences in the concentrations of C, N, P, and S were detected between the soils underneath the crusts and the non-crusted soils, but the former showed depletion of non-biogenic elements, indicating that the leaching effect of crust microbes extends downward in the soil. These patterns speak to the need for a sustained input of allochthonous material, possibly dust, to maintain BSC fertility. These elemental patterns can be considered a biosignature that may be preserved in the rock record and might help identify ancient microbial communities on land. 相似文献