A review of assessment methods for river hydromorphology

The work leading to this paper has received funding for the EU’s FP7 under Grant Agreement No. 282656 (REFORM

Benthic and Hyporheic Macroinvertebrate Distribution Within the Heads and Tails of Riffles During Baseflow Conditions

The distribution of lotic fauna is widely acknowledged to be patchy reflecting the interaction between biotic and abiotic factors. In an in-situ field study, the distribution of benthic and hyporheic invertebrates in the heads (downwelling) and tails (upwelling) of riffles were examined during stable baseflow conditions. Riffle heads were found to contain a greater proportion of interstitial fine sediment than riffle tails. Significant differences in the composition of benthic communities were associated with the amount of fine sediment. Riffle tail habitats supported a greater abundance and diversity of invertebrates sensitive to fine sediment such as EPT taxa. Shredder feeding taxa were more abundant in riffle heads suggesting greater availability of organic matter. In contrast, no significant differences in the hyporheic community were recorded between riffle heads and tails. We hypothesise that clogging of hyporheic interstices with fine sediments may have resulted in the homogenization of the invertebrate community by limiting faunal movement into the hyporheic zone at both the riffle head and tail. The results suggest that vertical hydrological exchange significantly influences the distribution of fine sediment and macroinvertebrate communities at the riffle scale

Both phytochrome A and phytochrome B are required for the normal expression of phototropism in Arabidopsis thaliana seedlings

The role of phytochrome A (phyA) and phytochrome B (phyB) in phototropism was investigated by using the phytochrome-deficient mutants phyA-101, phyB-1 and a phyA/phyB double mutant. The red-light-induced enhancement of phototropism, which is normally observed in wild-type seedlings, could not be detected in the phyA/phyB mutant at fluences of red light between 0.1 and 19 000 mu mol m(-2). The loss of phyB has been shown to have no apparent effect on enhancement, while the loss of phyA resulted in a loss of enhancement only in the low fluence range (Janoudi et al. 1997). The conclusions of the aforementioned study can now be modified based on the current results which indicate that phototropic enhancement in the high fluence range is mediated by either phyA or phyB, and that other phytochromes have no role in enhancement. First positive phototropism was unaffected in phyA-101 and phyB-1. However, the magnitude of first positive phototropism in the phyA/phyB mutant was significantly lower than that of the wild-type Landsberg parent. Thus, the presence of either phyA or phyB is required for normal expression of first positive phototropism. The time threshold for second positive phototropism is unaltered in the phyA-101 and phyB-1 mutants. However, the time threshold in the phyA/phyB mutant is about 2 h, approximately six times that of the wild type. Finally, the magnitude of second positive phototropism in both phyA-101 and phyB-1 is diminished in comparison with the wild-type response. Thus, phyA and phyB, acting independently or in combination, regulate the magnitude of phototropic curvature and the time threshold for second positive phototropism. We conclude that the presence of phyA and phyB is required, but not sufficient, for the expression of normal phototropism.nul

Both phytochrome A and phytochrome B are required for the normal expression of phototropism in Arabidopsis thaliana seedlings

The role of phytochrome A (phyA) and phytochrome B (phyB) in phototropism was investigated by using the phytochrome-deficient mutants phyA-101, phyB-1 and a phyA/phyB double mutant. The red-light-induced enhancement of phototropism, which is normally observed in wild-type seedlings, could not be detected in the phyA/phyB mutant at fluences of red light between 0.1 and 19 000 mu mol m(-2). The loss of phyB has been shown to have no apparent effect on enhancement, while the loss of phyA resulted in a loss of enhancement only in the low fluence range (Janoudi et al. 1997). The conclusions of the aforementioned study can now be modified based on the current results which indicate that phototropic enhancement in the high fluence range is mediated by either phyA or phyB, and that other phytochromes have no role in enhancement. First positive phototropism was unaffected in phyA-101 and phyB-1. However, the magnitude of first positive phototropism in the phyA/phyB mutant was significantly lower than that of the wild-type Landsberg parent. Thus, the presence of either phyA or phyB is required for normal expression of first positive phototropism. The time threshold for second positive phototropism is unaltered in the phyA-101 and phyB-1 mutants. However, the time threshold in the phyA/phyB mutant is about 2 h, approximately six times that of the wild type. Finally, the magnitude of second positive phototropism in both phyA-101 and phyB-1 is diminished in comparison with the wild-type response. Thus, phyA and phyB, acting independently or in combination, regulate the magnitude of phototropic curvature and the time threshold for second positive phototropism. We conclude that the presence of phyA and phyB is required, but not sufficient, for the expression of normal phototropism.nul

The effects of potassium nitrate and NO-donors on phytochrome A- and phytochrome B-specific induced germination of Arabidopsis thaliana seeds

Nitrogenous compounds, such as potassium nitrate, potentiate germination of different species of light-requiring seeds. Using light-induced Arabidopsis thaliana seed germination as a model system, our data suggested that only phytochrome A (phyA)-specific induced germination was affected after the exogenous application of nitrates, different nitric oxide (NO)-donors (such as organic nitrates) or sodium nitroprusside. The stimulative effect was very pronounced. Treated seed samples reached maximal germination after very short periods of red-light irradiation. To a far lesser extent, these substances affected phytochrome B (phyB)-specific induced germination. In phyB-specific induced germination, potassium nitrate was most effective, but germination percentages never exceeded 50%. The least effective was sodium nitroprusside, which practically did not affect phyB-specific induced germination. These results were confirmed using corresponding phytochrome mutants.nul

The effects of potassium nitrate and NO-donors on phytochrome A- and phytochrome B-specific induced germination of Arabidopsis thaliana seeds

Nitrogenous compounds, such as potassium nitrate, potentiate germination of different species of light-requiring seeds. Using light-induced Arabidopsis thaliana seed germination as a model system, our data suggested that only phytochrome A (phyA)-specific induced germination was affected after the exogenous application of nitrates, different nitric oxide (NO)-donors (such as organic nitrates) or sodium nitroprusside. The stimulative effect was very pronounced. Treated seed samples reached maximal germination after very short periods of red-light irradiation. To a far lesser extent, these substances affected phytochrome B (phyB)-specific induced germination. In phyB-specific induced germination, potassium nitrate was most effective, but germination percentages never exceeded 50%. The least effective was sodium nitroprusside, which practically did not affect phyB-specific induced germination. These results were confirmed using corresponding phytochrome mutants.nul