The Effect of Phytohormones on Chlorophyll(ide), Protochlorophyll(ide) and Carotenoid Formation in Greening Dark Grown Wheat Leaves

The influence of phytohormones on chlorophyll and carotenoid formation during the greening of irradiated dark grown wheat leaves (Triticum aestivum L. cv. Starke II Weibull) was studied. Leaves were floated on solutions of abscisic acid, gibberellic acid and kinetin for 24 h. The chlorophyll and carotenoid contents were determined during a subsequent period of 48 h of continuous irradiation. Leaves treated with abscisic acid showed a longer lag phase and a lower rate of accumulation of chlorophyll as compared to the control than did leaves treated with gibberellic acid and kinetin. The carotenoid content was low both in leaves treated with abscisic acid and in those treated with gibberellic acid. Treatment with abscisic acid lowered the protochlorophyllide regeneration after a saturating light flash while gibberellic acid as well as kinetin had no effect. The influence of ABA was partly dependent on an increase of the wounded part of the cut leaf segments. The accumulation of protochlorophyllide in leaves treated with δ-aminolevulinic acid was not affected by the different hormonal treatments. These results suggest that the main effect of abscisic acid is probably outside the chloroplast, i.e. on the formation or transport of δ-aminolevulinic acid.     

The influence of large wood on brown trout (Salmo trutta) behaviour and surface foraging

1. Changes in riparian vegetation owing to forest harvesting may affect the input of large wood, a major structural element, to streams. Studies of large wood impacts on stream fish have focused on population‐level responses, whereas little attention has been given to how wood affects fish behaviour. 2. In a laboratory stream experiment, we tested how two size classes of brown trout, Salmo trutta, (mean size of 85 and 125 mm), alone and together, responded to a gradient of large wood in terms of activity, foraging on terrestrial drift and interactions between conspecifics. 3. The results showed that the presence of large wood significantly reduced the overall activity of the fish, the number of agonistic interactions between individuals and the proportion of captured prey. However, activity decreased relatively more than the proportion of captured prey, resulting in a significant positive net effect of wood on the number of prey captures per time spent active (PTA). This indicates that trout living in habitats with high wood density may have a higher net energy gain than trout living in habitats with less wood. 4. There were no observable size‐class differences in the benefits of large wood or in the utilisation of surface‐drifting terrestrial prey. 5. These results suggest that the presence of large wood may be an important factor shaping stream communities and that a lack of structural complexity may decrease energy gain, increase agonistic interactions and, consequently, lower the production of brown trout.     

Aerobic nitrogen fixation is confined to a subset of cells in the non-heterocystous cyanobacterium Symploca PCC 8002

Symploca PCC 8002 Kützing is a filamentous cyanobacterium that lacks the specialized cells, known as heterocysts, that protect nitrogenase from O₂ in most aerobic N₂-fixing cyanobacteria. Nevertheless, Symploca is able to carry out N₂ fixation in the light under aerobic conditions. When cultures were grown under light/dark cycles, nitrogenase activity commenced and increased in the light phase and declined towards zero in the dark. Immunolocalization of dinitrogenase reductase in sectioned Symploca trichomes showed that the enzyme was present only in 9% of the cells. These cells lacked any obvious mechanical protection against atmospheric O₂ and their ultrastructural characteristics were similar to those of cells that did not contain any dinitrogenase reductase. The nitrogenase-containing cells possessed carboxysomes that were rich in ribulose-1,5-bisphosphate carboxylase/oxygenase and phycoerythrin, a light harvesting pigment of PS II. This indicates that these cells had a capacity for both N₂ fixation and photosynthesis. The significance of the localization pattern for dinitrogenase reductase is discussed in the context of N₂ fixation in Symploca PCC 8002.