Competition between isoprene emission and pigment synthesis during leaf development in aspen

In growing leaves, lack of isoprene synthase (IspS) is considered responsible for delayed isoprene emission, but competition for dimethylallyl diphosphate (DMADP), the substrate for both isoprene synthesis and prenyltransferase reactions in photosynthetic pigment and phytohormone synthesis, can also play a role. We used a kinetic approach based on post‐illumination isoprene decay and modelling DMADP consumption to estimate in vivo kinetic characteristics of IspS and prenyltransferase reactions, and to determine the share of DMADP use by different processes through leaf development in Populus tremula. Pigment synthesis rate was also estimated from pigment accumulation data and distribution of DMADP use from isoprene emission changes due to alendronate, a selective inhibitor of prenyltransferases. Development of photosynthetic activity and pigment synthesis occurred with the greatest rate in 1‐ to 5‐day‐old leaves when isoprene emission was absent. Isoprene emission commenced on days 5 and 6 and increased simultaneously with slowing down of pigment synthesis. In vivo Michaelis–Menten constant (K_m) values obtained were 265 nmol m^?2 (20 μm ) for DMADP‐consuming prenyltransferase reactions and 2560 nmol m^?2 (190 μm ) for IspS. Thus, despite decelerating pigment synthesis reactions in maturing leaves, isoprene emission in young leaves was limited by both IspS activity and competition for DMADP by prenyltransferase reactions.     

Provision of nestboxes raises the breeding density of Great Tits Parus major equally in coniferous and deciduous woodland

Nestbox provision is a technique used to increase nest-site availability for secondary cavity-nesting birds. However, little is known about the demographic consequences of nestbox provision in different habitat types. To assess how nestbox provision affects the density of hole-nesting birds simultaneously in two contrasting habitats, we compared the breeding density of Great Tits along transects without nestboxes with that in transects where nestboxes were provided. Although the initial density of breeders was considerably higher in the deciduous habitat than in the coniferous habitat, provision of nestboxes increased density by a similar number of additional pairs in each habitat type. Thus, the provision of nestboxes in managed coniferous forests may be as effective in increasing the breeding opportunities of cavity nesters as in deciduous stands. Moreover, previous research showed that pairs in deciduous habitat with nestboxes have consistently lower breeding success than those in coniferous habitat with nestboxes. It is possible that the addition of nestboxes in the preferred habitat increased density to such an extent that density-dependent effects became apparent.     

Photosynthetic rate and dynamic environment. * Kazutoshi Yabuki, 2004. * Dordrecht/Boston/London: Kluwer Academic Publishers. * {euro}50 (hardback). 130 pp.

In photosynthesis, CO₂ enters theleaf from the atmosphere and moves to the active site of thecarboxylating enzyme, to be bound in an organic compound. Theprocess is largely diffusional and the pathway, although complicatedin detail, is usually split into sections related to differentanatomic structures, such as chloroplasts, cell walls, intercellularair space, stomatal pores and, finally the leaf boundary layer.Biologists have mainly been concerned with those sections thatare embedded within the leaf, considering the boundary layeras something external, not under the control by biological processes.Well, light is also not controlled     

Calculation of Leaf Photosynthetic Parameters Considering the Statistical Distribution of Stomatal Apertures

It was shown earlier (Laisk, Oja, and Kull, 1980) that differentstomata on a barley leaf are open to different degrees. Therefore,stomatal conductance is a quantity which is statistically distributedover a large range in the geometry of one leaf. Gas exchangemeasurements based on transpiration rates represent the averagevalue of stomatal conductance in the leaf chamber. The conventionalmethod of calculating mesophyll resistance involves subtractingstomatal resistance from total leaf resistance. It is incorrect,however, to average the stomatal resistance before this subtraction.Therefore, the conventional method for calculating the mesophyllresistance contains an error as it neglects the statisticaldistribution of stomatal apertures. The error is significantwhen the diffusion resistance between neighbouring substomatalcavities is large and when stomatal apertures vary over a widerange. Key words: Mesophyll resistance, Stomatal conductance, Statistics     

Statistical Distribution of Stomatal Apertures of Vicia faba and Hordeum vulgare and the Spannungsphase of Stomatal Opening

Plants of Vicia faba and Hordeum vulgare were grown in growthboxes with 7 mW cm^–2 PAR, 14 h day/10 h night, at 22/20°C. Stomata of attached leaves were measured under controlledconditions by means of an optical microscope and the distributionfunctions of the widths of pores were established. For Viciafaba they appeared to be symmetrical bell-shaped functions.In the process of stomatal opening or closure the shape of thedistribution remained constant, its maximum sliding left andright along the aperture axis. This result has been interpretedto mean that increments or decrements of apertures were equalfor all stomata independent of their individual apertures. Theconclusion has been drawn that the ‘driving force’is evenly distributed, equal for all stomata, and varies withinwider limits than is possible for stomatal apertures. Stomatalopening is limited by the closed state from below and by ananatomically possible maximum aperture from above.