Do Variations in Local Leaf Irradiance Explain Changes to Leaf Nitrogen within Row Maize Canopies?

Numerous studies have dealt with the relationship between leafnitrogen content and leaf irradiance. However, most of themrefer to dense stands presenting reduced horizontal heterogeneityof foliage distribution. Both gradients of leaf nitrogen andleaf irradiance related to canopy depth are significant undersuch conditions, and modelling radiative exchange using a turbid-mediumanalogy and dividing the canopy into vegetation layers is sufficient.Conversely, row crops such as maize are characterized by stronghorizontal heterogeneity of foliage distribution and the one-dimensional(1D) approach may be unsuitable. We thus modelled the three-dimensional(3D) geometry of maize canopies with varying densities and atdifferent developmental stages using plant digitizing underfield conditions. The nitrogen content per unit area of eachleaf part was obtained subsequently by nitrogen analysis. Wenext calculated radiative exchange using a 3D volume-based approachwithin the canopies in order to estimate local leaf irradianceon a daily integration scale. Vertical gradients in leaf nitrogencontent per unit area observed in dense stands during the vegetativephase corresponded largely to those reported in the literature.We also identified significant gradients in nitrogen contentalong the leaves, which had not before been clearly demonstrated.Our study shows that local light climate during plant developmentplays a major role in leaf nitrogen distribution and remobilization.Moreover, brutal plant thinning involves rapid changes in leafnitrogen partitioning. It is concluded that taking account ofthe 3D heterogeneity of nitrogen and irradiance distributionmay have implications for modelling crop photosynthesis andproduction. Copyright 1999 Annals of Botany Company 3D plant architecture, horizontal gradients in leaf nitrogen, leaf irradiance, leaf nitrogen content per unit area, maize, nitrogen partitioning, nitrogen remobilization, virtual plant, Zea mays L.     

Étude par électrophorèse en gel de polyacrylamide de I'évolution enzymatique des tissus de Poire Passe-Crassane pendant la maturation du fruit cueilli

Evolution of different enzymes (glucose 6-phosphate dehydrogenase EC 1.1.1.49, fructose 1–6 diphosphate aldolase EC 4.1.2.1.3, malic enzyme EC 1.1.1.40, pyruvic decarboxylase EC 4.1.1.1) was followed by polyacrylamide gel electrophoresis and specific staining during the maturation of the pear (cv. Passe-Crassane) harvested and stored at +15°C. During the increase of the respiration rate, the glucose 6 P dehydrogenase activity declines while the three other enzymes activity increases. Results obtained are discussed.