Wilco Jordi

Effects of elevated CO2 concentration on photosynthetic acclimation and productivity of two potato cultivars grown in open-top chambers

In two subsequent years, an early maturing potato cultivar with low leaf area index (LAI) and a late culti- var with high LAI were grown at concentrations of 350 and 700 µL CO2 L -1 in open-top chambers. The average increase of tuber dry matter yield by elevated CO2 was 27% in 1995 and 49% in 1996. During the first weeks after planting, elevated CO2 stimulated the light-saturated rate of photosynthesis (Amax) of both cultivars by 80%. However, Amax under elevated CO2 declined to the level of the low-CO2 treatment in the course of the growing season. In 1995 this convergence due to acclimation of photosynthesis was completed within 6 weeks, but in 1996, accli- mation proceeded until the end of the growing season. Photosynthetic acclimation was accompanied by a reduced Rubisco content, and was correlated more closely with accumulation of sucrose than of starch. From fluorescence measurements it was concluded that, in contrast to the carboxylation efficiency, the efficiency of photosynthetic reactions centers was not affected by acclimation to elevated CO2. The faster photosynthetic acclimation in 1995 coincided with overall lower values of Amax, crop growth rate and growth response to elevated CO2. It is shown that the indeterminate growth pattern of potato with its large sink capacity does not preclude acclimation. The effect of acclimation on yield was quantified by computer simulations. The simulated results indicated that photosynthetic acclimation reduced the positive effect of elevated CO2 on tuber yield by 50%.

Functional significance of shade-induced leaf senescence in dense canopies: an experimental test using transgenic tobacco

Canopy photosynthesis models have predicted an optimal leaf area index (LAI; leaf area per unit surface area) and leaf nitrogen distribution at which whole‐plant carbon gain per unit N is maximized. In this study we experimentally tested these models, using transgenic PSAG12‐IPT tobacco (SAG; Nicotiana tabacum L.) plants with delayed leaf senescence and therefore a greater LAI and more uniform N distribution than the wild type (WT). In a competition experiment, the increased density of surrounding WT plants caused a greater reduction in dry mass of mature SAG target plants than in that of WT target plants, indicating negative effects of delayed leaf senescence on performance at high canopy density. Vegetative SAG plants achieved a lower calculated daily carbon gain than competing WT plants because the former retained leaves with a negative carbon gain in the shaded, lower part of the canopy. Sensitivity analyses showed that the carbon gain of SAG plants would increase if these lower leaves were shed and the N reallocated from these leaves were used to form additional leaf area at the canopy top. This strategy, which is adopted by the WT, is most advantageous because it results in the shading of competing neighbors.

Plant members of the α1→3/4‐fucosyltransferase gene family encode an α1→4‐fucosyltransferase, potentially involved in Lewisa biosynthesis, and two core α1→3‐fucosyltransferases1

Three putative α1→3/4‐fucosyltransferase (α1→3/4‐FucT) genes have been detected in the Arabidopsis thaliana genome. The products of two of these genes have been identified in vivo as core α1→3‐FucTs involved in N‐glycosylation. An orthologue of the third gene was isolated from a Beta vulgaris cDNA library. The encoded enzyme efficiently fucosylates Galβ1→3GlcNAcβ1→3Galβ1→4Glc. Analysis of the product by 400 MHz 1H‐nuclear magnetic resonance spectroscopy showed that the product is α1→4‐fucosylated at the N‐acetylglucosamine residue. In vitro, the recombinant B. vulgaris α1→4‐FucT acts efficiently only on neutral type 1 chain‐based glycan structures. In plants the enzyme is expected to be involved in Lewisa formation on N‐linked glycans.