No abstract

Adaptation to low water availability in sugar beet includes the accumulation of solutes relevant for the technical quality of the beet. Two sugar beet genotypes were grown in pot experiments under drought stress of different severity to study effects on taproot composition and concentration of solutes relevant for technical quality, reversibility of drought effects after re-watering and genotypic differences in drought response. Differences in stress sensitivity between the genotypes were not observed as reductions in taproot and leaf dry weight and white sugar yield were the same. Increasing dry matter concentration with decreasing water supply could, in part, be attributed to an increase in the concentration of cell wall components. The major solutes in the taproot were sucrose, potassium, amino N (the sum of amino acids) and betaine. Sucrose concentration decreased considerably under drought, indicating limited availability of assimilates. In contrast, all further solutes increased in concentration with increasing severity of stress. However, the response of individual solutes varied largely. Changes in amino N and nitrate were most pronounced and probably reflect accumulation of non-utilized metabolites under limited growth. The drought-induced accumulation of taproot solutes implicates a considerable decrease in the technical quality of the beet. It was only in part reversible by re-watering. Genotypic variability for solute accumulation under water deficiency was observed but was not linked to drought tolerance.

Depending on genotype, sugar beet can differ considerably in yield and quality characteristics. These are additionally modified by environmental conditions with drought stress recently gaining in importance, restricting growth and altering the chemical composition of the beet. The occurrence and development of these genotypic differences during the vegetation period and their possible interaction with environmental conditions were investigated. In 2002 and 2003, four sugar beet genotypes differing in yield and quality and putative different with regard to drought tolerance were tested in field trials, partly under irrigated conditions, in a total of 10 environments with consecutive harvests starting in early summer. In 2 years of stress and non‐stress conditions they exhibited significant differences for taproot and leaf dry matter and the concentration of sucrose, K, Na and α‐amino nitrogen in the taproot. These differences existed already in mid‐June and virtually did not change any more from this time on. Accordingly, interactions between genotype and harvest date did not occur. For sugar beet, genotype by environment interactions generally do not exist. Water supply, as an important single determinant of the effect of the environment, was studied separately analysing data from selected locations. Under drought conditions, withholding irrigation reduced leaf and taproot growth and root‐to‐leaf ratio, decreased the percentage of sucrose in dry matter and resulted in an accumulation of α‐amino N. Interactions between genotype and water supply did not occur for any of the parameters under study. A genotype‐specific high α‐amino N content, which might be of advantage for osmoregulation, did not improve the adaptation to drought. Differences in leaf maintenance or taproot‐to‐leaf ratio during drought also did not affect yield response. Due to the lack of interaction between genotype and harvest date as well as between genotype and irrigation it is concluded that harvest date or climatic factors of the growing region do not have to be taken into consideration when choosing a variety.

Currently, the authorisation process for plant protection products (PPPs) relies on the testing of acute and topological toxicity only. Contrastingly, the evaluation of active substances includes a more comprehensive set of toxicity studies. Nevertheless, mixture effects of active ingredients and co-formulants may result in increased toxicity. Therefore, we investigated effects of surface active co-formulants on the toxicity of two PPPs focussing on qualitative and quantitative toxicokinetic effects on absorption and secretion. The respective products are based on the active substances abamectin and fluroxypyr-meptyl and were tested for cytotoxicity in the presence or absence of the corresponding surfactants and co-formulants using Caco-2 cells. In addition, the effect of co-formulants on increased cellular permeation was quantified using LC–MS/MS, while potential kinetic mixture effects were addressed by fluorescence anisotropy measurements and ATPase assays. The results show that surface active co-formulants significantly increase the cytotoxicity of the investigated PPPs, leading to more than additive mixture effects. Moreover, analytical investigations show higher efflux ratios of both active substances and the metabolite fluroxypyr upon combination with certain concentrations of the surfactants. The results further point to a significant and concentration-dependent inhibition of Pgp transporters by most of the surfactants as well as to increased membrane fluidity. Altogether, these findings strongly support the hypothesis that surfactants contribute to increased cytotoxicity of PPPs and do so by increasing the bioavailability of the respective active substances.

Pulp as a feed stuff produced in the sugar factory is estimated by the marc concentration in sugar beet, which consists of the insoluble cell wall compounds. To identify factors affecting level and development of marc concentration during the growing season, several field trials and pot experiments were carried out in 2000, 2001 and 2002. The results show that marc concentration decreased until 100 days after sowing, but then did not change markedly until October, when it ranged between 34 and 45 g kg −1 beet. Marc concentration was affected more by site and variety than by year. Differences in marc concentration were already established very early in the season (65 days after sowing). This was attributed to the formation of cambial rings and parenchyma cells in the root during this period, which determine sucrose storage. There was a positive correlation between marc and dry matter, sucrose and betaine, but a negative correlation to root yield and amino N. Marc concentration was about 10% lower than reported in the past, which is supposed to be due to a change in the optimal cell volume for sucrose storage and the cell wall thickness of new sugar beet varieties.