Untitled

Abstract

Previous investigations in our laboratory have shown that leaf developmental programming in tobacco is regulated by source strength. One hypothesis to explain how source strength is perceived is that hexokinase acts as a sensor of carbohydrate flux to regulate the expression of photosynthetic genes, possibly as a result of sucrose cycling through acid invertase and hexokinase. We have turned to Arabidopsis as a model system to study leaf development and have examined various photosynthetic parameters during the ontogeny of a single leaf on the Arabidopsis rosette grown in continuous light. We found that photosynthetic rates, photosynthetic gene expression, pigment contents and total protein amounts attain peak levels early in the expansion phase of development, then decline progressively as development proceeds. In contrast, the flux of (14)CO(2) into hexoses increases modestly until full expansion is attained, then falls in the fully expanded leaf. Partitioning of carbon into hexoses versus sucrose increases until full expansion is attained, then falls. The in vitro activities of hexokinase, vacuolar acid invertase, and cell wall acid invertase do not change until the late stages of senescence, when they increase markedly. At this time there are also dramatic increases in hexose pool sizes and in senescence-associated gene (SAG) expression. Taken together, our results suggest that invertase and hexokinase activities do not control the partitioning of label into hexoses during development. We conclude that our data are not readily compatible with a simple model of leaf development, whereby alterations in photosynthetic rates are mediated directly by hexose flux or by hexose pool sizes. Yet, these factors might contribute to the control of gene expression.

Phenomic and Physiological Analysis of Salinity Effects on Lettuce

“…Plants were grown in controlled conditions under continuous light to avoid daily and seasonal fluctuations in environmental conditions that can interfere with results of experiments. Constant cultivation conditions allow for more consistent measurements of photosynthetic rates and chlorophyll levels [98,99] regardless of time of the day, thus avoiding complications resulting from the effect of photoperiod [99]. Compared to a previous study [54], control plants in the present experiment reached approximately 4–5 times higher FWs, allowing for a better distinction between sensitive and tolerant accessions.…”

Carbon source–sink relationship in Arabidopsis thaliana: the role of sucrose transporters

“…5 a), especially glucose, to sustain maintenance and growth respiratory as indicated by the constant increase of rosette DW (Table S3). As senescence in A. thaliana starts before rosette is fully developed (Stessman et al 2002 ), we cannot exclude that the slight increase in hexose content during the vegetative phase was provided by this process in the older leaves, since leaf sugars increase with leaf ageing (Quirino et al 2001 ; Stessman et al 2002 ). This trend was confirmed by a reduction in starch content which, nevertheless, remained, however, high in rosette during this phase (Fig.…”

Responsiveness of Early Response to Dehydration Six-Like Transporter Genes to Water Deficit in Arabidopsis thaliana Leaves

“…Glucose content was still maintained (although a little bit decreased), whereas sucrose content increased 2-fold in comparison to that in SD phase and fructose significantly increased. As the accumulation of soluble sugars has been shown to increase during senescence in several plant species, including Arabidopsis (Quirino et al, 2001;Stessman et al, 2002;Diaz et al, 2005) and that sugars are considered as a metabolic signal to trigger senescence (Pourtau et al, 2006;Rolland et al, 2006), it is tempting to suggest that the wilted plants having a WC lower than 76% were going to enter the senescence stage. However, this might not be really the case as we observed the repression of ESL3.13/SFP1, which has been described to be specifically induced during FIGURE 11 | Summary of the evolution of the sugar content and of the expression of vacuolar SUTs in the leaves of A. thaliana Col-0 and esl1.02/erdl6 mutant, under water deficit.…”