Reduced carbohydrate availability enhances the susceptibility of Arabidopsis toward Colletotrichum higginsianum.

Colletotrichum higginsianum is a hemibiotrophic ascomycete fungus that is adapted to Arabidopsis (Arabidopsis thaliana). After breaching the host surface, the fungus establishes an initial biotrophic phase in the penetrated epidermis cell, before necrotrophic growth is initiated upon further host colonization. We observed that partitioning of major leaf carbohydrates was shifted in favor of sucrose and at the expense of starch during necrotrophic fungal growth. Arabidopsis mutants with impaired starch turnover were more susceptible toward C. higginsianum infection, exhibiting a strong negative correlation between diurnal carbohydrate accumulation and fungal proliferation for the tested genotypes. By altering the length of the light phase and employing additional genotypes impaired in nocturnal carbon mobilization, we revealed that reduced availability of carbon enhances susceptibility in the investigated pathosystem. Systematic starvation experiments resulted in two important findings. First, we showed that carbohydrate supply by the host is dispensable during biotrophic growth of C. higginsianum, while carbon deficiency was most harmful to the host during the necrotrophic colonization phase. Compared with the wild type, the increases in the total salicylic acid pool and camalexin accumulation were reduced in starch-free mutants at late interaction stages, while an increased ratio of free to total salicylic acid did not convey elevated pathogenesis-related gene expression in starch-free mutants. These observations suggest that reduced carbon availability dampens induced defense responses. In contrast, starch-free mutants were more resistant toward the fungal biotroph Erysiphe cruciferarum, indicating that reduced carbohydrate availability influences susceptibility differently in the interaction with the investigated hemibiotrophic and biotrophic fungal pathogens.

Individual values, learning routines and academic procrastination.

BACKGROUND: Academic procrastination, the tendency to postpone learning activities, is regarded as a consequence of postmodern values that are prominent in post-industrialized societies. When students strive for leisure goals and have no structured routines for academic tasks, delaying strenuous learning activities becomes probable. AIMS: The model tested in this study posits that postmodern value orientations are positively related to procrastination and to a lack of daily routines concerning the performance of academic activities. In contrast, modern values are negatively related to procrastination and positively to learning routines. Academic procrastination, in-turn, should be associated with the tendency to prefer leisure activities to schoolwork in case of conflicts between these two life domains. SAMPLE: Seven hundred and four students from 6th and 8th grade with a mean age of 13.5 years participated in the study. The sample included students from all tracks of the German educational system. METHOD: Students completed a questionnaire containing two value prototypes as well as scales on learning routines and procrastination. Decisions in motivational conflicts were measured using two vignettes. RESULTS AND CONCLUSIONS: Results from structural equation modelling supported the proposed model for the whole sample as well as for each school track. A planned course of the day can prevent procrastination and foster decisions for academic tasks in case of conflicts. Students' learning takes place within a societal context and reflects the values held in the respective culture.