Arabidopsis plants were exposed to high light or sulphur depletion alone or in combination for 6 d, and changes of photosynthetic parameters and metabolite abundances were quantified. Photosynthetic electron transport rates (ETRs) of plants exposed to sulphur depletion and high light decreased strongly at day 2 of the acclimation period. After 3 d of treatment, the photosynthetic capacity recovered in plants exposed to the combined stresses, indicating a short recovery time for re-adjustment of photosynthesis. However, at metabolic level, the stress combination had a profound effect on central metabolic pathways such as the tricarboxylic acid (TCA) cycle, glycolysis, pentose phosphate cycle and large parts of amino acid metabolism. Under these conditions, central metabolites, such as sugars and their phosphates, increased, while sulphur-containing compounds were decreased. Further differential responses were found for the stress indicator proline accumulating already at day 1 of the high-light regime, but in combination with sulphur depletion first declined and after a recovery phase reached a delayed elevated level. Other metabolites such as raffinose and putrescine seem to replace proline during the early combinatorial stress response and may act as alternative protectants. Our findings support the notion that plants integrate the selectively sensed stress factors in central metabolism.

Background and aims Aluminium (Al) toxicity limits pasture production in acidic soils, and there is evidence that antioxidant enzymes such as superoxide dismutase (SOD) play a key role against Al-induced oxidative stress. We have investigated (i) the relationship between Al-toxicity and oxidative damage as well as the time-course of SOD activity and (ii) the expression profiles of two SOD isoforms in the roots of two ryegrass cultivars. Methods Jumbo (Al-sensitive) and Nui (Al-semi-tolerant) ryegrass cultivars were cultured hydroponically with 0 or 0.2 mM Al. Roots were colleted during 48 h to determine Al uptake, lipid peroxidation, SOD activity and the expression of LpCu/Zn-SOD and LpFe-SOD isolated genes. Results LpCu/Zn-SOD and LpFe-SOD were classified phylogenetically as putative mitochondrial and plastidial SODs, respectively. Although Al accumulation did not differ between the two cultivars, lipid peroxidation increased 2.2-fold in Jumbo but only scarcely in Nui by the end of the time-course. An early response in terms of total SOD activity and differential expression of LpCu/Zn-SOD and LpFe-SOD genes occurred in both cultivars after Al treatment. Conclusions SOD isoforms were up-regulated over a longer period in Nui compared with Jumbo, leading finally to a greater protection in roots against the short term Al-toxicity.

We compared the aluminum tolerance of two highbush blueberry (Vaccinium corymbosum) cultivars, Legacy and Bluegold, grown in a greenhouse in Hoagland's solution with increasing concentrations of Al (0, 25, 50, 100, and 200 μm) for 7 to 20 days, using root lipid peroxidation (LP), radical scavenging activity (RSA), Al uptake by roots, and relative growth rate (RGR) as criteria. Leaf physiological [photochemical and non-photochemical parameters of photosystem II (PSII)] and biochemical (pigments, LP, RSA, and total soluble carbohydrates) responses to Al stress were also analyzed and then a principal component analysis (PCA) was performed. The results indicated that ‘Bluegold’ showed the highest Al uptake and LP in roots and a lower RGR in contrast to ‘Legacy’. The photochemical parameters were more affected in ‘Bluegold’ than in ‘Legacy’, particularly at the beginning of the experiment. At this point, a sharp increase in RSA was found in ‘Legacy’. According to these parameters, ‘Legacy’ was more Al tolerant than ‘Bluegold’. PCA revealed that among the underlying processes affected by Al toxicity in the highbush blueberry, the photochemical efficiency of PSII followed by modifications of photosynthetic pigment contents are of greatest significance after long-term Al stress. Additionally, RSA plays an important role in the long-term acclimation response mechanisms to Al stress in highbush blueberry leaves.

High altitude (HA) exposure may affect human health and performance by involving the body timing system. Daily variations of melatonin may disrupt by HA exposure, thereby possibly affecting its relations with a metabolic parameter like the respiratory quotient (RQ). Sea level (SL) volunteers (7 women and 7 men, 21.0 ± 2.04 y) were examined for daily changes in salivary melatonin concentration (SMC). Sampling was successively done at SL (Antofagasta, Chile) and, on acute HA exposure, at nearby Caspana (3,270 m asl). Saliva was collected in special vials (Salimetrics Oral Swab, United Kingdom) at sunny noon (SMCD) and in the absence of blue light at midnight (SMCN). The samples were obtained after rinsing the mouth with tap water and were analyzed for SMC by immunoassay (ELISA kit; IBL International, Germany). RQ measurements (n = 12) were realized with a portable breath to breath metabolic system (OxiconTM Mobile, Germany), between 8:00 PM and 10:00 PM, once at either location. At SL, SMCD, and SMCN values (mean ± SD) were, respectively, 2.14 ± 1.30 and 11.6 ± 13.9 pg/ml (p < 0.05). Corresponding values at HA were 8.83 ± 12.6 and 13.7 ± 16.7 pg/ml (n.s.). RQ was 0.78 ± 0.07 and 0.89 ± 0.08, respectively, at SL and HA (p < 0.05). Differences between SMCN and SMCD (SMCN–SMCD) strongly correlate with the corresponding RQ values at SL (r = -0.74) and less tight at HA (r = -0.37). Similarly, mean daily SMC values (SMC) tightly correlate with RQ at SL (r = -0.79) and weaker at HA (r = -0.31). SMCN–SMCD, as well as, SMC values at SL, on the other hand, respectively, correlate with the corresponding values at HA (r = 0.71 and r = 0.85). Acute exposure to HA appears to loosen relations of SMC with RQ. A personal profile in daily SMC variation, on the other hand, tends to be conserved at HA.