Organic acids reduce aluminum toxicity in maize root membranes

Application of 10–50 μ M Al ions to a plasma membrane-enriched microsomal fraction, isolated from roots of maize ( Zea mays L.), resulted in decreased Mg²-ATPase activity. This was probably caused by changes in membrane structure as detected by the use of spin probes. Both enzymatic activity and membrane structure could in part be protected from Al injury when organic acids, similar to those found in maize root tissue, were administered prior to the metal. When stressed by application of Al ions, the Al-tolerant maize hybrid, W64, maintained higher concentrations of organic acids, especially malic and trans -aconitic, than the Al-sensitive maize hybrid, A632. We hypothesize that citric and malic acid, because of their high stability constants with Al and/or the acid's concentration reduce Al toxicity in maize root tissue, especially in the Al-tolerant line.     

Regulation of T Cell Activation and Anergy by the Intensity of the Ca2+ Signal in Cooperation with Other Signals

The results of our previous in vitro study indicated that the intensity of the Ca²⁺ signal could determine T cell activation and anergy. We show here that the T cell response of mice that had been treated with cyclosporine A during oral tolerance induction was higher than that of control mice, indicating that the Ca²⁺ signal could also determine T cell activation and tolerization in vivo. However, T cell activation was not apparent at any concentration of ionomycin, although a low dose of anti-CD3 monoclonal antibody (mAb) induced activation, while a high dose induced anergy in vitro. These results indicate that the balance between the Ca²⁺ signal and other signals which can also be induced by anti-CD3 stimulation, but not the actual intensity of the Ca²⁺ signal or the presence of co-stimulation, played an important role in regulating T cell activation and anergy.     

Identification of a Nuclear Retinoic Acid-binding Activity Representative of Endogeneous Retinoic Acid Receptors in the Nuclei of Rat Liver and Testis

We found a nuclear RA-binding activity by using a sucrose-density-gradient assay from rat liver and testis. From the sedimentation analysis, and the comparison with cloned RARs, it is likely that these binding activities represent endogenous RARs. Furthermore we showed that these binding activities were constant irrespective of the retinoid status in the rat.     

Individual differences in the cortisol-awakening response during the first two years of shift work: A longitudinal study in novice police officers

Cortisol acts as a critical biological intermediary through which chronic stressors like shift work impact upon multiple physiological, neuro-endocrine and hormonal functions. Therefore, the cortisol awakening response (CAR) is suggested as a prime index of shift work tolerance. Repeated assessments of the CAR (calculated as MnInc) in a group of 25 young novice police officers showed that in the interval between about 4 and 14 months after transitioning from regular day work to rotating shift work, mean values began to rise from baseline to significantly higher levels at about 14 months after they commenced shift work. Visual inspection of the individual trends revealed that a subgroup of 10 subjects followed a monotonically rising trend, whereas another 14 subjects, after an initial rise from about 4–14 months, reverted to a smaller, baseline level cortisol response at about 20 months after the start of shift work. If the initial increase in the cortisol response marks the development of a chronic stress response, the subsequent reversal to baseline levels in the subgroup of 14 participants might be indicative of a process of recovery, possibly the development of shift work tolerance.     

Life‐history constraints in grassland plant species: a growth‐defence trade‐off is the norm

Plant growth can be limited by resource acquisition and defence against consumers, leading to contrasting trade‐off possibilities. The competition‐defence hypothesis posits a trade‐off between competitive ability and defence against enemies (e.g. herbivores and pathogens). The growth‐defence hypothesis suggests that strong competitors for nutrients are also defended against enemies, at a cost to growth rate. We tested these hypotheses using observations of 706 plant populations of over 500 species before and following identical fertilisation and fencing treatments at 39 grassland sites worldwide. Strong positive covariance in species responses to both treatments provided support for a growth‐defence trade‐off: populations that increased with the removal of nutrient limitation (poor competitors) also increased following removal of consumers. This result held globally across 4 years within plant life‐history groups and within the majority of individual sites. Thus, a growth‐defence trade‐off appears to be the norm, and mechanisms maintaining grassland biodiversity may operate within this constraint.     

Indices of water deficit in susceptible and resistant cucumbers in response to infection by cucumber mosaic virus

Indices of water deficit were determined under conditions of non-limited water supply in cucumber mosaic virus (CMV)-infected seedlings of the susceptible cv. Bet Alpha. An increase in the concentration of soluble solids, decrease of water and osmotic potentials, and increase of proline concentration were found in the CMV-infected cotyledons. In the cv. Shimshon, which is resistant to CMV, virus infection caused only a slight change in the concentration of the soluble solids and in the osmotic potential; water potential and proline content were not affected. Concomitantly, infectivity of cotyledons by CMV was much lower in the tolerant cv. Shimshon than in the susceptible cv. Bet Alpha. The possible association of water deficit with virus-induced growth retardation is discussed.     

Drought‐stress and plant resistance affect herbivore performance and proteome: the case of the green peach aphid Myzus persicae (Hemiptera: Aphididae)

Little is known about the simultaneous effects of drought stress and plant resistance on herbivorous insects. By subjecting the green peach aphid Myzus persicae Sulzer to well‐watered and drought‐stressed plants of both susceptible and resistant peach (Prunus persica), the effects of both stressors on aphid performance and proteomics are tested. Overall, the influence of the water treatment on aphid performance is less pronounced than the effect of host plant genetic resistance. On the susceptible cultivar, aphid survival, host acceptance and ability to colonize the plant do not depend on water treatment. On the resistant cultivar, aphid survival and ability to colonize are higher on drought‐stressed than on well‐watered plants. A study examining the pattern of protein expression aiming to explain the variation in aphid performance finds higher protein expression in aphids on the drought‐stressed susceptible cultivars compared with the well‐watered ones. In the susceptible cultivar, the regulated proteins are related to energy metabolism and exoskeleton functionality, whereas, in the resistant cultivar, the proteins are involved with the cytoskeleton. Comparison of the protein expression ratios for resistant versus susceptible plants reveals that four proteins are down‐regulated in well‐watered plants and 15 proteins are down‐regulated in drought‐stressed plants. Drought stress applied to the susceptible cultivar induces the regulation of proteins in M. persicae that enable physiological adaptation to maintain an almost unaltered aphid performance. By contrast, for aphids on the resistant cultivar subjected to drought stress, the down‐regulation of proteins responds to an induced host susceptibility effect.     

The DNA-binding box of human SPARTAN contributes to the targeting of Polη to DNA damage sites

Inappropriate repair of UV-induced DNA damage results in human diseases such as Xeroderma pigmentosum (XP), which is associated with an extremely high risk of skin cancer. A variant form of XP is caused by the absence of Polη, which is normally able to bypass UV-induced DNA lesions in an error-free manner. However, Polη is highly error prone when replicating undamaged DNA and, thus, the regulation of the proper targeting of Polη is crucial for the prevention of mutagenesis and UV-induced cancer formation. Spartan is a novel regulator of the damage tolerance pathway, and its association with Ub-PCNA has a role in Polη targeting; however, our knowledge about its function is only rudimentary. Here, we describe a new biochemical property of purified human SPARTAN by showing that it is a DNA-binding protein. Using a DNA binding mutant, we provide in vivo evidence that DNA binding by SPARTAN regulates the targeting of Polη to damage sites after UV exposure, and this function contributes highly to its DNA-damage tolerance function.