Individual Variability and Test-Retest Reliability Revealed by Ten Repeated Resting-State Brain Scans over One Month

Individual differences in mind and behavior are believed to reflect the functional variability of the human brain. Due to the lack of a large-scale longitudinal dataset, the full landscape of variability within and between individual functional connectomes is largely unknown. We collected 300 resting-state functional magnetic resonance imaging (rfMRI) datasets from 30 healthy participants who were scanned every three days for one month. With these data, both intra- and inter-individual variability of six common rfMRI metrics, as well as their test-retest reliability, were estimated across multiple spatial scales. Global metrics were more dynamic than local regional metrics. Cognitive components involving working memory, inhibition, attention, language and related neural networks exhibited high intra-individual variability. In contrast, inter-individual variability demonstrated a more complex picture across the multiple scales of metrics. Limbic, default, frontoparietal and visual networks and their related cognitive components were more differentiable than somatomotor and attention networks across the participants. Analyzing both intra- and inter-individual variability revealed a set of high-resolution maps on test-retest reliability of the multi-scale connectomic metrics. These findings represent the first collection of individual differences in multi-scale and multi-metric characterization of the human functional connectomes in-vivo, serving as normal references for the field to guide the use of common functional metrics in rfMRI-based applications.     

Light and Electron Microscopy Studies on the Infection of a Wild‐type and Metalaxyl‐resistant Isolate of Phytophthora sojae in Soybean Hypocotyls

Resistance of soybean cultivars, depending on single dominant genes to Phytophthora sojae, may easily be overcome by emerging new virulent races. Light microscopy (LM) and electron microscopy (EM) were used to study the infection process of the wild‐type isolate Ps411 and metalaxyl‐resistant mutant Ps411‐M of P. sojae in hypocotyls of soybean seedlings grown from untreated and metalaxyl‐treated seeds. The isolate Ps411‐M of P. sojae exhibited a high degree of resistance to metalaxyl compared to Ps411. The pathogenic fitness of Ps411‐M in hypocotyls of soybean seedlings was lower compared to Ps411. LM observations showed distinct differences in the infection process of both isolates in hypocotyls of treated soybean seedlings. EM studies revealed differences in the prepenetration stage between Ps411 and Ps411‐M on hypocotyls grown from seeds treated with 0.02% metalaxyl until the whole seed surface coated. The number of infection sites was markedly reduced and few hyphae continued to spread. Numerous ultrastructural alterations in hyphae were observed in treated hypocotyls infected with Ps411, including pronounced thickening of hyphal cell walls and encasement of haustorium‐like bodies; electron‐dense material was deposited in host cell walls in contact with hyphal cells. Neither the prepenetration process nor penetration or spread of hyphae in the hypocotyls of the resistant isolate was affected in treated compared to non‐treated tissue. While in treated hypocotyls infected with the wild‐type isolate, host defence reactions were induced, no such reactions were detected in treated hypocotyls infected with the resistant isolate. Hypocotyls from metalaxyl‐treated seeds infected with the wild‐type isolate resembled an incompatible interaction, whereas during infection with the metalaxyl‐resistant mutant, the compatible interaction was not changed.     

Physiological acclimation of two psammophytes to repeated soil drought and rewatering

To understand physiological acclimation of psammophyte to repeated soil drought and rewatering, two psammophytes (Setaria viridis and Digitaria ciliaris) were subjected to three cycles of soil drought and rewatering. The response process of leaf relative water content (RWC), membrane permeability, lipid peroxidation, gas exchange characteristics, antioxidant enzymes, soluble protein, and free proline was examined. Leaf RWC, the net photosynthesis rate, stomatal conductance, and water use efficiency decreased, while membrane permeability, lipid peroxidation, intercellular CO₂ concentration, soluble protein, and free proline increased during three soil drought periods for both psammophytes. These physiological characteristics were recovered to the control levels following rewatering for 4 days. However, activities of SOD, CAT, and POD were induced continuously under soil drought conditions, and remained higher than those in the control throughout the whole experiment period, which agrees with our hypothesis that drought hardening activates defensive systems of both psammophytes continuously. Decreasing level of leaf RWC and increasing levels of leaf membrane permeability and lipid peroxidation were suppressed with increasing the number of drought cycles, suggesting that drought hardening alleviates damages of both psammophytes and improves their drought tolerance and acclimation to soil drought conditions in the future. Additionally, the photosynthesis decreased more slowly in the subsequent drought cycles than in the first cycle, allowing both psammophytes to maximize assimilation in response to repeated soil drought conditions. Thus, both psammophytes acclimatize themselves to repeated soil drought.