Reliability of handgrip strength measurements and their relationship with muscle power.

BACKGROUND: Handgrip peak force and rate of force development (RFD) have been shown to be useful measurements at characterizing the strength capacities of numerous muscle groups, including those of the lower extremities. However, the reliability of these measurements and their relationship with peak muscle power remain uncertain. We aimed to examine the reliability of handgrip peak force and RFD measurements. A secondary aim was to determine if these measurements are correlated with peak muscle power. METHODS: Twenty young women (21±3 years) reported for testing on two different occasions. Handgrip contractions were performed during each testing session to assess peak force, peak RFD, and RFD at 0-100 (RFD100) and 0-200 (RFD200) ms. Peak power was assessed from a vertical jump test. RESULTS: Handgrip peak force and RFD measurements were highly consistent between sessions, with intraclass correlation coefficients of 0.89-0.92 and coefficients of variation of 4.9-6.4%. There were significant correlations between peak power and handgrip peak force (r=0.612, P=0.004), peak RFD (r=0.731, P<0.001), RFD100 (r=0.671, P=0.001), and RFD200 (r=0.701, P=0.001). Stepwise multiple regression analysis indicated that handgrip peak RFD was the single best predictor of peak power (R2=0.535). CONCLUSIONS: Our results showed that handgrip peak force and RFD measurements are highly reliable and significantly associated with performance during a vertical jump test. The output from our multiple regression analysis suggests that handgrip peak RFD may be an effective predictor of muscle power.

Mechanical regulation of photosynthesis in cyanobacteria.

Photosynthetic organisms regulate their responses to many diverse stimuli in an effort to balance light harvesting with utilizable light energy for carbon fixation and growth (source-sink regulation). This balance is critical to prevent the formation of reactive oxygen species that can lead to cell death. However, investigating the molecular mechanisms that underlie the regulation of photosynthesis in cyanobacteria using ensemble-based measurements remains a challenge due to population heterogeneity. Here, to address this problem, we used long-term quantitative time-lapse fluorescence microscopy, transmission electron microscopy, mathematical modelling and genetic manipulation to visualize and analyse the growth and subcellular dynamics of individual wild-type and mutant cyanobacterial cells over multiple generations. We reveal that mechanical confinement of actively growing Synechococcus sp. PCC 7002 cells leads to the physical disassociation of phycobilisomes and energetic decoupling from the photosynthetic reaction centres. We suggest that the mechanical regulation of photosynthesis is a critical failsafe that prevents cell expansion when light and nutrients are plentiful, but when space is limiting. These results imply that cyanobacteria must convert a fraction of the available light energy into mechanical energy to overcome frictional forces in the environment, providing insight into the regulation of photosynthesis and how microorganisms navigate their physical environment.

Translational genomics using Arabidopsis as a model enables the characterization of pennycress genes through forward and reverse genetics.

Thlaspi arvense (pennycress) has the potential for domestication as a new oilseed crop. Information from an extensive body of research on the related plant species Arabidopsis can be used to greatly speed this process. Genome-scale comparisons in this paper documented that pennycress and Arabidopsis share similar gene duplication. This finding led to the hypothesis that it should be possible to isolate Arabidopsis-like mutants in pennycress. This proved to be true, as forward genetic screens identified floral and vegetative pennycress mutants that were similar to mutants found in Arabidopsis. Extending this approach, it was shown that most of the pennycress genes responsible for the formation of oxidized tannins could be rapidly identified. The causative mutations in the pennycress mutants could be identified either by PCR amplification of candidate genes or through whole-genome sequencing (WGS) analysis. In all, WGS was used to characterize 95 ethyl methane sulfonate mutants, which revealed a mutation rate of 4.09 mutations per megabase. A sufficient number of non-synonymous mutations were identified to create a mutant gene index that could be used for reverse genetic approaches to identify pennycress mutants of interest. As proof of concept, a Ta-max3-like dwarf mutant and Ta-kcs5/cer60-like wax mutants deficient in the biosynthesis of long chain fatty acids were identified. Overall, these studies demonstrate that translational genomics can be used to promote the domestication of pennycress. Furthermore, the ease with which important findings could be made in pennycress makes this species a new potential model plant.

Spring flowering habit in field pennycress (Thlaspi arvense) has arisen multiple independent times.

Field pennycress (Thlaspi arvense L.) is currently being developed as a new cold-tolerant oilseed crop. In natural populations, pennycress, like many Brassicaceae relatives, can exhibit either a winter or spring annual phenotype. Pennycress is a diploid relative of Arabidopsis thaliana, a model species that has been used to study many adaptive phenotypes, including flowering time and developmental timing. In Arabidopsis and other Brassicaceae species, mutations in negative regulators of flowering, including FLOWERING LOCUS C and FRIGIDA can cause the transition to a spring annual habit. The genetics underlying the difference between spring and winter annual pennycress lines are currently unknown. Here, we report the identification of four natural alleles of FLC in pennycress that confer a spring annual growth habit identified through whole genome sequencing, cosegregation analyses, and comparative genomics. The global distribution of these spring annual alleles of FLC suggests that the spring annual growth habit has arisen on several independent occasions. The two spring annual FLC alleles present in European accessions were only identified in North American accessions collected in southern Montana, which indicates accessions harboring these two alleles were introduced to North America, likely after pennycress became a widespread species on the continent. These findings provide new information on the natural history of the introduction and spread of spring annual pennycress accessions from Europe into North America. At the molecular level, these findings are important for the ongoing development of pennycress as a winter annual crop. An enhanced understanding of the regulation of flowering in this species should allow for the fine-tuning of flowering in commercial varieties.