Auxin and its transport play a role in plant tolerance to arsenite‐induced oxidative stress in Arabidopsis thaliana

The role of auxin in plant development is well known; however, its possible function in root response to abiotic stress is poorly understood. In this study, we demonstrate a novel role of auxin transport in plant tolerance to oxidative stress caused by arsenite. Plant response to arsenite [As(III)] was evaluated by measuring root growth and markers for stress on seedlings treated with control or As(III)‐containing medium. Auxin transporter mutants aux1, pin1 and pin2 were significantly more sensitive to As(III) than the wild type (WT). Auxin transport inhibitors significantly reduced plant tolerance to As(III) in the WT, while exogenous supply of indole‐3‐acetic acid improved As(III) tolerance of aux1 and not that of WT. Uptake assays using H³‐IAA showed As(III) affected auxin transport in WT roots. As(III) increased the levels of H₂O₂ in WT but not in aux1, suggesting a positive role for auxin transport through AUX1 on plant tolerance to As(III) stress via reactive oxygen species (ROS)‐mediated signalling. Compared to the WT, the mutant aux1 was significantly more sensitive to high‐temperature stress and salinity, also suggesting auxin transport influences a common element shared by plant tolerance to arsenite, salinity and high‐temperature stress.     

Expression of a Pteris vittata glutaredoxin PvGRX5 in transgenic Arabidopsis thaliana increases plant arsenic tolerance and decreases arsenic accumulation in the leaves

Chinese brake fern Pteris vittata hyperaccumulates arsenic in its fronds. In a study to identify brake fern cDNAs in arsenic resistance, we implicated a glutaredoxin, PvGRX5, because when expressed in Escherichia coli , it improved arsenic tolerance in recombinant bacteria. Here, we asked whether PvGRX5 transgenic expression would alter plant arsenic tolerance and metabolism. Two lines of Arabidopsis thaliana constitutively expressing PvGrx5 cDNA were compared with vector control and wild-type lines. PvGRX5-expressors were significantly more tolerant to arsenic compared with control lines based on germination, root growth and whole plant growth under imposed arsenic stress. PvGRX5-expressors contained significantly lower total arsenic compared with control lines following treatment with arsenate. Additionally, PvGRX5-expressors were significantly more efficient in their arsenate reduction in vivo . Together, our results indicate that PvGRX5 has a role in arsenic tolerance via improving arsenate reduction and regulating cellular arsenic levels. Paradoxically, our results suggest that PvGRX5 from the arsenic hyperaccumulator fern can be used in a novel biotechnological solution to decrease arsenic in crops.     

Compensation in grain yield components in a panicle of rainfed sorghum

In a field experiment with rainfed grown sorghum hybrid CSH-6, various proportions of spikelets from the apex, base or random regions of the panicles were removed at the time of anthesis and the yield compensation in grain number and grain size within a panicle was investigated. The distribution of grain number and grain yield in a control panicle from apex to base was parabolic while grain size showed a progressive linear decrease. Full grain yield compensation occurred due to an increase in grain number and size when the panicles lost up to 20% of their portions at the base or at random. No grain number compensation was, however, recorded at the apical region. Irrespective of the number of spikelets retained, the size of grains in the upper part of the panicle was always larger than those in the lower part. The grain number compensation, which occurred when spikelets were removed at the time of anthesis and the decreasing grain size from apex to base of the panicle would suggest hormonal involvement in the determination of potential grain number and size.     

Larval survival of two species of forensically important blowflies (Diptera: Calliphoridae) after submergence in water

Survival of larvae of known ages after 2 to 6 h of submersion under water was assessed by observing pupation and adult emergence in the cases of two blowflies of forensic importance, Chrysomya megacephala (Fabricius) and Chrysomya rufifacies (Macquart). Lowest survival occurred among 10‐h‐old larvae, which could not tolerate more than 2 h of submergence. Even with such a small period of submergence success of survival was only 33%. There were no survivors when 20‐ and 30‐h‐old larvae were submerged for more than 3 and 4 h, respectively. In the cases of 40‐, 50‐, 60‐ and 70‐h‐old larvae there were no survivors if submergence was more than 5 h. The results show that there is an inverse relationship between submergence period and survival rate: the longer the submergence period, the lesser is the survival rate. This study provides data that are potentially useful in estimating the minimum time since submergence (TSS) of a corpse during forensic investigations.