Comparative study on the toxicity of pyrethroids, α-cypermethrin and deltamethrin to Ceriodaphnia dubia.

Two synthetic pyrethroid pesticides, α-cypermethrin and deltamethrin were investigated as potential toxic contaminants. The acute and chronic bioassays were conducted using Ceriodaphnia dubia. The toxicity of α-cypermethrin and deltamethrin to C. dubia increased with increasing concentrations and exposure time. C. dubia was three times more sensitive to deltamethrin than to α-cypermethrin with 48-h EC(50) of 0.06 µg/L and 0.23 µg/L, respectively. The chronic EC(50) values for α-cypermethrin and deltamethrin were 97.8 and 34.7 ng/L, respectively. Eight-day growth of Ceriodaphnia neonates during chronic exposures was the most sensitive endpoint measured in comparison to the endpoints of survival and number of neonates produced. To gain a better understanding of the link between acute and chronic toxicity, the acute-to chronic ratios (ACRs) were also calculated for survival, growth and reproduction endpoints. ACRs varied between 11 and 224 for the two pyrethroids. These results suggest that at environmentally relevant low concentrations, α-cypermethrin and deltamethrin could have significant adverse effects on the survival, reproduction and growth of C. dubia.

RETARDED PALEA1 controls palea development and floral zygomorphy in rice.

Poaceae, one of the largest flowering plant families in angiosperms, evolved distinct inflorescence and flower morphology diverging from eudicots and other monocots. However, the mechanism underlying the specification of flower morphology in grasses remains unclear. Here we show that floral zygomorphy along the lemma-palea axis in rice (Oryza sativa) is partially or indirectly determined by the CYCLOIDEA (CYC)-like homolog RETARDED PALEA1 (REP1), which regulates palea identity and development. The REP1 gene is only expressed in palea primordium during early flower development, but during later floral stages is radially dispersed in stamens and the vascular bundles of the lemma and palea. The development of palea is significantly retarded in the rep1 mutant and its palea has five vascular bundles, which is similar to the vascular pattern of the wild-type lemma. Furthermore, ectopic expression of REP1 caused the asymmetrical overdifferentiation of the palea cells, altering their floral asymmetry. This work therefore extends the function of the TCP gene family members in defining the diversification of floral morphology in grasses and suggests that a common conserved mechanism controlling floral zygomorphy by CYC-like genes exists in both eudicots and the grasses.

[Genetic analysis and mapping of the rice leafy-hull mutant Oslh].

Oslh (lh=leafy hull), in the japonica cultivar 9522 background, a mutant of Oryza sativa L. spp. japonica cv. 9522 identified from an M(2) population, was mutagenized by irradiation with (60)Co gamma-ray. The Oslh mutant plants flowered about 15 days later than the wild-type plants (Fig.1e). The paleas, lemmas and lodicules of the flowers of Oslh mutant were transformed into leaf-like structures (Fig.1b, d). Genetic analysis of the F(2) progeny from a cross between the Oslh mutant and wild-type japonica cv. 9522 revealed that the Oslh mutant arouse from a single recessive nuclear gene mutation of the cv. 9522. To map the Oslh locus, an F(2) population generated by crossing between Oslh (japonica) mutant and Guangluai4 (indica) was analyzed. The Oslh locus was mapped to the long arm of rice chromosome 3, between a SSR marker RM5475 and an InDel marker GY305, 2.9 and 1.5 cM away from these two markers respectively (Fig.4). These results are useful for further cloning and functional analysis of the OsLH gene.