A Multi-market Comparison of the Intraday Lead-Lag Relations Among Stock Index-Based Spot, Futures and Options.

Using 1-min data, we explore the dynamic variation of the intraday lead-lag relations between stock indices and their derivatives through a comprehensive study with broader coverage of research objectives and methodologies. This paper provides explicit evidence that the futures and options exhibit price leadership over the spot market, and the options is ahead of the futures on most trading days in all three markets. This paper also reports a new finding that the relation between the derivative and its underlying index reverses when the index return has a significantly larger mean value, and the reversal phenomenon is also observed in the relations between the futures and the options, which enriches the empirical results of intraday lead-lag relations. Moreover, these conclusions still hold under the impact of extreme events, e.g., the outbreak of the Covid-19. Finally, we construct a pair trading strategy based on the intraday lead-lag relationships, which can get better performance than the corresponding spot index. Our findings can potentially help regulators understand the price discovery process between the index and its derivatives, and also be of great value for timely adjustment of investors intraday trading strategies.

The ferroxidases LPR1 and LPR2 control iron translocation in the xylem of Arabidopsis plants.

Iron (Fe) deficiency is common in agricultural crops and affects millions of people worldwide. Translocation of Fe in the xylem is a key step for Fe distribution in plants. The mechanism controlling this process remains largely unknown. Here, we report that two Arabidopsis ferroxidases, LPR1 and LPR2, play a crucial and redundant role in controlling Fe translocation in the xylem. LPR1 and LPR2 are mainly localized in the cell walls of xylem vessels and the surrounding cells in roots, leaves, and stems. Knockout of both LPR1 and LPR2 increased the proportion of Fe(II) in the xylem sap, and caused Fe deposition along the vascular bundles especially in the petioles and main veins of leaves, which was alleviated by blocking blue light. The lpr1 lpr2 double mutant displayed constitutive expression of Fe deficiency response genes and overaccumulation of Fe in the roots and mature leaves under Fe-sufficient supply, but Fe deficiency chlorosis in the new leaves and inflorescences under low Fe supply. Moreover, the lpr1 lpr2 double mutant showed lower Fe concentrations in the xylem and phloem saps, and impaired 57Fe translocation along the xylem. In vitro assays showed that Fe(III)-citrate, the main form of Fe in xylem sap, is easily photoreduced to Fe(II)-citrate, which is unstable and prone to adsorption by cell walls. Taken together, these results indicate that LPR1 and LPR2 are required to oxidize Fe(II) and maintain Fe(III)-citrate stability and mobility during xylem translocation against photoreduction. Our study not only uncovers an essential physiological role of LPR1 and LPR2 but also reveals a new mechanism by which plants maintain Fe mobility during long-distance translocation in the xylem.

High-Affinity Sulfate Transporter Sultr1;2 Is a Major Transporter for Cr(VI) Uptake in Plants.

Chromate (Cr[VI]) is a highly phytotoxic contaminant that is ubiquitous in soils. However, how Cr(VI) is taken up by plant roots remains largely unknown. Here, we show that the high-affinity sulfate transporter Sultr1;2 is responsible for Cr(VI) uptake by the roots of Arabidopsis thaliana. Sultr1;2 showed a much higher transport activity for Cr(VI) than Sultr1;1 when expressed in yeast cells. Knockdown of Sultr1;2 expression in Arabidopsis markedly reduced the Cr(VI) uptake rate, whereas knockout of Sultr1;1 had no or little effect. A double-knockout mutant (DKO) of the two genes lost the ability of Cr(VI) uptake almost completely. The Sultr1;2 knockdown mutant or DKO plants displayed higher resistance to Cr(VI) under normal sulfate conditions as a consequence of the lower tissue Cr accumulation. Overexpression of Sultr1;2 substantially increased Cr(VI) uptake with shoot Cr concentration being 1.6-2.0 times higher than that in the wild-type. These results indicate that Sultr1;2 is a major transporter responsible for Cr(VI) uptake in Arabidopsis, while Sultr1;1 plays a negligible role. Taken together, our study has identified a major transporter for Cr(VI) uptake in plants, providing potential strategies for engineering plants with low Cr accumulation and consequently enhanced Cr(VI) resistance and also plants with enhanced accumulation of Cr for the purpose of phytoremediation.