Accumulation of livestock manure-derived heavy metals in the Hexi Corridor oasis agricultural alkaline soil and bioavailability to Chinese cabbage (Brassica pekinensis L.) after 4-year continuous application

Hexi Corridor is one of the most important base of vegetable producing areas in China. Livestock manure (LM) applied to agricultural field could lead to soil heavy metal (HM) pollution. Previous studies have focused on HM pollution following LM application in acidic polluted soils; however, fewer studies have been conducted in alkaline unpolluted soils. A 4-year field vegetable production experiment was conducted using pig manure (PM) and chicken manure (CM) at five application rates (0, 15, 30, 45, and 60 t ha-1) to elucidate potential risks of HMs in an alkaline unpolluted soil in the Hexi Corridor oasis agricultural area and HM uptake by Chinese cabbage. The results showed that LM application caused a significant build-up of Cu, Zn, Pb, Cd, and Ni content in topsoil by 30.6-99.7%, 11.4-51.7%, 1.4-31.3%, 5.6-44.9%, 14%-40.8%, respectively. The Cd, Cu, Zn could potentially exceed the soil threshold in next 8-65 years after 15-60 t ha-1 LM application. Under LM treatment, the soil DTPA-extractable Cu, Zn, Fe, the acid-extractable fraction of Cu, Zn, Fe, Cd, Ni, and the Oxidable fraction of Cu, Zn, Fe, Mn, Cd, Ni significantly increased, but the DTPA-extractable Pb, Cd, the acid-extractable fraction of Pb, and the reducible fraction of Cd significantly decreased. Cu and Zn could migrate to the deeper soil and relatively increase in DTPA-extracted Cu, Zn were found in 20-40 cm soil depth after LM application. The pH and SOM could influence the bioavailability of HMs in soil. The bioaccumulation factor and transfer factor (TF) values were <1 except Mn (TF > 1). HMs in leaf did not approach the threshold for HM toxicity due to the "dilution effect". Recommend the type of manure was the PM and the annual PM application rate was 30 t ha-1 to ensure a 20-year period of clean production in alkaline unpolluted Fluvo-aqiuc vegetable soils.

Four plasma membrane-localized MGR transporters mediate xylem Mg2+ loading for root-to-shoot Mg2+ translocation in Arabidopsis

Magnesium (Mg²⁺), an essential structural component of chlorophyll, is absorbed from the soil by roots and transported to shoots to support photosynthesis in plants. However, the molecular mechanisms underlying root-to-shoot Mg²⁺ translocation remain largely unknown. We describe here the identification of four plasma membrane (PM)-localized transporters, named Mg²⁺ release transporters (MGRs), that are critical for root-to-shoot Mg transport in Arabidopsis. Functional complementation assays in a Mg²⁺-uptake-deficient bacterial strain confirmed that these MGRs conduct Mg²⁺ transport. PM-localized MGRs (MGR4, MGR5, MGR6, and MGR7) were expressed primarily in root stellar cells and participated in the xylem loading step of the long-distance Mg²⁺ transport process. In particular, MGR4 and MGR6 played a major role in shoot Mg homeostasis, as their loss-of-function mutants were hypersensitive to low Mg²⁺ but tolerant to high Mg²⁺ conditions. Reciprocal grafting analysis further demonstrated that MGR4 functions in the root to determine shoot Mg²⁺ accumulation and physiological phenotypes caused by both low- and high-Mg²⁺ stress. Taken together, our study has identified the long-sought transporters responsible for root-to-shoot Mg²⁺ translocation in plants.

Conserved mechanism for vacuolar magnesium sequestration in yeast and plant cells

Magnesium (Mg²⁺) is an essential nutrient for all life forms. In fungal and plant cells, the majority of Mg²⁺ is stored in the vacuole but mechanisms for Mg²⁺ transport into the vacuolar store are not fully understood. Here we demonstrate that members of ancient conserved domain proteins (ACDPs) from Saccharomyces cerevisiae and Arabidopsis thaliana function in vacuolar Mg²⁺ sequestration that enables plant and yeast cells to cope with high levels of external Mg²⁺. We show that the yeast genome (as well as other fungal genomes) harbour a single ACDP homologue, referred to as MAM3, that functions specifically in vacuolar Mg²⁺ accumulation and is essential for tolerance to high Mg. In parallel, vacuolar ACDP homologues were identified from Arabidopsis and shown to complement the yeast mutant mam3Δ. An Arabidopsis mutant lacking one of the vacuolar ACDP homologues displayed hypersensitivity to high-Mg conditions and accumulated less Mg in the vacuole compared with the wild type. Taken together, our results suggest that conserved transporters mediate vacuolar Mg²⁺ sequestration in fungal and plant cells to maintain cellular Mg²⁺ homeostasis in response to fluctuating Mg²⁺ levels in the environment.

Characterization of the complete chloroplast genome of Murraya exotica (Rutaceae) from Yunnan Province, China

Murraya exotica L. (Rutaceae) has important horticultural and medicinal values. Here, we reported the complete chloroplast (cp) genome of M. exotica using the next-generation sequencing method. The cp genome is 160,179 bp in length, including a large single-copy region (LSC, 87,726 bp), a small single-copy region (SSC, 18,465 bp), and a pair of inverted repeats (IR) regions 26,994 bp. A maximum-likelihood phylogenomic analysis showed that M. exotica was sister to Murraya paniculate. These findings will provide useful information for further investigation of cp genome evolution in Murraya.

Plant Membrane Transport Research in the Post-genomic Era

Membrane transport processes are indispensable for many aspects of plant physiology including mineral nutrition, solute storage, cell metabolism, cell signaling, osmoregulation, cell growth, and stress responses. Completion of genome sequencing in diverse plant species and the development of multiple genomic tools have marked a new era in understanding plant membrane transport at the mechanistic level. Genes coding for a galaxy of pumps, channels, and carriers that facilitate various membrane transport processes have been identified while multiple approaches are developed to dissect the physiological roles as well as to define the transport capacities of these transport systems. Furthermore, signaling networks dictating the membrane transport processes are established to fully understand the regulatory mechanisms. Here, we review recent research progress in the discovery and characterization of the components in plant membrane transport that take advantage of plant genomic resources and other experimental tools. We also provide our perspectives for future studies in the field.