Yimin Liang

Arbuscular mycorrhizal fungi are considered as a potential biotechnological tool for improving phytostabilization efficiency and plant tolerance to heavy metal-contaminated soils. However, the mechanisms through which AMF help to alleviate metal toxicity in plants are still poorly understood. A greenhouse experiment was conducted to evaluate the effects of two AMF species on the growth, Pb accumulation, photosynthesis and antioxidant enzyme activities of a leguminous tree at Pb addition levels of 0, 500, 1000 and 2000 mg kg-1 soil. AMF symbiosis decreased Pb concentrations in the leaves and promoted the accumulation of biomass as well as photosynthetic pigment contents. Mycorrhizal plants had higher gas exchange capacity, non-photochemistry efficiency, and photochemistry efficiency compared with non-mycorrhizal plants. The enzymatic activities of superoxide dismutase, ascorbate peroxidases and glutathione peroxidase were enhanced, and hydrogen peroxide and malondialdehyde contents were reduced in mycorrhizal plants. These findings suggested that AMF symbiosis could protect plants by alleviating cellular oxidative damage in response to Pb stress. Furthermore, mycorrhizal dependency on plants increased with increasing Pb stress levels, indicating that AMF inoculation likely played a more important role in plant Pb tolerance in heavily contaminated soils. Overall, both F. mosseae and R. intraradices were able to maintain efficient symbiosis with R. pseudoacacia in Pb polluted soils. AMF symbiosis can improve photosynthesis and reactive oxygen species scavenging capabilities and decrease Pb concentrations in leaves to alleviate Pb toxicity in R. pseudoacacia. Our results suggest that the application of the two AMF species associated with R. pseudoacacia could be a promising strategy for enhancing the phytostabilization efficiency of Pb contaminated soils.

Strong Turing Determinacy, or ${\mathrm {sTD}}$, is the statement that for every set A of reals, if $\forall x\exists y\geq _T x (y\in A)$, then there is a pointed set $P\subseteq A$. We prove the following consequences of Turing Determinacy ( ${\mathrm {TD}}$ ) and ${\mathrm {sTD}}$ over ${\mathrm {ZF}}$ —the Zermelo–Fraenkel axiomatic set theory without the Axiom of Choice: (1) ${\mathrm {ZF}}+{\mathrm {TD}}$ implies $\mathrm {wDC}_{\mathbb {R}}$ —a weaker version of $\mathrm {DC}_{\mathbb {R}}$.(2) ${\mathrm {ZF}}+{\mathrm {sTD}}$ implies that every set of reals is measurable and has Baire property.(3) ${\mathrm {ZF}}+{\mathrm {sTD}}$ implies that every uncountable set of reals has a perfect subset.(4) ${\mathrm {ZF}}+{\mathrm {sTD}}$ implies that for every set of reals A and every $\epsilon>0$ :(a)There is a closed set $F\subseteq A$ such that $\mathrm {Dim_H}(F)\geq \mathrm {Dim_H}(A)-\epsilon $, where $\mathrm {Dim_H}$ is the Hausdorff dimension.(b)There is a closed set $F\subseteq A$ such that $\mathrm {Dim_P}(F)\geq \mathrm {Dim_P}(A)-\epsilon $, where $\mathrm {Dim_P}$ is the packing dimension.

For a subgroup A of ( R, + ) $(\mathbb {R},+)$ left parenthesis double struck upper R comma plus right parenthesis and a real x, define A + x A = { a + x b : a, b ∈ A } $A+xA=\{ a + x b : a, b \in A \}$ upper A plus x upper A equals left brace a plus x b colon a comma b element of upper A right brace and X A = { x ∈ R : A + x A = R } $X_A=\{x\in \mathbb {R}:A + x A=\mathbb {R}\}$ upper X Subscript upper A Baseline equals StartSet x element of double struck upper R colon upper A plus x upper A equals double struck upper R EndSet. We show that there is an F σ $F_\sigma $ upper F Subscript sigma subgroup A of ( R, + ) $(\mathbb {R},+)$ left parenthesis double struck upper R comma plus right parenthesis such that dim H ( A ) ≤ 1 2 $\mathrm {dim_H} (A) \le \frac {1}{2}$ dimension Subscript normal upper H Baseline left parenthesis upper A right parenthesis less than or equals one half and X A ≠ ∅ $X_A \neq \emptyset $ upper X Subscript upper A Baseline not equals normal empty set. However, if A ⊆ R $A \subseteq \mathbb {R}$ upper A subset of or equal to double struck upper R is a subring of R $\mathbb {R}$ double struck upper R and X A ≠ ∅ $X_A \neq \emptyset $ upper X Subscript upper A Baseline not equals normal empty set, then A = R $A =\mathbb {R}$ upper A equals double struck upper R. Moreover, assuming the continuum hypothesis, there is a subgroup A of ( R, + ) $(\mathbb {R},+)$ left parenthesis double struck upper R comma plus right parenthesis with dim H ( A ) = 0 $\mathrm {dim_H} (A) = 0$ dimension Subscript normal upper H Baseline left parenthesis upper A right parenthesis equals 0 such that X A = R ∖ Q $X_A =\mathbb {R}\backslash \mathbb {Q}$ upper X Subscript upper A Baseline equals double struck upper R minus double struck upper Q. The proof of this theorem combines several techniques in recursion theory and algorithmic dimension. Several other theorems on analytic subgroups and subfields of the reals are presented. We also discuss some of these results in the p-adics.

Tight control and multifactorial regulation of gene expression are important challenges in genetic engineering and are critical for the development of regulatory circuits. Meeting these challenges will facilitate transgene expression regulation and support the fine-tuning of metabolic pathways to avoid the accumulation of undesired intermediates. By employing the endoribonuclease Csy4 and its recognition sequence from Pseudomonas aeruginosa and manipulating 5'UTR of mRNA, we developed a two-component expression-repression system to tightly control synthesis of transgene products. We demonstrated that this regulatory device was functional in monocotyledonous and dicotyledonous plant species, and showed that it can be used to repress transgene expression by >400-fold and to synchronize transgene repression. In addition to tissue-specific transgene repression, this system offers stimuli-dependent expression control. Using a bioinformatics approach, we identified 54 orthologous systems from various bacteria, and then validated in planta the activity for a few of those systems, demonstrating the potential diversity of such a two-component repressor system.