Effects of LaCl3 on photosynthesis and the accumulation of tanshinones and salvianolic acids in Salvia miltiorrhiza seedlings

Smoke-Isolated Karrikins Stimulated Tanshinones Biosynthesis in Salvia miltiorrhiza through Endogenous Nitric Oxide and Jasmonic Acid

Although smoke-isolated karrikins (KAR₁) could regulate secondary metabolism in medicinal plants, the signal transduction mechanism has not been reported. This study highlights the influence of KAR₁ on tanshinone I (T-I) production in Salvia miltiorrhiza and the involved signal molecules. Results showed KAR₁-induced generation of nitric oxide (NO), jasmonic acid (JA) and T-I in S. miltiorrhiza hairy root. KAR₁-induced increase of T-I was suppressed by NO-specific scavenger (cPTIO) and NOS inhibitors (PBITU); JA synthesis inhibitor (SHAM) and JA synthesis inhibitor (PrGall), which indicated that NO and JA play essential roles in KAR₁-induced T-I. NO inhibitors inhibited KAR₁-induced generation of NO and JA, suggesting NO was located upstream of JA signal pathway. NO-induced T-I production was inhibited by SHAM and PrGall, implying JA participated in transmitting signal NO to T-I accumulation. In other words, NO mediated the KAR₁-induced T-I production through a JA-dependent signaling pathway. The results helped us understand the signal transduction mechanism involved in KAR₁-induced T-I production and provided helpful information for the production of S. miltiorrhiza hairy root.

Hormetic dose responses induced by lanthanum in plants

Rare earth elements (REEs) have recently received particular attention due to their accumulation in the environment. Such heightened recognition prompted our evaluation of the possible occurrence of La-induced plant hormesis in the peer-reviewed literature. This study revealed 703 La-induced hormetic concentration/dose responses in plants, which were quantitatively and qualitatively assessed. The maximum (MAX) biological response to low La concentrations/doses is commonly below 150% of control response, with a geometric mean of 142% at 56 μM (geometric mean). The geometric mean concentration of the no-observed-adverse-effect-level (NOAEL) was 249 μM. The MAX:NOAEL distance was commonly below 5-fold, with a geometric mean of 4.5-fold. Hormetic concentration/dose responses varied as per the growth substrate pH, number of concentrations/doses below the NOAEL, and time window. These results provide a unique insight into the effects of low doses of La on plant growth, as well as offer means for improving experimental designs to assess low dose effects.

Combined effects of simulated acid rain and lanthanum chloride on chloroplast structure and functional elements in rice

Acid rain and rare earth element (REE) pollution exist simultaneously in many agricultural regions. However, how REE pollution and acid rain affect plant growth in combination remains largely unknown. In this study, the combined effects of simulated acid rain and lanthanum chloride (LaCl3) on chloroplast morphology, chloroplast ultrastructure, functional element contents, chlorophyll content, and the net photosynthetic rate (P n) in rice (Oryza sativa) were investigated by simulating acid rain and rare earth pollution. Under the combined treatment of simulated acid rain at pH 4.5 and 0.08 mM LaCl3, the chloroplast membrane was smooth, proteins on this membrane were uniform, chloroplast structure was integrated, and the thylakoids were orderly arranged, and simulated acid rain and LaCl3 exhibited a mild antagonistic effect; the Mg, Ca, Mn contents, the chlorophyll content, and the P n increased under this combined treatment, with a synergistic effect of simulated acid rain and LaCl3. Under other combined treatments of simulated acid rain and LaCl3, the chloroplast membrane surface was uneven, a clear "hole" was observed on the surface of chloroplasts, and the thylakoids were dissolved and loose; and the P n and contents of functional elements (P, Mg, K, Ca, Mn, Fe, Ni, Cu, Zn and Mo) and chlorophyll decreased. Under these combined treatments, simulated acid rain and LaCl3 exhibited a synergistic effect. Based on the above results, a model of the combined effects of simulated acid rain and LaCl3 on plant photosynthesis was established in order to reveal the combined effects on plant photosynthesis, especially on the photosynthetic organelle-chloroplast. Our results would provide some references for further understanding the mechanism of the combined effects of simulated acid rain and LaCl3 on plant photosynthesis.

Effect and Accumulation of Lanthanum on the Growth and Physiological Activities of Cymbopogon Flexuosus (Nees Ex Steud.)W.Watson

The rare earth elements are a set of seventeen chemical elements which involve the lanthanide series from Lanthanum (La), Tolutetium (Lu), Scandium (Sc), and Yttrium (Y) in the periodic table. Even if Rare Earth Elements are used widely in industry and agriculture in China as well as India for a long time, there has been increasing interest in the application of REEs to plants in recent years. In this paper, we discussed the effect of REE on growth and physiological activities of the plant. By compilation and investigation of these data, we found that REEs have promoting impact at certain concentration. An increase in Chlorophyll, enzymes and protein content further indicated the stimulating effect of La on physiological activities of the selected plants. Depending on the results of this preliminary investigation we can say that a new REE hyperaccumulator, Cymbopogon flexuosus (Lemon grass), was discovered which could accumulate Lanthanum is 20.725 mg g-1 and 25.625 mg g-1 dry mass in root and shoot part respectively under natural growth conditions. Advanced research should be invested regarding the impacts of REEs on yields of cultivated plants.

Jasmonic acid (JA) acts as a signal molecule in LaCl(3)-induced baicalin synthesis in Scutellaria baicalensis seedlings

Rare earth elements (REEs) have been widely used to increase accumulation of biomass and secondary metabolites in medicinal plants in China. However, very few studies have investigated how REEs mediate secondary metabolism synthesis in medicinal plants. Lanthanum (La), an important REE, is known to improve the accumulation of secondary metabolites in medicinal plants and is widely distributed in China. However, few studies have evaluated the signal transduction leading to La-induced secondary metabolism in medicinal plants. In this study, LaCl(3) treatment-induced multiple responses in Scutellaria baicalensis seedlings, including the rapid generation of jasmonic acid (JA), sequentially followed by the enhancement of baicalin production. Direct application of JA also promoted the synthesis of baicalin in the absence of LaCl(3). LaCl(3)-induced baicalin synthesis was blocked by two different JA synthesis inhibitors. Our results showed that JA acts as a signal component within the signaling system leading to La-induced baicalin synthesis in S. baicalensis seedlings.