No abstract

This study investigates the effect of added silicon (Si, as sodium silicate) on water status–related parameters, osmolytes accumulation and gas exchange in the leaves of hydroponically grown upland rice seedlings under polyethylene glycol (PEG‐6000)‐induced water stress, the aims being to explore whether Si has been involved in osmotic adjustment (OA) in upland rice plants. Fifty‐five‐day‐old seedlings were subjected to 8.5 % (m/v) PEG‐6000 treatment without or with 2.5 mm Si for 7 days. The results showed that addition of Si to culture solution could partially improve total, free, and bound water contents in both leaves and roots, which were all decreased under water stress. Application of Si increased water potential (Ψw) and osmotic potential (Ψπ) in both roots and leaves while maintained higher turgor pressure (Ψp), in comparison with the plants without Si application. Added Si also stimulated the active accumulation of some osmolytes in both leaves and roots of stressed plants, which suggested enhanced OA ability. Analysis of gas exchange in leaves showed that net photosynthetic rate, transpiration, and water‐use efficiency (WUE) were decreased under water stress, whereas application of Si enhanced the photosynthesis and improved the WUE. This study suggests that PEG‐induced water stress in rice could be partially alleviated by addition of Si. This alleviative effect was partially attributable to enhanced OA ability by means of active accumulation of osmolytes.

The present study assesses the effects of 5‐aminolevulinic acid (ALA, 0, 0.1, 1 and 10 mg l−1) on the growth of oilseed rape (Brassica napus L. cv. ZS758) seedlings under water‐deficit stress induced by polyethylene glycol (PEG 6000, 0 and −0.3 MPa). Water‐deficit stress imposed negative effects on seedling growth by reducing shoot biomass, cotyledon water potential, chlorophyll content and non‐enzymatic antioxidants (glutathione and ascorbic acid) levels. On the other hand, water‐deficit stress enhanced the malondialdehyde (MDA) content, reactive oxygen species (ROS) production, enzymatic antioxidants activities, reduced/oxidized glutathione ratio (GSH/GSSG) and reduced/oxidized ascorbic acid (ASA/DHA) ratio in seedlings. Application of ALA at lower dosages (0.1 and 1 mg l−1) improved shoot weight and chlorophyll contents, and decreased MDA in rape seedlings, whereas moderately higher dosage of ALA (10 mg l−1) hampered the growth. The study also indicated that 1 mg l−1 ALA improved chlorophyll content, but reduced MDA content and ROS production significantly under water‐deficit stress. Lower dosages of ALA (0.1 and 1 mg l−1) also enhanced GSH/GSSG and ASA/DHA as compared to the seedlings under water‐deficit stress. The antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase and superoxide dismutase) enhanced their activities remarkably with 1 mg l−1 ALA treatment under water‐deficit stress. It was also revealed that 1 mg l−1 ALA treatment alone induced the expression of APX, CAT and GR substantially and under water‐deficit stress conditions ALA treatment could induce the expression of POD, CAT and GR to a certain degree. These results indicated that 0.1–1 mg l−1 ALA could enhance the water‐deficit stress tolerance of oilseed seedlings through improving the biomass accumulation, maintaining a relative high ratio of GSH/GSSG and ASA/DHA, enhancing the activities of the specific antioxidant enzymes and inducing the expression of the specific antioxidant enzyme genes.

Plants combat drought stress by coordinating various metabolic enzymes, and endogenous phytohormones, such as indole acetic acid (IAA) and abscisic acid (ABA). In the present study, 37-day-old wheat seedlings were subjected to the Hoagland solution with 20% PEG for 7 days (to create the artificial osmotic stress environment) in the greenhouse, and were supplemented with an optimized concentration (1.0 mM) of silicon (Si) to alleviate the negative effects of former stress on physiological, biochemical and phytohormones contents. Exogenous Si significantly improved plant growth parameters under osmotic stress compared to PEG treatment alone (the increase was up to 6 and 9% for shoot and root fresh weight, 4 and 12% for shoot and root dry weight, respectively). Moreover, Si significantly decreased the HO, MDA contents, electrolyte leakage, antioxidant enzyme activity (POD), and mineral contents (K and Ca) under osmotic stress but markedly increased the ascorbic acid(AsA), soluble sugar and mineral (Mg and Si) contents. Interestingly, Si application under water-deficit stress differently modulated the endogenous levels of ABA, IAA and JA in wheat plants compared to PEG treatment alone. This study suggests that exogenous Si improves the plant growth by modulating the nutrient (Na, Mg and Si) uptake and phytohormone levels in wheat under water-deficit stress.

Lanthipeptides are a class of cyclic peptides characterized by the presence of one or more lanthionine (Lan) or methyllanthionine (MeLan) thioether rings. These cross-links are produced by α,β-unsaturation of Ser or Thr residues in peptide substrates by dehydration, followed by a Michael-type conjugate addition of Cys residues onto the dehydroamino acids. Lanthipeptides may be broadly classified into at least five different classes, and the biosynthesis of classes I–IV lanthipeptides requires catalysis by LanC cyclases that control both the site-specificity and the stereochemistry of the conjugate addition. In contrast, there are no current examples of LanCs that occur in class V biosynthetic clusters, despite the presence of lanthionine rings in these compounds. In this work, bioinformatics-guided co-occurrence analysis identifies more than 240 putative class V lanthipeptide clusters that contain a LanC cyclase. Reconstitution studies demonstrate that the cyclase-catalyzed product is notably distinct from the product formed spontaneously. Stereochemical analysis shows that the cyclase diverts the final product to a configuration that is distinct from one that is energetically favored. Structural characterization of the final product by multi-dimensional NMR spectroscopy reveals that it forms a helical stapled peptide. Mutational analysis identified a plausible order for cyclization and suggests that enzymatic rerouting to the final structure is largely directed by the construction of the first lanthionine ring. These studies show that lanthipeptide cyclases are needed for the biosynthesis of some constrained peptides, the formations of which would otherwise be energetically unfavored.