A Beginner's Guide to Osmoprotection by Biostimulants.

Water is indispensable for the life of any organism on Earth. Consequently, osmotic stress due to salinity and drought is the greatest threat to crop productivity. Ongoing climate change includes rising temperatures and less precipitation over large areas of the planet. This is leading to increased vulnerability to the drought conditions that habitually threaten food security in many countries. Such a scenario poses a daunting challenge for scientists: the search for innovative solutions to save water and cultivate under water deficit. A search for formulations including biostimulants capable of improving tolerance to this stress is a promising specific approach. This review updates the most recent state of the art in the field.

Molecular analysis of menadione-induced resistance against biotic stress in Arabidopsis.

Menadione sodium bisulphite (MSB) is a water-soluble derivative of vitamin K3, or menadione, and has been previously demonstrated to function as a plant defence activator against several pathogens in several plant species. However, there are no reports of the role of this vitamin in the induction of resistance in the plant model Arabidopsis thaliana. In the current study, we demonstrate that MSB induces resistance by priming in Arabidopsis against the virulent strain Pseudomonas syringae pv. tomato DC3000 (Pto) without inducing necrosis or visible damage. Changes in gene expression in response to 0.2 mm MSB were analysed in Arabidopsis at 3, 6 and 24 h post-treatment using microarray technology. In general, the treatment with MSB does not correlate with other publicly available data, thus MSB produces a unique molecular footprint. We observed 158 differentially regulated genes among all the possible trends. More up-regulated genes are included in categories such as 'response to stress' than the background, and the behaviour of these genes in different treatments confirms their role in response to biotic and abiotic stress. In addition, there is an over-representation of the G-box in their promoters. Some interesting functions are represented among the individual up-regulated genes, such as glutathione S-transferases, transcription factors (including putative regulators of the G-box) and cytochrome P450s. This work provides a wide insight into the molecular cues underlying the effect of MSB as a plant resistance inducer.

Enhanced carnosic acid levels in two rosemary accessions exposed to cold stress conditions.

Two rosemary accessions were subjected to chilling temperatures in control environmental cabins analyzing their variations in rosmarinic and carnosic acids together with their adaptability to these stress conditions. Cold stressed plants of both accessions showed increases in caffeic acid and carnosic acid concentration levels, while other secondary metabolites such as rosmarinic acid, naringin, cirsimaritin, hispidulin, and carnosol showed different responses in both accessions. In addition, cold stressed plants exhibited significant reductions in chlorophylls, beta-carotene, and violaxanthin levels as well as the maximum quantum yield of PSII in both accessions. Hydrogen peroxide and lipid peroxidation levels showed similar responses in both accessions, which were positively and negatively correlated with rosmarinic and carnosic acids. From these results it is therefore suggested that carnosic acid biosynthesis in rosemary plants is induced by chilling periods. On the other hand, we demonstrate that not all rosemary accessions are equally well adapted to chilling temperatures. In fact, for (one) accession cold treated plants severe losses in chlorophyll, beta-carotene, and even xanthophylls (including zeaxanthin and antheraxanthin) were observed, despite no visual symptoms of leaf injury. More research is needed to understand rosmarinic acid variations in rosemary plants under stress conditions.

Dimerization of ferulic and caffeic acids by purified peroxidase isolated from Bupleurum salicifolium callus culture.

A novel peroxidase that catalyses the transformation of caffeic acid and ferulic acid via oxidative coupling was purified from callus cultures of Bupleurum salicifolium petioles. The enzyme, which was purified over 2,900-fold, is a glycoprotein with a molecular weight of 38,000, determined by SDS/PAGE and gel filtration. The K(m) values obtained were 2.4x10(-4) M for caffeic and 2.6x10(-4) M for ferulic acid, while the K(m) values for H2O2 with caffeic acid was 4x10(-5) M and for H2O2 with ferulic acid was 4.8x10(-4) M. The purified peroxidase exhibits lower activity with typical peroxidase substrates (guaiacol and pyrogallol) than it does with caffeic and ferulic acids, but does not exhibit any activity with other phenylpropanoids tested (cinnamic acid, coumaric acid, and 3,4-dimethoxycinnamic acid).