Root high-affinity K+ and Cs+ uptake and plant fertility in tomato plants are dependent on the activity of the high-affinity K+ transporter SlHAK5.

Root K+ acquisition is a key process for plant growth and development, extensively studied in the model plant Arabidopsis thaliana. Because important differences may exist among species, translational research supported by specific studies is needed in crops such as tomato. Here we present a reverse genetics study to demonstrate the role of the SlHAK5 K+ transporter in tomato K+ nutrition, Cs+ accumulation and its fertility. slhak5 KO lines, generated by CRISPR-Cas edition, were characterized in growth experiments, Rb+ and Cs+ uptake tests and root cells K+ -induced plasma membrane depolarizations. Pollen viability and its K+ accumulation capacity were estimated by using the K+ -sensitive dye Ion Potassium Green 4. SlHAK5 is the major system for high-affinity root K+ uptake required for plant growth at low K+ , even in the presence of salinity. It also constitutes a pathway for Cs+ entry in tomato plants with a strong impact on fruit Cs+ accumulation. SlHAK5 also contributes to pollen K+ uptake and viability and its absence produces almost seedless fruits. Knowledge gained into SlHAK5 can serve as a model for other crops with fleshy fruits and it can help to generate tools to develop low Cs+ or seedless fruits crops.

Arabidopsis K+ transporter HAK5-mediated high-affinity root K+ uptake is regulated by protein kinases CIPK1 and CIPK9.

The high-affinity K+ transporter HAK5 is the major contributor to root K+ uptake from dilute solutions in K+-starved Arabidopsis plants. Its functionality is tightly regulated and its activity is enhanced under K+ starvation by the transcriptional induction of the AtHAK5 gene, and by the activation of the transporter via the AtCBL1-AtCIPK23 complex. In the present study, the 26 members of the Arabidopsis CIPK protein kinase family were screened in yeast for their capacity to activate HAK5-mediated K+ uptake. Among them, AtCIPK1 was the most efficient activator of AtHAK5. In addition, AtCIPK9, previously reported to participate in K+ homeostasis, also activated the transporter. In roots, the genes encoding AtCIPK1 and AtCIPK9 were induced by K+ deprivation and atcipk1 and atcipk9 Arabidopsis KO mutants showed a reduced AtHAK5-mediated Rb+ uptake. Activation of AtHAK5 by AtCIPK1 did not occur under hyperosmotic stress conditions, where AtCIPK1 function has been shown to be required to maintain plant growth. Taken together, our data contribute to the identification of the complex regulatory networks that control the high-affinity K+ transporter AtHAK5 and root K+ uptake.

Chemical Composition of Wild Collected and Cultivated Edible Plants (Sonchus oleraceus L. and Sonchus tenerrimus L.).

The present work investigates the nutritional and bioactive composition, as well as the organoleptic and sensory properties, of S. oleraceus and S. tenerrimus, two wild plant species traditionally used in the gastronomy of the Mediterranean area. Additionally, the effect of cultivation on leaf composition was assessed to explore their potential for large-scale production and commercialization from the point of view of possible losses or gains in quality. Both species were characterized as a good source of bioactive compounds, such as vitamins, pro-vitamins and carotenoids, with health-promoting and antioxidant properties that are highly appreciated. The sensory profile revealed a good general acceptance of S. oleraceus and S. tenerrimus, indicating that they could be included in the diet. Although the cultivation of S. oleraceus resulted in a decrease in the concentration of phenolic compounds when compared to wild-harvested plants, the opposite occurred for vitamin C. In S. tenerrimus, cultivation also increased the concentration of other compounds with important nutritional and healthy properties, such as sugars, organic acids and ß-carotene. The results of the composition, organoleptic and sensory properties of S. oleraceus and S. tenerrimus support the idea of their potential to be used as edible leafy vegetables and as promising assets for functional foods.

Phenolic and Carotenoid Profile of Lamb's Lettuce and Improvement of the Bioactive Content by Preharvest Conditions.

This study characterizes the phenolic, carotenoid and chlorophyll profile of lamb's lettuce, a vegetable whose consumption in salads and ready-to-eat products is constantly growing. The MS/MS analysis allowed the identification of thirty-five phenolic compounds including hydroxybenzoic and hydroxycinnamic acids, flavanones, flavanols and flavanones, many of which are reported here in lamb's lettuce for the first time. Chlorogenic acid was the principal phenolic compound found (57.1% of the total phenolic concentration) followed by its isomer cis-5-caffeoylquinic. Other major phenolic compounds were also hydroxycinnamic acids (coumaroylquinic, dicaffeoylquinic and feruloylquinic acids) as well as the flavones luteolin-7-rutinoside, diosmetin-apiosylglucoside and diosmin. Regarding carotenoids, seven xanthophyll and four carotenes, among which ß-carotene and lutein were the major compounds, were detected from their UV-Vis absorption spectrum. In addition, chlorophylls a and b, their isomers and derivatives (pheophytin) were identified. Preharvest factors such as reduced fertilization levels or salinity increased some secondary metabolites, highlighting the importance of these factors on the final nutritional value of plant foods. Lamb's lettuce was seen to be a good potential source of bioactive compounds, and fertilization management might be considered a useful tool for increasing its nutritional interest.

High Ca(2+) reverts the repression of high-affinity K(+) uptake produced by Na(+) in Solanum lycopersycum L. (var. microtom) plants.

Potassium (K(+)) is an essential nutrient for plants which is acquired by plant roots through the operation of specific transport systems. Abiotic stress conditions such as salinity impair K(+) nutrition because, in addition to other effects, high salt concentrations in the solution bathing the roots inhibit K(+) uptake systems. This detrimental effect of salinity is exacerbated when external K(+) is very low and the only system capable of mediating K(+) uptake is one with high-affinity for K(+), as that mediated by transporters of the HAK5 type. Increasing external Ca(2+) has been shown to improve K(+) nutrition under salinity and, although the specific mechanisms for this beneficial effect are largely unknown, they are beginning to be understood. The genes encoding the HAK5 transporters are induced by K(+) starvation and repressed by long-term exposure to high Na(+). This occurs in parallel with the hyperpolarization and depolarization of root cell membrane potential. In the present study it is shown in tomato plants that the presence of high Ca(2+) during the K(+) starvation period that leads to LeHAK5 induction, counteracts the repression exerted by high Na(+). High Ca(2+) reduces the Na(+)-induced plasma membrane depolarization of root cells, resorting one of the putative first steps in the low-K(+) signal cascade. This allows proper LeHAK5 expression and functional high-affinity K(+) uptake at the roots. Thus, the maintenance of HAK5-mediated K(+) nutrition under salinity by high Ca(2+) can be regarded as a specific beneficial effect of Ca(2+) contributing to salt tolerance in plants.