How does an Al-hyperaccumulator plant respond to a natural field gradient of soil phytoavailable Al?

Ecology as a Tool to Assist Conservation of a Rare and Endemic Mediterranean Plantago Species

Reviewing the ecological studies on the endangered endemic Plantago almogravensis Franco, an Al-hyperaccumulator plant, and combining these with morphological, physiological, biochemical, and molecular data, significant knowledge on the limiting factors that cause its narrow geographical distribution and rarity status is achieved, which can contribute to suited conservation guidelines. Emphasis was given on (i) the major factors limiting P. almogravensis’ ecological niche (biotic and abiotic); (ii) phases of the life cycle and population dynamics; and (iii) and the phylogenetically close taxa (Plantago subulata aggregate) in order to fill the knowledge gaps in the uniqueness of P. almogravensis ecology, its phylogeny, and conservation status. The identification of relevant ecological data and using plant functional (morphological and physiological) traits, as well as genetic attributes, substantiate into a powerful tool to guide protection and conservation measures, usable toward this and other endangered hyperaccumulator plant species. Knowledge of the limitations of this strongly narrowly distributed plant allows for better design of conservation measures and to guide value and investment strategies in order to secure the species’ current area (habitat conservation and reclamation), direct the expansion of the existing population (assisting in populational densification and colonization), and/or grant ex situ conservation (genetic resources conservation).

Subcellular distribution of aluminum associated with differential cell ultra-structure, mineral uptake, and antioxidant enzymes in root of two different Al+3-resistance watermelon cultivars

Crop plants, such as watermelon, suffer from severe Aluminum (Al³⁺)-toxicity in acidic soils with their primary root elongation being first arrested. However, the significance of apoplastic or symplastic Al³⁺-toxicity in watermelon root is scarcely reported. In this work, we identified a medium fruit type (ZJ) and a small fruit type (NBT) as Al⁺³-tolerant and sensitive based on their differential primary root elongation rate respectively, and used them to show the effects of symplastic besides apoplastic Al distribution in the watermelon's root. Although the Al content was higher in the root of NBT than ZJ, Al⁺³ allocated in their apoplast, vacuole and plastid fractions were not significantly different between the two cultivars. Thus, only a few proportion of Al⁺³ differentially distributed in the nucleus and mitochondria corresponded to interesting differential morphological and physiological disorders recorded in the root under Al⁺³-stress. The symplastic amount of Al⁺³ substantially induced the energy efficient catalase pathway in ZJ, and the energy consuming ascorbate peroxidase pathway in NBT. These findings coincided with obvious starch granule visibility in the root ultra-structure of ZJ than NBT, suggesting a differential energy was used in supporting the root elongation and nutrient uptake for Al⁺³-tolerance in the two cultivars. This work provides clues that could be further investigated in the identification of genetic components and molecular mechanisms associated with Al⁺³-tolerance in watermelon.

Nickel phytoremediation potential of the Mediterranean Alyssoides utriculata (L.) Medik

This study investigated the accumulation and distribution of nickel in the leaves and roots of the Mediterranean shrub Alyssoides utriculata to assess its potential use in phytoremediation of Ni contaminated soils. Total (AAS and ICP-MS) Ni, Ca and Mg contents were analyzed in the plants and related to their bioavailability (in EDTA) in serpentine and non-serpentine soils. To find the relationships between the soil available Ni and the Ni content of this species, we also evaluated possible interactions with Ca and Mg. The bioaccumulation factor (BF) and the translocation factor (TF) were determined to assess the tolerance strategies developed by A. utriculata and to evaluate its potential for phytoextraction or phytostabilization. The leaf Ni is higher than 1000 μg g(-1) which categorizes the species as a Ni-hyperaccumulator and a great candidate for Ni-phytoextraction purposes. In addition to the accumulation of Ni, the leaf Mg is also correlated with soil bioavailable concentrations. The Ca uptake and translocation were significantly lower in serpentine plants (higher Ni), as such, the leaf Ca is probably greatly influenced either by the soil's Ni or the soil Ca/Mg ratio. The BFs and TFs are strongly higher than 1 and generally did not significantly differed between plants from serpentine (higher Ni) and non-serpentine soils (lower Ni). The present study highlights for the first time that A. utriculata could be suitable for cleaning Ni-contaminated areas and provides a contribution to the very small volume of data available on the potential use of native Mediterranean plant species from contaminated sites in phytoremediation technologies.

Aluminum inhibits root growth and induces hydrogen peroxide accumulation in Plantago algarbiensis and P. almogravensis seedlings

We have evaluated the impact of aluminum (Al) on germination, relative root growth, Al accumulation in roots tips, H2O2 levels, plasma membrane integrity, pigment levels, protein content, and the activities of superoxide dismutase (SOD) and catalase (CAT) in seedlings of the endangered Portuguese species Plantago algarbiensis and Plantago almogravensis. We found that up to 400 μM Al had no impact on the germination percentage in either species but inhibited root growth in a concentration-dependent manner (more severely in P. algarbiensis). Al accumulation in the root tips of both species was concentration dependent up to 200 μM but declined thereafter despite the absence of membrane damage. We observed a concentration-dependent induction of SOD activity but no change in CAT activity resulting in the accumulation of H2O2 (a known growth inhibitor), although its impact in P. almogravensis may be partially ameliorated by the accumulation of carotenoid pigments. Our data suggest an association between Al uptake, H2O2 production, and the inhibition of root growth during early seedling development in P. algarbiensis and P. almogravensis, although the latter is more tolerant towards higher concentrations of the metal.