Physiological responses of the hybrid larch (Larix × eurolepis Henry) to cadmium exposure and distribution of cadmium in plantlets

Abstract

Phytoextraction of Cd is a growing biotechnology although we currently know few Cd hyperaccumulators, i.e., plant species able to accumulate at least 0.1 mg Cd g(-1) dry weight in aerial organs. Owing their deep root system and high biomass, trees are more and more preferred to herbaceous species for phytoextraction. Assuming that conifers could be relevant models under cold climates, we investigated cadmium tolerance of the hybrid larch Larix × eurolepis Henry (Larix decidua × Larix kaempferi) and the efficiency of this species to store this metal. In vitro grown larches were chosen in order to reduce time of exposure and to more rapidly evaluate their potential efficiency to accumulate Cd. One-month-old plantlets were exposed for 2 and 4 weeks to 250 and 500 μM Cd. Results showed that they tolerated a 4-week exposure to 250 μM Cd, whereas the content of photosynthetic pigment strongly dropped in plantlets growing in the presence of 500 μM Cd. In the presence of 250 μM Cd, shoot growth slightly decreased but photosynthetic pigment and total soluble carbohydrate contents were not modified and no lipid peroxidation was detected. In addition, these plantlets accumulated proline, particularly in shoots (two to three times more than control). In roots, Cd concentration in the intracellular fraction was always higher than in the cell wall fraction contrary to shoots where Cd concentration in the cell wall fraction increased with time and Cd concentration in the medium. In shoots, Cd concentration was lower than in roots with a ratio of 0.2 after 4 weeks of exposure but stayed around 0.2 mg g(-1) dry weight, thus a value higher than the threshold requested for Cd hyperaccumulators. Hybrid larch would thus be a relevant candidate for field test of Cd phytoextraction.

Mycorrhization protects Betula pubescens Ehr. from metal-induced oxidative stress increasing its tolerance to grow in an industrial polluted soil

“…It has also been hypothesized that proline plays an important role in plants stress tolerance, since, apart from being an osmolyte, it can play a role in ROS and HM scavenging. Thus, accumulation of free proline is expected under HM exposure as it has been observed in several studies [1,57]. However, we observed proline decrease in plants grown in polluted soil, which was concomitant with a decrease in the soluble protein concentration observed in the same conditions.…”

“…Metal contamination due to human or industrial activities has become a major environmental problem nowadays [1,2]. Some heavy metals (HM), such as Zn or Cu, are essential for normal plant growth and development, however all are toxic at elevated concentrations.…”

“…Because of their deeper root system, considerable tolerance to HM and greater biomass, they can improve the effectiveness of phytoremediation [1,12,13]. In natural conditions, roots of trees associate with soil fungi forming ectomycorrhizas [14,15].…”

Effects of Drought and Salinity on European Larch (Larix decidua Mill.) Seedlings

“…For example, drought or salinity treatments have been shown to cause Pro accumulation in pine species [69][70][71], or in spruce [27,49,72]. In one-month-old plantlets of Larix × eurolepis Henry (Larix decidua × Larix kaempferi) grown in the presence of cadmium, Pro contents were reported to increase about three-fold over control values [73], similarly to what we have detected in the present study in salt-treated European larch seedlings. Moreover, embryogenic tissue of transgenic hybrid larch Larix leptoeuropaea containing high Pro levels-by overexpression of the pyrroline 5-carboxylate synthase gene from Vigna aconitifolia-was found to be more resistant than the non-transformed controls to high salinity, as well as to other abiotic stresses, such as cold or frost [74].…”

In vitro acclimation to prolonged metallic stress is associated with modulation of antioxidant responses in a woody shrub Daphne jasminea

“…An insight into plant functioning under metallic stress using in vitro culture models has been achieved for representatives of woody plants, including Cydonia (Schuch et al 2010), Larix (Bonet et al 2016), andVaccinium (Manquián-Cerda et al 2018), as well as herbaceous plants, like Plantago (Martins et al 2013). Recently in vitro culture systems were employed in HM-related studies on extremophytes, such as metallicolous Dianthus and Alyssum ecotypes (Muszynska and Hanus-Fajerska 2017;Muszynska et al 2018a, c), and halophytic Sesuvium (Fourati et al 2019).…”