Lead tolerance mechanism in Conyza canadensis: subcellular distribution, ultrastructure, antioxidative defense system, and phytochelatins

Abstract

We used hydroponic experiments to examine the effects of different concentrations of lead (Pb) on the performance of the Pb-tolerable plant Conyza canadensis. In these experiments, most of the Pb was accumulated in the roots; there was very little Pb accumulated in stems and leaves. C. canadensis is able to take up significant amounts of Pb whilst greatly restricting its transportation to specific parts of the aboveground biomass. High Pb concentrations inhibited plant growth, increased membrane permeability, elevated antioxidant enzyme activity in roots, and caused a significant increase in root H2O2 and malondialdehyde content. Analysis of Pb content at the subcellular level showed that most Pb was associated with the cell wall fraction, followed by the nucleus-rich fraction, and with a minority present in the mitochondrial and soluble fractions. Furthermore, transmission electron microscopy and energy dispersive X-ray analysis of root cells revealed that the cell wall and intercellular space in C. canadensis roots are the main locations of Pb accumulation. Additionally, high Pb concentrations adversely affected the cellular structure of C. canadensis roots. The increased enzyme activity suggests that the antioxidant system may play an important role in eliminating or alleviating Pb toxicity in C. canadensis roots. However, the levels of non-protein sulfhydryl compounds, glutathione, and phytochelatin did not significantly change in either the roots or leaves under Pb-contaminated treatments. Our results provide strong evidence that cell walls restrict Pb uptake into the root and act as an important barrier protecting root cells, while demonstrating that antioxidant enzyme levels are correlated with Pb exposure. These findings demonstrate the roles played by these detoxification mechanisms in supporting Pb tolerance in C. canadensis.

In-situ localization and biochemical analysis of bio-molecules reveals Pb-stress amelioration in Brassica juncea L. by co-application of 24-Epibrassinolide and Salicylic Acid

“…Our findings corroborated with the study carried out by Li, et al . 112 who reported enhancement in amino acids content in response to 24-EBL application. Similarly, application of SA resulted in elevation in levels of amino acids specifically proline, glycine betaine and glutathione in the present study.…”

Uptake, transport and distribution of molybdenum in two oilseed rape (Brassica napus L.) cultivars under different nitrate/ammonium ratios

“…The frozen plant fresh leaves (1 g) were homogenized and the subcellular fractions were separated according to Su et al (2014) and Li et al (2016). Each plant sample was homogenized in 12-ml precooled extraction buffer containing 250 mmol/L sugar, 50 mmol/L Tris-HCl (pH 7.5), 1 mmol/L MgCl 2 , and 10 mmol/L cysteine using a chilled mortar and pestle.…”

Subcellular Compartmentalization and Chemical Forms of Lead Participate in Lead Tolerance of Robinia pseudoacacia L. with Funneliformis mosseae

“…Copper (Cu) bound to the cell walls in fibrous roots of Malus sieversii mainly exists in phosphate and oxalate forms, which can explain some of the variation in Cu sensitivity in M. sieversii (Wang et al, 2016). Recently, Li et al (2016) reported that the cell walls and intercellular spaces are the main location of Pb accumulation in the roots of Conyza canadensis . The cell walls restrict Pb uptake into plant roots and act as an important barrier to protect root cells (Wang Y. et al, 2015).…”