Facing metal stress by multiple strategies: morphophysiological responses of cardoon (Cynara cardunculus L.) grown in hydroponics

Abstract

The contamination of environments by heavy metals has become an urgent issue causing undesirable accumulations and severe damages to agricultural crops, especially cadmium and lead which are among the most widespread and dangerous metal pollutants worldwide. The selection of proper species is a crucial step in many plant-based restoration approaches; therefore, the aim of the present work was to check for early morphophysiological responsive traits in three cultivars of Cynara cardunculus (Sardo, Siciliano, and Spagnolo), helping to select the best performing cultivar for phytoremediation. For all three tested cultivars, our results indicate that cardoon displays some morphophysiological traits to face Cd and Pb pollution, particularly at the root morphology level, element uptake ability, and photosynthetic pigment content. Other traits show instead a cultivar-specific behavior; in fact, stomata plasticity, photosynthetic pattern, and antioxidant power provide different responses, but only Spagnolo cv. achieves a successful strategy attaining a real resilience to metal stress. The capacity of Spagnolo plants to modify leaf structural and physiological traits under heavy metal contamination to maintain high photosynthetic efficiency should be considered an elective trait for its use in contaminated environments.

Antioxidant Activity and Photosynthesis Efficiency in Melissa officinalis Subjected to Heavy Metals Stress

“…In particular, Kovácik et al [ 30 ] found that the activation of the enzyme phenylalanine ammonia-lyase (PAL) increases the concentration of phenolic metabolites in Matricaria chamomilla . Decline in plant photosynthesis, as induced by heavy metals stress, is usually combined with stomatal restrictions [ 31 ]. In those circumstances, limiting stomata openings reduces the stream of carbon dioxide entering the leaf cells.…”

Metals Induce Genotoxicity in Three Cardoon Cultivars: Relation to Metal Uptake and Distribution in Extra- and Intracellular Fractions

“…Based on the latter result, we hypothesize that these smaller cells could entrap a higher fraction of metals into their cell walls, which are well known as metal sequestration sites, e.g., [30]. Accordingly, the same cultivar, in the presence of Cd and Pb, developed more numerous and smaller stomata to preserve net photosynthesis efficiency under metalstress [23].…”

“…Our results showed that both metals entered the cytoplasm of the three cultivars here examined, but Sardo showed an accumulation of Cd and Pb significantly higher than the other two cultivars, especially in the roots. In a previous work [23], similar intra-cellular metal fractions (i.e., concentrations in EDTA washed leaves) were measured in the same three cardoon cultivars after 30 days of growth. The shorter exposure time chosen here to show genotoxicity [16], could have highlighted a peculiar trait (i.e., a faster metal accumulation capacity) of Sardo during the early growth stages.…”

“…To evaluate the total amounts of intra-and extra-cellular fractions of Cd and Pb, an EDTA washing was used. This step is part of the sequential elution technique [23,[35][36][37] and moves away the metal fraction weakly bound to the plant tissues (i.e., the extracellular one), that includes the metal present in the intercellular space solution and the metal bound to the wall (i.e., the apoplast). What remains in the plant tissues after washing with EDTA represents, therefore, the intracellular fraction.…”

Physiological Toxicity and Antioxidant Mechanism of Photoaging Microplastics on Pisum sativum L. Seedlings

“…The decrease in root elongation induced by photoaging is a result of plant defense against this external stress. It has also been reported [ 28 , 29 ] that the inhibition of cell elongation and local cell division is a common manifestation of stress-induced morphological changes in plants to mitigate toxicity effects. In contrast, pristine MP exposure showed no significant effect on the growth of seedling stems, and only the particles photoaged for 14 d caused the stems to exhibit an increase in elongation.…”