In vitro morphophysiological responses of Alternanthera tenella colla (Amaranthaceae) to stress induced by cadmium and the attenuating action of silicon

Despite having the ability to bioaccumulate trace elements such as cadmium (Cd), many species also present morphophysiological disorders that can hamper their use as phytoremediation plants. Since it can lead to alterations in biomass accumulation, the employment of elements that mitigate stress, such as silicon (Si), can diminish the deleterious effects caused by trace elements. The objective of this study was to analyze the anatomical and physiological modulations induced by the synergy between Cd and Si in Alternanthera tenella Colla plants, as well as to elucidate whether Si can mitigate the harmful effects caused by Cd under in vitro conditions. Nodal segments were cultured in MS medium containing a concentration gradient of Cd (0, 50, 100, or 200 μM) combined with two levels of Si (0 or 40 μM) for a total of eight treatments. After 34 days, the plants' anatomy, physiology, and tolerance index were analyzed. The plants presented anatomical adjustments such as lower stomatal index and number of vessel elements, suggesting lower translocation of Cd to the aerial part. When cultured with 200 μM Cd, the plants presented the lowest Chl a/b ratio (5.55). In the presence of Si, the decline of this ratio was smaller (6.66). Plants exposed to Cd concentrations of 50 μM without Si presented a significant decrease in the performance of the photosynthetic apparatus and tolerance index. The presence of Si in the medium reduced the damages caused by cadmium to the plants' physiology, resulting in greater growth and higher tolerance to this element.