Morpho-anatomical and growth alterations induced by arsenic in Cajanus cajan (L.) DC (Fabaceae)

Abstract

Arsenic (As) is a toxic element to most organisms. Studies investigating anatomic alterations due to As exposure in plants are scarce but of utmost importance to the establishment of environmental biomonitoring techniques. So, this study aimed to investigate the effects of As on the development and initial root growth in Cajanus cajan (Fabaceae), characterize and quantify the possible damages, evaluate genotoxic effects, and identify structural markers to be used in environmental bioindication. Plants were exposed hydroponically to 0.5, 1.0, 1.5, and 2.0 mg As L(-1), as sodium arsenate. Growth parameters were measured, and in the end of the exposure, root samples were analyzed for qualitative and quantitative anatomical alterations. Arsenic genotoxicity was evaluated through analysis of the mitotic index in the root apex. Compared to the control, As-treated seedlings showed an altered architecture, with significantly decreased root length (due to the lower mitotic index in the apical meristem and reduced elongation of parenchyma cells) with darkened color, and abnormal development of the root cap. A significant increase in vascular cylinder/root diameter ratio was also detected, due to the reduction of the cellular spaces in the cortex. The secondary xylem vessel elements were reduced in diameter and had sinuous walls. The severest damage was visible in the ramification zone, where uncommon division planes of phellogen and cambium cells and disintegration of the parenchyma cells adjacent to lateral roots were observed. The high sensibility of C. cajan to As was confirmed, since it caused severe damages in root growth and anatomy. The main structural markers for As toxicity were the altered root architecture, with the reduction of the elongation zone and increase of ramification zone length, and the root primordia retained within the cortex. Our results show a new approach about As toxicity and indicate that C. cajan is a promising species to be used for bioindication of environmental contamination by As.

Effects of short-term arsenic exposure in Arabidopsis thaliana: tolerance versus toxicity responses

“…Exposure of Cajanus cajan seedlings to 20 M arsenate led to an increase in density of root cortex cells as well as a reduction in the percentage of intercellular spaces (Pita-Barbosa et al 2015). In leaves of A. thaliana exposed to As, the spongy parenchyma was the most severely affected, which in turn is likely to interfere in respiration and photosynthesis via reductions in mesophyll conductance.…”

The Anatomical Basis of Heavy Metal Responses in Legumes and Their Impact on Plant–Rhizosphere Interactions

“…In addition to length reduction, root color of treated Vicia villosa plants were brownish and darker. Root growth reduction, which was particularly prominent in lateral roots, as well as abnormal development of the root cap, occurred in Cajanus cajani plants treated with As [ 33 ].…”

“…Findings reported by Ibañez et al [ 32 ] indicate that root diameter, cortex length, and vascular cylinder size in V. villosa roots treated with As (V) (25 µM) were reduced, but no significant changes were noted in samples treated with As (III) at the same concentration. Pita-Barbosa et al [ 33 ] recorded an increase in the vascular cylinder/root diameter ratio in Cajanus cajan (L.) DC roots treated with As (1.5 mg L −1 ), accompanied by a reduction in secondary xylem vessel diameter due to the negative effect of arsenic on cambium activity.…”

Variation in Root System Architecture Response to Arsenic during Establishment and Onset of Storage Root Formation in Two Sweetpotato (Ipomoea batatas L.) Cultivars

“…It is necessary to understand how plants respond to natural levels of As and other toxic elements to develop management practices for food safety and human health. Recent evidence from model plants and wellstudied crop species revealed that As reshapes the spatial configuration of roots in thale cress (Arabidopsis thaliana) (Kumar et al 2020;Piacentini et al 2020), pigeon pea (Cajanus cajan) (Pita- Barbosa et al 2015), peanut (Arachis hypogea) (Bianucci et al 2017), and rice (Oryza sativa) (Ronzan et al 2019;Wang et al 2018), among others. The presence of As exerts a profound effect on root architecture that is tightly coordinated with the detoxification machinery (Navarro et al 2022).…”