ALTERAÇÕES ANATÔMICAS EM FOLHAS DE GIRASSOL (Helianthus annus L.) CULTIVADOS EM SOLO CONTAMINADO COM CÁDMIO

Abstract

Soil contamination by toxic elements represents an increasing environmental concern, with cadmium (Cd) standing out due to its high toxicity, elevated mobility, and ease of uptake by plants. This metal is introduced into the environment mainly through anthropogenic activities, such as the use of phosphate fertilizers and the improper disposal of waste, where it can bioaccumulate within the food chain and pose environmental and human health risks even at low concentrations. In plants, Cd induces morphological, physiological, and anatomical alterations, including impairment of photosynthesis, transpiration, stomatal function, and, consequently, plant growth and development. Although several studies have investigated the morphophysiological effects of Cd on sunflower (Helianthus annuus L.), information regarding the anatomical responses of this species to Cd contamination remains limited. Therefore, the present study aimed to evaluate the anatomical changes in sunflower leaves exposed to different Cd concentrations. The experiment was conducted under greenhouse conditions using three Cd concentrations (2.5, 5.0, and 7.5 mg dm⁻³), in addition to a control treatment, applied as CdCl₂, with five replicates per treatment. Sixty days after germination, samples from the median region of fully expanded leaves were collected, fixed, and processed for microscopic analyses. Control plants exhibited the typical leaf structure, consisting of a uniseriate epidermis with stomata and trichomes on both leaf surfaces, a dorsiventral mesophyll, and vascular bundles. Exposure to Cd resulted in progressive, concentration dependent anatomical alterations, including epidermal collapse, elongation and disorganization of mesophyll cells, enlargement of intercellular spaces, and severe structural deformation at the highest Cd concentrations. It is concluded that Cd causes significant anatomical damage to sunflower leaves, even at relatively low concentrations, demonstrating the high structural sensitivity of this species to Cd exposure. Furthermore, the findings highlight the importance of plant anatomy as a bioindicator tool for assessing the ecotoxicity of potentially toxic elements, including Cd.