Cacti (Cactaceae) are plants of arid and semi-desert regions of North and South America. Their characteristic morphology includes succulent stems, areoles from which transformed leaves called spines grow, and surface roots. Although they are not classified as typical halophytes, they nonetheless exhibit certain mechanisms of salt and drought tolerance similar to those found in halophytes. The water-storing tissue of the stem, capable of absorption and storage of water, is crucial for survival in arid environments. Some cacti utilize alternative C4 and CAM photosynthetic pathways that occur on the stem surface. Spines, besides serving as a defence against herbivores, prevent water loss by reducing the surface area of the stem exposed to direct sunlight, thus limiting evaporation. They also create shade and lower the surface temperature of the cactus and can help collect and direct water to the roots. Some cactus species are capable of accumulating excess amounts of Na and Cl in their aerial parts. The aim of the study was to assess the uptake of Na and Cl in the water-storing, photosynthetic tissue, and spines of seven different species of cacti under normal growth conditions and with the addition of NaCl to simulate additional salt stress. We performed analyses of total element concentrations in the aerial parts of the cacti using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) or with Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and tissue-specific element distributions using micro-Particle-Induced X-ray Emission beam (micro-PIXE). We found that the concentration of Na and Cl increased in cacti treated with NaCl compared to the control. The highest concentration of both elements was detected in the spines, and not in the photosynthetic and water-storing tissue. There were differences in the concentrations of Na and Cl among the different species, indicating species-specific element accumulation.
|
