Architectural and biochemical changes in embryonic tissues of maize under cadmium toxicity

Heavy metals greatly alter plant morphology and architecture, however detailed mechanisms of such changes are not fully explored. Two experiments were conducted to investigate the influence of cadmium (CdCl2 · 2.5H2 O) on some germination, morphological, biochemical and histological characteristics of developing embryonic tissue of maize. In the first experiment, maize seeds were germinated in increasing levels of CdCl2 (200-2000 μm) in sand and measurements were taken of changes in germination and seedling development attributes. Based on these parameters, 1000 μM CdCl2 was chosen for detailed biochemical and histological measurements. In the second experiment, seeds were germinated in Petri dishes and supplied with 0 (control) or 1000 μM CdCl2 (Cd-treated). Radicle, plumule, coleoptile and coleorhiza were measured for biochemical and histological changes. The highest amount of Cd was in the coleorhiza and radicle. Free proline, soluble sugars, anthocyanin, soluble phenolics, ascorbic acid, H2 O2 and MDA were significantly higher in coleorhizae, followed by the coleoptile, radicle and plumule. Although the radicle and coleorhiza were relatively poor targets of Cd than the other tissues, Cd stress reduced cortical cell size and vascular tissues, and deformed xylem and phloem parenchyma in all plant parts. In conclusion, the main reason for reduced germination was the influence of Cd on architecture of the coleorhiza and coleoptile, which was the result of oxidative stress and other physiological changes taking place in these tissues.