Comprehensive assessment of morphophysiological characteristics in Нelianthus annuus L. seedlings under combined stress

Pollution with heavy metals has become a major concern in food security. Their accumulation levels in different plants are strongly influenced by weather conditions. In this study, several series of experiments were carried out to assess the individual and combined effects of two stress factors (moisture deficit and heavy metal pollution) on morphometric parameters, physiology, and antioxidant status of sunflower plants. Drought stress significantly reduced shoot length, promoted root elongation, and caused alterations in cotyledon shape. The highest concentrations of malondialdehyde (MDA), a known marker of oxidative stress, were found in the plants under drought alone and in combination with heavy metal stress. Individual stresses led to a suppression of the low-molecular-weight antioxidant system in the plants, while combined stresses activated it as a primary defense mechanism, coinciding with the decreased contents of photosynthetic pigments. Aridification (drought) intensified cadmium accumulation in the plants without any visible changes in the morphology of their aboveground biomass, but with the stimulation of root system growth through an increase in the number of lateral roots. Among the tested heavy metals, lead was the most toxic when applied individually, resulting in a linear decrease in the contents of photosynthetic pigments as its concentration in the substrate increased.

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