Mineral nutrition of Scots pine seedlings under the chronic effect of zinc ions

Seedlings of Scots pine (Pinus sylvestris L.) are a convenient model object for studying the mechanisms of conifers adaptation to dangerous pollutant action such as zinc. The aim of this study was to determine the nature and mechanisms of toxic zinc action on the individual macro- and micronutrients content and on the mineral nutrition of seedlings integrally. We grew pine seedlings in hydroponic for six weeks with different concentrations of zinc sulfate (1.26 (control), 50, 150 and 300 uM). We determined nutrients content by atomic absorption spectrophotometry. Zinc chronic action resulted in a significant reduction in the rate of mass accumulation of pine seedlings as compared to the control: on 66.1% with 300 uM ZnSO₄. Increasing the zinc concentration in the nutrient solution was accompanied by a scale-up increasing zinc contents in the seedlings axial organs: up to 35.0 times in the roots at 300 uM ZnSO₄ and up to 23.4 times in hypocotyls, compared to the control. The zinc content in the seedlings cotyledons and needles was not of the concentration dependence, increasing, in average, in 3.7 times (cotyledons) and 8.0 times (needles). Limited intake of zinc in assimilating organs of Scots pine seedlings can be attributed to zinc excluders. The experimental data indicate a serious breach of mineral nutrition of Scots pine seedlings in the conditions of zinc action, which is associated with a decrease in nutrients absorption by root system and their disproportional translocation into the aerial organs. Deficiency of potassium and calcium in the seedlings organs was mainly caused by general zinc toxicity, associated with decreased metabolic processes and transpiration rate. Strengthening of magnesium and manganese deficiency in the seedlings organs was a consequence of the inhibition by zinc of active transport of these elements. Decreasing of magnesium content in the needles, with an increase in the cotyledons indicates the absence of reutilization, capable to compensate the lack of this element in the growing organs. Significant increasing of zinc content in cotyledons led to the increase in phosphorus pool, probably in the form of phytate, necessary for heavy metal detoxification. Zinc toxicity was responsible for the observed imbalance of certain trace elements, which is expressed in manganese deficiency and increased iron content. Intensification of iron transition to ferrous form as a consequence of manganese deficiency could enhance the toxic effect of zinc. Toxic effect of zinc together with the mineral nutrition disorder resulted in decreased synthesis of the photosynthetic pigments, slowing metabolism and therefore a downfall of rate of growth and plant development.

Keywords

Authors

References