Effect of Prolonged Water Deficiency of Various Intensities on Growth,Water Homeostasis and Physiological Activity of Pine Seedlings

Russian Journal of Plant Physiology - Plant growth is the physiological process that is generally the most affected by drought, and growth inhibition is one of the main contributors to ecosystem...     

Effect of mineral composition and medium pH on Scots pine tolerance to toxic effect of zinc ions

Effect of mineral composition and pH of nutrient medium on the growth of Scots pine (Pinus sylvestris L.) seedlings and their tolerance to toxic effect of zinc ions was investigated by modifying the standard Knop-Hoagland medium (pH 6.6) (M1). The improved medium (M2) was more acid (pH 4.5) and notable for 2.7-fold lower osmolarity, with equimolar ratio between ammonia and nitrate nitrogen, assimilable form of iron (9 μM Fe²⁺), and the presence of 0.02 μM Co²⁺ and 2 mM Cl^?. Owing to balanced mineral composition and low pH, M2 enhanced seedling growth under normal conditions and reduced the toxic effect of 100 μM ZnSO₄. Rapid development of the root system (main root, the number and total length of lateral roots) on M2 was maintained even under stress conditions (100 μM Zn²⁺); as a result, the ratio between the biomass of aboveground organs and the biomass of the root system remained on the level of 2.5, whereas on M1, it increased to 3.9. At the same time, on M2 we observed accelerated production of the needles with elevated content of photosynthetic pigments therein. Investigation of the operation of individual components of antioxidant system (superoxide dismutase, catalase, ascorbate peroxidase, and guaiacol peroxidases) and peculiarities of proline accumulation showed that Scots pine seedlings grown on M2 experienced less oxidative stress than the seedlings grown on M1. The probable physiological foundation of the observed phenomena is discussed.     

Scots pine as a model plant for studying the mechanisms of conifers adaptation to heavy metal action: 1. Effects of continuous zinc presence on morphometric and physiological characteristics of developing pine seedlings

Effects of zinc (50–150 μM ZnSO₄) on seed germinability, morphometric and physiological characteristics of Scots pine (Pinus sylvestris L.) seedlings during first 6 weeks of their development were studied. Scots pine turned out to be rather sensitive to elevated zinc concentrations. This was manifested in reduced seed germinability, root system growth retardation and suppression of its development (primarily, reduction in the size of the zone of secondary root formation, their number, and total length), a disturbance in the dynamics of biomass accumulation by various organs, primarily true needles, and also the content of main photosynthetic pigments. A specificity of zinc accumulation in seedling organs was established; it depended on the degree of root system development. A competition between cotyledons and needles for essential elements was observed. It was concluded that Scots pine high sensitivity to relatively low zinc concentrations (50–150 μM) makes it a more convenient model than currently used model plants (Arabidopsis thaliana L., Mesembryanthemum crystallinum L., Brassica napus L., and others) for studying physiological and molecular mechanisms of conifers adaptation to heavy metals and also for predictions of possible ecological consequences of environment pollution with zinc for tree phytocenoses.     

Scots pine as a model plant for studying the mechanisms of conifers adaptation to heavy metal action: 2. Functioning of antioxidant enzymes in pine seedlings under chronic zinc action

Functioning of antioxidant enzymes (superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APO), and guaiacol peroxidases (GPO)) and low-molecular organic ROS scavengers (proline and phenolic compounds) in various organs (roots, cotyledons, stem, and needle) of 6-week-old seedlings of pine (Pinus sylvestris L.) developing in the chronic presence of ZnSO₄ (50, 100, and 150 μM). Pine seedlings were grown in water culture in the climate-controlled chamber at an irradiance of 37.6 W/m² with a 16-h photoperiod, an air temperature of 23 ± 1/15 ± 1°C (day/night), and a relative humidity of 55/70% (day/night). Endogenous Zn content was a key factor determining SOD activity decomposing superoxide into H₂O₂ and O₂. Hydrogen peroxide produced is efficiently destroyed by CAT and also by APO and GPO. At the same time, the content of proline increased (especially at 150 μM ZnSO₄), but the content of phenolic compounds remained unchanged. All these processes help to maintain stable intracellular levels of O₂^⊙− and H₂O₂ at elevated zinc concentrations and to prevent generation of hydroxyl radical and development of oxidative stress.     

Development of scots pine seedlings and functioning of antioxidant systems under the chronic action of lead ions

This study has shown that the effect of Pb²⁺ ions (10–150 μM) on Scots pine seedlings is manifested by a biomass decrease and a delay in development of the root system, including shortening of the main root, reduction of the lateral root formation zone, and reduction of the number of lateral roots. The ability of the root system to deposit Pb²⁺ ions and to perform a barrier function, preventing Pb²⁺ uptake into assimilating organs, has been revealed. This ability is blocked if the Pb²⁺ concentration in the nutrient medium exceeds 80 μM. In the case of elevated Pb²⁺ concentrations, the content of photosynthetic pigments in pine needles decreases, whereas that in cotyledons increases. Analysis of the proline content and the functioning of the antioxidant enzyme system (superoxide dismutase, catalase, ascorbate peroxidase, and peroxidase) shows that the presence of Pb²⁺ ions in a wide concentration range does not induce intensive oxidative stress in pine seedlings.