Mechanism Of Uptake And Release Of Calcium By Root And Leaf Of Potamogeton Crispus

Calcium is an essential nutrient of plant, which play an extremely important role on plant growth and response to environmental stress. Calcium is an indispensable element in cell wall, at the same time, calcium can promote cell elongation and root growth and stabilize cell membranes. As second passing messenger, calcium can reduce the generation of reactive oxygen with enzymatic function and osmoregulation. The role on Ca2+of cells include uptake Ca2+and release Ca2+. Cells are not able to absorb Ca2+unlimitedly, and high concentration of Ca+in intracellular can cause poisoning. Therefore, the process of cell uptake Ca2+can maintain Ca2+balance in intracellular, and Ca2+transport proteins can complete this balance process. At present, many domestic and international research on calcium absorption mechanism for plants has made great progress, there are two forms of calcium absorption and transport in plants, which is passive absorption and active absorption, active absorption consume energy, and relate to root activity; passive absorption is mainly affected by transpiration of plant.Comprehensive understanding of the aquatic plant uptake, secrete, and transport of Ca2+will be crucial on development of phytoremediation technology. This paper have studied that calcium was absorbed, secreted and transferred by roots and stems and leaves of the submerged plant Potamogeton crispus L. The experiment was designed that plants grows under different calcium concentrations to observe whether or not there are a significant difference between the growth rates. In10mg/L of Ca2+concentration, separate and extract different components of leaves and analyze the percentage of calcium content of each part, so to know the calcium concentrated at which part during uptake and secrete process. Two-container system was used for investigating the migration kinetics of uptake and exudation of calcium in P. crispus. SEM, EDS and light microscopy were used to observe leaves environment. Micro-electrodes was used to measure redox potential, dissolved oxygen concentration within240min continuously of root and stems and leaves. The main conclusions are:(1) High concentrations of calcium inhibited the growth of P. crispus. When the concentration of calcium in solution was10mg/L, the plant grows fastest; the growth rate is twice of5mg/L treatment, P. crispus grows slowly at20mg/L and30mg/L high concentration of calcium.(2) Calcium is absorbed from the root to the leaf in P. crispus. It can be seen from the results that calcium uptake by root and release by stems and leaves were increased over time, calcium concentration in stems and leaves chamber increased5mg/L after4d, and the root chamber increase2mg/L or so after4d. There has some calcium release situation of roots and stems in the calcium absorption process, but the overall trend is still roots uptake and transfer to the leaves and stems and then released. (3) Calcium mainly concentrated in the cell wall, followed by the soluble fraction, a smaller amount of calcium concentrated in the organelles during the transfer process. Meanwhile, with time, calcium first migrates from the cell wall to the soluble fraction, and then move from soluble fraction to another part of the cell wall.(4) When calcium concentration is10mg/L in root chamber, P. crispus had the best exudation ability to the ion. When calcium concentration in root chamber is80mg/L, due to calcium concentration is too high, break the calcium transport system stability, migration of calcium ion in P. crispus is no longer controlled by transport system.(5) Seen under light microscope, when treated with different concentrations of calcium solution, there had a lot of crystals which exist on leaf epidermal cells of P. crispus, crystal quantity on the upper epidermis was more than that on the lower epidermis. The quantity of crystal on the upper epidermis was maximum under the conditions of10mg/L in root chamber.(6) The epidermis cells of P. crispus leaves were closely packed under observing by SEM. The crystal substance was mainly scattered in the upper epidermal cells, and surrounded around the cell wall. In a certain concentration range, the quantity of crystals of upper epidermal cells was more than lower epidermal cells.(7) Root uptake of Ca2+was not a simple passive absorption affected by Ca2+-ATPase activity, and NaVO3inhibited the enzyme activity which affected root uptake of Ca2+. Stems and leaves secreted Ca2+activity which was not affected by NaVO3. Oxygen concentration and redox potential of the stems and leaves cells had no significant changes over time.