Responses Of Root And Border Cells To Cadmium Toxicity In Vegetables With Different Types Of Root Apical Meristem

Cadmium is one of the most toxical heavy metals that is movable in the biosphere. It is absorbed easily by plants and has toxical effect on the plant root system especially to root system inlcuding root cap, meristematic zone, elongation zone. Root apical meristem is broadly divided into three types: basic open, intermediate-open, closed.Border cells located in peripheral of the root cap, originated from the root cap meristem. Root border cells is different from the root cells and possibly have special function such as producing and releasing of specific substances, regulating rhizosphere, reducing the mechanical resistance of the root system to protect the root tip. It is speculated that there is some correlations between the number or activity of border cells and the types of organizational structure as well as between types of root meristem and cadmium tolerance of root. However, little is known about it.The results from the studies on the the response of border cells of vegetables root with open and closed apical meristem to cadmium are follows:1. Using pea and cucumber representing open RAM organization, and tomato, Chili and eggplant closed RAM organization for material, the number and viability of border cells were significanly thigher in species exhibiting open RAM organization than species exhibiting closed apical organization.2. Vegetable seeds fog-pei-kan, and a hydroponic vegetable seedlings were used to study the different types of meristem root vegetables in the physiological response to cadmium stress differences, The results showed that: dealing with the same concentration, the open vegetable radicle elongation was relatively higher than the closed, the relative increase in MDA closed below that: an open-resistant root vegetable was strong in the closed cadmium.3. Useing hydroponic vegetable seedlings in response to cadmium poisoning, the results showed that: dealing with the same concentration of cadmium, the open vegetable seedling shoot MDA, POD activity of the relative increase was significantly higher than closed, the cadmium content which the root system absorbed was significantly higher than the closed. It Showed that the open hydroponic vegetable seedlings maked the greater degree of cadmium poisoning.4. The number and viability of root border cells in the different vegetables under Cd stress in situ and in vitro were studied. The results showed that: the number and viability of root border cells in situ and in vitro recused significant under cadmium treatment at a dose dependent manner especailly for open RAM organization5. Mist culture was used to explore the protective effect of root border cells to vegetables under the cadmium stress. The results showed that after the removal of border cells, MDA of roots from open RAM organization were higher than the closed, the root activity was significantly lower than the closed, and Cadmium content was higher than the closed. It indicated that border cells protected roots from open RAM organization more effectively than the closed.In conclusion, there was stronger cadmium resistance in the open RAM organization than the closed. The number and the activity of root border cells from open RAM organization were higher than the closed. Under the cadmium stress, there was active response in open RAM organization in border cells. After the removal of root border cells, the root from open RAM organization was damaged more than the closed. It speculated that the cadmium tolerance of the vegetables may be correlated with the number and viability of root border cells to respond to cadmium stress.