Of Hco <sub> 3 </ Sub> ~ - The Impact Of Root Morphology And Organic Acid Metabolism In Zinc Efficiency Of Rice Varieties

Calcareous soil is one of the main Zinc (Zn) deficient soil. Rice (Oryza sativa L.) plant vary very much between different genotype in zinc efficiency. Identification of the difference in structural, physiological and biochemical responses of rice genotypes varying in Zn efficiency to HCO3~ or high pH is an approach which may facilitate to understanding the mechanisms in rice in tolerance to Zn deficiency in calcareous soil. Two rice genotypes, Zn efficient (1R36) and Zn efficient (1R26), were selected in the present study. By means of hydroponic culture, alternations of the root morphology and ultrastructure , nutrient absorption and balance, physiological and biochemical responses to high concentration of HC03 or high pH were examined. The results obtained are summarized as follows: 1, The biomass yields of the two genotype were affected by high concentration of HCO;. In comparison with that of 1R26, the dry weights of roots and shoots of 1R36 increased significantly in treatment of 10mM HC03. High pH inhibited the biomass yields regardless genotype. 2, There was no difference in decrease of root length by high pH between Zn efficient and inefficient. Root length of 1R36 plant was increased by 10mM HCO3~, roots of which diameter less than 0.2 mm were increased most prominently. Root tips and root surface area were also promoted. By contrast, root growth of JR26 plant decreased in 10mM HCO; solution, especially <0.2mm root. 3, Root structure was also influenced by HCO; treatment. Root cells of IR~6 swelled and separation between cell wall and cell membrane was 94 observed. However, JR36 root cells were not affected.. 4,Translocation of Zn from root to shoot was stimulated by 10mM HCO31s 1R36, but little was affected in JR26. Uptake of Ca, P, K, Mg, Mn, Cu and Fe were increased by 10mM HCO; in JR36. By contrast, nutrient uptake was inhibited by 10mM HCO31n JR26 5, Addition of organic acid to culture solution reduced plant growth of JR36 and JR26. And the reduction increased with increasing acid concentration. The reduction was due to its impact to growth of small root (<0.2mm). 7,Accumulation of malic and citric acids in rice roots of JR36 was much less than that in 1R26.When plants were exposed to 10mM HC03 concentration of malic in JR26 root was 2.74 times of that in JR36.Further more, respiration inhibitor also increased root acid accumulation. However, there was no difference between JR36 and JR in response to the inhibition. 8, Activities of malic dehydrogenase and succinic dehydrogenase in rice roots were stimulated and peaked at 12h after treatment 10mM HC03 or respiration inhibitor. The enzyme in 1R36 was maintained at relatively high levels all the time. By contrast, they decreased dramatically in JR26 root in treatment of HC03, whilst no difference of the enzyme activities in response to malic acid...