Effects Of Soil Water Contents On Carbohydrates Partitioning And Reactive Oxygen Species Metabolism In Different Organs Of Robinia Pseudoacacia

In order to investigate the effects of drought on carbohydrates partitioning and reactiveoxygen species metabolism in different organs, the leaf photosynthesis, contents of solublesugar and starch, hydrogen peroxide (H2O2) and superoxide anion (O2-) in different organs ofRobinia pseudoacacia under non-limiting soil water availability, medium water deficit, andsevere water dificit were studied. The results showed that:(1) Under decreased soil water contents, biomass of leaves, stem, and fine roots ofRobinia pseudoacacia reduced significantly, while biomass of coarse roots tended also toreduce, however, the rate of roots to shoot increased; leaf net photosynthetic rate andmaximum net photosynthetic rate reduced significantly, but dark respiration rate increased,light compensation point increased significantly, concomitant with light saturation pointdecreased gradually, and the apparent quantum yield also reduced.(2) Soluble sugar contents in leaves were not affected by soil water contents, but starchcontents reduced significantly, while in stem, coarse and fine roots the contents of solublesugar and starch increased; the total contents of soluble sugar and starch in leaves and stemdecreased significantly, also tended to reduce in coarse and fine roots. The results indicatedthat when photosynthesis was inhibited and carbohydrate assimilation was decreased withdecreasing soil water condition, limited carbohydrate tended to accumulate in roots.(3) Decreasing water contents led to a significant increase in leaf H2O2and O2-level,especially in guard cell H2O2level, concomitant with a reduction in stomatal conductance andnet photosynthesis rate; H2O2contents in guard cells in dark were significantly higher than inlight, which further confirming that H2O2level is closely related to stomatal aperture in thisspecies.(4) In roots, the meristematic zone was the primary region of H2O2generation; droughtled to significant increase in H2O2level in the meristematic zone, the vessels, and theelongation zone, H2O2contents in coarse roots (diameter≥1mm) and O2-contents in bothcoarse roots and fine roots (diameter <1mm) of Robinia pseudoacacia increased significantly, but did not change H2O2contents in fine root.(5) Both H2O2and O2-levels in stem xylem of Robinia pseudoacacia increasedsignificantly with decreased soil water contents; In phloem H2O2and O2-levels was notaffected by drought. In all tested organs and tissues O2-levels were generally far below H2O2levels.In conclusion, under reduced soil water contents, leaf photosynthesis ability reduced,and limited carbohydrates were preferentially partitioned to non-photosynthetic organs,resulting in an increased rate of roots to shoot. Drought led to a significant stimulation ofH2O2generation in leaves and fine roots and of H2O2translocation from roots to the shoot viathe xylem. But H2O2translocation from leaves to the roots via the phloem was not affected bysoil water contents. Drought-induced the significant increase in guard cell H2O2level isclosely related to stomatal aperture.