Chin J Plan Ecolo ›› 2005, Vol. 29 ›› Issue (5): 706-712.

• Research Articles •

### VARIATIONS OF ROOT HYDRAULIC CONDUCTANCE OF MANCHURIAN ASH SEEDLINGS IN DIFFERENT CONCENTRATIONS

SUN Hai_Long, WU Chu XU, Wen_Jing, and WANG Zheng_Quan

1. School of Forestry, Northeast Forest University
• Online:2005-08-30 Published:2005-08-30
• Contact: WANG Zheng_Quan

Abstract:

Roots absorb water from the soil and play an essential role in their water balance. In wet soil, the root system is the primary limitation for plant water uptake and can contribute up to approximately 50% of the overall hydraulic resistance of the plant. The root hydraulic conductance (Lp) based on the root surface area has a major influence on the shoot water status, plant growth and development. Recent studies show that radical water transport is an important determinant of root Lp, because aquaporins in the protoplasm and vacuole membranes play a key role in the radial water transport of plant roots, i.e., higher activity of aquaporins favors higher water transport, and Lp is an effective index in determining the relationship between aquaporins and water transport. However, most studies on Lp have used the same uptake solution, (e.g., deionized water), and variation of Lp in solutions of different substances has been ignored. The objectives of this study were to 1) compare differences in Lp in deionized water and various concentrations of NH4NO3 solutions, and 2) examine changes ofLp when treated with deionized water and NH4NO3 solutions after HgCl2 treatment to inhibit aquaporins.  The experiment was conducted in May 2002. Manchurian Ash (Fraxinus mandshurica ) seedlings were grown for 40－45 d on a bench in a greenhouse at the Northeast Forestry University. Greenhouse temperatures were approximately 25 ℃ day maximum and 18 ℃ night minimum, and average photosynthetic photon flux was 500-800 μmol photons•m-2•s-1 during this period. Roots were placed in treatments of deionized water and NH4NO3 solutions with concentrations of 16, 8, 4, and 1 mmol•L-1for 15 min and Lp measured by the pressure_flux approach. Roots were treated with HgCl2 (50μmol•L-1) and then again placed in the different treatment solutions andLp measured.  The results showed that the Lp of roots in deionized water was 22% higher than when treated with HgCl2 and 16% higher than both HgCl2_treated and mercapto ethanol_treated plants. In NH4NO3 solutions of various concentrations, Lp increased with increasing concentrations of NH4NO3, and the maximum Lp occurred at 8 mmol•L-1NH4NO3. The average Lp in NH4NO3 solutions was 77% higher than in deionized water After HgCl2 treatment, Lp still increased from lower to higher NH4NO3 concentrations but was reduced by 68%, which was three folds higher than the 22% reduction in HgCl2_treated roots in deionized water. In contrast to other studies , the percent Lp reduction in nutrient solutions was higher than in deionized water after HgCl2 treatment.  These results suggest that aquaporins are very important in regulating water movement in the roots of Manchurian ash, and nutrient ions can have a significant effect on the activity of aquaporins. In plants not treated by HgCl2, nutrient ions can stimulate aquaporins and increase their activity. After aquaporins were inhibited by the HgCl2 treatment, the Lp of roots in different solutions decreased significantly and inhibition of HgCl2 increased with ion solution concentrat ions. Our results indicate that there are HgCl2_sensitive aquaporins and ion cha nn els in the protoplasm and vacuole membranes of the roots. However, these need to be experimentally tested in the future.

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