Miyamoto N, Steudle E, Hirasawa T, Lafitte R
Lehrstuhl Pflanzenökologie, Universität Bayreuth, Universitätsstrasse 30, D-95440 Bayreuth, Germany.
J Exp Bot. 2001 Sep;52(362):1835-46. doi: 10.1093/jexbot/52.362.1835.
A pressure chamber and a root pressure probe technique have been used to measure hydraulic conductivities of rice roots (root Lp(r) per m(2) of root surface area). Young plants of two rice (Oryza sativa L.) varieties (an upland variety, cv. Azucena and a lowland variety, cv. IR64) were grown for 31-40 d in 12 h days with 500 micromol m(-2) s(-1) PAR and day/night temperatures of 27 degrees C and 22 degrees C. Root Lp(r) was measured under conditions of steady-state and transient water flow. Different growth conditions (hydroponic and aeroponic culture) did not cause visible differences in root anatomy in either variety. Values of root Lp(r) obtained from hydraulic (hydrostatic) and osmotic water flow were of the order of 10(-8) m s(-1) MPa(-1) and were similar when using the different techniques. In comparison with other herbaceous species, rice roots tended to have a higher hydraulic resistance of the roots per unit root surface area. The data suggest that the low overall hydraulic conductivity of rice roots is caused by the existence of apoplastic barriers in the outer root parts (exodermis and sclerenchymatous (fibre) tissue) and by a strongly developed endodermis rather than by the existence of aerenchyma. According to the composite transport model of the root, the ability to adapt to higher transpirational demands from the shoot should be limited for rice because there were minimal changes in root Lp(r) depending on whether hydrostatic or osmotic forces were acting. It is concluded that this may be one of the reasons why rice suffers from water shortage in the shoot even in flooded fields.
采用压力室和根压探针技术测量了水稻根系的水力传导率（每平方米根表面积的根Lp(r)）。两个水稻（Oryza sativa L.）品种（一个旱稻品种，Azucena品种；一个水稻品种，IR64品种）的幼苗在12小时光照、500 μmol m(-2) s(-1)光合有效辐射（PAR）以及日/夜温度分别为27℃和22℃的条件下生长31 - 40天。在稳态和瞬态水流条件下测量根Lp(r)。不同的生长条件（水培和气培）在两个品种的根系解剖结构上均未造成明显差异。通过水力（静水）和渗透水流获得的根Lp(r)值约为10(-8) m s(-1) MPa(-1)，并且使用不同技术时结果相似。与其他草本物种相比，水稻根系单位根表面积的水力阻力往往更高。数据表明，水稻根系总体水力传导率较低是由于根外部（外皮层和厚壁（纤维）组织）存在质外体屏障以及内皮层发育强烈，而非由于通气组织的存在。根据根系的复合运输模型，水稻适应地上部更高蒸腾需求的能力可能有限，因为无论作用的是静水力还是渗透力，根Lp(r)的变化都很小。得出的结论是，这可能是水稻即使在淹水田地中地上部也会缺水的原因之一。
