Regulatory mechanisms in transport of host materials to the parasitic weed Striga hermonthica

根寄生杂草独脚金是非洲谷物生产的一个主要生物制约因素，它完全依赖其宿主提供水、养分和碳水化合物。本研究进行描绘的机制强调水和溶质运输从主机，高粱，寄生虫。独脚金叶片的呼吸速率与光合速率处于同一数量级，几乎不受水分胁迫的影响。通过气孔阻力和气孔开度测定，独脚金的蒸腾速率对水分胁迫的敏感性低于高粱。尽管寄生虫光系统的光化学能力较高，但独脚金的光合速率低于高粱。这些结果表明，在水分胁迫下，独脚金对寄主碳的依赖性很强，能够维持水分和溶质的运输，证实了干旱使独脚金对寄主的伤害最大化的观点，并表明独脚金叶绿体的CO_2固定能力限制了光合速率。

The root parasitic weed Striga hermonthica, a major biotic constraint to cereal production in Africa, relies solely on its hosts for water, nutrients and carbohydrates. The present study was undertaken to delineate the mechanisms underlining water and solute transport from the host, sorghum, to the parasite. Respiration rate in leaves of Striga was of the same order as its photosynthetic rate and was hardly affected by water stress. Transpiration rate in Striga, as indicated by stomatal resistance and stomatal aperture of leaves, was less susceptible to water stress than that of sorghum. Photosynthetic rate of Striga was lower than that of sorghum despite the higher photochemical capacity of the parasite photosystem. These results indicate a substantial reliance on host carbon, maintenance of water and solute transport under water stress, confirm the notion that drought maximizes Striga damage to its hosts and suggest that CO_2 fixation capacity in Striga chloroplast limits photosynthetic rate.