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

根寄生杂草Striga hermonthica是非洲谷物生产的主要生物限制，它完全依赖宿主提供水、营养和碳水化合物。本研究旨在揭示水和溶质从寄主高粱到寄生虫的运输机制。藻藻叶片的呼吸速率与光合速率在同一量级，几乎不受水分胁迫的影响。从气孔阻力和叶片气孔孔径来看，刺蒺藜的蒸腾速率对水分胁迫的敏感性低于高粱。寄生光系统具有较高的光化学能力，但寄生菌的光合速率低于高粱。这些结果表明，在水分胁迫下，寄生菌对寄主碳、水分维持和溶质运输的依赖很大，证实了干旱使寄生菌对寄主的伤害最大化的观点，表明寄生菌叶绿体对CO_2的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.