Mingo Darren M, Bacon Mark A, Davies William J
The Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK.
J Exp Bot. 2003 Apr;54(385):1205-12. doi: 10.1093/jxb/erg120.
Tomato (Lycopersicon esculentum cv. Solairo) fruit growth, fruit mesocarp and leaf epidermal cell turgor, and fruit and leaf sub-epidermal apoplastic pH were monitored as plants were allowed to dry the soil in which they were rooted. Soil drying regimes involved splitting the root system of plants between two halves of a single pot separated by a solid impervious membrane to form a split-root system. Plants were then allowed to dry the soil in both halves of the pot (a soil-drying (SD) treatment) or water was supplied to one-half of the pot (a partial root-drying (PRD) treatment), allowing only one-half of the root system to dry the soil. A well-watered control treatment watered the soil on both halves of the pot. The rate of fruit growth was highly correlated with the soil water content of both sides of the SD treatment and the dry side of the PRD treatment. Soil drying caused a significant restriction in fruit growth rate, which was independent of any changes in the turgor of expanding fruit mesocarp cells in the PRD treatment. By supplying water to half of the root system, the turgors of mesocarp cells were maintained at values above those recorded in well-watered controls. The turgor of leaf epidermal cells exhibited a similar response. The pH of the sub-epidermal apoplastic compartment in leaves and fruit increased with soil drying. The dynamics of this increase in leaves and fruit were identical, suggesting free transport of this signal from shoot to fruit. Fruit growth rate and sub-epidermal pH within the fruit showed a strong correlation. The similarity of fruit growth response in the SD and PRD treatment, suggests that tomato plants respond to a discrete measure of soil water status and do not integrate measures to determine total soil water availability. The results of this study are not consistent with Lockhartian models of growth regulation in expanding fruit of a higher plant. A non-hydraulic, chemical-based signalling control of fruit growth in plants growing in drying soil is proposed.
在番茄（Lycopersicon esculentum cv. Solairo）植株使扎根土壤变干的过程中，监测了其果实生长、果实中果皮和叶片表皮细胞膨压，以及果实和叶片亚表皮质外体pH值。土壤干燥处理方式包括，通过固体防渗膜将植株根系分隔在单个花盆的两半，形成分根系统。随后让植株使花盆两半的土壤变干（土壤干燥（SD）处理），或者向花盆的一半供水（部分根干燥（PRD）处理），仅让一半根系使土壤变干。充分浇水的对照处理则对花盆两半的土壤都进行浇水。果实生长速率与SD处理两侧以及PRD处理干燥侧的土壤含水量高度相关。土壤干燥导致果实生长速率显著受限，这与PRD处理中正在膨大的果实中果皮细胞膨压的任何变化无关。通过向一半根系供水，中果皮细胞膨压维持在高于充分浇水对照所记录的值。叶片表皮细胞膨压表现出类似反应。叶片和果实中亚表皮质外体区室的pH值随土壤干燥而升高。叶片和果实中这种升高的动态是相同的，表明该信号可从地上部自由传输至果实。果实生长速率与果实内亚表皮pH值呈现强相关性。SD和PRD处理中果实生长反应的相似性表明，番茄植株对土壤水分状况的离散度量做出反应，而不是整合各项度量来确定土壤总有效水分。本研究结果与高等植物膨大果实生长调控的洛克哈特模型不一致。提出了一种基于化学信号而非水力信号的、对生长在干燥土壤中的植物果实生长的控制机制。
