Abstract
Flooding is a common stress factor in both natural and agricultural systems, and affects plant growth by the slow diffusion rate of gases in water. This results in low oxygen concentrations in submerged tissues, and hence in a decreased respiration rate. Understanding the responses of plants to flooding is essential for the management of wetland ecosystems, and may benefit research to improve the flood tolerance of crop species. This study describes the response to partial submergence of bittersweet (Solanum dulcamara). Bittersweet is a Eurasian species that grows both in dry habitats such as coastal dunes, and in wetlands, and therefore is a suitable model plant for studying responses to a variety of environmental stresses. A further advantage is that the species is closely related to flood-intolerant crops such as tomato and eggplant. The species constitutively develops dormant primordia on the stem, which we show to have a predetermined root identity. We investigated adventitious root growth from these primordia during flooding. The synchronized growth of roots from the primordia was detected after 2-3 days of flooding and was due to a combination of cell division and cell elongation. Gene expression analysis demonstrated that the molecular response to flooding began within 2 h and included activation of hypoxia and ethylene signalling genes. Unexpectedly, these early changes in gene expression were very similar in primordia and adjacent stem tissue, suggesting that there is a dominant general response in tissues during early flooding.
Highlights
Flooding is a significant abiotic stress factor that affects plant growth and development in natural ecosystems (Blom and Voesenek 1996; Visser et al 1996a)
Adventitious root primordia were constitutively present on the stem and internodes of this species and developed into adventitious roots when the stem was submerged for several days in the greenhouse (Fig. 1C)
Even when flooding was applied to only a section of the stem, adventitious roots emerged, indicating that their induction is independent of flooding of the primary root system (Fig. 1D)
Summary
Flooding is a significant abiotic stress factor that affects plant growth and development in natural ecosystems (Blom and Voesenek 1996; Visser et al 1996a). It severely reduces the exchange of gaseous compounds between the plant and its environment, because gas diffusion is around 10 000-fold slower in water than in air (Armstrong et al 1991). Oxygen deficiency causes poor respiration in submerged plant tissues. This is especially so in organs such as roots when buried in anoxic
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