Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa, Nagoya, Japan.
Department of Horticulture, School of Horticulture and Plant Protection, Yangzhou University, Yangzhou, Jiangsu, P.R. China.
Ann Bot. 2018 Mar 14;121(4):723-732. doi: 10.1093/aob/mcx205.
Soil waterlogging often causes oxygen deficiency in the root systems of plants and severely inhibits plant growth. Formation of aerenchyma - interconnected spaces that facilitate the movement of gases between and within the aerial and submerged parts of plants - is an adaptive trait for coping with waterlogged conditions. Soybean (Glycine max) forms porous secondary tissues known as aerenchymatous phellem (AP), which are derived from the outermost cell layer of phellogen. To understand what factors other than waterlogging are involved in phellogen and AP formation, we examined how their formation in soybean seedlings was affected by darkness, CO2 deficiency and blockage of phloem transport.
Aerenchymatous phellem and phellogen formation were expressed as area ratios in cross-sections of hypocotyl. CO2 was depleted by use of calcium oxide and sodium hydroxide. Phloem transport was blocked by heat-girdling of hypocotyls. Sucrose levels were measured by spectrophotometry.
Under light conditions, waterlogging induced the accumulation of high concentrations of sucrose in hypocotyls, followed by phellogen and AP formation in hypocotyls. Phellogen formation and AP formation were inhibited by darkness, CO2 deficiency and blockage of phloem transport. Phellogen formation and AP formation were also inhibited by excision of shoots above the epicotyl, but they recovered following application of sucrose (but not glucose or fructose application) to the cut surface.
The results demonstrate that sucrose derived from leaves is essential for AP and phellogen formation in soybean hypocotyls under waterlogged soil conditions. Maintenance of a high sucrose concentration is thus essential for the development of phellogen and AP and the differentiation of phellogen to AP.
土壤积水常常导致植物根系缺氧，严重抑制植物生长。通气组织的形成——植物地上和水下部分之间气体流动的连通空间——是植物适应水淹条件的一种特性。大豆（Glycine max）形成称为通气性木栓（AP）的多孔次生组织，其来源于木栓形成层的最外层细胞。为了了解除水淹以外的因素如何参与木栓形成层和 AP 的形成，我们研究了黑暗、CO2 缺乏和韧皮部运输阻断对大豆幼苗中它们形成的影响。
通过下胚轴横切面上的面积比来表示通气性木栓和木栓形成层的形成。通过使用氧化钙和氢氧化钠来耗尽 CO2。通过对下胚轴进行热环割来阻断韧皮部运输。通过分光光度法测量蔗糖水平。
在光照条件下，水淹诱导下胚轴中蔗糖浓度升高，随后在下胚轴中形成木栓形成层和 AP。黑暗、CO2 缺乏和韧皮部运输阻断抑制木栓形成层形成和 AP 形成。去除上胚轴以上的茎也抑制木栓形成层形成和 AP 形成，但在将蔗糖（而非葡萄糖或果糖）应用于切口表面后，它们会恢复。
结果表明，在水淹土壤条件下，来自叶片的蔗糖对于大豆下胚轴中 AP 和木栓形成层的形成是必需的。因此，维持高蔗糖浓度对于木栓形成层和 AP 的发育以及木栓形成层向 AP 的分化是必不可少的。
