Sato Masashi, Tsutsumi Maki, Ohtsubo Akane, Nishii Kanae, Kuwabara Asuka, Nagata Toshiyuki
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.
Planta. 2008 Jun;228(1):27-36. doi: 10.1007/s00425-008-0715-3. Epub 2008 Feb 29.
Although elongation of epidermal cells in submerged leaves is thought to be a common feature of heterophyllous aquatic plants, such elongation has not been observed in Ludwigia arcuata Walt. (Onagraceae). In this study we found that reduced culture temperature induced the elongation of epidermal cells of submerged leaves in L. arcuata. Since such submerged leaves also showed a reduction in the number of epidermal cells aligned across the leaf transverse axis, these data indicate that heterophyllous leaf formation in L. arcuata is partially temperature sensitive, i.e., the elongation of epidermal cells was temperature sensitive while the reduction in the number of epidermal cells did not show such temperature sensitivity. To clarify the mechanisms that cause such temperature sensitivity, we examined the effects of ethylene, which induced the formation of submerged-type leaves on aerial shoots at the relatively high culture-temperature of 28 degrees C. At 23 degrees C, ethylene induced both cell elongation and reduction in the number of epidermal cells across the leaf transverse axis, while cell elongation was not observed at 28 degrees C. Moreover, both submergence and ethylene treatment induced a change in the arrangement of cortical microtubules (MTs) in epidermal cells of developing leaves at 23 degrees C. Such changes in the arrangement of MTs was not induced at 28 degrees C. Factors involved in the temperature-sensitive response to ethylene would be critical for temperature-sensitive heterophyllous leaf formation in L. arcuata.
虽然人们认为沉水叶中表皮细胞的伸长是异型叶水生植物的一个共同特征，但在弧茎柳叶菜（柳叶菜科）中尚未观察到这种伸长现象。在本研究中，我们发现降低培养温度会诱导弧茎柳叶菜沉水叶的表皮细胞伸长。由于这种沉水叶在叶横轴上排列的表皮细胞数量也减少了，这些数据表明弧茎柳叶菜的异型叶形成部分对温度敏感，即表皮细胞的伸长对温度敏感，而表皮细胞数量的减少则不表现出这种温度敏感性。为了阐明导致这种温度敏感性的机制，我们研究了乙烯的作用，乙烯在相对较高的28℃培养温度下诱导气生枝条上形成沉水型叶片。在23℃时，乙烯诱导细胞伸长以及叶横轴上表皮细胞数量的减少，而在28℃时未观察到细胞伸长。此外，在23℃时，淹水和乙烯处理均诱导发育中叶表皮细胞中皮质微管（MTs）排列的变化。在28℃时未诱导MTs排列的这种变化。参与乙烯温度敏感反应的因素对于弧茎柳叶菜温度敏感的异型叶形成至关重要。
