Analysis about the role of ethylene in the low-pH-induced root hair formation in lettuce.

当生菜幼苗在pH值为4的条件下培养时，根上可诱导出较高密度的根毛。植物激素乙烯参与了这一现象。在本研究中，研究了编码乙烯合成酶和乙烯受体的基因的贡献。从生菜幼苗中分离到2个ACC合成酶基因(命名为LsACSland LsACS2)和4个乙烯受体基因(命名为LsERS1、LsETR1、LsETR2和LsETRS)。ACSL的表达在30分钟后增加约2倍，pH从6降至4的2小时后，ACS2的表达在30分钟后增加约3倍，1小时内降至初始水平。再次证实了乙烯在低诱导根毛形成中的中介作用。在ACC合成酶基因表达方面，蓝光照射3~6小时是根毛生长所必需的。经3小时蓝光照射后，ACS1的表达增加了约6倍。蓝光对ACS2的表达没有影响。pH降低后30min内，根表皮细胞内皮质微管的排列由垂直排列变为随机排列。考虑到基因表达的时程和光照对基因表达的影响，ACS2介导了微管的随机化和根毛原基的启动，ACS1介导了根毛的生长。

High density of root hairs were induced on a lettuce root when a lettuce seedling was cultured at pH 4.Phytohormone ethylene mediated on this phenomenon. In this research, contribution of genes which encode ethylene synthesis enzyme and ethylene receptor was investigated. Two ACC synthase genes (named LsACSland LsACS2) and 4 ethylene receptor genes (named LsERSl, LsETRl, LsETR2 and LsETRS) were newly isolated from lettuce seedlings. Expression of ACSl increased about 2 times after 30 min to 2 hr after lowering of pH form 6 to 4.Expression of ACS2 increased about 3 times at 30 min after and reduced to the initial level within 1hr. Mediation of ethylene on the lowpEHnduced root hair formation was reconfirmed. on the point of ACC synthase gene expression.Irradiation of blue light for 3 to 6 hr was essential for the growth of root hairs. Expression of ACS1 was increased about 6 times by the 3hr blue light irradiation. Blue light had no effect on the expression ofACS2.Arrangement of cortical microtubules in a root epidermal cell was changed from perpendicular to random within 30 min after pH lowering. Application ofACC could induce the randomization of cortical microtubules.Considering the time course of genes expression and the effects of light on the genes expression, ACS2 mediated in the randomization of microtubules and initiation of root hair primordial and ACS1 mediated in the growth of root hairs.