Gravity-induced modification of auxin transport and distribution for peg formation in cucumber seedlings: possible roles for CS-AUX1 and CS-PIN1
Gravity-induced modification of auxin transport and distribution for peg formation in cucumber seedlings: possible roles for CS-AUX1 and CS-PIN1
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DOI：
10.1007/s00425-003-1072-x
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发表时间：
2003-11-01
期刊：
影响因子：
4.3
通讯作者：
Takahashi, H
中科院分区：
文献类型：
--
作者：
Kamada, M;Yamasaki, S;Takahashi, H
葫芦幼苗可能在下胚轴和根之间的过渡区两侧都有一个栓。水平位置生长的幼苗对重力的响应抑制了过渡区上侧的钉的发育。这种抑制是由于生长素水平降低到阈值以下而发生的。我们在本研究中发现，重刺激幼苗过渡区上部的游离吲哚-3-乙酸（IAA）含量较低，而IAA偶联物明显较下部丰富。在切除的过渡区观察到生长素诱导基因CS-IAA1 mRNA的短暂增加。结果表明，过渡区是生长素的来源。经生长素运输抑制剂处理的黄瓜幼苗表现出向力生长，并在过渡区两侧形成一个聚乙二醇。生长素运输抑制剂还导致过渡区CS-IAA1 mRNA积累增加，表明由于生长素外排受阻，细胞内生长素浓度升高。为了研究生长素运输系统在peg形成中的作用，我们从黄瓜（Cucumis sativus L.）植物中分离出生长素内流载体CS-AUX1和外流载体CS-PIN1的cdna。两个基因（特别是CS-AUX1）都是生长素诱导的。CS-AUX1和CS-PIN1 mrna在过渡区的维管组织、皮层和表皮中积累。CS-AUX1 mRNA在重刺激过渡区上侧的表达水平较下侧降低。因此，有可能生长素内流和外流载体活动的平衡控制了过渡区的细胞内生长素浓度，从而导致黄瓜幼苗中peg的侧向放置。
Cucurbit seedlings potentially develop a peg on each side of the transition zone between the hypocotyl and root. Seedlings grown in a horizontal position suppress the development of the peg on the upper side of the transition zone in response to gravity. It is suggested that this suppression occurs due to a reduction in auxin levels to below the threshold value. We show in this study that the free indole-3-acetic acid (IAA) content is low, while IAA conjugates are significantly more abundant in the upper side of the transition zone of gravistimulated seedlings, compared to the lower side. A transient increase in mRNA of the auxin-inducible gene, CS-IAA1, was observed in the excised transition zone. The result suggests that the transition zone is a source of auxin. Cucumber seedlings treated with auxin-transport inhibitors exhibited agravitropic growth and developed a peg on each side of the transition zone. Auxin-transport inhibitors additionally caused an increase in CS-IAA1 mRNA accumulation at the transition zone, indicating a rise in intracellular auxin concentrations due to a block of auxin efflux. To study the involvement of the auxin transport system in peg formation, we isolated the cDNAs of a putative auxin influx carrier, CS-AUX1, and putative efflux carrier, CS-PIN1, from cucumber (Cucumis sativus L.) plants. Both genes (CS-AUX1 in particular) were auxin-inducible. Accumulation of CS-AUX1 and CS-PIN1 mRNAs was observed in vascular tissue, cortex and epidermis of the transition zone. A reduced level of CS-AUX1 mRNA was observed in the upper side of the gravistimulated transition zone, compared with the lower side. It is therefore possible that a balance in the activities of auxin influx and efflux carriers controls intracellular auxin concentration at the transition zone, which results in lateral placement of a peg in cucumber seedlings.