Rungruchkanont Karnchana, Ketsa Saichol, Chatchawankanphanich Orawan, van Doorn Wouter G
Department of Horticulture, Faculty of Agriculture, Kasetsart University, Chatuchak, Bangkok 10900, Thailand.
National Center for Genetic Engineering and Biotechnology (BIOTEC), Kasetsart University, Kamphaengsaen Campus, Nakhon Pathom 73140, Thailand.
Funct Plant Biol. 2007 Oct;34(10):885-894. doi: 10.1071/FP07146.
Dendrobium flower buds and flowers have an abscission zone at the base of the pedicel (flower stalk). Ethylene treatment of cv. Miss Teen inflorescences induced high rates of abscission in flower buds but did not affect abscission once the flowers had opened. It is not known if auxin is a regulator of the abscission of floral buds and open flowers. The hypotheses that auxin is such a regulator and is responsible for the decrease in ethylene sensitivity were tested. Severed inflorescences bearing 4-8 floral buds and 4-6 open flowers were used in all tests. The auxin antagonists 2,3,5-triiodobenzoic acid (TIBA, an inhibitor of auxin transport) or 2-(4-chlorophenoxy)-2-methyl propionic acid (CMPA, an inhibitor of auxin action) were applied to the stigma of open flowers. Both chemicals induced high flower abscission rates, even if the inflorescences were not treated with ethylene. The effects of these auxin antagonists virtually disappeared when the inflorescences were treated with 1-methylcyclopropene (1-MCP), indicating that the abscission induced by the auxin antagonists was due to ethylene. Removal of the open flowers at the distal end of the pedicel hastened the time to abscission of the remaining pedicel, and also resulted in an increase in ethylene sensitivity. Indole-3-acetic acid (IAA) in lanolin, placed on the cut surface of the pedicel, replaced the effect of the removed flower. Treatments that promoted abscission of open flowers up-regulated a gene encoding a β-1,4-glucanase (Den-Cel1) in the abscission zone (AZ). The abundance of Den-Cel1 mRNA was highly correlated with β-1,4-glucanase activity in the AZ. The results show that auxin is an endogenous regulator of floral bud and flower abscission and suggest that auxin might explain, at least partially, why pedicel abscission of Dendrobium cv. Miss Teen changes from very ethylene-sensitive to ethylene-insensitive.
石斛的花芽和花朵在花梗（花茎）基部有一个离层区。对“少女小姐”品种的花序进行乙烯处理，会导致花芽的离层率很高，但一旦花朵开放，乙烯处理就不会影响离层。目前尚不清楚生长素是否是花芽和开放花朵离层的调节因子。我们对生长素是这样一种调节因子并导致乙烯敏感性降低的假设进行了测试。所有测试均使用带有4 - 8个花芽和4 - 6朵开放花朵的切断花序。生长素拮抗剂2,3,5 - 三碘苯甲酸（TIBA，一种生长素运输抑制剂）或2 - (4 - 氯苯氧基)-2 - 甲基丙酸（CMPA，一种生长素作用抑制剂）被施用于开放花朵的柱头。即使花序未用乙烯处理，这两种化学物质也会诱导很高的花朵离层率。当花序用1 - 甲基环丙烯（1 - MCP）处理时，这些生长素拮抗剂的作用几乎消失，这表明生长素拮抗剂诱导的离层是由乙烯引起的。去除花梗远端的开放花朵会加快剩余花梗的离层时间，并且还会导致乙烯敏感性增加。放置在花梗切割表面的羊毛脂中的吲哚 - 3 - 乙酸（IAA）替代了被去除花朵的作用。促进开放花朵离层的处理会上调离层区（AZ）中一个编码β - 1,4 - 葡聚糖酶（Den - Cel1）的基因。Den - Cel1 mRNA的丰度与AZ中的β - 1,4 - 葡聚糖酶活性高度相关。结果表明，生长素是花芽和花朵离层的内源性调节因子，并表明生长素可能至少部分解释了为什么“少女小姐”品种石斛的花梗离层从对乙烯非常敏感变为对乙烯不敏感。
