Ethylene action in carnation petals
Abstract
Ethylene plays a key regulatory role in carnation flower senescence. Carnation flowers produce significant amounts of ethylene during senescence. The perception of this ethylene has been shown to be essential to complete the senescence program. In addition, changes in ethylene responsiveness have been observed during carnation petal development leading up to the ethylene climacteric. Molecular changes in ethylene responsiveness of carnation petals and their underlying causes were investigated to obtain a better understanding between increases in ethylene responsiveness during flower development and flower senescence. Ethylene dose-response curves of petals at tight bud and anthesis stage of development show an increase in ethylene responsiveness during carnation flower development confirming earlier reports of changes in responsiveness to ethylene. Dos-response and time-response analysis of sensescence-related (SR) gene mRNA accumulation indicate that SR genes can be divided into two groups according to their response to ethylene. The first group includes the ethylene biosynthetic genes ACC synthase and ACC oxidase and is characterized by a marked delay in mRNA accumulation and high apparent dissociation constants of the response (Kr). The mRNA accumulation of the other SR genes, SR5, SR8, SR12, and DCCP, that were investigated show an almost immediate accumulation of their respective mRNAs and have low Kr values. These genes represent a second ethylene response group. Despite the differences in these two groups both groups of genes show an increase in responsiveness to ethylene as measured by mRNA accumulation during petal development. In order to understand the global changes in responsiveness we investigated the transcriptional control of ethylene receptors in carnation. Two putative ethylene receptor encoding genes, DCETR and DCERS2, were cloned from petals and their respective steady state mRNA levels measured. Transcript levels largely remained unchanged, less than two-fold changes in mRNA abundance during flower development in petals, ovaries, and styles. Immature root and leaf tissue showed higher transcript levels of DCETR and DCERS2 than mature tissues. mRNA levels of both genes remained fairly constant upon ethylene exposure of petals, and declined in senescing tissues and petals of norbornadiene-treated flowers. A model of ethylene action in carnation petals is presented and discussed.
Degree
Ph.D.
Advisors
Woodson, Purdue University.
Subject Area
Plant sciences
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