Cin Valeriano Dal, Danesin Marcello, Boschetti Andrea, Dorigoni Alberto, Ramina Angelo
Department of Environmental Agronomy and Crop Science, University of Padova, Viale dell'Università 16, I-35020 Legnaro (Padova), Italy.
J Exp Bot. 2005 Nov;56(421):2995-3005. doi: 10.1093/jxb/eri296. Epub 2005 Oct 3.
Abscission was studied in immature apple fruits (cv. Golden Delicious) during the physiological drop. Fruitlet populations, characterized by different abscission potential, were analysed. Non-abscising fruitlets (NAF) were obtained from central flowers borne in clusters where all the lateral flowers had been removed at bloom while abscising fruitlets (AF) were derived from lateral fruitlets of trees sprayed with benzylaminopurine (BAP) at 200 ppm, 17 d after petal fall (APF), when the fruit cross diameter was about 10-12 mm. Fruit shedding, monitored at the end of the June drop, was significantly different in the two populations, being less than 10%, and more than 90%, in NAF and AF, respectively. In AF, fruit drop peaked around 33 d after petal fall (APF) and was preceded by an increase in ethylene around 20 d APF. Transcript analysis was performed from 17-24 d APF, since preliminary experiments pointed out that major changes in expression of abscission related genes occurred within this period. Transcript accumulation of genes involved in ethylene biosynthesis (MdACS5B and MdACO) and action (MdERS1, MdETR1, and MdCTR1) was studied in the seed, cortex, peduncle, and abscission zone (AZ) of the two fruit populations. MdACS5B and MdACO transcripts accumulated along the experimental period in AF population, even though at a different magnitude, while ethylene evolution declined after peaking at day three. MdETR1, MdERS1, and MdCTR1 expression patterns depended on tissue and/or population. The ERS/ETR ratio was higher in AF than in NAF populations. Overall results pointed out that apple fruitlet drop is preceded by a stimulation of ethylene biosynthesis and a gain in sensitivity to the hormone.
在生理落果期间，对未成熟苹果果实（品种：金冠）的脱落情况进行了研究。分析了具有不同脱落潜力的小果群体。不脱落小果（NAF）取自花序中部的花朵，在开花时去除了所有侧花，而脱落小果（AF）则来自花瓣脱落（APF）17天后用200 ppm苄基腺嘌呤（BAP）喷洒的树的侧生小果，此时果实横径约为10 - 12毫米。在6月落果结束时监测到的果实脱落情况，两个群体有显著差异，NAF中果实脱落率低于10%，AF中则超过90%。在AF中，落果高峰出现在花瓣脱落后约33天，且在花瓣脱落后约20天乙烯含量先增加。由于初步实验表明脱落相关基因表达的主要变化在此期间发生，因此在花瓣脱落后17 - 24天进行了转录分析。研究了两个果实群体的种子、皮层、果梗和脱落区（AZ）中参与乙烯生物合成（MdACS5B和MdACO）和作用（MdERS1、MdETR1和MdCTR1）的基因的转录积累情况。在AF群体中，MdACS5B和MdACO转录本在整个实验期间都有积累，尽管积累量不同，而乙烯释放量在第三天达到峰值后下降。MdETR1、MdERS1和MdCTR1的表达模式取决于组织和/或群体。AF群体中的ERS/ETR比值高于NAF群体。总体结果表明，苹果小果脱落之前会有乙烯生物合成的刺激以及对该激素敏感性的增加。
