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.

No abstract

L-Aminoethoxyvinylglycine (AVG) and 1-naphthylacetic acid (NAA) are known to affect preharvest fruit drop, fruit quality and fruit maturation in Golden Delicious apples (Malus 9 domestica Borkh). Experiments were carried out on GD/M9 trees treated at three different developmental stages (41, 28 and 17 days before the beginning of the commercial harvest) with AVG and NAA. Both chemicals significantly reduced fruit drop without significantly affecting the fruit weight. Background colour development and ripening were both delayed by AVG, whereas NAA significantly enhanced yellowing without affecting the evolution of ripening. Ethylene evolution and transcription profiles of genes involved in ethylene biosynthesis (MdACS1 and MdACO1) and action (MdETR1, MdERS1 and MdCTR1) were monitored in cortex from the date of the first treatment until the beginning of fruit drop in the control trees (21 days after the beginning of commercial harvest). AVG blocked or efficiently reduced the ethylene evolution. This effect was paralleled by a down-regulation of MdACS1, MdACO1, MdETR1 and MdERS1. NAA at the second and third date of application enhanced the onset of ethylene evolution, although, at the end of the experiment, no difference was found between control and treated fruits. The chemical applied in the first date significantly down-regulated the transcription of the genes at the end of the experiment. MdCTR1 expression, basically unaffected by AVG and NAA, appeared to be transiently down-regulated. The initial downregulation is under developmental control, whereas the late regain of transcript accumulation paralleled the ethylene evolution.Abbreviations ACS 1-Aminocyclopropane-1-carboxylate synthase ACO 1-Aminocyclopropane-1-carboxylate oxidase ETR

Several protocols and commercial kits are used for the extraction of nucleic acids from different plant tissues. Although there are several procedures available to remove sugars, which hinder the extraction of clean genomic DNA, there are few to assist with extraction of RNA. Those presently used include precipitations with ethylene glycol monobutyl ether or lithium chloride (LiCl), or centrifugation in cesium chloride (CsCl) gradients, but these generally either do not allow high recovery of RNA, are time consuming, rely on hazardous chemicals or need special equipment. Here we present the use of the simple cation, Ca2+, which has been tested and shown to be very efficient for the precipitation of high molecular weight pectic sugars during RNA extraction. Results are presented for different plant tissues, especially tissues of peach and apple fruits at varying ripening stages.

The influence of internal and external factors such as tree fruit load and elevation on ethylene biosynthesis and action was assessed during apple fruit development and ripening. Ethylene biosynthesis, as well as transcript accumulation of the hormone biosynthetic enzymes (MdACS1 and MdACO1), receptors (MdETR1 and MdERS1) and an element of the transduction pathway (MdCTR1), were evaluated in apples borne by trees with high (HL) and low (LL) fruit load. Orchards were located in two localities differing in elevation and season day degree sum. These parameters significantly affected the date of bloom and commercial harvest, and the length of the fruit developmental cycle. Trees from the low elevation (LE) bloomed and the fruit ripened earlier than those from the high elevation (HE), displaying also a shortened fruit developmental cycle. Dynamics of ethylene evolution was apparently not affected by elevation. The onset of ethylene evolution started 130 days after bloom (DAB) at both elevations. During early ripening, fruits from LL trees produced significantly more ethylene than those from HL trees. Expression analysis of MdACS1, MdACO1 and MdERS1 indicated that the transcript accumulation well correlated with ethylene evolution. MdCTR1 was expressed at constant level throughout fruit growth and development up to 130 DAB, thereafter, the transcript accumulation decreased up to commercial harvest, concurrently with the onset of ethylene evolution.