The effect of UV-C irradiation on jasmonates, abscisic acid (ABA), polyamines and antioxidant activities was investigated in apple plants (Malus domestica Borkh.). The EC 50 values of O 2 --scavenging activity in the UV-C treated leaves were lower than those in the untreated control. In addition, total ascorbic acid and polyphenolic concentrations in the UV-C treated leaves were generally higher than those in the untreated control. Although the endogenous ABA concentrations were not significantly different between the untreated control and UV-C treatment, the endogenous jasmonic acid, putrescine, and spermine concentrations in the UV-C treated plants were higher than those in the untreated control. However, the application of PDJ before UV treatment inhibited the rise of endogenous jasmonate and putrescine concentrations. The increase of ascorbic acid was also inhibited by PDJ application before UV treatment. These facts suggest that the increase of jasmonates and polyamines may be associated with UV-C stimulation, and UV-C irradiation may be effective for increasing antioxidant activity in apple leaves.

No abstract

Characterization of the North American ginseng (Panax quinquefolius L.) inflorescence, the floret abscission zone, and its stimulation by ethylene were undertaken to gain insights into the potential for floret abscission induction as a replacement for the industry practice of expensive manual removal of the inflorescence. In each of 3 years, peduncle length of 3-year-old cultivated ginseng inflorescences increased rapidly in June, reaching maximal values of 140–180 mm. During this period, seed head diameter also increased to about 35 mm, while seed head fresh mass increased in July and August to 6.5–8.0 g. Flowering in 1996 and 1997 began in the last 2 weeks of June and lasted through July, with open flowers never exceeding 35%. Anatomical studies and manual dissection of 1- and 3-year-old perennating buds revealed development of the floral primordia first at their periphery and progressing centripetally. Stamen initials were seen as a pentamerous whorl just under the petal primordia, and the characteristic inferior ovary initiated as a slight depression at the centre of the floral meristem. Sections through 3-year-old inflorescences harvested on May 23, 1996, showed that distal floral apices had already formed constriction zones between the flower and the pedicel, indicating the position of the abscission zone. Length of time to ethylene-induced abscission zone formation was less than 24 h in 3-year-old ginseng harvested on July 23, 1997. The abscission threshold for ginseng berry drop was in the range of 10-100 µL·L–1 ethylene.Key words: anatomy, flowering, Panax quinquefolius, perennating bud.

Field experiments over 2 years were used to determine the effect of ethephon on: plant growth, weight of berries, proportion of red, green and immature berries, and root weight (economic yield) of 3-year-old north american ginseng plants (Panax quinquefolius L.). Ethephon sprays applied during bloom that thoroughly wetted the foliage and inflorescences immediately induced crop canopy descent (epinasty) exposing inflorescences and subsequently reducing plant height. Within a week the desired inflorescence and peduncle browning and flower drop took place. In each of four experiments ethephon, over the range 500 to 4000 mg·L-1, reduced berry weight and percent red berries, and increased the percent immature berries linearly. However, the responses to ethephon were variable. The highest concentration of 4000 mg·L-1 ethephon caused similar results in both years to the traditional practice of hand removal of inflorescences, but foliar reddening and some defoliation were observed. Buffering ethephon sprays at pH 2.6, 4.0, 5.0, and 6.0 gave similar results. The surfactant Tween 20 did not increase the effectiveness of the sprays. Generally, multiple applications of ethephon at lower concentrations were no more effective than comparable single higher concentration sprays. Carry-over effect of ethephon in the second year included crop stunting, an increase in root weight, and berry weights and berry color proportions similar to those plants on which hand removal was carried out in the first year. Chemical names used: 2-chloroethyl phosphonic acid (ethephon).

Varying concentrations (500-4000 mg·L–1) of ethephon, an ethylene-releasing compound, were applied to 3-year-old ginseng (Panax quinquefolium L.) plants in fields of southern Ontario. The effects of this chemical on fruit removal, plant damage, infructescence morphology, and root mass were studied and compared to the normal practice of manual inflorescence removal. The highest concentrations had the highest rates of removal but also caused the greatest amount of damage to the whole plants when compared to the mid-range concentrations. The lowest concentrations showed less foliar damage but did not provide sufficient fruit removal to mimic hand removal. When individual inflorescences of the ethephon treatments were studied, the seed heads had fewer ripe berries and more unpollinated florets than the untreated controls. When root masses were compared, high and low concentrations showed lower masses than those of the standard production practice of hand removal. However, mid range concentrations showed similar root mass increase to manual removal. When all parameters were considered, the concentration range giving the best results was 1000-1500 mg·L–1. Multiple applications of ethephon, at weekly intervals, had an additive effect on flower removal and plant damage. Treatments having an additive concentration of over 2000 mg·L–1 had detrimental effects on all parameters. Those within the 1000–1500 mg·L–1 range showed the highest similarity to the hand removal benefits.