Well before pollen tube penetration, ethylene has begun to disseminate from pollinated styles of Petunia hybrida flowers. Previous stigmatic application of aminoethoxyvinylglycine (AVG) completely prevented this ethylene synthesis, indicating that the endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) in pollen is not readily converted on the stigma. Compared to other flower parts, the capacity of the ethylene forming enzyme was largest in the stigma. When applied to the stigma, ACC caused ethylene synthesis, but did not accelerate wilting, unless high concentrations (20 nanomols) were used. Upon pollination or stigma wounding, the early ethylene evolved exclusively from the gynoecium, much later followed by the synthesis of corolla ethylene. Employing wideneck Erlenmeyer flasks, the competitive inhibitor of ethylene action, norbornadiene, was applied to entire flowers in situ, with delaying effects on wound-induced wilting. In contrast, norbornadiene treatment of styles alone, using capillaries, could not postpone wilting. Pollination with foreign pollen species did not lead to accelerated corolla wilting, notwithstanding considerable synthesis of ethylene during the frst 5 hours. In situ treatment of the stigma with AVG considerably delayed wound-and pollination-induced wilting. Removal of the entire AVG-treated style 6 hours after stigma wounding still allowed for the postponement of the accelerated wilting, even at very low concentrations of AVG. It is concluded that early stylar ethylene does not play a role in the acceleration of wilting but that, much later, corolla ethylene does, induced by a mobile wilting factor from the stigma, which is ACC. levels ofthe immediate precursor, ACC' (24). The sequential rise in ACC content of carnation stigmas, ovaries, receptacles, and petals upon pollination strongly suggests that ACC might be the mobile wilting stimulus (12). Pollen itself might be the trigger in this respect as it sometimes contains large amounts of ACC (F.

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M, 1991, Priming relieves dormancy in lettuce seeds independently of changes in osmotic constituents, -Phvsiol, Plant 81; 527-533,The relationship was studied between germination and dormancy of lettuce seeds (Lactuca sativa L, cv. Musette) and both soluble amino nitrogen metabolism and osmotic potential. Germination at 15°C in darkness coincided with a rise in the levels of free amino adds and total soluble amino nitrogen compounds and in the activity of giutamine synthetase (GS, EC nr, 6,3,1,2), In further experiments GS activity was used as indicator of soluble amino nitrogen metabolism, GS activity increased after the start of growth indicated by an increasing intolerance to desiccation. At 30°C seeds did not germinate, unless dormancy was broken beforehand during incubation at 2" or 15°C (priming). The alleviation of dormancy occurred much earlier than the rise in the activity of GS Priming at 15°C in polyethylene glycol instead of water retarded the breaking of dormancy and at -1,28 MPa even stimulated the induction of secondary dormancy, but did not prevent a continued rise in the activity of GS. GS activity was also not reduced during induction of secondary dormancy by dehydration of primed seeds, which antagonized the benefidai effect of priming, Psychrometric measurements showed that osmotic potential (v^) of the seeds remained constant during prolonged priming in polyethylene glycol at 15°C, During incubation in water, % increased both prior to and after the moment of germination to less negative values, l! is concluded that changes in the level of dormancy in lettuce seeds occur independently of soluble amino nitrogen metabolism and of changes in \f,.

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