The effects of seed priming on germination and endo-β-mannanase activity at inhibitory and non-inhibitory temperatures in thermosensitive ‘Dark Green Boston’ (DGB) and in thermotolerant ‘Everglades’ (EVE) lettuce were investigated. A single-seed endo-β-mannanase assay was used to follow the enzyme activity during priming. Seeds were primed at 15°C in aerated solutions of polyethylene glycol (PEG) with constant light, then redried. Primed and non-primed seeds germinated 100% at 20°C. At 35°C, non-primed and primed EVE seeds germinated 100%, whereas non-primed seeds of DGB germinated only 4%. During priming, endo-β-mannanase activity increased between 24 and 48 h in EVE and between 24 and 72 h in DGB after the beginning of osmotic imbibition. Endo-β-mannanase activity persisted in primed seeds following seed drying, was detected before radicle protrusion and was present in the micropylar region in front of the radicle tip. Higher enzyme activity was observed in primed seeds and EVE compared with non-primed and DGB seeds. The results suggest that priming may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-β-mannanase activity, possibly leading to a weakening of endosperm, thus overcoming thermodormancy.
Chlorophyll (Chl) and total soluble protein decreased and proteolytic activity increased over a 12-day period during dark-induced senescence in detached leaves of Tara, a yellowing cultivar (Y) of Dendranthema grandiflora. In Boaldi, a non-yellowing cultivar (NY), Chl and soluble protein remained near initial levels and little change in proteolytic activity was observed. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of soluble proteins showed no major differences in banding patterns between the two cultivars at day 0; however, all of the resolved proteins were diminished in Tara by day 12. On the other hand, in NY Boaldi, the intensity of the protein bands did not change over the 12-day period. Attached and detached leaves exhibited similar senescence patterns for each cultivar. Ethylene (100 µl l-1) accelerated the rate of Chl loss in detached leaves of Tara, but had no effect on Boaldi. These observations suggest that Boaldi is a stay-green genotype, possibly a functional type. The results are discussed in relation to the role of ethylene in chrysanthemum leaf senescence.
Temperatures above 30 °C may delay or inhibit germination of most of commercial lettuce cultivars. Ethylene enhances lettuce seed germination at high temperatures. Enzyme-mediated degradation of endosperm cell walls appears to be a crucial factor for lettuce germination at high temperature. The galactomannan polysaccharides in lettuce endosperm cell wall are mobilized by endomannanase. The role of endo-mannanase during germination of lettuce seeds at high temperature (35 °C) and the possible role of etlene in enzyme regulation were investigated. Seeds of thermotolerant (`Everglades'-EVE) and thermosensitive (`Dark Green Boston'-DGB) lettuce genotypes were incubated at 20 and 35 °C in water, 10 mM of 1-aminocyclopropane-1-carboxylic acid (ACC), or 20 mM of silver thiosulphate (STS). Also, seeds were primed in an aerated solution of polyethylene glycol (PEG), or PEG+ACC, or PEG+STS. Untreated seeds germinated 100% at 20 °C. At 35 °C, EVE germinated 100%, whereas DGB germinated only 33%. Seed priming or adding ACC during imbibition increased germination of DGB to 100% at 35 °C. Adding STS during imbibition led to a decrease in germination at 35%C in EVE and completely inhibited germination of DGB. Priming with STS led to reduced germination at 35%C of both genotypes. EVE produced more ethylene than DGB during germination at high temperature. Providing ACC either during priming or during germination led to an increase in endo-mannanase activity, whereas STS inhibited mannanase activity. Higher endo-mannana activity was observed in EVE than DGB seeds. The results suggest that ethylene might overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds via weakening of endosperm due to increased endo-mannanase activity.
Carrot (Daucus carota) seed germination can be erratic or reduced under temperatures above 35ºC. Priming circumvents seed thermoinhibition in several crops, including carrot. The involvement of ethylene in germination at supra-optimal temperatures has been reported in other species, but its role in carrot seed germination has not been examined. The objective of this study was to determine whether priming-mediated improvement in carrot seed germination at high temperature was associated with increased ethylene production. Seeds of two tropical carrot genotypes (Alvorada and Brasília) were incubated over a range of temperatures. 'Brasilia' seeds were primed for 72 hours in aerated PEG solution at 15ºC under light conditions and germination tested at 20 and 35ºC. Seeds of a thermosensitive genotype 'Arrowhead' were primed for 0, 4, 8 and 12 days in aerated PEG 6000 solutions at 15ºC under light conditions. Seeds were incubated at 20 and 35ºC, and ethylene production was measured immediately before visible primary root protrusion. Temperatures above 30ºC decreased seed germination percentage of 'Alvorada' and 'Brasilia'. Priming increased 'Brasilia' seed germination at 35ºC. 'Arrowhead' germinated 96% at 20ºC, and 13% at 35ºC. Seed germination and ethylene production of 'Arrowhead', a thermosensitive genotype, increased in response to increased duration of priming. The results suggest that seed priming circumvents thermoinhibition of carrot seed germination by increasing ethylene production at high temperatures.
Abstract Cellulose contents in acetone powders derived from tomato ( Lycopersicon esculentum Mill. ‘Sunny’) fruit pericarp and locular gel were measured. In the pericarp, cellulose increased throughout development, whereas C x -cellulase activity increased during ripening. Locular gel cellulose content was lower than that in pericarp at all developmental stages, increasing through the breaker stage. Beyond the breaker stage, during the terminal period of gel formation, locular gel cellulose decreased. Levels of C x -cellulase were high in gel tissue, and maximum activity was attained prior to the decrease in gel cellulose indicating that C x -cellulase and cellulose may be important features of gel formation.
In previous studies, 1-methylcyclopropene (1-MCP) was shown to significantly suppress peel degreening and appearance of senescent spotting of banana fruit (Stanley and Huber, 2004). In the present study, the effect of the ethylene antagonist on banana pulp soluble sugar levels and on peel soluble and total phenolics was measured. One hundred and sixty hands (10 boxes) of banana fruit ( Musaacuminata cv. Cavendish) were treated with ethylene (300 μL·L -1 , 24 h, 15 °C, 90% RH) at a commercial ripening facility in Bradenton, Fla., and transported by truck (15 °C) to the University of Florida. Fruit were sorted and placed in 174-L ripening chambers, where 80 hands received 500 nL·L -1 1-MCP for two 12-h periods at 18 °C, while the other 80 hands (controls) were maintained in identical containers without 1-MCP for equal time periods at 18 °C. Mean whole fruit firmness in both treatment groups was 140 N and decreased to 15 N (controls) and 30 N (1-MCP) by day 12. Soluble sugars in the pulp of control fruit achieved levels between 160–180 mg·g -1 fresh weight by day 8, while 1-MCP treated fruit required about 12 days to achieve similar soluble sugar levels. Total phenolic compounds present in peel tissue of control and 1-MCP treated fruit required 10 and 14 days, respectively, to achieve levels of about 4000 μg·g -1 fresh weight. Chlorogenic acid levels, a subset of total peel phenolic compounds, peaked above 500 μg·g -1 by day 10 in control fruit and by day 12 in 1-MCP treated fruit. Maintenance of fruit firmness along with the achievement of acceptable sugar levels of 1-MCP treated fruit demonstrate possible benefits of suppression of ethylene action for retail and processing markets for banana fruit.
Abstract A vacuum infiltration technique that allowed precise control of both infiltration rate and amount of solution administered to whole tomato ( Lycopersicon esculentum ) fruit was developed. Controlled volumes of 5 m m solutions of CuSO 4 , Cu(NO 3 ) 2 , HgCl 2 , CaSO 4 , KNO 3 , (NH 4 ) 2 C 2 O 4 , Na 2 HPO 4 , citrate and 1 m m EDTA or EGTA were infiltrated into intact, mature-green tomato fruit and evaluated with regard to their effect on the pattern of tomato ripening. Copper significantly accelerated lycopene accumulation and influenced both the timing and magnitude of climacteric ethylene production. Infiltration with HgCl 2 elicited similar effects as copper, but severe phytotoxicity was observed. In contrast, CaSO 4 , KNO 3 , and chelators had no significant effect on the pattern of ripening. Copper initiated wound ethylene production in the ripening mutant rin that reached up to 50% of the wound levels observed in normal fruit, but rin was not induced to ripen.
High temperatures during lettuce seed imbibition can delay or completely inhibit germination and the endosperm layer appears to restrict the radicle protrusion. The role of endo-beta-mannanase during lettuce seed germination at 35°C and the influence of ethylene in endo-beta-mannanase regulation were investigated. Seeds of 'Dark Green Boston' (DGB) and 'Everglades' (EVE) were germinated in water, or 10 mmol L-1 of 1-aminocyclopropane-1-carboxylic acid (ACC), or 10 mmol L-1 of aminoethoxyvinylglycine (AVG), or 20 mmol L-1 of silver thiosulphate (STS). Seeds were also primed in polyethylene glycol (PEG), or PEG + ACC, PEG + AVG, or PEG + STS. Untreated seeds germinated 100% at 20°C. At 35°C, EVE seeds germinated 100%, whereas DGB seeds germinated only 33%. Seed priming or adding ACC during incubation increased germination at 35°C. Higher ethylene evolution was detected in EVE than in DGB during germination at 35°C. AVG did not inhibit seed germination of DGB at 35°C, but STS did. Higher endo-beta-mannanase activity was observed in EVE compared with DGB seeds. Providing ACC either during priming or during germination increased endo-beta-mannanase activity, whereas AVG and STS led to decreased or no activity. Ethylene may overcome the inhibitory effect of high temperature in thermosensitive lettuce seeds due to increased endo-beta-mannanase, possibly leading to weakening of the endosperm.
