RESUMEN
Germination of lettuce seeds (Lactuca sativa L. cv Grand Rapids) in the dark was nearly 100% at 20 degrees C but was inhibited at 27 degrees C and higher temperatures (thermoinhibition). A single 5-minute exposure to red light completely overcame the inhibition at temperatures up to 28 degrees C, above which the effectiveness of single light exposures gradually declined to reach a negligible level at 32 degrees C. However, the promotive effect of light could be extended to 34 degrees C by repeated irradiations. At any one temperature, increased frequency of irradiations increased germination percentage, and with each degree increase in temperature, increasingly frequent irradiations were necessary to elicit maximal germination. Loss of the effectiveness of single irradiations with increase in temperature may result either from acceleration of the thermal reversion of the far red-absorbing form of phytochrome or decrease in seed sensitivity toward a given percentage of the far red-absorbing form of phytochrome. Using continuous red light to induce germination, the role of endogenous C(2)H(4) in germination at 32 degrees C was studied. Ethylene evolution from irradiated seeds began to increase 2 hours prior to radicle protrusion, whereas the dark-incubated (nongerminating) seeds produced a low, constant amount of C(2)H(4) throughout the 24 hour incubation period. Inhibition of C(2)H(4) synthesis with 2-aminoethoxyvinyl glycine and/or inhibition of C(2)H(4) action with 2,5-norbornadiene blocked the promotive effect of light. Exogenous C(2)H(4) overcame these blockages. The results showed that participation by endogenous C(2)H(4) was essential for the light-induced relief of thermoinhibition of lettuce seed germination. However, light did not act exclusively via C(2)H(4) since exogenous C(2)H(4) alone in darkness did not promote germination.
RESUMEN
Application of exogenous ethylene in combination with gibberellic acid (GA(3)), kinetin (KIN), and/or CO(2) has been reported to induce germination of lettuce seeds at supraoptimal temperatures. However, it is not clear whether endogenous ethylene also plays a mediatory role when germination under these conditions is induced by treatment regimes that do not include ethylene. Therefore, possible involvement of endogenous ethylene during the relief of thermoinhibition of lettuce (Lactuca sativa L. cv Grand Rapids) seed germination at 32 degrees C was investigated. Combinations of GA(3) (0.5 millimolar), KIN (0.05 millimolar), and CO(2) (10%) were used to induce germination. Little germination occurred in controls or upon treatment with ethylene, KIN, or CO(2). Neither KIN nor CO(2) affected the rate of ethylene production by seeds. Both germination and ethylene production were slightly promoted by GA(3). Treatments with GA(3)+CO(2), GA(3)+KIN, or GA(3)+CO(2)+KIN resulted in approximately 10-to 40-fold increases in ethylene production and 50 to 100% promotion of germination as compared to controls. Initial ethylene evolution from the treated seeds was greater than from the controls and a major surge in ethylene evolution occurred at the time of visible germination. Application of 1 millimolar 2-aminoethoxyvinyl glycine (AVG), an inhibitor of ethylene synthesis, in combination with any of above three treatments inhibited the ethylene production to below control levels. This was accompanied by a marked decline in germination percentage. Germination was also inhibited by 2,5-norbornadiene (0.25-2 milliliters per liter), a competitive inhibitor of ethylene action. Application of exogenous ethylene (1-100 microliters per liter) overcame the inhibitory effects of AVG and 2,5-norbornadiene on germination. The results demonstrate that endogenous ethylene synthesis and action are essential for the alleviation of thermoinhibition of lettuce seeds by combinations of GA(3), KIN, and CO(2). It also appears that these treatment combinations do not act exclusively via promotion of ethylene evolution as the application of exogenous ethylene alone did not promote germination.
RESUMEN
The role of ethylene in herbicidal injury induced by 4-amino-3,5,6-trichloropicolinic acid (picloram) or 3,6-dichloropicolinic acid (clopyralid) was investigated in sunflower (Helianthus annuus L.) and rapeseed (Brassica napus L. cv Altex). Picloram induces herbicide injury in both species, whereas clopyralid induces injury only in sunflower. Picloram applied to the third leaf of a rapeseed plant increased ethylene evolution several-fold. Clopyralid had no effect on ethylene production in rapeseed. In sunflower, both picloram and clopyralid elevated ethylene production. Ethylene biosynthesis induced by the herbicide treatment was not restricted to treated areas. When clopyralid was applied only to the lower stem and cotyledons of sunflower, the herbicide treatment resulted in an increase in the rate of ethylene production from the true leaves. Increased ethylene production preceded or coincided with the onset of morphological responses induced by a herbicide application to a susceptible species. The contrast in ethylene production by these two plant species cannot be accounted for by differences in absorption and translocation of clopyralid and picloram.Treatment with aminoethoxyvinylglycine (AVG) before picloram or clopyralid application prevented an increase in ethylene production. Pretreatment with AVG also delayed the development of morphological changes induced by picloram or clopyralid. It appears that enhanced ethylene biosynthesis after application of picloram or clopyralid to the susceptible plant species was a factor involved in resulting morphological changes.
RESUMEN
Effects of ethylene, gibberellins, and kinetin on the germination of two lots of Chenopodium album L. seeds, collected from the field in 1982 and 1983, were studied in relation to the availability of nitrate. The experiments were conducted in darkness and at temperatures ranging from 12 to 32 degrees C. Ethylene induced over 75% germination in the 1983 seed but had little effect on the 1982 seed. Nitrate was only slightly promotive in either of the two seed lots. A combination of ethylene and nitrate, however, acted synergistically on 1982 seed, resulting in as much germination as that induced in 1983 seed by ethylene alone. In 1983 seed, a combination of ethylene and nitrate was only marginally more effective than ethylene. A similar relationship was observed in the effects of gibberellic acid(4+7) (GA(4+7)) and nitrate on seeds from the two lots. The 1982 seed, which responded synergistically to combinations of nitrate with ethylene or GA(4+7) was found to contain an extremely low endogenous level of nitrate as compared to 1983 seed. Thus, high levels of either endogenous or applied nitrate appeared to enhance the germination response to ethylene or GA(4+7).Kinetin had no effect on 1982 seed and only a small promotive effect on 1983 seed. There was no synergism between kinetin and nitrate in either of the seed lots.
RESUMEN
The effect of light on the rate of ethylene production was monitored using two different techniques-leaf segments incubated in closed flasks versus intact plants in a flow-through open system. Three different plants were used, viz sunflower (Helianthus annuus), tomato (Lycopersicon esculentum), and soybean (Glycine max). Experiments were conducted both in the presence and absence of 1-aminocyclopropane-1-carboxylic acid (ACC).The results obtained indicate that, in all three species studied, light strongly inhibits ethylene production when cut leaf segments are incubated in the presence of ACC in closed flasks. When ethylene measurements are made with ACC-sprayed intact plants using a continuous flow system, the effect of light on ethylene production is only marginal. In leaf segments of sunflower and soybean incubated only in distilled H(2)O in closed flasks, light promotes ethylene production. In tomato, there is no difference between the rate of ethylene production between light and darkness under such conditions. When measurements are made with intact plants in a continuous flow system, the rate of ethylene production is almost identical in light and darkness, in the three plants studied.It is concluded that the effect of light on cut leaf segments incubated in the presence of ACC in closed flasks can be attributed to the techniques used for these measurements. Light has little effect on ethylene production by intact plants in an open system.
RESUMEN
High CO(2) concentration (0.5%) increased the rate of ethylene production, measured in a continuous flow system, in intact sunflower (Helianthus annuus L.) plants. However, the rate of ethylene production subsided to near control levels after approximately 24 hours. The effect of high CO(2) could only be observed in light. Although high CO(2) concentration had no effect on the rate of ethylene production in darkness, prolonged exposure (approximately 16 hours) of plants to high CO(2) in the dark prevented the increase in ethylene production when the plants were exposed to light and high CO(2).
RESUMEN
A continuous flow system was used to study the interactions between carbon dioxide and ethylene in intact sunflower (Helianthus annuus L.) plants. An increase in the concentration of carbon dioxide above the ambient level (0.033%) in the atmosphere surrounding the plants increased the rate of ethylene production, and a decrease in carbon dioxide concentration resulted in a decrease in the rate of ethylene production. The change in the rate of ethylene production was evident within the first 15 minutes of the carbon dioxide treatment. Continuous treatment with carbon dioxide was required to maintain increased rate of ethylene production. The rate of carbon dioxide fixation increased in response to high carbon dioxide treatment up to 1.0%. Further increases in carbon dioxide concentration had no additional effect on carbon dioxide fixation. Carbon dioxide concentrations higher than 0.11% induced hyponasty of the leaves whereas treatment with 1 microliter per liter ethylene induced epinasty of the leaves.
RESUMEN
The relationship between the temperature at which germination of 50% of the seeds is inhibited in the light (GT(50) Light) and secondary dormancy was investigated in three cultivars of Lactuca sativa L. Seeds were incubated for varying periods under non-germinating conditions and subsequent germination in response to red light (R) was determined over a wide range of temperatures. Dark incubation at 32 C reduced the GT(50) Light of cv. New York but did not affect germination at temperatures below 24 C. Dark, 32 C incubation had no effect on the GT(50) Light of cv. Great Lakes. In cv. Grand Rapids, dark incubation at 15, 24, 32, or 35 C initially reduced the GT(50) Light. However, longer incubations induced a secondary dormancy, i.e., the seeds became unable to germinate at all temperatures in response to R given after the high temperature incubation. A single exposure to R at the beginning of a 32 C incubation slowed the induction of secondary dormancy. Repeated exposures to R prevented the induction of secondary dormancy, but did not prevent a decline in the GT(50) Light. GA(3) mimicked the effect of repeated R.The differences in the germination behavior of the three cultivars suggest that there may be qualitative differences in the germination mechanism of these cultivars. This research demonstrates the significance of monitoring germination at a range of temperatures to avoid misinterpretation of the data.
RESUMEN
A cuvette is described for simultaneous measurement of ethylene production and CO(2) fixation by intact shoots under controlled environmental conditions. This design overcomes potential problems associated with closed systems conventionally used for studies on ethylene production, allowing accurate determination of rates of ethylene production in plants exposed to different environmental conditions.
RESUMEN
A random sampling analysis of laboratory air and of air from commercially available cylinders indicated that they contain appreciable amounts of low molecular weight hydrocarbons, viz. methane, ethane, and ethylene, as contaminants. These impurities could lead to erroneous conclusions in studies of plant growth and metabolism. Different methods for removal of these contaminants were compared and evaluated in the present investigation for their suitability in plant studies. Most of the methods currently being used were found inadequate. The use of metal catalysts at high temperature, adapted from gas analysis techniques, provides an inexpensive and efficient method for removing hydrocarbons from air in both closed and continuous flow systems.
RESUMEN
The effect of interrupting darkness with red light in the presence or absence of 0.03% CO(2) was studied in relation to flowering of Xanthium pennsylvanicum and germination of light-sensitive lettuce seeds. The results indicate that CO(2) is essential for red light to be effective in either process.