Effects of sodium chloride on prevention of thermodormancy, ethylene and protein synthesis and respiration in Grand Rapids lettuce seeds

Grand Rapids lettuce ( Lactuca saliva L.) seeds entered into a state of secondary dormancy (thermodormancy) when they were imbibed at 40°C for 72 h. The effect of 40°C in inducing thermodormancy was largely reduced by imbibing seeds at 40°C in solutions of polyethylene glycol (PEG), mannitol and NaCl. Despite similar water potentials of solutions, NaCl pretreatment was more effective. Subsequent germination in the dark at 25°C of saline, high-temperature-pretreated seeds required only gibberellic acid (GA₃), as was the case with nonthermodormant seeds. Thermodormancy reduced total respiratory capacity (V_T) and increased the ratio of alternate pathway (V_alt) to cytochrome pathway (V_cyt) respiration. This was prevented by saline pretreatment. Ethylene production and protein synthesis were depressed in thermodormant seeds, and this was partly alleviated by saline pretreatment. The patterns of protein synthesis in saline- and nonsaline-freated seeds at 40°C were similar, differing only in that the saline treated seeds produced in addition a 78 kDa polypeptide. The pattern of protein synthesis at 40°C differed significantly from that at 25°C.     

Developmental changes in tomato fruit composition in response to water deficit and salinity

Processing tomato ( Lycopersicon esculentum Mill. cv. UC82B) plants were subjected to moderate levels of water deficit and salinity (Na₂SO₄/CaCl₂) in sand culture. Fruit water content and the relative contributions of organic and inorganic constituents to fruit solute potential (_Ψ) and soluble solids content were determined throughout development. Fruit _Ψ averaged –0.63, –0.86 and –0.77 MPa in the control, salinity and water deficit plants, respectively. Reduced net water import and maintenance of solute accumulation, irrespective of water import, accounted for the reductions in _Ψ of stressed fruits. Mineral ions (Na⁺, K⁺, Ca²⁺, Mg²⁺, Cl⁻ and SO^2-₄) contributed –0.31 MPa to _Ψ in salinized fruit, compared with –0.19 MPa in control and water deficit treatments. Changes in net carbon accumulation were not observed among treatments, despite considerable differences in fruit K⁺ status. Starch accumulation in immature fruit was increased and hexose accumulation was decreased by both salinity and water deficit. Maximum starch levels were negatively correlated with total fruit _Ψ, but were independent of fruit K⁺. Organic acid levels were generally higher throughout development in salinized plants, relative to control plants, and correlated with increased inorganic cation rather than anion accumulation in these fruits.     

Study of the inheritance of seed primary dormancy and the ability to enter secondary dormancy in Petunia: influence of temperature, light and gibberellic acid on dormancy

Abstract. The germination behaviour of two Petunia hybrida lines. M₃₀ and Th₇, and their reciprocal hybrids was studied. Two sets of experimental conditions appeared helped to distinguish between dormant and non-dormant parental lines: (1) 25 and 35 °C in the dark, in the latter case after 2 months of dry storage at 20 °C; (2) 35 and 40 °C in the light. Photosensitivity was tested in the first case and sensitivity to GA₃ in the second case. The predominance of paternal control over dormancy was evident. A maternal or tegumentary control of photosensitivity and of sensitivity to GA₃ was also shown. Transferring the seeds, originally imbibed in conditions expressing primary dormancy, to conditions which previously supported their germination, allowed us to show that secondary dormancy could be easily induced when a deeper primary dormancy had already developed in the seeds.     

Factors affecting the induction and release of secondary dormancy in Kalanchoë seeds

Abstract. Several short daily R irradiations are required from the first day of incubation on water to induce germination of Kalanchoë seeds. When the same light treatment is given after a prolonged dark incubation period at 20°C, secondary dormancy prevents germination. Factors controlling the induction and breaking of secondary dormancy have been investigated. The induction of secondary dormancy is very temperature dependent. Locally puncturing the seed coat strongly delays it. Secondary dormancy is not induced in the presence of GA₃ during the first 10 d of dark incubation, although this growth substance cannot induce dark germination. Prolonged or cyclic daily R irradiations can relieve secondary dormancy of seeds kept on water, even after a dark period of 20 d. A 24 h treatment at 4°C restores responsiveness to short R exposures of slightly secondarily dormant seeds. The synergism between GA₃ and Pfr in non-dormant Kalanchoë seeds, leading to high effectiveness of even one short FR irradiation, still occurs in seeds made secondarily dormant before transfer to GA₃, but more R or FR irradiations, in combination with GA₃, are required for the release of secondary dormancy. A combination of red light and 6-benzyl-aminopurine is ineffective in removing dormancy.     

Genotypic variation in tissue water relations of leaves and roots of black walnut (Juglans nigra) seedlings

Genetic variation in the drought response of leaf and root tissue water relations of seedlings of eight sources of black walnut ( Juglans nigra L.) was investigated using the pressure-volume technique. Tissue water relations were characterized at three stages of a drying cycle during which well-watered plants were allowed to desiccate and then were reirrigated.
Sources varied both in the capacity for and degree of leaf and root osmotic adjustment, and in the mechanism by which it was achieved. A decrease in osmotic potential at the turgor loss point (ψ_πp) of 0.4 MPa was attributable to increased leaf tissue elasticity in seedlings of four sources, while seedlings of an Ontario source exhibited a 0.7–0.8 MPa decline in ψ_πp as a result of both increased solute content and increased leaf tissue elasticity. Seedlings of a New York source showed no detectable osmotic adjustment.
In roots, decreased ψ_πp (osmotic potential at full hydration) and ψ_πp were observed under drought. Sources that exhibited significant leaf osmotic adjustment also generally showed a similar response in roots. Tissue elasticity and ψ_πp of roots were higher than those of shoots, whereas ψ_πp of the two organs was similar for most sources. Because of greater elasticity, roots exhibited a more gradual decline in turgor and total water potential than did leaves as tissue relative water content decreased.     

Differences in the nature of thermodormancy and far-red dormancy in lettuce seeds

Lettuce seeds cv. Noran germinate at 23°C in light as well as in darkness. However dormancy can be induced either by a long exposure (24 h) to far-red radiation or by an exposure of 48–72 h to a temperature of 37°C. The difference in response of these two types of dormant seeds to conditions inducing germination indicate that in both types P_fr is inactivated, but that a dark process required for immediate action of P_fr does not proceed at 37°C as it does during far-red radiation.     

Effects of temperature and drying rate during dehydration of celery seeds on germination, leakage and response to gibberellin and cytokinin

A high temperature treatment of 32°C which prevents dehydration injury in celery seeds imbibed for 3 days at 17°C and then dried at 20°C, reduced leakage during rehydration, compared with seeds not given the high temperature treatment. Treatments which would normally release celery seeds from dormancy, such as low temperature imbibition or gibberellin (GA_4/7) and benzyladenine (BA) applications had little effect on the germination of seeds exhibiting desiccation injury. However, GA_4/7 did induce splitting of the seed coat and swelling of the endosperm, and this effect was enhanced by BA. It is suggested that in celery seeds high temperature prevents irreversible embryo damage, including membrane damage, caused by drying.     

Antagonistic effects of abscisic acid and gibberellic acid on the breaking of dormancy of Fagus sylvatica seeds

Study of the factors involved in the dormancy of Fagus sylvatica seeds shows that such dormancy is due partly to the seed coats and partly to endogenous factors. Seed coat removal accelerates both the release from dormancy and the effects of the other treatments that abolish it. The dormancy of these seeds is eliminated by cold treatment at 4°C over a period longer than 8 weeks, and exogenous application of abscisic acid (ABA) reverses the effects of low temperature, the seeds remaining in an ungerminated state. Additionally, ABA reduces protein synthesis but slightly increases RNA synthesis, which suggests its involvement in the synthesis of RNAs related to this process. In vitro translation of the RNAs isolated from these seeds shows that ABA delays the disappearance of at least 2 polypeptides (of ca 22 and 24 kDa), which are abundant in dormant seeds and under conditions that prevent the release from dormancy, but which disappear under treatments that abolish it. Exogenous application of gibberellic acid (GA₃) proved to be efficient in breaking the dormancy of these seeds and in substituting for cold treatment as well as in antagonizing the effects of ABA on the synthesis of both DNA and proteins. GA₃ also accelerates the disappearance of the two polypeptides abundant in dormant seeds and in ABA-treated seeds. These findings suggest that both ABA and GA₃ could be involved in the regulation of nucleic acid and protein metabolism during dormancy, acting antagonistically in these processes and, specifically, in the regulation of the synthesis of the two proteins that appear to play a role in the maintenance of dormancy in these seeds.     

Effect of atmospheric ammonia on the nitrogen metabolism of Scots pine (Pinus sylvestris) needles

Four-year-old seedlings of Scots pine ( Pinus sylvestris L.) were exposed to filtered air (FA), and to FA supplemented with NH₃ (60 and 240 μg m⁻³) in controlled-environment chambers for 14 weeks. Exposure to the higher NH₃ concentration resulted in an increased activity of glutamine synthetase (GS, EC 6.3.1.2), and an increase in the concentrations of soluble proteins, total nitrogen, free amino acids and leaf pigments in the needles. The GS activity (μmol g⁻¹ fresh weight h⁻¹) in the needle extract increased to levels 69% higher than in FA and the soluble protein concentration to levels 22% higher. Total nitrogen concentration in the needles was 42% higher than in FA, while the free amino acid concentration was 300% higher, which was caused by an increase in arginine, glutamate, aspartate and glutamine. Chlorophyll a , chlorophyll b and carotenoid concentrations were 29, 38 and 11% higher, respectively. Neither the glutamate dehydrogenase (GDH, EC 1.4.1.2) activity nor the concentrations of free NH₄⁺ and glucose in the needles were affected by exposure to NH₃. After NH₃ fumigation at 240 μg m⁻³ the starch concentration decreased by 39% relative to the FA. The results indicate that the metabolism of Scots pine acclimates to concentrations of NH₃ which are 3 to 10 times higher than the average concentration in areas with intensive stock farming. The possible mechanisms underlying acclimation to NH₃ are discussed.     

Development of seed coat-imposed dormancy during seed maturation in Cynoglossum officinale

The relationship between seed phenolics and appearance of seed coat–imposed dormancy during seed development in Cynoglossum officinale L. was studied. Up to 24 days after anthesis, seeds failed to germinate upon imbibition in Petri dishes at 25°C. At 44 days after anthesis, seeds were fully germinable; removal of seed coats did not improve their germination or O₂ uptake. At 72 days after anthesis, mature seeds at the base of the cyme did not germinate unless their coats were removed. Removal of seed coat also stimulated O₂ uptake at this harvest date. The methanol-soluble phenolic content of the seeds increased during the early stages of seed development, in both the seed coat and the embryo. As seed development continued, the methanol-soluble phenolic content of the embryo stabilized, but that of the seed coat declined. This decline was associated with an increase in the thioglycolic acid–soluble phenolics, presumably lignins, in the seed coat. These results suggest that polymerization of methanol–soluble phenolics into lignins in the seed coat during later stages of seed development renders the seed coat of C. officinale impermeable to 03, and thus keeps the seed dormant.     

The effect of single step and fluctuating temperature changes on the oxygen consumption of flounders, Platichthys flesus (L.): Lack of temperature adaptation

The standard oxygen consumption of flounders, PLatichthys flesus , adapted for two months to 5 and 15° C was measured during single step and fluctuating temperature changes, A considerable recovery period from handling was required before standard levels were recorded, although no locomotor activity was evident. The Q ₁₀(adapt) value between 5 and 15° C was 2.0. Q ₁₀ (acute) values were higher. The responses of oxygen consumption to temperature rise conform to Type I11 metabolic compensation (Precht, 1958). No compensatory response was evident at lower temperatures. An alternative explanation of the results in terms ofexcitement metabolism is suggested.     

Interaction of triacontanol with gibberellin in control of lettuce seed germination

Triacontanol at concentrations from 2.3 × 10^-9 M to 2.3 × 10^-7 M did not affect the germination of lettuce ( Lactuca sativa L., cv. Grand Rapids) seeds in darkness, stimulated by light at 25°C or by benzyladenine at 31°C. Stimulation of seed germination by gibberellin A₃ (10^-5 M ) was significantly inhibited by triacontanol; the most effective concentration was 4.6 × 10^-8 M. Pulse experiments demonstrated that triacontanol was ineffective when applied later than gibberellin, whereas an inverse sequence of treatment caused an inhibition comparable to that resulting from continuous treatment of seeds with both factors. Possible interaction of triacontanol with gibberellin receptor is discussed.     

Effect of nitrogen supply on frost resistance, nitrogen metabolism and carbohydrate content in white clover (Trifolium repens)

Effects of mineral nitrogen (2, 4, 6 and 8 m M NH₄NO₃) and nodulation with Rhizobium on frost hardiness in seedlings of white clover ( Trifolium repens ) have been studied. Seedlings of a population from Bodø (67°N lat.) were grown in Leonard jars under controlled conditions in a phytotron. For induction of frost hardening, plants were first exposed to 12 h photoperiod conditions for 2 weeks at 18°C, then for 2 weeks at 6°C and finally for 2 weeks at 0.5°C. Frost hardiness after treatments at 6 and 0.5°C was significantly enhanced by increasing nitrogen supply and was positively correlated with total nitrogen content of the stolons. Frost hardiness of nodulated plants correlated to the tissue nitrogen concentration. Content of soluble proteins in stolons decreased during hardening at 6°C but did not change during treatment at 0.5°C. There were minor changes in total amount of free amino acids during hardening. Both absolute and relative amounts of proline and arginine increased, and those of asparagine decreased during hardening. Absolute amounts of all free amino acids increased with increasing nitrogen supply, but the changes during hardening were similar in all treatments. There was a significant increase in the content of soluble carbohydrates during hardening. However, this increase was inversely related to nitrogen supply.     

Changes in sensitivity of Amaranthus retrof/exus L. seeds to ethylene during preincubation. I. Constant temperatures

Abstract. Germination responses of redroot pigweed ( Amaranthus retroflexus L.) seeds to ethylene were determined at 25, 30, 35, or 40° C after preincubation at various temperatures (15–35° C) for different periods (0.5–32 d). After 7 d preincubation, seeds showed a log-linear germination response to ethylene concentration in most of the temperature treatments. Sensitivity to ethylene increased with longer preincubation; response thresholds of 0.03−0.09 cm³ m⁻³ were observed after 32 d, compared to 0.18−1.6 cm³ m⁻³ after 7 d of preincubation. Preincubation at 15 or 20° C generally enhanced germinability, whereas 25 or 30° C produced secondary dormancy, which was readily broken with ethylene. Temperature during preincubation also significantly influenced the slope of the dose-response curve. The responses of preincubated redroot pigweed seeds to ethylene suggested that, in the field, seeds would probably not lose their sensitivity to this gas during prolonged burial in soil.     

Respiration and soluble sugar metabolism in sugar pine embryos

Embroys excised from dormant seeds of sugar pine ( Pinus lambertiana Dougl.) incubated at 25°C (non-dormancy-breaking) or stratified at 5°C (dormancy-breaking) were analyzed to determine temperature effects on the relative activities of respiration and fermentative metabolism, the levels of soluble sugers and the activities of the hydrolytic enzymes, invertase and sucrose synthase, as related to the release of dormancy and germinatio. At 25°C, despite a sharp drop in embryo oxygen uptake after 48 h, a simultaneous decline in acetaldehyde and ethanol concentrations indicated that there was not a shift to fermentative metabolism. The concentrations of soluble sugars showed no treatment effects. Embryo invertase (EC 3.2.1.26) activity changed only slightly at either temperature, while stratification was accompanied by a 4-fold increase in sucrose synthase (EC 2.4.1.13) activity (cleavage direction). Upon transfer of stratified seeds to 25°C, embryo sucrose synthase activity rapidly increased almost 10-fold, with the increase beginning prior to germination, while mvertase activity increased 20-fold, concomitant with germination.     

Inositol 1,4,5-trisphosphate formation in leaves of winter oilseed rape plants in response to freezing, tissue water potential aed abscisic acid

Time courses of formation of inositol 1,4,5-trisphosphate (IP₃) were followed in the leaves of non-acclimated and cold (2°C)-acclimated winter oilseed rape ( Brassica napus L. var. oleifera ) plants, subjected to different freezing temperatures or to polyethylene glycol 8000 (PEG) and abscisic acid (ABA) treatments. Changes in water potential (Ψ_w) and in ABA level in the frost- and PEG-treated tissues were also determined. Results obtained indicate that temperatures sligthly higher than LT₅₀ induced a transient and substantial increase in IP₃ level, both in non-acclimated and cold-acclimated tissues. At comparable freezing temperature (–5°C) the response of cold-acclimated leaves was lower than that of non-acclimated ones. The PEG-depedent decrease in Ψ_w to –0.9 MPa or ABA (0.1 m M ) treatment gave rise to a transient increase in IP₃ content in non-acclimated tissues only. Collectively, the data indicate that cold acclimation of plants may lead to lower cell responsiveness to the factors studied in terms of induction of IP₃ formation. Changes in the IP₃ content, observed in the present experiments, support our previous suggestion that non-killing freezing temperatures may induce the phosphoinositide pathway, both in non-acclimated and cold-acclimated tissues. Lowering of tissue water potential to some threshold value or a high exogenous ABA supply may mimic the freezing-dependent reaction in the non-acclimated leaves.     

Indirect effect of abscisic acid on the induction of secondary dormancy in lettuce seeds

During temporary incubation at 25°C in buffered solutions (pH 4.0) of abscisic acid (ABA) seeds of lettuce ( Lactuca sativa L. cv. Olof) lost the red-light initiated ability to germinate in buffer. The development of secondary dormancy required an inhibitory ABA content in the seeds during a number of days. A temporary incubation in ABA during 24 h met these requirements only if the solution was about 100-fold more concentrated than during continuous incubation. Studies with 2-¹⁴C-ABA showed that the amount of ABA which had penetrated in 24 h was reduced by a factor 100 within 3 to 4 days during subsequent incubation in buffer. Both leaching and metabolic changes were involved in the reduction process. The nature of the metabolic products remained obscure. A shift to 2°C after incubation in ABA prevented the induction of secondary dormancy, but inhibited ABA metabolism. ABA did not interfere with the induction rate of secondary dormancy, and it was not required to maintain the state of dormancy. The sole function of ABA was the non-specific inhibition of germination, which indirectly facilitated the development of an ABA independent secondary dormancy. – The level of endogenous ABA was compared to the amount of ABA found in the embryo during and after incubation in ABA solutions marked with 2-¹⁴C-ABA. The level of endogenous ABA in air-dry seeds (0.11 ng/mg dry weight) corresponded to the minimal level at which penetrated ABA inhibited germination. This level had to be present at least during 4 to 5 days to inhibit the effect of red light. Since endogenous ABA was quickly reduced upon imbibition, a regulatory function of endogenous ABA in the inhibition of red light induced germination can be ruled out. A function in the temporary inhibition of dark germination and, consequently, in the development of secondary light irresponsiveness cannot be excluded, however.     

Changes in phenolic acids and abscisic acid in sugar pine embryos and megagametophytes during stratification

The phenolic acids and abscisic acid (ABA) of sugar pine ( Pinus lambertiana Dougl.) embryos and megagametophytes, separated by high-pressure liquid chromatography, were analyzed during 90 days stratification of the seeds. The phenolic acids occurred mainly as glycosides. Following hydrolysis, the majority of phenolics present could be identified as common benzoic and ciranamic acid derivatives. Levels of phenolic acids were relatively low in dormant seeds, but increased substantially in the embryos during stratification at 5°C, particularly cinnamic acid, p -coumaric acid, ferulic acid, and one unknown. This active synthesis during stratification did not support an inhibitory function for phenolic acids. During stratification at 5°C, changes in ABA levels in both tissues followed a triphasic pattern, with no loss during the first 30 days, a significant decrease the second 30 days, and a lesser decrease the last 30 days. Loss of ABA from moist seeds at 25°C occurred three times as rapidly, so that by 30 days the ABA level of these seeds was equivalent to that of seeds stratified 90 days at 5°C; however, dormancy was not alleviated at 25°C. Application of exogenous ABA (10⁻⁷ to 10⁻⁴M) to stratified seeds did not significantly reduce germination. Together, the above results did not support a primary role for ABA in the maintenance of dormancy in sugar pines.
A correlated increase in phenylpropanoid metabolism and respiratory capacity with increased germinability during stratification suggests that loss of dormancy may be more closely dependent on increased levels of growth promoters or shifts in metabolic pathways.     

Sporulation of Clostridium putrefaciens and the Resistance of the Spores to Heat, γ-Radiation and Curing Salts

Clostridium putrefaciens grew well in most media used routinely for culturing anaerobes, but produced spores only on lactose-egg yolk agar. The D_80° was 8–14 min, z value was 4°–6° and D _γ, 0.16 Mrad. The inhibitory interactions of pH, NaCl, NaNO₂ and incubation temperature are described.