Imbibition Temperature Research Articles

Winterfat (Eurotia lanata(Pursh) Moq.) Seedbed Ecology: Low Temperature Exotherms and Cold Hardiness in Hydrated Seeds as Influenced by Imbibition Temperature

Thermal analyses of freezing events in hydrated lettuce (Lactuca sativaL.) seeds show a correlation between low temperature exotherms (LTEs) (evidence of ice crystal formation) and seed death. Yet, weather patterns common to the Northern Great Plains of North America regularly create conditions where non-dormant seeds of native plants hydrate with snow melt and are subsequently exposed to -30 °C or colder conditions. To determine if such weather patterns decimate dispersed seeds, we measured the effects of freezing on fully hydrated winterfat (Eurotia lanata(Pursh) Moq.) seeds harvested from the Northern Plains at two USA and one Canadian location. Survival of hydrated seeds to -30 °C at a cooling rate of 2.5 °C h-1was similar to that of seeds not subjected to cooling, even though both a high temperature exotherm (HTE) and an LTE were observed. Although the LTE was not related to winterfat seed survival, freeze-stressed seeds had reduced germination rates and reduced seedling vigour, particularly for the collection with the lightest seeds. The temperature of LTEs was similar among seed collections with a mean of -17.6 °C, but was warmer when the seeds were imbibed at 0 °C compared to 5, 10 or 20 °C. We found a significant correlation between the HTE and LTE temperatures. The difference and the correlation may be due to the higher moisture content of seeds imbibed at 0 °C. After pericarp removal, only one exotherm in the range of the LTE was observed. This was also true for the naked embryo. We conclude that an LTE indicates ice formation in the embryo, but that it does not signal the death of a winterfat seed.

Effect of Seed Moisture on Wyoming Big Sagebrush Seed Quality

Seed germination and seedling vigor of Wyoming big sagebrush (Artemesia tridentata Nutt. ssp. wyomingensis) were evaluated following manipulation of seed moisture, a practice benefitting many species. At the time of harvest, seed moisture ranged from 2.3 to 9.0% for 5 collections tested and seeds with moisture between 5 to 6% had the highest and most rapid germination. Seed moisture changed during storage, but germination percentage was not affected by post-harvest seed moisture change, indicating that germination is related more to habitat or genetic variations than the initial moisture content. Seedling vigor increased after storage, suggesting that after-ripening may be required. Seeds of 2 commercial collections were subsequently humidified at 2, 5, 10, and 15 degrees C for up to 15 days, or to 60% moisture content. Seed moisture increased most gradually at 2 degrees C and seeds held at 10 degrees C attained a higher moisture level than at other temperatures. Germination percentage, germination rate, and seedling vigor were similar between treatments and controls regardless of seed moisture change. Imbibition temperature did not affect germination percentage or seedling vigor, but the time to 50% germination decreased with increasing imbibition temperature. We conclude that artificial seed moisture management did not affect germination percentage, germination rate, or seedling vigor of this species when tested under optimum moisture conditions. Germination is more related to habitat or genetic variables than initial seed moisture content.

Very low fluence and low fluence response in the induction and inhibition of seed germination in Celosia argentea

AbstractSeeds of Celosia argentea L. displayed an absolute requirement for light for germination. Germination could be induced by far-red light as well as red light, and therefore, the effect of red light was not completely reversible by far-red light. A considerable proportion of the seed population was sensitive to red light within the range 0.01–0.1 μmol m−2, which suggested that phytochrome was operating in the very low fluence response mode. Seeds showed a gradual increase in germination in response to red light with an increasing duration of previous dark imbibition. Interruption of the dark imbibition period with very low fluence (10−4−10–1 μmol m−2) or low fluence (1–103 μmol m−2) red light prevented germination subsequent to a terminal, saturating red light irradiation. Increasing responsiveness to red light with increase in imbibition temperature and inhibition of development of photosensitivity by cycloheximide suggested that phytochrome synthesis occurred during the dark imbibition period. An absolute requirement for light for seed germination, inhibition of seed germination on interrupting the dark imbibition period with very low fluence or low fluence red light, and the recovery from photoinhibition of seeds in darkness are consistent with the hypothesis that PhyA is the principal phytochrome involved in the photoregulation of seed germination in C. argentea.

Cation Concentration in Post-Imbibed Winterfat Seeds as Influenced by Imbibition Temperature

Winterfat [Eurotia lanata (Pursh) Moq.] is a chenopod shrub often used in range seedings because of its palatability and nutritive value. Environmental conditions influence winterfat germination and seedling vigor and, therefore, seedling success. We tested the hypothesis that seed imbibition at warm temperatures damages seed membranes, resulting in lower post-imbibition concentrations of seed cations. Energy-dispersive x-ray microanalysis of Cl uptake and fresh weight increase over time gave evidence that winterfat seeds imbibe more rapidly at 25 than at 4 degrees C. However, imbibition of seeds at 20 degrees C did not result in consistently lower post-imbibition cation concentrations. Although imbibition is more rapid at warm temperatures, the post-imbibition concentration of cations in seeds imbibed at 20 degrees C does not justify the conclusion that warm imbibition damages winterfat seed membranes.

Water relations of lettuce seed thermoinhibition. II. Ethylene and endosperm effects on base water potential

A water relations (hydrotime) model was employed to characterize the responses of lettuce (Lactuca sativa L.) seed germination to temperature, water potential (ψ), endosperm disruption, and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The base water potentials (ψb), standard deviations of base water potential and hydrotime constants (θH) estimated by the model were used to predict the germination rates at reduced ψ and supraoptimal temperatures in the presence or absence of ACC. The distribution of ψb values among seeds in the population (ψb(g)) increased (became more positive) as the imbibition temperature increased, indicating a greater sensitivity of seeds to reduced ψ at thermoinhibitory temperatures. Slitting the seeds at the cotyledonary end to disrupt the integrity of the endosperm extended the high temperature range for germination and maintained lower ψb(g) distributions compared with intact seeds as temperature increased. ACC (10 mm) in the imbibition solution raised the upper temperature limit for germination by about 2°C, and also lowered ψb(g) values by 0.1 to 0.2 MPa. The effect of ACC on ψb(g) was more pronounced at higher imbibition temperatures and in slit seeds. ACC (via conversion to ethylene) extends the high temperature limit for lettuce seed germination by acting in the embryo to maintain a lower ψ threshold for the initiation of growth as temperature increases. Evidence from other species as well suggests that this may be a general mechanism for the action of ethylene in promoting seed germination.

Water relations of lettuce seed thermoinhibition. I. Priming and endosperm effects on base water potential

A water relations (hydrotime) model was employed to characterize the responses of lettuce ( Lactuca sativa L.) seed germination to temperature, water potential (ψ), endosperm disruption, and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The base water potentials (ψ b ), standard deviations of base water potential and hydrotime constants (θ H ) estimated by the model were used to predict the germination rates at reduced ψ and supraoptimal temperatures in the presence or absence of ACC. The distribution of ψ b values among seeds in the population (ψ b ( g )) increased (became more positive) as the imbibition temperature increased, indicating a greater sensitivity of seeds to reduced ψ at thermoinhibitory temperatures. Slitting the seeds at the cotyledonary end to disrupt the integrity of the endosperm extended the high temperature range for germination and maintained lower ψ b ( g ) distributions compared with intact seeds as temperature increased. ACC (10 m m ) in the imbibition solution raised the upper temperature limit for germination by about 2°C, and also lowered ψ b ( g ) values by 0.1 to 0.2 MPa. The effect of ACC on ψ b ( g ) was more pronounced at higher imbibition temperatures and in slit seeds. ACC (via conversion to ethylene) extends the high temperature limit for lettuce seed germination by acting in the embryo to maintain a lower ψ threshold for the initiation of growth as temperature increases. Evidence from other species as well suggests that this may be a general mechanism for the action of ethylene in promoting seed germination.

Light and temperature action in germination of seeds of the empress tree (Paulownia tomentosa)

Seeds of the empress tree (Paulownia tomentosa Steud.) were imbibed for two weeks in darkness at constant temperatures (18, 23 or 28°C), and then irradiated with red light for 5 min. Germination was poor if it took place at the same temperature as imbibition, but a high percentage was achieved if the seeds were exposed to higher or lower temperatures before they were irradiated. Maximum germination was obtained when the difference between pretreatment and imbibition was about 10°C. The effect increased with the duration of the pretreatment and was optimal at 24 h. The effect decreased as the time lapse between temperature pretreatment and red light irradiation increased, and it was lost after two days. If pretreatment was shorter than 24 h (12 h). a high percent of germination was obtained by alternating pretreatment and imbibition temperatures. The germination of seeds imbibed in 40% heavy water was also stimulated by temperature pretreatments. Light and temperature also exhibited an interactive effect in the germination of seeds that were imbibed in darkness for only 3 days. For each of the germination phases there was a temperature at which the time needed for 50% germination was the shortest, namely 35°C during imbibition, 37.5°C in the period of Pfr activity. and 32.5°C during radicle protrusion. The data obtained are shortly discussed in relation to the domestication of empress tree in Southern Europe.

Seedbed Ecology of Winterfat: Imbibition Temperature Affects Post-Germination Growth

Seed imbibition is a critical first step in the awakening of an embryo plant. To determine if imbibitional conditions influenced post-germination growth, seeds of 3 winterfat (Eurotia lanata) ecotypes were imbibed at 5 temperatures from 0 to 20 degrees C, and at 5 oxygen concentrations from 0 to 40%. After a 4-day imbibition period the seeds were either dried and weighed or they were cultured in the dark at 20 degrees C. Seedling axial length was measured 5 times between 5 and 14 days post-germination to assure that maximum growth was measured. The study was repeated 3 times for each ecotype. Oxygen concentration had little effect except at 0%. As imbibition temperature increased both post-imbibition dried seed weight and seedling axil length decreased. This indicates the probability for successful termination, establishment, and survival of winterfat decreases when seeds are imbibed at 15-20 degrees C as compared to 5 degrees C. Therefore winterfat should be sown during those parts of the year when diaspores will imbibe at cool temperatures. Winterfat should be imbibed and held at 5 degrees C for 4 days, then germinated at 15 degrees C when testing germination.

Seed germination of melon ( Cucumis melo) at sub- and supra-optimal temperatures

The rate (mean time of germination, MTG) and total germination of two melon ( Cucumis melo) accessions (‘Noy Yizre'el’ and ‘Persia 202’) in response to various temperatures between 7 and 47°C were examined. ‘Persia 202’ had a broader temperature range for germination than ‘Noy Yizre'el’. Full and fast germination (85%) was obtained in the 13–41°C range for ‘Persia 202’, compared with 19–35°C for ‘Noy Yizre'el’. Water uptake during imbibition was faster and greater in ‘Persia 202’ seeds than in the ‘Noy Yizre'el’ seeds. The temperature of imbibition did not affect total water absorption in either of the two accessions. Untreated ‘Noy Yizre'el’ seeds were unable to germinate at 14°C, but germination was much improved by seed coat removal, exposure to gibberellin (GA 4+7) solution, or initial imbibition at 25°C.

IMBIBITION, ELECTROLYTE LEAKAGE, AND GERMINATION OF SWEET CORN HYBRIDS CARRYING sh2 MUTANT ENDOSPERM

Seeds of two shrunken-2 (sh2) sweet corn (Zea mays L.) cultivars, Crisp N' Sweet 711 and How Sweet It Is were used to analyze seed quality factor differences between the cultivars. Negative correlations occurred among germination percentage and imbibition, electric conductivity, potassium concentration and total soluble sugars of the seed leachate. Imbibition and total soluble sugar in the leachate significantly increased as imbibition temperature increased from 5°C to 25°C in both cultivars. A significant increase in conductivity of the leachate also occurred in `Crisp N' Sweet 711' when temperature increased. Cracks in the seed coat were more frequent in `How Sweet It Is' than `Crisp N' Sweet 711'. The higher concentrations of soluble sugars in the seed, greater imbibition rate, leakage conductivity, potassium and sugar concentration in the leachate may have been directly related to the poorer seed quality of `How Sweet It Is'. The alteration in cell membrane structure caused by a rapid water uptake in `How Sweet It Is' may have led to the high concentration of electrolytes in the seed leachate. This, in turn, might provide a greater nutritive subtrate for fungi development.

Cauliflower (Brassica oleraceaL.) Seed Vigour: Imbibition Effects

Machine vision was used to follow the inhibition process in a small seeded Brassica species, namely cauliflower, by quantifying the visible swelling of the imbibing seed. This allowed the effects of imbibition rate, imbibition temperature, and test a damage on seedling development to be investigated

Initial Moisture Content and Temperature of Imbibition Determine Extent of Imbibitional Injury in Pollen

Summary Imbibitional chilling damage was frequently observed in air-dry pollen from different plant species, although partial resistance did occur. Damage included excessive leakage of endogenous soluble components into the in vitro medium and loss of vitality. Prehydration in humid air largely prevented the leakage of K + and NAD + . Similarly, imbibition of air-dry pollen in media at 29°C prevented most of the leakage and conserved germinative capacity. However, further reduction of pollen moisture levels increasingly induced imbibitional damage, even at 29°C. A strong negative correlation was established between leakage of NAD+ and fluorescence score in tests with the vital stain, fluorescein diacetate. Since initial pollen moisture content and temperature of imbibition evoke similar patterns of reduced vitality and membrane leakage, we conclude that both imbibitional damage and cold hydration-induced injury are not essentially different. On the basis of literature data on phase behaviour of pure phospholipids in relation to water content, we suggest that the injury in pollen originates from the presence of gel phase lipid during the uptake of liquid medium. No correlation was found between sensitivity to imbibitional stress in several pollen species and composition of fatty acids in the phospholipids.

The Effect of Changing Temperatures During Imbibition on Ultrastructure in Germinating Pea Embryonic Radicles

Hodson, M. J., Di Nola, L. and Mayer, A, M. 1987. The effect of changing temperatures during imbibition on ultrastructure in germinating pea embryonic radicles.—J. exp. Bot. 38: 525-534. Pea seeds were imbibed at 5 °C or at 25 °C for 5-6 h and then germinated at the same temperature or transferred to the other temperature for 15 h. After imbibition or germination the embryonic axis was removed, fixed and the ultrastructure of the radicle tip examined. Exposure of the seeds to 5 °C during imbibition resulted in the cessation of almost all ultrastructural changes during subsequent germination at 5 °C. When the seeds were transferred to 25 °C development of ultrastructure was far slower than expected. In particular, mitochondrial structure failed to develop, there were few Golgi and little ER, and lipid bodies located near the plasma membrane disappeared or fused much more slowly with the membrane. An attempt is made to relate the observations on ultrastructure with data previously reported on the metabolism of phospholipids in the plasma membrane and ER of the embryonic axis. A tentative hypothesis to account for the effect of temperature of imbibition on subsequent seed germination is proposed.

Ethanolamine incorporation into membranes of pea embryonic axes during germination

Changes in the ethanolamine pool of the embryonic axes of pea seeds exposed to different temperatures during imbibition and germination were followed. The ethanolamine pool decreased except during imbibition at 25°. Label from ethanolamine was incorporated almost entirely into phosphatidylethanolamine with incorporation into phosphatidylcholine being observed only after imbibition and germination at 25°. The incorporation of ethanolamine was apparently less sensitive to temperature than that of choline and glycerol, previously reported. Preliminary results also show an effect of the imbibition temperature on some of the membrane proteins, but most did not seem to be affected.

Dormancy phases in seeds ofVerbascum thapsus L.

Seeds ofVerbascum thapsus were imbibed on filter papers in Petri dishes and were exposed to a series of temperatures of 4°C→10°C→20°C→10°C→4°C in darkness. After each temperature treatment lasting one month, samples were removed and tested in light and darkness over a range of alternating temperatures. The results showed us that the dormancy state changes gradually according to the imbibition temperatures simulating the seasonal cycle. The ecological implications of the dormancy phases for the regulation of germination in natural conditions are discussed.

Imbibitional Stress and Transverse Cracking of Bean, Pea, and Chickpea Cotyledons

Abstract Transverse cracking was examined in cotyledon tissue of snap bean (Phaseolus vulgaris L. ‘Apollo’), pea (Pisum sativum L. ‘Garfield 81’), and chickpea (Cicer arietinum L. ‘Surutato 77’). The hypothesis that imbibitional cracks develop along lines of least resistance or along preexisting cracks was evaluated. Columns of tissue were cut from cotyledons. Time from the start of imbibition to detection of the first crack was compared between whole bean cotyledons and columns. Bean columns cracked transversely with respect to the long axes of the columns. They did not crack longitudinally, even if the long axis of a column was originally perpendicular to the long axis of the cotyledon. These results do not support the hypothesis that imbibitional cracks form along preexisting cracks or along lines of weakness. Imbibitional stresses induced new cracks to form. The mean time to first crack and SE associated with its measurement were both significantly reduced in columns relative to the corresponding values for whole cotyledons (40 ± 2.6 and 100 ± 8.0 min, respectively) at an imbibition temperature of 19.3°C. Pea and chickpea cotyledon tissues also cracked transversely when they were cut into long, narrow columns.

Effect of temperature on glycerol metabolism in membranes and on phospholipases C and D of germinating pea embryos

The effect of temperature of imbibition on the synthesis and turnover of membrane phosphatidyl choline was studied. Pea seeds ( Pisum sativum cv. Alaska) were imbibed in [U- 14C]glycerol and then germinated. Seeds were kept constantly either at 5° or 25°, or were imbibed at one temperature and then germinated at the other one. Glycerol incorporation into phosphatidyl choline in the ER and the plasma membrane, obtained from the embryonic axes after germination, and the glycerol pool were measured. Embryos from seeds kept constantly at 25° showed a rapid incorporation of glycerol into membranes followed by a loss of label; in embryos from seeds kept at 5° incorporation was much lower. Embryos from seeds transferred from 25° to 5° behaved as if continuously kept at 25°, while the behaviour of the embryos from seeds transferred from 5° to 25° resembled embryos from seeds maintained at 5°. The glycerol content of the axes rose during imbibition and fell thereafter. The activities of phospholipases C and D also responded to the initial temperature of imbibition, but the two activities changed differently. The results are discussed in relation to the effect of transient exposure to temperature changes in the seed membranes and the possible way in which such changes are sensed.

Effect of temperature of imbibition on phospholipid metabolism in pea embryonic axes

Pea seeds were imbibed in radioactive choline and then germinated. Treatments were either at 5° or 25° and the seeds were imbibed for 5 hr at one temperature and then transferred to the other. [ Me - 14C]Choline incorporation into phosphatidyl choline in the ER and the plasma membrane obtained from the embryonic axes after germination was measured. Seeds kept constantly at 25° had a very rapid initial incorporation of choline followed by a loss of label. Seeds kept at 5° had a very much lower rate of incorporation. However, seeds transferred from 5 to 25° behaved for at least 48 hr as if continuously kept at 5°, while in seeds transferred from 25 to 5° incorporation stopped after 15 hr. The seeds apparently respond to transient exposure to temperature by a changed metabolism of phospholipid. Data are also given for the choline content of the seeds under the different treatments and for the changes in total phospholipid.

Low-temperature-induced GA3 Sensitivity of Wheat. V. Sterol Conversions in the Wheat Aleurone Tissue during Imbibition

Sterol profiles during imbibition and low temperature preincubation of aleurone tissue from Kite (Rht 2) and F6 Rht 3/rht 3 lines were studied. There was a dramatic disappearance of sterol derivatives during imbibition and a coincident appearance of an equivalent increment of free sterols in all three aleurone tissues. None of the preincubation conditions had any effect on the sterol content or spectrum of either the Rht-containing aleurone tissue (Kite and dwarf selection) or the non-Rht-containing aleurone tissue (tall selection). The results indicate that the sterol derivatives of the wheat aleurone tissue may serve a storage role for free sterols.

Effect of high temperatures on imbibition, germination, and thermal death of velvetleaf (Abutilon theophrasti) seeds

Seeds of velvetleaf (Abutilon theophrasti Medic.) were treated for various durations at temperatures from 40 to 60 °C. Rate of water uptake increased with temperature of imbibition. Germination of imbibed (soft) seeds was not affected by 40 °C imbibition for 30 h. At temperatures ≥ 43 °C, an inverse relationship was seen between temperature and time of imbibition required to reduce germination by a given level. Seeds exposed to temperatures up to 55 °C in dry or humid air or imbibed in osmotica of polyethylene glycol 6000 showed inhibitory effects on germination increased as time of exposure and seed water content increased. Seeds with low water content required longer exposures or higher temperatures to reduce germination. Heat treatments of <2 h caused greater germination reduction when applied after 24 h of imbibition than at the beginning. A heat stress of 1 h at 52 °C at the beginning and repeated after 24 h imbibition produced greater germination inhibition of soft seeds than a single 2 h 52 °C treatment at the beginning.