Imbibition period as the critical temperature sensitive stage in germination of lima bean seeds

Lima bean seeds (Phaseolus lunatus L.) and excised embryonic axes can be injured during imbibition at temperatures below 25°. The early imbibitional stage is critical; imbibition at 25° followed by low temperature exposure does not cause injury. Sensitivity to chilling injury is conditioned by the pre-harvest seed history. Low vigor (bleached) seeds are most sensitive to injury, the effects of which can be intensified by restricted oxygen supply during early axis growth. The seed coat, by preventing water uptake, can permit the seed to avoid injury. This protective mechanism is most effective at low temperature and high moisture stress. Immediately following low temperature imbibition, injured axes lose organic materials, probably nucleotides. This organic leachate is a potential influence on soil microorganisms and, together with the temperature sensitivity, vigor, and seed coat effect undoubtedly is important in controlling the potential variability in germination shown by a seed population.     

Relationship between Thermal Transitions and Freezing Injury in Pea and Soybean Seeds

In an attempt to correlate freezable water with freezing injury, the thermal behavior of pea (Pisum sativum L.) and soybean (Glycine max L. Merr) seed parts at different moisture contents were compared with survival of the seeds when exposed to low temperatures. Thermal transitions between −150 and 10°C were studied using differential scanning calorimetry. In pea, reduction of germinability, after exposure of seeds to temperatures between − 18 and − 180°C, occurred at a constant moisture content (about 0.33 gram H₂O/gram dry weight) regardless of the temperature; this moisture level was above that at which freezable water was first detectable by differential scanning calorimetry (0.26 gram H₂O/gram dry weight). In contrast, damage to soybean seeds was observed at progressively lower moisture contents (from 0.33 to 0.20 gram H₂O/gram dry weight) when the temperature was decreased from −18°C to −50°C. At −18 and −30°C, moisture contents at which damage to soybean seeds was evident were above that at which freezable water was first detectable (0.23 gram H₂O/gram dry weight). However, at −50, −80, and −180°C, damage was evident even when freezable water was not detectable. The data suggest that, while the quantity of water is important in the expression of freezing injury, the presence of freezable water does not account for the damage.     

Genetic Parameters of Serum Cholesterol Levels, Activity and Growth in Mice

Heritabilities (h²) of, and phenotypic and genetic correlations among, serum cholesterol (SC), levels of physical activity, growth, and body moisture content were estimated from data on 466 sire-son pairs of random-bred, ICR albino mice. Heritability estimates of SC and body moisture content were 0.31 ± 0.07 and 0.29 ± 0.11, respectively. Estimates of h² for activity measured by standard exercise wheels at 28, 49 and 70 days of age were 0.31 ± 0.17, 0.50 ± 0.11 and 0.27 ± 0.14 and for weight at 21, 44 and 67 days of age, were 0.11 ± 0.09, 0.33 ± 0.09 and 0.42 ± 0.08, respectively. The estimates of h² for weight gain ranged from 0.22 ± 0.07 to 0.27 ± 0.08. Significant negative phenotypic correlations occurred between activity and rate of body weight gain. A negative genetic correlation of -0.70 ± 0.11 between SC and body moisture implied that SC and percent body fat are positively correlated. Genetic correlations among SC values and activity scores and between SC values and body weight gains were near zero.     

Imbibition temperature sensitivity of lima bean seeds controlled by initial seed moisture

Excised embryonic axes and whole seeds of Phaseolus lunatus L. were previously shown to be injured if exposed to low (5°-15°) temperature during the initial stages of imbibition. Present data show that this chilling injury during imbibition of liquid water can be prevented if axes are first allowed to absorb water vapor. The increase of initial water content to 20% increases growth even of unchilled axes, and reduces leaching of 264 mμ absorbing compounds. Protection resulting from increased water content is at first independent of the temperature at which water vapor was absorbed. However, longer exposure of high moisture axes to low temperature results in typical chilling injury. The response to initial seed moisture is repeatedly reversible with changes in water content. Because the same response occurs in intact seeds, it may be possible both to protect them against low temperature injury and to increase vigor by increasing seed water-content prior to planting.     

Oxidative Processes in Soybean and Pea Seeds: Effect of Light, Temperature, and Water Content

Oxidative processes are probable determinants of longevity of seeds in storage. Measurements of actual oxygen uptake rates were made for soybean and pea seeds as a comparison of short and long lived seeds when light, temperature, and moisture contents were varied. In both peas and soybeans, the oxygen uptake was depressed at low temperatures (<16°C) and low water contents (<0.25 gram H₂O per gram dry weight). Apparent activation energies under these conditions are very high, while apparent activation energies of seeds at higher water contents and at temperatures greater than 22°C are much less. Light enhances the level of oxygen uptake in pea, but reduces the level of oxygen uptake in soybean. The complexities of the interactions of oxygen uptake with environmental conditions in soybean compared to pea suggest that oxidative processes occur in soybean at low water contents, but are essentially absent in pea. It is suggested that the additional oxidative processes in soybean with moisture contents between 0.10 and 0.24 gram per gram may contribute to the poorer longevity of soybean seed compared to pea seed.     

Effects of cooling rate on seeds exposed to liquid nitrogen temperatures

The effect of cooling rate on seeds was studied by hydrating pea (Pisum sativum), soybean (Glycine max), and sunflower (Helianthus annuus) seeds to different levels and then cooling them to − 190°C at rates ranging from 1°C/minute to 700°C/minute. When seeds were moist enough to have freezable water (> 0.25 gram H₂O/gram dry weight), rapid cooling rates were optimal for maintaining seed vigor. If the seeds were cooled while at intermediate moisture levels (0.12 to 0.20 gram H₂O per gram dry weight), there appeared to be no effect of cooling rate on seedling vigor. When seeds were very dry (< 0.08 gram H₂O per gram dry weight), cooling rate had no effect on pea, but rapid cooling rates had a marked detrimental effect on soybean and sunflower germination. Glass transitions, detected by differential scanning calorimetry, were observed at all moisture contents in sunflower and soybean cotyledons that were cooled rapidly. In pea, glasses were detectable when cotyledons with high moisture levels were cooled rapidly. The nature of the glasses changed with moisture content. It is suggested that, at high moisture contents, glasses were formed in the aqueous phase, as well as the lipid phase if tissues had high oil contents, and this had beneficial effects on the survival of seeds at low temperatures. At low moisture contents, glasses were observed to form in the lipid phase, and this was associated with detrimental effects on seed viability.     

Chilling Stress to Soybeans during Imhibition

Embryos, excised from seed coats of soybeans (Glycine max Merr. cv. `Wayne'), leak profusely during the first minutes of imbibition. A discontinuity of temperature/leakage patterns occurs between 10 and 15 C; as embryos imbibe at 10 C or lower, disproportionately more solutes leak out per unit of water imbibed. Short periods of imbibition at or below 12 to 14 C reduce embryo germination and axis elongation; injury results from imbibition at 2 C for as little as 5 minutes. Humidifying embryos to 35 to 50% moisture before imbibition reduced leakage during imbibition and imparted some resistance to imbibitional chilling injury.

The period of profuse leakage is interpreted as a time of membrane reorganization. Imposing a low temperature during this period prolongs the rapid leakage, suggesting delayed or faulty membrane reorganization. Reduced cold sensitivity of embryos with an initial 35 to 50% moisture content is presumed to be due to at least partial membrane reorganization in the embryo before imbibition. These data collectively are taken to indicate that low temperature interferes with normal membrane reorganization during imbibition, probably by modifying the physical state of membrane phospholipids, and that the consequent abnormal organization of membranes is a basic cause of low temperature injury.

     

Imbibitional chilling injury in pollen: involvement of the respiratory chain

Chilling injury is sustained by dry pollen of Typha latifolia L. upon hydration in germination medium at 0°C. This injury is evidenced as poor germination, low vigor, and depressed respiration. Isolated mitochondria showed multiple sites of impaired electron transport. Besides losses of cytochrome (Cyt) c and NAD⁺, the activities of membrane-bound enzyme complexes such as Cyt oxidase, NADH-duroquinone oxidoreductase, succinate-duroquinone oxidoreductase, and malate-duroquinone oxidoreductase were severely affected.

Similarly, as in isolated mitochondria, in situ tests of mitochondrial activity showed that Cyt c was partially lost from its site of action. Re-addition of the lost Cyt c to the grains restored the N,N,N′,N′-tetramethyl p-phenylenediamine dihydrochloride plus ascorbate-mediated electron transport from Cyt c to O₂, but did not significantly accelerate the overall O₂ uptake. Electron flow to duroquinone in the injured grains was low, indicating that lesions at the substrate side of ubiquinone determine the rate of O₂ consumption. Leakage of NAD⁺, and also of adenylate phosphates and Krebs cycle substrates out of the injured grains, was considerable.

Increasing the initial moisture content of the grains strongly enhanced their resistance to cold hydration. Below 17% moisture content (fresh weight basis), the decrease in vigor closely matched the loss of NAD⁺ and adenosine phosphates. Vitality was irreversibly lost by cold hydration below 10 to 12% initial moisture content.

Injury to dry pollen was prevented by imbibition at 27°C. Decrease of vigor and increased leakage, however, started below 20°C, and complete loss of vitality occurred below 10°C.

These results are interpreted as evidence that loss of membrane integrity is the primary cause of imbibitional chilling injury.

     

Antioxidant levels in germinating soybean seed axes in relation to free radical and dehydration tolerance

The axis of soybean seeds suffer dehydration injury if they are dried to 10% moisture at 36 hours of imbibition, but tolerate this stress if dried at 6 hours of imbibition. Deesterification of membrane phospholipids has been correlated with the increased permeability and increased lipid phase transition temperatures of membranes from dehydration injured tissues. Deesterification, measured as increased free fatty acid:phospholipid and decreased phospholipid:sterol ratios, occurred primarily when the tissue was in the dry state and did not change significantly (P ≤ 0.05) with increasing imbibition time.

When liposomes were exposed to free radicals in vitro, wide angle x-ray diffraction indicated that the phase transition temperature of liposomes prepared from membrane lipid from 36-hour axes (susceptible) increased from 6 to 31°C. In contrast, those from membrane lipid from 6-hour axes (tolerant) increased from 3 to only 8°C, indicating that the tolerance of free radicals previously observed in these membranes was due to a lipid-soluble component.

Lipid-soluble antioxidants were detected in 6-hour imbided axes in much greater quantities than in the 36-hour imbibed axes. The presence of lipid-soluble antioxidants in the membrane apparently contributes to the free radical tolerance of seed membranes observed during the early stages of germination, and these antioxidants may contribute to the dehydration tolerance of this tissue.

     

Heat Shock Proteins and Their mRNAs in Dry and Early Imbibing Embryos of Wheat

Two-dimensional gels of in vitro translation products of mRNAs isolated from quiescent wheat (Triticum aestivum) embryos demonstrate the presence of mRNAs encoding heat shock proteins (hsps). There were no detectable differences in the mRNAs found in mature embryos from field grown, from 25°C growth chamber cultivated, or from plants given 38°C heat stresses at different stages of seed development. The mRNAs encoding several developmentally dependent (dd) hsps were among those found in the dry embryos. Stained two-dimensional gels of proteins extracted from 25°C growth chamber cultivated wheat embryos demonstrated the presence of hsps, including dd hsps. A study of the relationship of preexisting hsp mRNAs and the heat shock response during early imbibition was undertaken. Heat shocks (42°C, 90 minutes) were administered following 1.5, 16, and 24 hours of 25°C imbibition. While the mRNAs encoding the low molecular weight hsps decayed rapidly upon imbibition, the mRNAs for dd hsps persisted longer and were still detectable following 16 hours of imbibition. After 1.5 hours of imbibition, the mRNAs for the dd hsps did not accumulate in response to heat shock, even though the synthesis of the proteins was enhanced. Thus, an applied heat shock appeared to lead to the preferential translation of preexisting dd hsp mRNAs. The mRNAs for the other hsps, except hsp 70, were newly transcribed at all of the imbibition times examined. The behavior of the hsp 70 group of proteins during early imbibition was examined by RNA gel blot analysis. The mRNAs for the hsp 70 group were detectable at moderate levels in the quiescent embryo. The relative level of hsp 70 mRNA increased after the onset of imbibition at 25°C and remained high through 25.5 hours of prior imbibition. The maximal levels of these mRNAs at 25°C was reached at 17.5 hours of imbibition. Heat shock caused modest additional accumulation of hsp70 mRNA at later imbibition times.     

Structural correlates of imbibitional injury in Typha pollen

The ultrastructure of Typha latifolia pollen was examined as a function of pollen moisture content and incubation temperature, in order to identify possible lesions induced by imbibitional chilling. A syndrome of structural traits was found which characterizes damaged grains. Compared to viable grains, the protoplast of damaged pollen has a higher proportion of its volume occupied by vesicles, and less volume occupied by cytoplasm. Damaged grains also tend to have dilated cisternae of endoplasmic reticulum, larger starch grains and lipid bodies, poorly preserved mitochondria and membranes, and, sometimes, numerous electron-dense globules associated with membranes. The percentage of grains exhibiting this damage syndrome correlates closely with the number of ungerminated grains in most samples, regardless of moisture content or incubation temperature. Injury due to rapid imbibition from the dry state or to imbibitional chilling appear to be similar structurally, regardless of whether the stresses are imposed singly or together. The injury is not confined to one cell component (e.g., mitochondria), but may involve a generalized disruption of membranes. These results suggest that similar stress responses are elicited by imbibition from the dry state and by imbibitional chilling.     

Thermotolerance is developmentally dependent in germinating wheat seed

During the initial 9 to 12 hours of imbibition, the imbibing wheat (Triticum aestivum L.) seed was found to exhibit substantial tolerance to high temperature relative to later times of imbibition. Tolerance was assessed by seed viability and seedling growth. This initial high temperature tolerance gradually declines with increasing time of seed imbibition. A range of 2 hour heat pretreatments (38-42°C) prior to imposition of a 2 hour heat shock (51-53°C) during this same 9 to 12 hour interval was unable to increase survival or seedling growth over that of seed that did not receive a pretreatment. However, after 9 to 12 hours of imbibition the pretreatment provided both increased survival and increased seedling growth, measured 120 hours later, i.e., classical thermotolerance could be acquired. This response is called a `thermotolerance transition.' Isolated embryos responded in a similar manner using a 2,3,5-triphenyltetrazolium chloride assay for viability determination following heat treatments. The high temperature tolerance during early imbibition indicates that the thermotolerance transition involves the loss of an existing thermotolerance coincident with acquiring the ability to become thermotolerant following heat pretreatment. Despite the inability to acquire thermotolerance, heat shock protein synthesis was induced by heat shock immediately upon imbibition of wheat seed or isolated embryos. Developmentally regulated heat shock proteins of 58 to 60, 46, 40, and 14 kilodaltons were detected at 1.5 hours of imbibition following heat shock, but were absent or greatly reduced by 12 hours. Constitutive synthesis of 70 and 90 kilodalton hsp groups appeared to be greater at 1.5 hours of imbibition than at 12 hours of imbibition.     

The effect soaking pea seeds with or without seedcoats has on seedling growth

Pea seeds (Pisum sativum L. `Alaska') with intact seedcoats (WC) and with seedcoats removed (WOC) were soaked in distilled water for 24 hours at 20°. The water, containing the pea diffusate, was decanted after the second, fourth, sixth, eighth, twelfth, and twenty-fourth hour and analyzed for total nitrogen, α-amino nitrogen, carbohydrate, and total solute dry weight. The seeds were germinated at 20° in a 16 hour photoperiod of 300 foot candles. Stem lengths and dry weights of roots, shoots and cotyledons were determined after 4, 11, and 18 days of growth. WOC seeds imbibed more water than WC seeds during the 24 hour imbibition period. Diffusates from WOC seeds always contained more solute than diffusates from WC seeds. Maltose, glucose, and fructose were not detected in the early diffusates from WOC seeds but were found in WC seed diffusates at all times. Seedlings from WC seeds had longer stems than those from WOC seeds. The dry weight of stems and roots of WC seedlings was greater than those from WOC seedlings. The dry weight of cotyledons from 18 day-old WC seedlings was less than from WOC seedlings. Water absorption by WC seeds was slower than by WOC seeds. Removal of the seedcoat allowed rapid imbibition resulting in seed injury presumably because of the loss of solutes which included monosaccharides, disaccharides, amino acids, and other nitrogen containing compounds. These results are consistent with the hypothesis that rapid imbibition disrupts membrane organization leading to reduction of seedling growth.     

Potential Role of Pyrophosphate:Fructose 6-Phosphate Phosphotransferase in Carbohydrate Metabolism of Cold Stored Tubers of Solanum tuberosum cv Bintje

To gain a better understanding of the mechanism of cold induced sweetening, sugar accumulation in potato, Solanum tuberosum cv Bintje, was compared to the maximum activity of inorganic pyrophosphate (PPi):fructose 6-phosphate 1-phosphotransferase (EC 2.7.1.90) and the concentration of two regulatory metabolites. Mature tubers accumulated reducing sugars and sucrose at an almost linear rate of 13.4 and 5.2 micromole per day per gram dry weight at 2°C and 4.5 and 1.3 micromole per day per gram dry weight, respectively, at 4°C. During storage at 8°C sugar accumulation was nil. Sugar accumulation was preceded by a lag phase of about 4 days. The accumulation of reducing sugars persisted for at least 4 weeks, whereas sucrose accumulation declined after 2 weeks of storage. The ratio of glucose:fructose changed concomitantly with sugar increase from 65:35 to equimolarity. The maximum activity of PPi:fructose 6-phosphate 1-phosphotransferase was 2.51 and 2.25 units per gram dry weight during storage at 2 and 8°C, respectively. The temperature coefficient of this enzyme from potatoes kept at 2 or 8°C was 2.12 and 2.48, respectively. The endogenous concentration of fructose 2,6-biphosphate increased from 0.15 to 1 nanomole per gram dry weight during storage at 2 and 4°C but remained the same throughout storage at 8°C. After exposure to 2°C an initial increase in the concentration of PPi was observed from 4.0 to 5.6 nanomoles per gram dry weight. Pyrophosphate concentration did not change during storage at 4°C but decreased slightly at 8°C. All observed changes became annulled after transfer of cold stored tubers to 18°C. These data strongly indicate that PPi:fructose 6-phosphate 1-phosphotransferase can be fully operational in cold stored potato tubers and the lack of increase in PPi concentration supports the functioning of this enzyme during sugar accumulation.     

Increases in the longevity of desiccation-phase developing rice seeds: response to high-temperature drying depends on harvest moisture content

Background and Aims Previous studies have suggested that the drying conditions routinely used by genebanks may not be optimal for subsequent seed longevity. The aim of this study was to compare the effect of hot-air drying and low-temperature drying on subsequent seed longevity for 20 diverse rice accessions and to consider how factors related to seed production history might influence the results.Methods Seeds of rice, Oryza sativa, were produced according to normal regeneration procedures at IRRI. They were harvested at different times [harvest date and days after anthesis (DAA), once for each accession] and dried either in a drying room (DR; 15 % relative humidity, 15 °C) or in a flat-bed heated-air batch dryer (BD; 45 °C, 8 h d^–1) for up to six daily cycles followed by drying in the DR. Relative longevity was assessed by storage at 10·9 % moisture content and 45 °C.Key Results Initial drying in the BD resulted in significantly greater longevity compared with the DR for 14 accessions (seed lots): the period of time for viability to fall to 50 % for seeds dried in the BD as a percentage of that for seeds dried throughout in the DR varied between 1.3 and 372·2 % for these accessions. The seed lots that responded the most were those that were harvested earlier in the season and at higher moisture content. Drying in the BD did not reduce subsequent longevity compared with DR drying for any of the remaining accessions.Conclusions Seeds harvested at a moisture content where, according to the moisture desorption isotherm, they could still be metabolically active (>16·2 %) may be in the first stage of the post-mass maturity, desiccation phase of seed development and thus able to increase longevity in response to hot-air drying. The genebank standards regarding seed drying for rice and, perhaps, for other tropical species should therefore be reconsidered.     

Mechanical Resistance of the Seed Coat and Endosperm during Germination of Capsicum annuum at Low Temperature

Decoated pepper (Capsicum annuum L. cv Early Calwonder) seeds germinated earlier at 25°C, but not at 15°C, compared to coated seeds. The seed coat did not appear to impose a mechanical restriction on pepper seed germination. Scarification of the endosperm material directly in front of the radicle reduced the time to germination at both 15°C and 25°C.

The amount of mechanical resistance imposed by the endosperm on radicle emergence before germination was measured using the Instron Universal Testing Machine. Endosperm strength decreased as imbibition time increased. The puncture force decreased faster when seeds were imbibed at 25°C than at 15°C. The reduction in puncture force corresponded with the ability of pepper seeds to germinate. Most radicle emergence occurred at 15°C and 25°C after the puncture force was reduced to between 0.3 and 0.4 newtons.

Application of gibberellic acid₄₊₇ (100 microliters per liter) resulted in earlier germination at 15°C and 25°C and decreased endosperm strength sooner than in untreated seeds. Similarly, high O₂ concentrations had similar effects on germination earliness and endosperm strength decline as did gibberellic acid₄₊₇, but only at 25°C. At 15°C, high O₂ concentrations slowed germination and endosperm strength decline.

     

Levels of Free and Conjugated Abscisic Acid in Developing Floral Organs of the Navel Orange (Citrus sinensi [L.] Osbeck cv Washington)

The levels of abscisic acid (ABA) and alkaline-hydrolyzable ABA-conjugate (putatively identified as the glucosyl ester, abscisyl-β-d-glucopyranoside) were determined by enzyme immunoassay in the organs of developing navel orange (Citrus sinensis [L.] Osbeck cv Washington) flowers. Although both compounds were detected in every tissue, developmentally related differences between organs in the total and relative contents were observed. The highest ABA levels were observed in the stigma/style shortly after anthesis (11.5 ± 0.6 nanomoles ABA per gram fresh weight and 4.8 ± 0.6 nanomoles ABA-conjugate per gram fresh weight); whereas, the highest ABA-conjugate levels were observed at the same time in the floral disc (hypogynous disc plus calyx; 3.5 ± 0.1 nmol nanomols ABA per gram fresh weight and 11.8 ± 0.9 nanomoles ABA-conjugate per gram fresh weight). These results suggest that differences in ABA content reflect tissue-specific variation in the facility for ABA conjugation. Increased ABA levels were observed in the stigma/style near anthesis; however, a relationship with pollination is discounted, since `Washington' navel orange flowers are male sterile and devoid of pollen.     

The Damaging Effect of Water on Dry Pea Embryos During Imbibition

When pea seeds were imbibed in water without their seed coats,vital staining revealed that cells on the abaxial surface ofthe cotyledons were dead. No damage occurred on the surfaceof cotyledons when the seeds were imbibed intact, or beneaththe testa when only half of the testa was removed. Cell deathoccurred as a result of rapid water uptake within the first2 min of imbibition, since reducing the rate of imbibition insolutions of Carbowax 4000 lessened the damage. Cell death wasrestricted to the outer layers of the cotyledons; inner tissuesremained alive. These observations supported the hypothesisthat rapid early leakage during imbibition of dry embryos resultedfrom the death of cells caused by the physical disruption ofmembranes. Imbibition damage resulted in reduced respirationand germination, a decline in the rate of food reserve transferfrom the cotyledons to the growing axis, and a lower growthrate in the seedlings produced. Greater sensitivity of embryosto imbibition damage at low temperature, and similarities betweenfeatures of imbibition damage and chilling injury led to thesuggestion that so-called chilling injury is the result of imbibitiondamage rather than the effects of low temperature.     

大豆种子吸胀冷害抗性与其质体膜脂不饱和度正相关

吸胀冷害是干种子在吸胀阶段遭受低温造成不萌发的现象,结果可能造成农作物损失严重。虽然吸胀过程中细胞膜的修复是关键事件,而且细胞膜在响应水分和温度胁迫中扮演重要角色,但是种子吸胀过程中膜变化的过程,特别是膜流动性变化过程研究较少。本文比较了吸胀冷害耐受型（LX）和敏感型（R5）两个大豆品种在吸胀冷害过程中膜脂不饱和度（double bond index, DBI）的变化,结果发现,LX和R5在常温（25℃）吸胀时变化趋势一致,质体膜脂DBI升高,质体外膜脂中磷脂酰甘油(phosphatidylglycerol, PG)分子DBI下降。LX和R5在低温（4℃）吸胀时DBI变化有很大差异,低温吸胀仅仅延缓了耐受型LX中质体膜脂DBI的升高,但是敏感性R5质体膜脂DBI不仅没有升高反而下降。用浓度33%的聚乙二醇 (polyethylene glycol, PEG)引发没有直接引起DBI变化,但是所引起的细微而显著的变化可能为萌发做好准备。PEG引发处理后的R5在吸胀冷害后第二和第三阶段质体膜脂DBI迅速增加,这个增加模式与LX的DBI增加相似。结果表明,吸胀冷害延缓或者阻滞了质体膜脂不饱和度的升高,大豆种子的吸胀冷害抗性与质体膜脂不饱和度正相关,提高质体膜质DBI可以提高吸胀冷害抗性。     

Association between Membrane Phase Properties and Dehydration Injury in Soybean Axes

Axes of soybean seeds are tolerant to dehydration at 6 hours of imbibition, but susceptible to dehydration injury if dried at 36 hours of imbibition. Smooth microsomal membranes were isolated from axes imbibed for 6 hours (dehydration tolerant state) and 36 hours (dehydration susceptible state) before and after dehydration treatment. The phase properties and the lipid composition of the membrane fraction were investigated. Wide angle x-ray diffraction patterns of microsomal membranes from axes imbibed for 6 or 36 hours indicated a liquid-crystalline to gel phase transition at approximately 7°C. Membranes from axes dehydrated at 6 or 36 hours of imbibition and rehydrated for 2 hours exhibited a phase transition at 7°C and 47°C, respectively. Changes in fatty acid saturation did not account for the changes in phase properties. However, the increased phase transition temperature of the membranes from dehydration injured axes was associated with an increase in free fatty acid:phospholipid molar ratio and a decrease in phospholipid:sterol ratio. These results suggests that dehydration prompted a deesterification of the linkage between glycerol and fatty acid side chains of the phospholipid molecules in the membrane. The resultant increase in free fatty acid content in the membrane is thought to alter the fluidity and phase properties of the membrane and contribute to dehydration injury.