Responses to Drying of Recalcitrant Seeds of Quercus nigra L.

It has been suggested that rate of desiccation can influencethe expression of recalcitrant behaviour in seeds, thus complicatingthe task of determining which seeds are truly recalcitrant.The objective of this study was to see if variable rates ofdesiccation influenced such behaviour inQuercus nigra L., atree seed known to be recalcitrant. Acorn moisture content, leachate conductivity, and germinationwere determined at various times during desiccation at threerates at 27 and 40°C. Moisture contents and germinationdecreased as the severity of desiccation increased. Leachateconductivity increased slightly but was not a sensitive indicatorof loss of viability. The critical (lethal) moisture contentfor these acorns was 10–15%, although rehydration within48 h of reaching this level prevented death in about 25% ofthe acorns. At 27°C any desiccation treatment that producedlosses of 30–50mg of moisture per g of acorn dry weightper day should be suitable as a test for recalcitrance in thegenus. Apparent physiological or fungal damage at 40°C rulesout the higher temperature for such a test. Quercus nigra L.; desiccation rate; temperature; recalcitrant; leachate conductivity; germination; viability     

Abscisic Acid Accumulation in Developing Seeds of Phaseolus vulgaris L

Free and bound abscisic acid (ABA) in the pod, seed coat, and embryo were determined separately throughout seed development of Phaseolus vulgaris L. cv. `Taylor's Horticultural.' An internal standard method of gas-liquid chromatography was used for ABA quantification. In the embryo, two peaks of free ABA occurred at days 22 (1.18 micrograms per gram or 5.5 micromolar) and 28 (1.74 micrograms per gram or 12 micromolar); and a single peak of bound ABA at day 30. In the seed coat, there was one peak of free ABA at day 22 and only small amounts of bound ABA. Very small amounts of ABA were detected in the pod at any stage of development. In cv. PI 226895, in which seed development is more rapid than in `Taylor's Horticultural,' the embryo ABA peaks occur on days 20 and 26. The timing of the ABA peak in the embryo, and the concentration attained, are consistent with previous reports on the natural pattern of RNA synthesis and with ABA inhibition of RNA synthesis in developing bean fruit.     

The Influence of Abscisic Acid on the Gibberellin Content in Apple Seeds During Stratification

Auto?i sledovali obsah endogenních giberelin? GA₄ a GA₇ v embryích jabloně pěstovaných ve vodě nebo v roztoku abscisové kyseliny (ABA). Embrya pocházela ze semen odpo?ívajících nebo ze semen stratifikovaných ve vodě nebo v roztoku ABA. Bylo zji?těno, ?e ABA vyvolává sní?ení obsahu giberelin?. Závislost mezi vlivem ABA a stadiem stratifikace bylo u GA₄ výrazněj?í ne? u GA₇. Auto?i p?edpokládají, ?e ABA inhibuje biosynthesu giberelin?.     

Abscisic Acid and Gibberellic Acid Contents in Ripening Barley Seeds

The ABA and GA3 contents were investigated in barley seeds during maturation and after harvest. The highest amount of ABA was found in milk and wax ripeness – 13 ng and 11 ng per seed respectively. The level decreased during the later stages of maturation and during release of dormancy and was 1 ng per seed 6 weeks after harvest. The content of gibberellic acid decreased in a similar way but in an earlier stage of maturation. The determined amounts of GA₃ were: 0.4, 0.1, 0.03 and about 0.05 ng per seed respectively, in milk, wax and full ripeness and after harvest. The results of quantitative determination, obtained with the GLC method, corresponded to the growth effects in the test of the first leaf of oat.     

Level of Abscisic Acid in Integuments, Nucellus, Endosperm, and Embryo of Peach Seeds (Prunus persica L. cv Springcrest) during Development

Free abscisic acid (ABA) in integuments, nucellus, endosperm, and embryo was determined throughout seed development of peach (Prunus persica L. cv Springcrest). Quantification of ABA was performed using combined high performance liquid chromatography-radioimmunoassay based on a monoclonal antibody raised against free (S)-ABA. In the integuments and endosperm, ABA concentration remained constant during the first 100 days after anthesis and rose in the following days when fresh weight was rapidly decreasing. In the nucellus, the ABA concentration variation pattern paralleled that of tissue growth. ABA concentration in the embryo increased constantly with the growth of the tissues to reach a maximum at the last growth stage. The role of ABA in peach seeds is discussed in relation to the development of the different seed tissues.     

Some Structural Changes During Ripening of Mangoes (Mangifera indica var. Alphonso) by Abscisic Acid Treatment

Abscisic acid at 10^–6 M concentration enhances ripeningof mangoes. The cells in the pulp of the fruit are large andparenchymatous and lose their integrity due to cell wall hydrolysisat the ripe stage. They contain abundant polysaccharides, consistingmainly of starch, which is degraded during ripening. The chloroplastsare transformed to chromoplasts containing red or yellow carotenoidpigment. Abscisic acid treatment enhances all of these processes.Mitochondria, on the other hand, retain their structural integritythroughout the ripening process in untreated and abscisic acid-treatedmangoes. Mangoes, ripening, abscisic acid, structure     

Involvement of Abscisic Acid in Regulating Water Status in Phaseolus vulgaris L. during Chilling

During the first hours of chilling, bean (Phaseolus vulgaris L., cv Mondragone) seedlings suffer severe water stress and wilt without any significant increase in leaf abscisic acid (ABA) content (P. Vernieri, A. Pardossi, F. Tognoni [1991] Aust J Plant Physiol 18: 25-35). Plants regain turgor after 30 to 40 h. We hypothesized that inability to rapidly synthesize ABA at low temperatures contributes to chilling-induced water stress and that turgor recovery after 30 to 40 h is mediated by changes in endogenous ABA content. Entire bean seedlings were subjected to long-term (up to 6 d) chilling (3°C, 0.2-0.4 kPa vapor pressure deficit, 100 μmol·m⁻²·s⁻¹ photosynthetic photon flux density, continuous fluorescent light). During the first 24 h, stomata remained open, and plants rapidly wilted as leaf transpiration exceeded root water absorption. During this phase, ABA did not accumulate in leaves or in roots. After 24 h, ABA content increased in both tissues, leaf diffusion resistance increased, and plants rehydrated and regained turgor. No osmotic adjustment was associated with turgor recovery. Following turgor recovery, stomata remained closed, and ABA levels in both roots and leaves were elevated compared with controls. The application of ABA (0.1 mm) to the root system of the plants throughout exposure to 3°C prevented the chilling-induced water stress. Excised leaves fed 0.1 mm ABA via the transpiration stream had greater leaf diffusion resistance at 20 and 3°C compared with non-ABA fed controls, but the amount of ABA needed to elicit a given degree of stomatal closure was higher at 3°C compared with 20°C. These findings suggest that endogenous ABA may play a role in ameliorating plant water status during chilling.     

Some Effects of Abscisic Acid and Water Stress on Stomata of Vicia faba L.

Vicia faba seedlings grown under a plastic tent in the laboratorywere either watered well throughout their growth period or weresubjected to a water stress treatment for several days priorto an experimental treatment. The effects of a further waterstress treatment or an application of an aqueous solution ofabscisic acid (ABA) on the stomata of these plants were determined.Stomata of previously water-stressed plants proved to be moresensitive than stomata of well watered plants to ABA appliedthrough the petiole via the transpiration stream and sprayedonto leaf surfaces. Stomata of previously water-stressed plantsclosed more rapidly and to a greater degree than stomata ofwell watered plants. The hormone had only a small effect whenapplied directly to epidermal fragments removed from both groupsof plants. Stomata of plants which had received a water stresspretreatment were less sensitive to a subsequent period of waterstress than were stomata of previously well watered plants.It is proposed that stomatal adaptation to water stress maybe related to changes in the hormonal balance of the plant.     

Water Potential and Embryonic Axis Viability in Recalcitrant Seeds of Quercus rubra

Desiccation of Quercus rubra fruits under three drying regimesof varying temperature and water potential confirmed their desiccationintolerance. However, a variable relationship between seed germinationand embryonic axis moisture content was observed, indicatingthat the rate and temperature of drying can modify this co-plot.The modification occurred primarily between an axis moisturecontent of 45–20%, which is equivalent to water potentials(     

Embryo Water Status and Survival in the Recalcitrant Species Quercus robur L: Evidence for a Critical Moisture Content

The responses of Q. robur L. fruits, seeds and embryonic axesto desiccation are characterized and discussed in relation tocurrent knowledge of recalcitrant seed behaviour. A relationshipbetween viability and seed moisture content is described. Thisrelationship was unaffected by rate of drying, year of harvestor presence of the pericarp. Desiccation sensitivity did notincrease with storage. Excised embryonic axes survived to lower moisture contents thanintact seeds. However, in the intact seed, loss of viabilityappeared to be determined by a critical moisture content inthe cotyledons. Consequently, the level of desiccation tolerancewithin the axis attached to cotyledons was not determined byaxis drying rate. A link is drawn between the difference in the desiccation toleranceof embryonic axes and of cotyledons, and estimates of theirdifferent levels of matrix-bound water. The results presentedare consistent with a critical moisture content for survivalwhich is determined by the loss of all free cellular water.This hypothesis takes account of the differential desiccationsensitivity of seed tissues and differences in desiccation tolerancebetween species.     

Abscisic Acid and Ethylene Interact in Rice Spikelets in Response to Water Stress During Meiosis

This study investigated whether and how the interaction between abscisic acid (ABA) and ethylene is involved in the regulation of rice (Oryza sativa L.) spikelet sterility when subjected to water stress during meiosis. Two rice cultivars, HA-3 (drought-resistant) and WY-7 (drought-susceptible), were used and subjected to well-watered and water-stressed (WS) treatments during meiosis (15–2 days before heading). Leaf water potentials of both cultivars markedly decreased during the day as a result of the WS treatment, but panicle water potentials remained constant. The percentage of sterile spikelets in WS plants was increased by 49.7% for WJ-7 but only 12.7% for HA-3. ABA, ethylene, and 1-aminocyclopropane-1-carboxylic acid were all enhanced in spikelets by the water stress, but ethylene was enhanced more than ABA in WY-7 when compared with that in HA-3. Spikelet sterility was significantly reduced when ABA or amino-ethoxyvinylglycine, an inhibitor of ethylene synthesis, was applied to the panicles of WS plants at the early meiosis stage. Application of ethephon, an ethylene-releasing agent, or fluridone, an inhibitor of ABA synthesis, had the opposite effect, and sterility was increased. The results suggest that antagonistic interactions between ABA and ethylene may be involved in mediating the effect of water stress on spikelet fertility. A higher ratio of ABA to ethylene would be a physiologic trait of rice adaptation to water stress.     

Growth Capacity of Embryo Axes Excised from Dormant and Germinating Horse Chestnut Seeds and Their Response to Exogenous Abscisic Acid

In embryo axes excised from mature horse chestnut (Aesculus hippocastanum L.) seeds, both freshly-fallen and subjected to cold stratification, the ability for growth was studied. While excised axes were kept on water at 28°C for 3 days, their fresh weight and length increased, the polypeptide composition of soluble proteins changed, the content of some heat-stable polypeptides decreased, and the capacity for protein synthesis in vivo retained. All these processes were similar to those in the axes of intact seeds during stratification until radicle protrusion. Growth of excised axes accelerated with the increasing duration of stratification. Cycloheximide (50 mg/l) and -amanitin (7 mg/l) inhibited axis growth, but an inhibitor of ABA synthesis fluridone (5 mg/l) and a natural cytokinin dihydrozeatin (10^–5 M) did not influence the growth rate. The growth capacity of axes excised from dormant and germinating horse chestnut seeds indicates the absence of dormancy in the axes of mature seeds. ABA (10^–5 M) suppressed completely the growth of axes detached from seeds experiencing cold stratification but still not germinating, although protein synthesis was not inhibited. The axes excised from the seeds after radicle emergence were insensitive to ABA and grew actively in its presence. ABA-induced growth inhibition might be related to the suppressed synthesis of minor polypeptides required for growth or to the activated synthesis of some growth-retarding proteins. The conclusion was drawn that the excised axes could be used as a model for studying the processes preceding visible germination of recalcitrant seeds.     

Functional Significance of Acid Phosphatase Distribution During Embryo Development in Pisum sativum L

The distribution of P₁, ester P and acid-insoluble nucleic acidP has been studied in relation to acid phosphatase activity(EC 3. 1. 3. 2) in the component parts of developing pea seeds(Pisum sativum L.). Despite the favourable pH of the liquidcontents of the embryo sac (pH 5.5), only very low acid phosphataseactivity was detected in this fluid (c. 0.01 units per seed).Potential substrates for phosphatase action were in fact absentfrom the secretion, the only form of P present being P_i, inconcentrations up to 8 mM. The data support the hypothesis thatthe high acid phosphatase activities which develop in the seed-coatsare involved in regulating the supply of P as P₁ to the developingembryo. Pisum sativum L., pea, embryo development, acid phosphatase, phosphorus, seed-coats, seed development     

Abscisic Acid Accumulation and Water Relations of Four Cultivars of Phaseolus vulgaris L. under Drought

Larqué-Saavedra, A., Rodriguez, M. T., Trejo, C. andNava, T. 1985. Abscisic acid accumulation and water relationsof four cultivars of Phaseolus vulgaris L. under drought.—J.exp. Bot 36: 1787–1792. Plants of four cultivars of Phaseolus vulgaris L. differingin drought resistance were grown in pots under greenhouse conditionsand prior to flowering water was withheld from the pots untilthe mid-day transpiration rate reached values below 1.0 µgH₂O cm^–2 s^–1 (designated the ‘drought’stage). At this point leaves were harvested on 3 or 4 occasionsover 24 h to determine the abscisic acid (ABA) concentration,total water potential (), solute potential (₁) and turgor potential(_p). Results showed that values of , ₁, and _p differed between cultivarswhen they reached the ‘drought’ stage. The stomatalsensitivity to changes in and _p, was as follows: Michoacán12A3 > Negro 150 Cacahuate 72 > Flor de Mayo. These datacorrelated well with the pattern of drought resistance reportedfor the cultivars. ABA accumulation at the ‘drought’ stage differedbetween cultivars at each sampling time, but overall differencesin ABA level between cultivars were not significant. ABA levelsdid not, therefore, correlate with the drought resistance propertiesreported for the cultivars. Results are discussed in relationto and hour of the day when bean samples were taken for ABAanalysis. Key words: Phaseolus vulgaris L., drought resistance, abscisic acid     

Concentrations of Abscisic Acid and Indole-3-Acetic Acid in Soybean Seeds during Development

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in seed parts were determined during reproductive development of soybean plants (Glycine max [L.] Merr. cv `Chippewa 64'). The concentration of ABA and IAA changed independently in individual seed parts with time. Measurement of the level of ABA and IAA in whole seeds masked the changes which occurred in individual seed tissues. The concentration of ABA was generally highest and that of IAA was generally lowest in the embryonic axis of soybean seeds. In the testa, the IAA concentration was generally highest while the ABA concentration was generally the lowest compared to other parts of the seed.     

豌豆中脱落酸含量、叶片导性与土壤含水量之间的关系

脱落酸与植物水分胁迫的关系已进行了大量的研究,现已明确脱落酸可以抑制气孔的开放(Jones和 Mansfield 1970,Weyers和 Hillman 1979,Henson等 1989),但它的作用机制仍然很不清楚。已有报告指出,当土壤水分亏缺时,ABA可以作为根与地上部间的通讯信号,由很运到地上部并抑制气孔的开放(Blackman和 Davies1985,Gollan等 1986,Zhang和 Davies     

Premature Drying, Fluridone-Treatment, and Embryo Isolation During Development of Maize Kernels (Zea mays L.) Induce Germination, but the Protein Synthetic Responses are Different. Potential Regulation of Germination and Protein Synthesis by Abscisic Acid

Freshly harvested, developing kernels of maize (Zea mays L.)do not germinate up to 77 d after pollination, but can be inducedto do so by fluridone, premature desiccation, and isolationof the developing embryo. The pattern of protein synthesis indeveloping maize embryos is distinct from that during germinationand subsequent seedling growth. Premature desiccation at 35DAP elicits a pattern of protein synthesis upon rehydrationwhich is similar to that in germinated embryos from mature drykernels. Fluridone-induced viviparous germination is accompaniedby changes in the synthesis of some proteins to a post-germinativepattern, but some developmental proteins continue to be synthesized.Embryos isolated from developing kernels at 35 DAP germinatewhen incubated on water; they also produce some developmentalproteins during germination. Kernels from developing cobs at35 DAP which are detached from the mother plant and maintainedin an atmosphere of high relative humidity (moist controls)do not germinate, but neither do they continue a clearly definedpattern of either developmental or germinative protein synthesis.Drying is thus critical to effect a clear transition of proteinsynthesis from a developmental to a germinative mode in maizeembryos. Abscisic acid within the developing embryos is reduced by fluridone,but to a lesser extent by premature drying or maturation drying.Changes in sensitivity to abscisic acid by the developing embryomay be as, or more, important in permitting germination, andthe attendant synthesis of proteins, than changes in abscisicacid content. Key words: Maize (Zea mays L.), germination, vivipary, desiccation, abscisic acid     

Abscisic Acid Inhibition of Kinetin Nucleotide Formation in Germinating Lettuce Seeds

Imbibing ‘Grand Rapids’ lettuce (Lactuca saliva L.) seeds take up ¹⁴C-kinetin, and metabolize this cytokinin to the 5′-nucleotide. The identity of the labeled nucleotide in seed extracts was verified by Sephadex LH-20 column chromatography, paper and thin layer chromatography, and high voltage paper electrophoresis. Incubations with kinetin in the presence of abscisic acid lead to an apparent specific inhibition of kinetin nucleotide formation. ABA has no effect on kinetin uptake, and does not inhibit kinetin nucleotide synthesis in vitro by a cell-free preparation from lettuce seeds. Additionally, ABA does not inhibit adenylate synthesis from exogenously supplied adenine. These results represent a specific cytokinin-ABA interaction, which might play a significant role in the hormonal regulation of lettuce seed germination.     

Abscisic Acid and Water Relations of Rice (Oryza sativa L.): Effects of Drought Conditioning on Abscisic Acid Accumulation in the Leaf and Stomatal Response

The effects of a period of water stress (drought conditioning)on responses to a second (challenge) stress were examined inyoung vegetative rice (Oryza sativa L.) plants. Drought conditioningdid not affect the rate of subsequent stress development, nor,in a first experiment, did it influence relations between turgor(_p) and total () leaf water potential. However, conditioningdid extend the range of _p over which stomata remained open andsignificantly reduced the amount of ABA which accumulated inthe leaf at a given _p. The change in stomatal behaviour (stomataladjustment) was quantitatively accounted for by the change inleaf ABA accumulation. The reduction in ABA accumulation due to conditioning did notinvolve a change in the potential capacity to produce ABA, asABA accumulation in partially dehydrated detached leaves wasnot reduced by conditioning. It is suggested that effects ofconditioning on leaf ABA content in the intact plant involvechanges in the rate of ABA export from the leaf. Oryza sativa L, rice, drought conditioning, stomata, water stress, abscisic acid     

Movement of Abscisic Acid into the Apoplast in Response to Water Stress in Xanthium strumarium L

The effect of water stress on the redistribution of abcisic acid (ABA) in mature leaves of Xanthium strumarium L. was investigated using a pressure dehydration technique. In both turgid and stressed leaves, the ABA in the xylem exudate, the `apoplastic' ABA, increased before `bulk leaf' stress-induced ABA accumulation began. In the initially turgid leaves, the ABA level remained constant in both the apoplast and the leaf as a whole until wilting symptoms appeared. Following turgor loss, sufficient quantities of ABA moved into the apoplast to stimulate stomatal closure. Thus, the initial increase of apoplastic ABA may be relevant to the rapid stomatal closure seen in stressed leaves before their bulk leaf ABA levels rise.

Following recovery from water stress, elevated levels of ABA remained in the apoplast after the bulk leaf contents had returned to their prestress values. This apoplastic ABA may retard stomatal reopening during the initial recovery period.