bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of plant growth regulators in the development and germination of the desiccation-sensitive (recalcitrant) seeds of Avicennia marina
Authors: Farrant Jill M. , Berjak Patricia , Cutting J. G. M. , Pammenter N. W.
Published: September 2008

The contents of the cytokinins zeatin (Z), zeatin riboside (ZR), and isopentenyladenine (IPA), the combined contents of gibberellins1 + 3 (GA), and the contents of indoleacetic acid (IAA) and abscisic acid (ABA) were measured during the development of the desiccation-sensitive seeds of Avicennia marina (Forssk.) Vierh. During the stage of histodifferentiation the amounts of these plant growth regulators (PGRs) were measured on whole fruits. During the phase of seed growth and reserve accumulation measurements were made on the embryonic axis, cotyledons and pericarp separately. Patterns in the amounts of PGRs present during histodifferentiation were similar to those reported for desiccation-tolerant seeds and it suggested that this process is under similar ‘hormonal’ control in A. marina as in orthodox seeds. Very high contents of cytokinins, particularly ZR, were present in both axes and cotyledons during reserve accumulation. This is thought to be related to the nature of the reserves accumulated (soluble sugars), rather than to the phenomenon of desiccation sensitivity. With the exception of ABA, embryonic contents of PGRs were relatively high at seed shedding, consistent with the rapid germination of this highly recalcitrant seed. ABA contents in the embryo were low during reserve accumulation, but concentrations in the pericarp increased throughout this development stage. ABA in the perticap could act to prevent precocious germination. The low concentrations of ABA in the embryo could be related to the desiccation-sensitivity of the seeds of A. marina.
Development and regulation of (1→3,1→4)-β-glucan endohydrolases in germinating wheat (Triticum aestivum)
Authors: Lai Doreen M. L. , Slade Amanda M. , Fincher Geoffrey B.
Published: September 2008

The development of (1→3,1→4)-β-glucan 4-glucanohydrolase (EC 3.2.1.73) has been examined in germinating wheat (Triticum aestivum cv. Millewa) grain, and in isolated aleurone layers and scutella. Activity is first detected in extracts of intact grain 2–3 days after the initiation of germination and thereafter increases until 6 days. In isolated aleurone layers, (1→3,1→4)-β-glucanase activity is secreted for up to 4 days. Treatment of aleurone layers with gibberellic acid (GA3) results in a 2-fold enhancement of secreted enzyme for the first 2 days, but activity decreases after 2 days. (1→3,1→4)-β-Glucanase secretion from GA3-treated aleurone layers clearly precedes the secretion of amylase and (1→4)-β-xylanase. Small but significant levels of cellulase are secreted from aleurone layers after GA3 treatment. Isolated scutella also secrete (1→3,1→4)-β-glucanase but GA3 has little apparent effect on secretion patterns from this tissue. Proteins secreted from excised aleurone layers and scutella, together with those in homogenates of intact, germinated grain, have been examined by Western blot analysis, using monoclonal antibodies against barley (1→3,1→4)-β-glucanases as probes. In each case the wheat (1→3,1→4)-β-glucanase is recognised only by the monoclonal antibody that is specific for barley isoenzyme El.
Storage lipid formation in seeds
Authors: Murphy Denis J. , Rawsthorne Stephen , Hills Matthew J.
Published: September 2008

The mechanisms and regulation of storage lipid formation in seeds are reviewed. Seed storage lipids are ultimately derived from simple carbon compounds, such as sucrose, which are imported into seeds from source tissues, such as leaves or pods. The partitioning of this important carbon towards storage lipid, carbohydrate or protein is regulated by a complex interaction between genetically-determined endogenous factors and external environmental influences. Storage lipids are synthesized from fatty acids, derived from acetyl-CoA, and glycerol 3-phosphate. Fatty acid biosynthesis and probably acetyl-CoA formation, occurs within the plastids to produce oleoyl-CoA. Further elaboration of oleoyl-CoA to produce polyunsaturates, hydroxylates or very long chain acyl-CoAs occurs on the endoplasmic reticulum, as does the esterification of acyl-CoAs to glycerol-3-phosphate to produce the final triacylglycerol storage oil. The temporal and hormonal regulation of storage lipid accumulation in seeds is discussed.
Identification of the sites of K leakage from imbibing seeds and grains
Authors: Beecroft Penny , Lott John N. A.
Published: September 2008

Seeds/grains of four species were imbibed for up to 90 minutes half embedded in agar. The agar was then freeze-dried and treated with a chromatographic reagent to detect the sites of potassium leakage from the imbibing seeds/grains. Soybean (Glycine maxcv. Marathon) and pea (Pisum sativumcv. Little Marvel) leaked K across the entire surface of their testas. Aged pea seeds leaked much more extensively than seeds of a fresher lot of the same cultivar. Squash (Cucurbita maximacv. Warted Hubbard) seeds leaked extensively from the flat sides of the seeds and at the hilum, but only slightly at the margins. Maize (Zea mayscv. Golden Beauty) leaked most extensively across the endosperm-only side (i.e. the side opposite the embryo) of the kernel, and kernels leaked more at the tip-cap end than at the broad end. Energy dispersive X-ray analysis determined that K was present in the testas/pericarps before imbibition in all species studied, and that the peak-to-background ratios of K were lower after the seeds/grains had been exposed to water. Neutron activation analysis verified that K was leaked out of the seeds/grains and absorbed into the agar. Seeds from all species studied showed varying amounts of seed-to-seed variation. These variations can be attributed in part to differences in testa/pericarp structure and condition.
Induction of thermodormancy in Avena sativa seeds
Authors: Corbineau F. , Black M. , Côme D.
Published: September 2008

Freshly harvested oat (Avena sativa L.) seeds are considered to be dormant because they are unable to germinate at relatively high temperatures (above 20°–25°C). This primary dormancy results partly from the structures surrounding or adjacent to the embryo (pericarp, testa and endosperm) and partly lies in the embryo itself. Incubation of imbibed dormant seeds at 30°C induces a thermodormancy which is expressed as germination in a narrower temperature range. Induction of thermodormancy is apparent after 3–8 hours at 30°C, is optimal after about 1–2 days at this temperature, but diminishes with longer treatment times. Although whole grains become more dormant as a result of such treatment, the embryos themselves become less dormant, therefore the tissues covering or adjacent to the embryos must have become more inhibiting or the embryos have become more sensitive to their inhibitory action. The germination and sensitivity to ABA or oxygen of embryos isolated from such seeds are no longer so dependent on temperature. The effect of high temperature on primary dormancy and induction of thermodormancy is discussed with reference to sensitivity to ABA and temperature.
Detecting and overcoming water-impermeable barriers in prickly sida (Sida spinosaL.) seeds
Authors: Egley G. H. , Paul R. N.
Published: September 2008

Barriers to water permeability in prickly sida seeds were characterized using solvents and water-soluble salts. The seeds imbibed water when barriers in the chalazal area broke down. The major barrier was in the distal region of the palisade layer bordered internally by the light line. Soaking dormant seeds in certain organic solvents overcame the barrier and enabled the seeds to imbibe water. The most active were non-polar solvents with dielectric constants between 3.7 and 18.5, and with a high ability to hydrate and swell cellulosic materials. We concluded that the most active solvents (pyridine, diethylamine) overcame the major barrier, entered the proximal portion of the palisade layer and caused the swelling of cellulosic cell components. The cellular expansion created stresses that broke thin walls of the underlying subpalisade cells in the chalazal area. The breakage resulted in separation of the cell layers and rapid entry of water into the seed. Highly non-polar or highly polar solvents had little or no activity. Some solvents overcame the barrier but did not cause swelling and disruption of the cell layers. We propose that the natural breakdown of impermeability in prickly sida seeds was due to the gradual seepage of water past the barrier in the distal portion of the coat in the chalazal area and into the inner portions where swelling of hygroscopic components triggered the breakage of subpalisade cell walls resulting in cell layer separation.
Rapid and efficient purification of seed messenger RNA without phenol:chloroform extraction
Authors: Pramanik S. K. , Reynolds T. L. , Maclsaac S. A. , Bewley J. D.
Published: September 2008

A novel method has been devised to extract poly (A+)RNA from seed tissues. The advantages of this technique include the speed of extraction and the elimination of the hazardous phenol:chloroform extraction step which usually precedes oligo (dT)-cellulose column chromatography. Instead, the crude supernatant, containing a high concentration of SDS and salts to effectively inhibit RNase activity, is passed directly over the oligo (dT)-cellulose column. The resultant isolated poly (A+)RNA is of high yield and purity and is suitable for in vitro translation and Northern blot analysis.
X-ray studies on changes in embryo and endosperm morphology during priming and imbibition of tomato seeds
Authors: Liu Y. , van der Burg W. J. , Aartse J. W. , van Zwol R. A. , Jalink H. , Bino R. J.
Published: September 2008

Morphological changes in tomato (Lycopersicon esculentumMill. cv. Moneymaker) seed during osmopriming and imbibition (‘hydropriming’) were followed using X-ray photographs. Embryo, endosperm and free space areas were measured. Both osmopriming and hydropriming resulted in free space development (+ 8.1% and + 10.8% of the whole seed planar area, respectively), almost all at the cost of the endosperm area. Planar dimensions of whole seeds were relatively constant and the dimension perpendicular to the planar surface, the thickness, could account for the volume increase of primed seeds reported in the literature. In dead seeds, only a small amount of free space developed while the planar area of the seed remained the same. In the imbibing viable seeds no deterioration of endosperm could be detected until the moment of root protrusion.

Seeds which were osmoprimed directly after harvest, i.e. in the fresh state, did not showthe induction of any free space, while free space developed normally after dehydration and a second priming treatment. Apparently, a dehydration step prior to the priming treatments is required for the development of free space in osmo- or hydroprimed seed.

X-ray photographs of hydroprimed seeds showed that the radicle tip adhered tightly to theendosperm cap. This results in various forms of damage to the root tips upon redrying. Priming did not introduce cotyledon abnormalities.
The effect of aerated hydration on DNA synthesis in embryos of Brassica oleracea L.
Authors: Thornton J. M. , Collins A. R. S. , Powell A. A.
Published: September 2008

Ageing causes a delay in the onset of DNA replication in seeds. Aerated hydration for 8 h, a treatment to invigorate seeds, resulted in a reduction of about 12 h in the time difference in the onset of DNA synthesis between unaged and aged embryos of brassica seed. This effect is consistent with a recovery process occurring during aerated hydration of the seed involving the repair of accumulated DNA damage. The occurrence of hydroxyurea-resistant 3H-thymidine incorporation in aged Brussels sprouts embryos during the period 16–32 h from the start of hydration supports this interpretation.
The mechanisms of desiccation tolerance in developing seeds
Authors: Leprince O. , Hendry G. A. F. , McKersie B. D.
Published: September 2008

Desiccation tolerance is one of the most fundamental properties of seeds. It is acquired late in seed development and is considered necessary for the completion of the plant's life cycle, as an adaptive strategy to enable seed survival during storage or environmental stress, and to ensure better dissemination of the species. The role of water status in desiccated tissues and problems related to testing tolerance in seeds are reviewed. The molecular mechanisms of desiccation tolerance has received extensive consideration only during this past decade. There is a general consensus that desiccation tolerance involves the protection of cellular membranes from the deleterious effect of water removal and the resultant necessity to maintain the bilayer structure in the absence of an aqueous environment. Therefore, some aspects of desiccation-induced membrane injury are described. Several strategies for coping with cellular desiccation have been identified the presence of high amounts of non-reducing sugars, the efficiency of free radical-scavenging systems and the expression of desiccation- and/or ABA-regulated genes. These molecular mechanisms allowing cellular protection are reviewed together with their respective role in dessication tolerance. It is concluded that desiccation tolerance is not likely to be ascribed to a single mechanism but rather to a multifactorial property in which each component is equally critical.
Release of dormancy in sunflower embryos by dry storage: involvement of gibberellins and abscisic acid
Authors: Bianco J. , Garello G. , Le Page-Degivry M. T.
Published: September 2008

Excised Helianthus annuus L. embryos became dormant during the third week after anthesis. At this stage a short drying treatment (3 d) led to a slight improvement in germination but a 6-week dry storage caused a complete release from dormancy. The short drying treatment, however, elicited the embryos' response to an exogenous concentration of GAs which was unable to promote germination of fresh embryos. It therefore appeared that a short drying treatment changed the sensitivity to GAs but was not capable of directing embryo metabolism completely towards a germinative mode. Moreover, this drying treatment reduced considerably the ABA content in both the axis and the embryo. Nevertheless, no correlation could be established between germinability and the ABA content since the amount of ABA was not modified by the 6-week dry storage. The key step for predisposing the seeds to germinate is the suppression of the capacity for ABA synthesis in the axis, a suppression which takes place during 6-week dry storage.
The fluorescence assay for Maillard product accumulation does not correlate with seed viability
Authors: Baker Ellen H. , Bradford Kent J.
Published: September 2008

A recent hypothesis states that the accumulation of amino-carbonyl reaction products of reducing sugars with proteins (Maillard products) is related to the loss of seed vigour and viability during ageing. Since Maillard products are biochemical end products, their accumulation should provide an index of seed deterioration. A simple fluorescence assay has been used to estimate the quantity of Maillard products in aqueous seed extracts. We tested whether an accumulation of fluorescent compounds correlates with the loss of seed viability during ageing. Fluorescence of extracts from lettuce (Lactuca sativa) embryonic axes increased after controlled deterioration, but was not correlated with ageing period. Fluorescence of extracts from whole broccoli (Brassica oleracea var. italica) seeds was either unchanged or declined during controlled deterioration. Extracts from naturally aged whole seeds of carrot (Daucus carota), tomato (Lycopersicon esculentum), and cauliflower (B. oleracea var. botrytis) had higher fluorescence than controls, but there was no consistent increase in fluorescence in proportion to the loss of viability. Extracts of naturally aged onion (Allium cepa) seeds exhibited less fluorescence than extracts from seeds with higher viability. We conclude that the fluorescence assay does not have general utility as an index of seed deterioration.
Cellular and metabolic damage induced by desiccation in recalcitrant Araucaria angustifolia embryos
Authors: Espindola L. Salmen , Noin M. , Corbineau F. , Côme D.
Published: September 2008

Embryos of Araucaria angustifolia seeds showed no dormancy; they germinated easily at temperatures ranging from 10° to 30°C, and the thermal optimum was about 25–30°C; they were recalcitrant. At harvest, their mean moisture content (dry weight basis) was about 120% and they completely lost viability when their moisture content fell to about 30%. The cotyledons were more sensitive to dehydration than the radicle. Dehydration induced deterioration of cell membranes as indicated by a high increase in leakage of solutes. It also resulted in damage in the nuclei, which was not repaired upon rehydration. During desiccation, respiratory activity decreased; however, O2 uptake was not an indication of germination ability, since it was significantly affected only when embryo moisture content reached the critical value of 30%. The decrease in the capacity to convert 1-aminocyclopropane 1-carboxylic acid to ethylene, which was observed at 30–60 min of dehydration, was a very early indicator of deterioration in embryos. Desiccation resulted also in a rapid decrease in the ability for protein synthesis as measured by [35S]methionine incorporation into total protein; 50% inhibition was observed after 30–60 min of desiccation for both axis and cotyledons.
Physical properties of water in Zizania embryos in relation to maturity status, water content and temperature
Authors: Vertucci C. W. , Crane J. , Porter R. A. , Oelke E. A.
Published: September 2008

Changes in the properties of water in excised embryos were measured during the late stages of grain development in two cultivars of Zizania palustris and a population of the endangered species Z. texana. The relationships between water content and water activity were determined from water sorption isotherms, measured at temperatures between 35 and 5°C and then derived for lower temperatures. The freezing and melting behaviour of water in embryos at different water contents was determined using differential scanning calorimetry. The moisture content of embryos at high water activities decreased with maturation, as did the moisture content at which freezing transitions were not observed. While the temperatures of freezing and melting transitions decreased as the moisture content of embryos decreased, there were no discernible differences among embryos at different developmental stages. The properties of water measured in maturing Zizania embryos approached those for orthodox seeds as determined from the strength of water sorption, the enthalpy of the melting transition and the moisture content at which water is unfreezable. From these data we conclude that the properties of water in recalcitrant Zizania embryos change with development to resemble those of embryos of desiccation-tolerant seeds, but that the seeds never achieve the orthodox condition. The effects of interactions between moisture content and temperature on desiccation damage, freezing damage and germination in Zizania are predicted, based on the physical properties of water reported here and the correspondence of these properties with physiological function reported for other species. The resulting ‘phase diagram’ defines possible combinations of moisture content and temperature for storage under equilibrium conditions.
Two-dimensional protein patterns of tomato (Lycopersicon esculentum Mill.) seeds; effects of isolation procedure and imbibition
Authors: Bergervoet J. H. W. , Kraak H. L. , De Vos C. H. R. , Bino R. J.
Published: September 2008

A computer-aided comparison of tomato (Lycopersicon esculentum Mill.) seed protein patterns, obtained after two-dimensional gel electrophoresis, was made for three different extraction procedures: TCA acetone/lysis buffer, lysis buffer only and modified Laemmli/lysis buffer. Comparison of the isolation methods showed that about half of the amount of proteins detected was common in each method. Also, proteins specific to some isolation methods were detected. Protein synthesis during imbibition was monitored using 35S-methionine. After labelling the proteins were extracted using TCA acetone/lysis buffer. Following two-dimensional gel electrophoresis the gels were first silver stained, to give a general picture of all proteins present in the seed, then the gels were exposed to a film for autoradiography. Comparison of the in vivo-synthesized protein patterns and the silver-stained proteins revealed that from day 0 to day 1 the protein pattern was changed but the total number of different spots was similar. After 1 day of imbibition, the number of protein spots increased greatly and the protein pattern changed again.
Wheat seed ageing and embryo protein degradation
Authors: Dell'Aquila A.
Published: September 2008

Wheat seed lots of different viability were obtained by an accelerated ageing technique in which seeds were hydrated up to 12.5–14.5% on a fresh weight basis and stored at 35°C. Ageing was accompanied by a progressive delay of the onset of germination and a decrease of [35S]-methionine uptake and incorporation into soluble proteins of the imbibing embryos. A detailed analysis of newly synthesized proteins by two-dimensional polyacrylamide gel electrophoresis showed that normal protein patterns during the germination process were impaired by ageing. Only two groups of polypeptides with molecular masses of 84.9–69.5 and 66.6–60.2 kDa, respectively, were actively produced while most proteins decreased or were definitely degraded. Our results suggest that the biochemical changes required for germination are gradually opposed by a deterioration process and that some newly-synthesized polypeptides can be taken as markers in assessing seed survival of ageing stress.
Gene expression during maize kernel development
Authors: Doehlert Douglas C. , Smith Leslie J. , Duke Edwin R.
Published: September 2008

Relationships have been investigated between gene transcript abundance, enzyme activities and storage product accumulation in developing maize (Zea maysL.) kernels from 10 to 55 days postpollination (DPP). At the early stages of kernel development, there was very little increase in dry weight but kernels accumulated high concentrations of sugars and amino acids. At the end of this ‘lag’ phase (at 15 DPP), many transcripts appeared with little evidence of their translation. The initiation of the kernel-fill period at 20 DPP was characterized by a sudden rise in total RNA, increases in enzyme activities, and the initiation of storage product accumulation. Zein accumulation during this phase was highly correlated with α-zein transcript abundance. Starch accumulation was correlated with both the activity of ADP-GIc pyrophosphorylase and the abundance of gene transcripts encoding this enzyme (Shrunken-2andBrittle-2). DNA content of kernels increased linearly up to 30 DPP as a result of endoreplication, but had no apparent relationship to gene expression. DNA may accumulate as a storage product. Kernel-fill terminated when the moisture content fell below 36% and was marked by a decline of transcripts and a reduction of enzyme activities.
Seed quality as cause for differences in longevity behaviour after seed pretreatment in wheat (Triticum aestivumL.)
Authors: Hofmann P. , Steiner A. M.
Published: September 2008

Hydration-dehydration seed pretreatments are well-known to improve germination rate, germination and vigour. However, contradictory results have been reported concerning the effect of a pretreatment on longevity. The present paper shows that the effect of a seed pretreatment on longevity is largely dependent on the quality of the seed at the time of pretreatment. Pretreating wheat seeds of high quality increased the rate of viability loss during subsequent storage. On the other hand, pretreating wheat seeds of relatively low quality decreased the rate of seed deterioration during subsequent storage. In the light of these findings, hitherto contradictory results in the literature could be explained.
Changes in the synthesis of some proteins during breaking of secondarily induced thermodormancy by respiration inhibitors (cyanide, azide) and BAP in embryos ofAgrostemma githagoL. seeds
Authors: Bernhardt D. , Gerth U.
Published: September 2008

Secondary dormancy (thermodormancy) inAgrostemma githagoL. seeds, caused by imbibing the seeds for 4 d at 35°C in the dark, is broken under the influence of cyanide (10 mM), azide (1 mM or BAP (0.44 mM). Both respiration inhibitors (cyanide and azide) and BAP increase the synthesis of five specific soluble proteins in the embryo axes and cotyledons. The activity of β-cyanoalanine synthase (β-CAS, EC 4.4.1.9.), which is able to detoxify cyanide, decreased in response to cyanide and azide. The relevance of these findings to the breaking of thermodormancy is discussed.
Increase of the content of QP47 (a desiccation-associated nuclear protein) in embryo cells during maturation of pea seeds
Authors: Chiatante Donato , Brusa Paola
Published: September 2008

A nuclear protein (QP47) is synthesized during the last stage of seed maturation when the embryo cells start to dehydrate and enter a condition of metabolic quiescence. This protein is localized in the nucleoplasm surrounding the chromosomes. The correlation existing between the synthesis of QP47 and arrest of cell proliferation, suggests that the presence of this protein in the nucleus could influence its metabolic activities. This hypothesis is supported by the fact that degradation of this protein precedes resumption of cell proliferation during the early stage of radicle elongation.
Maize seed response to successive imbibition/dryback cycles: viability and vigour
Authors: Davidson K. G. V. , Sowa S. , Moore F. D. , Roos E. E.
Published: September 2008

Electroconductivity tests are currently used for seed vigour assessment. They are rapid and simple and after further development, they may yet provide the seed industry with a non-destructive alternative to the standard germination test, which is thoroughly destructive to the sample, time consuming, and expensive. Seed injury, a result of soaking required by the electroconductivity test, was evaluated using high qualityZea maysL. seeds responding to successive imbibition/dryback cycles. If the soaking time is brief, injury to the seeds should be minimal, thus permitting successive tests on the same sample. We tested 5 imbibition/dryback cycles (C) and 5 imbibition periods, or cycle durations (CD) of 2, 4, 6, 7 and 8 h. Dryback periods lasted 5–7 d at room temperature. Seeds were permitted to dry back to 10% moisture. Electroconductivity readings were obtained at the end of each CD for each C. Each treatment (C × CD) sample, n=100 seeds, was germinated at 25°C for 7 d; radicle lengths were measured after 3 d. The experiment was repeated yielding a total of 50 observations. Viability and vigour losses were measured in response to successive C and increasing CD. Five cycles of 6 h each resulted in only a 10% loss of viability, but a 20% loss of relative vigour, confirming that vigour is more sensitive to the testing procedure. Cycles had the greatest effect on loss of seed quality since 45% of the readily leachable electrolytes were lost from the seeds during the first soaking period. There was no interaction between C and CD.
Observations on the survival of seeds of Agathis spp. stored at low moisture contents and temperatures
Authors: Dickie J. B. , Smith R. D.
Published: September 2008

Three seedlots of Agathis australis (Lambert) Steud. (kauri pine) were stored hermetically at moisture contents of 1.5–15.5% and at temperatures from −20° to 42°C; and one seedlot of Agathis macrophylla was stored at 7%, 9% or 13% moisture content and at 26°, 6° or −13°C. Seeds of A. australis showed orthodox storage behaviour; except that viability was progressively reduced with drying below about 5% moisture content, and, depending on seedlot, subsequent storage longevities were reduced at all temperatures. Seeds of A. macrophylla again showed essentially orthodox characteristics at 9 and 13% moisture content; but drying to 7% moisture content reduced viability significantly, and of those seeds surviving, a further proportion died as a result of transfer to −13°C, and the remainder survived for 2500 d with little further viability loss. Seeds of neither species conformed fully to orthodox characterisics, nor to those of the intermediate category. The results are discussed in relation to possible causes of this ‘sub-orthodox’ behaviour, especially current seed-harvesting methods, and the limits put upon ex situ conservation of these species in seed banks by their predicted comparatively short storage lives.
Survival of Zizania embryos in relation to water content, temperature and maturity status
Authors: Vertucci Christina W. , Crane Jennifer , Porter Raymond A. , Oelke Ervin A.
Published: September 2008

The interactions between water content and temperature on freezing and desiccation damage were examined for Zizania (wild rice) embryos at several stages of maturity. The water content of excised embryos was manipulated by flash drying at 35°C or room temperature to between 2.5 g H2O/g dw and 0.05 g/g. Embryos were then exposed to temperatures ranging from 5 to −50°C. Viability following the drying and cooling treatments was assayed by leakage of electrolytes and germination in culture. Viability of embryos decreased when embryos were dried below a critical water content. The critical water content was greatest for the least mature embryos. Critical water contents were also temperature dependent and increased with decreasing temperature. Even though the critical water content varied with developmental status and temperature, the water activity corresponding to the critical water content appeared to be constant at 0.90. The most mature embryos survived temperatures as low as −50°C while the least mature embryos survived only to −18°C. These trends were predicted by ‘phase diagrams’ based on the physical properties of water in embryos at different stages of maturity (Vertucci et al., 1994a). Our results confirm the earlier prediction that long term preservation of Zizania grains is possible at −20°C and the degree of success will be related to the maturity status of the embryos.
Reserves of aluminium and mineral nutrients in seeds ofEucalyptus calophylla(Myrtaceae) with reference to the globoid inclusions
Authors: Egerton-Warburton Louise M. , Griffin Brendon J. , Kuo John
Published: September 2008

Amounts of mineral nutrients and aluminium (Al) were assessed in the globoid inclusions, proteinaceous matrix and druse crystals ofEucalyptus calophyllaseeds collected from trees grown in coal-mine (mean soil pH 4.3, Al 260 μg g−1) and forest soils (pH 5.3, Al 10 μg g−1). Energy-dispersive X-ray microanalysis (EDX) of bulk frozen hydrated samples indicated that significantly higher amounts of Mg, P, S, K and Ca occurred in the globoid inclusions of mine- than forest-site seeds. In both seedstocks, Al was detected in the globoid inclusions but not in the proteinaceous matrix or druse crystals. Significantly higher amounts of Al occurred in mine-site samples of dry and germinating seeds than in forest-site seeds. It was concluded that globoid inclusions may be useful as indicators of the soil conditions in which the parent plant was grown.
A critical update on seed dormancy. I. Primary dormancy
Authors: Hilhorst Henk W. M.
Published: September 2008

The emphasis of modern dormancy research is almost entirely on the form of dormancy that is acquired during seed development, primary dormancy. Abscisic acid (ABA) appears to be intimately involved in its regulation. The action of abscisic acid has also been implied in many other developmental processes. The coincidence of developmental events, such as dehydration and completion of maturation, with the acquisition of primary dormancy suggests that dormancy is influenced by these processes. Germinability, both during development and after maturation, is sometimes directly correlated with ABA content. The lack of such a correlation may be explained by assuming a decisive role for the responsiveness to ABA or other overriding factors. ABA has been detected in all seed components. The different seed tissues may all contribute, to various extents, to the degree of whole seed dormancy. It is concluded that ABA action in dormancy regulation is not restricted to the embryo but is also located in endospermic tissue. In addition, a role of ABA in the morphological development of germination modifying seed tissues is proposed. The mechanism for ABA action appears to be associated with cell wall properties.
Thidiazuron stimulates germination and ethylene production inStriga hermonthica– comparison with the effects of GR-24, ethylene and 1-aminocyclopropane-1-carboxylic acid
Authors: Logan David C. , Stewart George R.
Published: September 2008

Seed germination of the hemiparasitic angiospermStriga hermonthicais elicited by compounds present in the root exudates of the host plant. A variety of chemicals can substitute for the host-derived signal although the exact mechanism through which these act is unknown. In the present study, thidiazuron (TDZ), a cytokinin-active urea derivative was found to stimulate germination. This thidiazuron-induced germination was shown to be mediated by endogenous ethylene, by a similar mechanism to germination induced by host-root exudate and the synthetic stimulant GR-24. Comparing the effects of TDZ, host-root exudate, GR-24 and the ethylene precursor 1-aminocyclopropane-1-car-boxylic (ACC) suggests that ethylene production increases as a result of increased ACC synthesis and is consistent with a model forStrigaseed germination in which host-derived signals and other stimulants act by eliciting the synthesis of ethylene via a stimulation of ACC synthase activity. All germination stimulants tested trigger a rapid increase in O2uptake by conditioned seeds. The patterns of O2uptake following TDZ or GR-24 treatments show similarities and three distinct phases of respiration are apparent. In contrast, stimulation of O2uptake by ethylene results in a different pattern, with no distinct phases obvious following the initial burst of activity.
Changes in the composition of globoids in castor bean cotyledons and endosperm during early seedling growth with and without complete mineral nutrients
Authors: Lott John N.A. , West M. Marcia , Clark Ben , Beecroft Penny
Published: September 2008

The endosperm and cotyledon tissues of Ricinus communis seeds and young seedlings were examined for changes in the mineral nutrient composition of globoids during early seedling growth. The effect on globoid composition of providing mineral nutrients to the developing seedling was also investigated. Globoids in endosperm and cotyledon tissues of castor bean seeds contained P, Mg and K, as well as trace amounts of Ca, Fe and Zn. Irrespective of the addition of mineral nutrients, K content in globoids of endosperm and cotyledon tissues declined significantly during initial seedling growth. During early seedling growth, amounts of Fe, Zn and Ca increased in cotyledon globoids. Ca contents of globoids of endosperm tissues also increased. The changes in Fe, Zn and Ca globoid contents were not influenced by providing mineral nutrients to growing castor bean seedlings.
The high reducing sugar content during germination contributes to desiccation damage in lettuce (Lactuca sativa L.) radicles
Authors: van der Toorn P. , McKersie B. D.
Published: September 2008

At the time of protrusion, radicles of lettuce seeds became susceptible to desiccation damage. Concomitant with radicle elongation, both the reducing sugar content and the amount of lipid-aldehydes increased. The role of the hydroxy- and lipid-aldehydes in browning reactions that occurred during desiccation and re-imbibition was analysed. It was concluded that both types of aldehydes reacted with amino-groups during desiccation and that the increase in lipid-aldehydes during germination could be due to the augmented reducing sugar content. Therefore, the high reducing sugar content in radicles of germinated lettuce seeds may be the primary source of hydroxyl radicals, and thereby, a principal cause of desiccation damage.
Does benzyladenine stimulate DNA metabolism by modifying gene expression during maize germination?
Authors: Zúñiga-Aguilar José Juan , López Imelda , Gómez Alberto , Vázquez-Ramos Jorge M.
Published: September 2008

Benzyladenine, a synthetic cytokinin, stimulates DNA metabolism during maize germination; apparently such stimulation occurs in two phases, and during the first phase stimulations of DNA synthesis, of protein kinase activity (both α-amanitin repressible), of DNA polymerase and poly ADP-ribosyl polymerase activities are observed. Since the evidence suggested that the effects produced by BA were due, at least partially, to transcriptional activation, attempts were made to discover genes, by subtractive hybridization of a cDNA library or by differential display, whose expression depended on the presence of BA; however these were unsuccessful. BA modulated the expression of a limited number of genes only. The possible mechanism by which BA could be promoting DNA metabolism during maize germination is discussed.
Maize DNA polymerase 2 (an α-type enzyme) suffers major damage after seed deterioration
Authors: Coello Patricia , Vázquez-Ramos Jorge M.
Published: September 2008

DNA polymerase 2 holoenzyme is an α-type polymerase present as a major activity in 24-h germinated maize embryo axes. At this time, several of the polypeptides that compose this multisubunit enzyme are phosphorylated. During the germination of artificially deteriorated maize embryo axes, total DNA polymerase activity decreases by around 50% when compared with activity in non-deteriorated axes. DNA polymerase 2 appears to be damaged by the deterioration treatment, greatly reducing its activity. This decrease in activity is related to protein degradation during germination since the amount of both the holoenzyme and the different polymerase 2 subunits is reduced as imbibition progresses. The decrease in amount is more dramatic for some of the subunits than for others, i.e., the amount of the 90-kDa catalytic subunit is reduced by about half, whereas all other subunits totally disappear at different times during germination. The phosphorylation state of the different polypeptides is also greatly affected.
Factors affecting endo-β-mannanase activity in the endosperms of fenugreek and carob seeds
Authors: Kontos Fanouris , Spyropoulos Caroline G. , Griffen Alison , Bewley J. Derek
Published: September 2008

Endosperms of fenugreek and carob which have been leached following their isolation exhibit increased activity of endo-β-mannanase, part of which is released into the surrounding incubation medium. This activity was suppressed by the addition to the endosperms of abscisic acid or endosperm/seed coat leachate. The leachate from carob inhibited the increase of endo-β-mannanase activity in fenugreek and that from fenugreek inhibited enzyme activity in carob but more weakly; neither of these leachates inhibited the production of α-amylase in wheat endosperm. Polyethylene glycol-induced stress on non-leached endosperms inhibited endo-β-mannanase production, but not when the stress was applied following endosperm leaching. However, the stress did reduce the amount of enzyme released into the surrounding incubation medium. Several isoenzymes of mannanase could be detected on isoelectric focusing activity gels in the endosperms of both fenugreek and carob, but their pis differed between the two species. When activity was suppressed by ABA or leachate, all pl forms declined equally.
Effects of pre-storage hydration treatments on germination performance, moisture content, DNA synthesis and controlled deterioration tolerance of tomato (Lycopersicon esculentum Mill.) seeds
Authors: van Pijlen Jaap G. , Groot Steven P. C. , Kraak H. Lieke , Bergervoet Jan H. W. , Bino Raoul J.
Published: September 2008

Storage of tomato seeds under deteriorating conditions reduced the rate of germination, the uniformity of germination, total germination and the proportion of normal seedlings. Pre-storage humidification and hydropriming of seeds resulted in a significant increase in resistance to deterioration. In contrast, osmoprimed seeds were more deterioration sensitive. Humidification or hydropriming for one day did not allow nuclei to enter the S phase of the cell cycle. Osmopriming strongly increased the percentage of nuclei with replicated DNA in the embryonic root tip, indicating initiation of the cell cycle and progression towards the G2 phase. The interaction between the prestorage treatments, cell cycle progression and deterioration resistance, is discussed. Based on the changes in moisture content equilibrium and cell cycle activity it is hypothesized that the beneficial effects of pre-storage humidification and hydropriming were related to metabolic activities induced by the partial hydration and that the adverse effects of osmopriming were caused by a decrease in DNA repair activity due to progression in the cell cycle.
A hydrothermal time model of seed after-ripening in Bromus tectorum L.
Authors: Christensen Maren , Meyer Susan E. , Allen Phil S.
Published: September 2008

Bromus tectorum L. is an invasive winter annual grass with seeds that lose dormancy through the process of dry after-ripening. This paper proposes a model for after-ripening of B. tectorum seeds based on the concept of hydrothermal time. Seed germination time course curves are modelled using five parameters: a hydrothermal time constant, the fraction of viable seeds in the population, base temperature, mean base water potential and the standard deviation of base water potentials in the population. It is considered that only mean base water potential varies as a function of storage duration and incubation temperature following after-ripening. All other parameters are held constant throughout after-ripening and at all incubation temperatures. Data for model development are from seed germination studies carried out at four water potentials (0, −0.5, −1.0 and −1.5 MPa) at each of two constant incubation temperatures (15 and 25°C) following different storage intervals including recently harvested, partially after-ripened (stored for 4, 9 or 16 weeks at 20°C) and fully after-ripened (stored for 14 weeks at 40°C). The model was fitted using a repeated probit regression method, and for the two seed populations studied gave R2 values of 0.898 and 0.829. Germination time course curves predicted by the model generally had a good fit when compared with observed curves at the incubation temperature/water potential treatment combinations for different after-ripening intervals. Changes in germination time course curves during after-ripening of B. tectorum can largely be explained by decreases in the mean base water potential. The simplicity and good fit of the model give it considerable potential for extension to simulation of after-ripening under field conditions.
Respiratory enzyme activities during germination inBrassicaseed lots of differing vigour
Authors: Bettey Mary , Finch-Savage W.E.
Published: September 2008

The rate of oxygen consumption by cabbage seeds increased on imbibition and there was a further sharp increase on germination. This was delayed in artificially aged seeds of low vigour. The increases in oxygen consumption reflect the increased oxidation of carbohydrates via respiratory pathways. The activities of key regulatory enzymes of glycolysis and the oxidative pentose phosphate pathway were measured in aged and unaged seed lots of cabbage. Differences in the activities of glucose 6-phosphate dehydrogenase and pyrophosphate:fructose 6-phosphate 1-phosphotransferase were correlated with the rate of germination (T50) in seed lots with large differences in seed vigour induced experimentally by artificial aging. However, the activities of these enzymes could not be used to distinguish between untreated seed lots which had smaller vigour differences apparent only under stress. The enzymes are presumably not controlling and determining seed vigour, but merely reflecting actual seed performance under the current conditions.
A comparative study of the seed germination biology of a narrow endemic and two geographically-widespread species ofSolidago(Asteraceae). 1. Germination phenology and effect of cold stratification on germination
Authors: Walck Jeffrey L. , Baskin Jerry M. , Baskin Carol C.
Published: September 2008

Solidago shortiiis endemic to a small area in northcentral Kentucky (USA), whereas two of its sympatric congeners,S. altissimaandS. nemoralis, are geographically widespread. Seeds (achenes) ofS. shortii(0.370 mg) are significantly larger (PLSD,P=0.05) than those ofS. altissima(0.070 mg) andS. nemoralis(0.068 mg). Germination percentages of freshly-matured seeds of the threeSolidagospecies collected in November 1991, 1992 and 1994 were 0–2% in light at 15/6°C, 1–37% at 20/10°C, 9–56% at 25/15°C and 10–85% at 30/15 and 35/20°C. Stratification increased the percentage and rate of germination and decreased the time to the onset of germination (measured by Timson's index only at 20/10°C in light) in the three species. Following 12 weeks of cold stratification in light, seeds of the three species germinated to 72–100% in the light and to 22–100% in darkness over the range of thermoperiods; those cold-stratified in darkness germinated to 39–100% in light. Freshly-matured seeds ofS. altissimaand ofS. nemoralisgerminated to 0–4% in darkness, whereas those cold-stratified for 12 weeks in darkness germinated to 0–28% in darkness. On the other hand, freshly-matured and cold-stratified (in darkness) seeds ofS. shortiigerminated to 0–13 and 13–73%, respectively, in darkness. Under near-natural temperatures in a glasshouse without temperature control, germination of the three species peaked in March. Thus, the primary difference in dormancy-breaking and germination requirements of the three species is that the endemic germinates to a much higher percentage in darkness than its two congeners. Seeds ofS. shortiido not have any special dormancy-breaking or germination requirements that could not be fulfilled outside its present-day geographic range.
2nd International Workshop on Desiccation-Tolerance and -Sensitivity of Seeds and Vegetative Plant Tissues
Authors: Berjak Patricia , Osborne Daphne , Pammenter Norman
Published: September 2008

How some plant cells can survive a period of desiccation to live again when other cells will die, was the theme of the recent Workshop in the mountain retreat of Franschhoek, near Cape Town, South Africa. Sixty-two biochemists and cell physiologists from around the world assembled to discuss these problems for the second time in three years.