First Hours Of Imbibition Research Articles

The interplay of PsABAUGT1 with other abscisic acid metabolic genes in the regulation of ABA homeostasis during the development of pea seeds and germination in the presence of H2O2

Inactivation of abscisic acid (ABA) in vitro may be catalyzed either by ABA 8′-hydroxylase (ABA8′OH) or by ABA uridine diphosphate glucosyltransferase (ABAUGT), which conjugates ABA with glucose. However, the involvement of these enzymes in the control of ABA content in vivo, especially ABAUGT, has not been fully elucidated. In pea seeds, both PsABAUGT1 and PsABA8′OH1 contribute to the reduction of ABA content during seed maturation and imbibition; however, during the first hours of imbibition, a high expression of only PsABAUGT1 was observed. Imbibition of seeds with H2O2 increased the ABA content despite the oxygen availability and altered the expression of metabolic genes. The expression of the biosynthetic gene 9-cis-epoxycarotene dioxygenase (PsNCED2) was increased, while that of PsABAUGT1 was decreased in each H2O2 experiment despite O2 availability. Under hypoxia, only seeds imbibed with H2O2 germinated, while under nonlimiting oxygen conditions, the germination rate was not altered by H2O2. Under hypoxia, the germination rate of H2O2-imbibed seeds seemed to not depend on the absolute ABA content and rather on the balance between ABA and gibberellins (GA), as H2O2 increased the expression of GA synthesis genes.Overexpression of PsABAUGT1 in Arabidopsis decreases seed ABA content, accelerates germination and reduces seed sensitivity to exogenously applied ABA, confirming the ability of PsABAUGT1 to inactivate ABA. Thus, PsABAUGT1 is a new player in the regulation of ABA content in maturating and imbibed pea seeds, both under standard conditions and in response to H2O2.

Integrating proteomics and enzymatic profiling to decipher seed metabolism affected by temperature in seed dormancy and germination

Temperature is an important environmental factor affecting seed dormancy and germination. The mechanism by which temperature induces germination in dormant seeds is however still unclear. Proteomic study has been performed in dormant sunflower seeds during imbibition at permissive and non-permissive temperatures for germination, 20 and 10 °C, respectively. Proteome analysis showed an increase of proteins belonging to metabolism and energy from the first hours of imbibition followed by a decrease of proteins involved in protein metabolism and seed storage in germinating compared to non-germinating seeds. Proteomic study was completed by polysome and proteasome activity assessment and enzymatic profiling on several altered proteins involved in metabolism and energy. Results showed that 20 °C treatment induced the activation of both protein synthesis and degradation processes, the latter being related to proteasome activity during the germination sensu stricto, and to other degradation processes such as proteases during the post-germination. Interestingly, enzymatic profiles showed that TCA cycle and glycolysis were more active in non-germinating seeds in the phase I of the germination sensu stricto. This result suggests the regulation of central metabolism activity in germinating seeds. The control of energy production during imbibition seems to be involved in molecular networks controlling seed dormancy and germination.

Russian

Damage of seeds which leads to destruction of the crystal lattice and the phase transition of polymers is formed under the pulse pressure (PP) treatment. Biopolymers such as starch compressed under specific conditions can be changed from crystalline to a glassy state; this transition is known to extend the life of seeds. The aging of seeds is involved in the enzymatic glycosylation of proteins and nucleic acids. Reducing sugars which have been produced in seeds by non-enzymatic hydrolysis enter into reaction of glycosylation with proteins and amino acids actively. The authors studied the water absorption by seeds of buckwheat (Fagopyrum esculentum Moench., cultivar Saulyk) treated by PP. The values of PP which were used to treat had an influence on water absorption during the first hours of imbibition. When water content was 60%, hydrolysis of reserve substances could begin, so water potential was created by osmotically active molecules. Gibbs energy calculation by method of groups' contribution indicated the reduction in probability of starch hydrolysis in plant seeds during transition from the crystalline to the glassy state. Keywords: pulse pressure; biopolymer; destruction; starch; buckwheat; hydrolysis. Введение. В качестве фактора, действующего на растения, было выбрано импульсное давление (ИД), создаваемое прохождением ударной волны. ИД в интервале 3-35 МПа способствует стимулированию физиологических процессов в семенах и растениях, ведущих к

Regulation of ribosome biogenesis in maize embryonic axes during germination

Ribosome biogenesis is a pre-requisite for cell growth and proliferation; it is however, a highly regulated process that consumes a great quantity of energy. It requires the coordinated production of rRNA, ribosomal proteins and non-ribosomal factors which participate in the processing and mobilization of the new ribosomes. Ribosome biogenesis has been studied in yeast and animals; however, there is little information about this process in plants. The objective of the present work was to study ribosome biogenesis in maize seeds during germination, a stage characterized for its fast growth, and the effect of insulin in this process. Insulin has been reported to accelerate germination and to induce seedling growth. It was observed that among the first events reactivated just after 3 h of imbibition are the rDNA transcription and the pre-rRNA processing and that insulin stimulates both of them (40-230%). The transcript of nucleolin, a protein which regulates rDNA transcription and pre-rRNA processing, is among the messages stored in quiescent dry seeds and it is mobilized into the polysomal fraction during the first hours of imbibition (6 h). In contrast, de novo ribosomal protein synthesis was low during the first hours of imbibition (3 and 6 h) increasing by 60 times in later stages (24 h). Insulin increased this synthesis (75%) at 24 h of imbibition; however, not all ribosomal proteins were similarly regulated. In this regard, an increase in RPS6 and RPL7 protein levels was observed, whereas RPL3 protein levels did not change even though its transcription was induced. Results show that ribosome biogenesis in the first stages of imbibition is carried out with newly synthesized rRNA and ribosomal proteins translated from stored mRNA.

A seed respiration-based index of cold-sensitivity during imbibition in four macrothermal species

A research was carried out to evaluate the influence of temperature on seed respiration response of maize, cotton, grain sorghum and sunflower during imbibition, and to define reliable indices for a fast evaluation of cold-sensitivity at germination level in plants. The seed respiration activity was measured during seed imbibition at 25 °C (optimal) and 15 °C (suboptimal) constant temperatures, using a homemade respiration chamber adapted to an infrared gas analyzer. At 15 °C, sunflower and sorghum maintained high levels of seed germination (≥90 %), whilst this last dropped in cotton (36.7 %) and maize (27.8 %). With respect to this, cotton and maize seem to be cold sensitive during germination. Instantaneous seed respiration during imbibition versus temperature or thermal time could not be used as a good indicator for cold tolerance, since the levels of CO2 recorded at 15 °C in cotton (higher than the other species) and maize (similar to that of sorghum and sunflower) did not correspond to adequate seed germination. Differently, the rates (b coefficient of linear regressions) of accumulation of CO2 respired at optimal and suboptimal temperatures during the first hours of imbibition (up to approximately 24 h from the start of experiment), were significantly different in maize and cotton, whilst they did not differ in sorghum and sunflower. Therefore, the shift between slopes may represent a reliable index for seed cold-sensitivity assessment during early germination.

A stress-associated protein containing A20/AN1 zing-finger domains expressed in Medicago truncatula seeds

MtSAP1 (Medicago truncatula stress-associated protein 1) was revealed as a down-regulated gene by suppressive subtractive hybridization between two mRNA populations of embryo axes harvested before and after radicle emergence. MtSAP1 is the first gene encoding a SAP with A20 and AN1 zinc-finger domains characterized in M. truncatula. MtSAP1 protein shares 54% and 62% homology with AtSAP7 (Arabidopsis thaliana) and OsiSAP8 (Oryza sativa) respectively, with in particular a strong homology in the A20 and AN1 conserved domains. MtSAP1 gene expression increased in the embryos during the acquisition of tolerance to desiccation, reached its maximum in dry seed and decreased dramatically during the first hours of imbibition. Abiotic stresses (cold and hypoxia), abscisic acid and desiccation treatments induced MtSAP1 gene expression and protein accumulation in embryo axis, while mild drought stress did not affect significantly its expression. This profile of expression along with the presence of anaerobic response elements and ABRE sequences in the upstream region of the gene is consistent with a role of MtSAP1 in the tolerance of low oxygen availability and desiccation during late stages of seed maturation. Silencing of MtSAP1 by RNA interference (RNAi) showed that the function of the encoded protein is required for adequate accumulation of storage globulin proteins, vicilin and legumin, and for the development of embryos able to achieve successful germination.

Defense Proteins from Vigna Unguiculata Seed Exudates: Characterization and Inhibitory Activity Against Fusarium Oxysporum

Plants exude a variety of substances through their roots, germinating seeds and aerial parts. Some of these released compounds seem to have an inhibitory effect against pathogens. The aim of this work was to investigate and identify antifungal proteins present in exudates from imbibed cowpea seeds (Vigna unguiculata (L.) Walp). The obtained exudation was analyzed in regard to specific protein activities by enzymatic or immunological assays for plant defense proteins, from 4 h to 48 h of seed imbibition. Our results show that cowpea seeds exudates present several defense related proteins characterized as β-1,3-glucanases, cystatins, vicilins and lipid transfer proteins (LTPs), as well as a storage vacuole membrane α-TIP protein, since the very first hours of imbibition. These exudates also have an “in vitro” inhibitory effect on the growth of the fungus Fusarium oxysporum f. sp. phaseoli. Our results suggest that seed exudates should promote seed protection from soil pathogens.

The plasma membrane H +-ATPase of maize embryos localizes in regions that are critical during the onset of germination

The H +-ATPase is a plasma membrane enzyme that hydrolyzes ATP and translocates protons from the cytosol to the apoplast space. The resulting acidification is used to promote stomata opening, pH homeostasis, secondary transport of nutrients, and cell elongation. The latter two processes are critical in germination, since radicle protrusion, requires the growth of embryo cells. Earlier studies have shown that the plasma membrane H +-ATPase is already active during the first hours of imbibition. Here, the localization of this enzyme was studied in maize embryos by histochemical and immunochemical techniques at 2 h of imbibition. The enzyme is mainly located in regions of the embryo that require high transport activity or that participate in cell elongation: the scutellum, the root and the plumule. The cells that were more immunolabeled were those located in the epidermis, in the parenchyma and in the elements of the vascular bundles. These results suggest that the plasma membrane H +-ATPase levels present in the first hours of imbibition are preserved and/or are newly synthesized to fulfill the demands of transport and elongation of the embryo on the onset of seed germination.

Protein phosphorylation is suppressed when wheat embryos are hydrated and remain growth arrested

An early difference in net protein phosphorylation activity occurred in dormant and after-ripened wheat (Triticum aestivum L.) grains within the first hour of imbibition at 30°C. Embryos from dry, dormant and after-ripened caryopses exhibited a high degree of protein phosphorylation, particularly of four proteins (68, 54, 51 and 42 kDa). Upon hydration, protein phosphorylation activity in dormant embryos decreased within 1 h and reached minimal phosphorylation activity by 5 h. Protein phosphorylation activity in after-ripened (germinable) embryos was not suppressed and remained high during germination. If the hydrated dormant embryos were dried, protein phosphorylation activity was restored. Application of the protein phosphatase inhibitor, okadaic acid, partially overcame dormancy and slowed the decrease in phosphorylation activity. These results suggested that reduction of protein phosphorylation activity slowed the rate of germination.

Seedcoat Structure and Oxygen-enhanced Environments Affect Germination of Triploid Watermelon

Triploid or seedless watermelon [Citrullus lanatus (Thunb.) Matsum & Nakai] cultivars often have erratic germination and low seedling vigor. The morphology of the seedcoat on two triploid cultivars—Tri X 313 and Tri X Sunrise—was examined by scanning electron microscopy (SEM) to identify structural differences compared to diploid seeds. Triploid seeds incubated with oxygen-enhanced treatments that included nicking, 1% hydrogen peroxide (H2O2), and 40% oxygen were investigated at low and high medium moisture levels. Triploid seed has a thicker seedcoat with a dense endotesta layer and a larger and highly variable air space surrounding the embryonic axis as compared with diploid seed. All cultivars rapidly imbibed water (≈50% of the original weight) during the first hour of imbibition, with a faster increase for triploids than for diploids. High moisture affected germination to a lesser extent in diploid than triploid seeds. Triploid germination under low medium moisture ranged from 96% to 76%, but was severely reduced to <27% under high medium moisture. Triploid seed germination was significantly improved at high moisture by H2O2 and by 40% oxygen. Triploid watermelon seed is very sensitive to submerged conditions, possibly due to a combination of physiological and morphological defects. The rapid imbibition and excess water collected in the seedcoat and air space surrounding the embryo, could reduce oxygen diffusion and impair metabolic pathways leading to normal germination and seedling development.

Preventing thermoinhibition in a thermosensitive lettuce genotype by seed imbibition at low temperature

Lettuce (Lactuca sativa L.) seed germination is strongly temperature dependent and under high temperatures, germination of most of genotypes can be erratic or completely inhibited. Lettuce seeds of 'Dark Green Boston' (DGB) were incubated at temperatures ranging from 15° to 35°C at light and dark conditions. Other seeds were imbibed in dark at 20°; 25°; 30°; and 35°C for 8 and 16 hours and then transferred to 20 or 35°C, in dark. Seeds were also incubated at constant temperature of 20° and 35 °C, in the dark, as control. In another treatment, seeds were primed for 3 days at 15°C with constant light. DGB lettuce seeds required light to germinate adequately at temperatures above 25°C. Seeds incubated at 20°C had 97% germination, whereas seeds incubated at 35°C did not germinate. Seeds imbibed at 20°C for 8 and 16 hours had germination. At 35°C, seeds imbibed initially at 20°C for 8 and 16 hours, had 89 and 97% germination, respectively. Seeds imbibed at 25°C for 16 hours, germinated satisfactory at 35°C. High temperatures of imbibition led to no germination. Primed and non-primed seeds had 100% germination at 20°C. Primed seeds had 100% germination at 35°C, whereas non-primed seeds germinate only 4%. The first hours of imbibition are very critical for lettuce seed germination at high temperatures.

VARIEDADES DE SOJA DIFEREM NA VELOCIDADE E CAPACIDADE DE ABSORVER ÁGUA

As sementes iniciam a retomada dos processos metabólicos a partir da embebição. Esta supre a necessidade de água para reduzir a resistência mecânica do tegumento, hidratar o embrião e cotilédones, induzindo o embrião a ativar enzimas que aceleram o processo de quebra de materiais de reserva usados para dar início à germinação da semente. Este experimento, realizado na Faculdade de Agronomia da Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, no ano de 1993, objetivou avaliar o comportamento de cultivares de soja quanto à capacidade máxima e velocidade de absorção de água, em intervalos de hora, até oito horas consecutivas, quando em embebição total em água. Foram utilizadas sementes de 17 cultivares com tamanho uniformizado para diâmetro maior que 6,3 mm e ausência de rachaduras no tegumento quando observadas através de lupa. A cultivar ‘RS 6 Guassupí’ apresentou a maior velocidade e capacidade total de absorção de água. ‘FT Abyara’ e ‘Bragg’ apresentaram a menor velocidade e menor capacidade total de absorção nas primeiras horas de embebição, mas nas ultimas horas foi a ‘RS 7 Jacuí’ que apresentou a menor capacidade de absorção. Este estudo permitiu concluir que existem diferenças na velocidade e na capacidade total de absorver água entre as cultivares testadas, devido a alguma característica distinta entre elas, que não foi investigada neste trabalho e que torna suas sementes mais ou menos permeáveis a água.

Decrease in sunflower (Helianthus annuus) seed viability caused by high temperature as related to energy metabolism, membrane damage and lipid composition

The aim of the present work was to investigate whether loss of germination ability and viability of sunflower (Helianthus annuus L.) seeds during incubation at a high temperature (45°C) was related to changes in energy metabolism, loss of membrane integrity, and/or changes in lipid composition. Pre‐treatment of seeds at 45°C progressively reduced subsequent germination at the optimal temperature (25°C). Seeds did not germinate at 45°C and almost all of them were dead after 72 h of soaking at this high temperature. This loss of seed viability was associated with a large increase in leakage of K+ and total electrolytes into the incubation medium, and with production of malondialdehyde in the embryonic axis and cotyledons, suggesting a loss of membrane integrity probably due to lipid peroxidation. ATP and ADP levels increased sharply during the first hours of imbibition at 45°C, remained high for about 24 h and then decreased. As a consequence, the energy charge followed a similar pattern. If the treatment at 45°C did not exceed 48 h, seeds recovered an apparently normal energy metabolism after transfer to 25°C, even though they lost their ability to germinate at this temperature. Therefore, energy metabolism at the whole embryo level cannot be considered as an indicator of germination ability. Incubation of seeds at 45°C resulted in an increase in triacylglycerols and diacylglycerols without a significant change in their fatty acid composition. It also induced a slight increase in phospholipid content with an increase in C16:0, C18:0 and C18:1, but with no change in C18:2. In phospholipids, the C18:2/C18:1 and (C18:1 + C18:2)/ (C16:0 + C18:0) ratios thus declined during treatment at 45°C. The results obtained suggest that deterioration of sunflower seeds during incubation at a high temperature is mainly related to membrane damage and alteration of energy metabolism, and that accumulation of malondialdehyde, which is an index of lipid peroxidation, does not correspond to a decrease in total lipids and phospholipids nor to a significant change in fatty acid composition, except in PL in which the C18:2/C18:1 and (C18:1 + C18:2)/ (C16:0 + C18:0) ratios slightly declined.

Using a Puncture Test to Identify the Role of Seed Coverings on Thermotolerant Lettuce Seed Germination

Temperature is an important environmental factor that affects lettuce (Lactuca sativa L.) germination. The present research was conducted to determine the role of seed coverings on lettuce seed germination at high temperature. Five lettuce genotypes were primed in order to bypass thermoinhibitional effects on germination. During germination of primed and nonprimed seeds, imbibition followed a normal triphasic pattern. Primed seeds had higher final water content, a decreased imbibitional phase II, and germinated at 36 °C compared to nonprimed seeds of thermosensitive genotypes, which did not germinate at 36 °C. Puncture tests were conducted to determine the force required to penetrate the whole seed or endosperm of the five genotypes at 24 and 33 °C. `Dark Green Boston', a thermosensitive genotype, had the highest mean resistance (0.207 N) and PI 251245, a thermotolerant genotype, had the lowest (0.139 N). Resistance to penetration of the endopserm of the five genotypes was different at both temperatures. However, three thermotolerant genotypes had lower endosperm resistance than two thermosensitive types. At 36 °C, the penetration force for primed and nonprimed seeds was compared after the first hour of imbibition and 1 hour before radicle protrusion. The force required to penetrate the seed was affected by genotype, seed priming, and duration of imbibition. Puncture force decreased as imbibition time at 36 °C increased in primed and nonprimed seed of each thermotolerant genotype but not in the thermosensitive genotypes. Priming reduced the initial force necessary to penetrate the seed and endosperm in all genotypes. Thus, for radicle protrusion to occur, there must first be a decrease in the resistance of the endosperm layer as evidenced by priming or thermotolerant genotype. Then, the pericarp and integument are sufficiently weakened so that tissue resistance is lower than the turgor pressure of the expanding embryo, allowing germination to be completed.

Protein degradation and nitrogen supply during germination and seedling growth of vetch ( Vicia sativa L.)

Published reports on storage protein degradation during and after legume seed germination have nearly exclusively been focussed on the cotyledons as storage organs. There, concomitantly with an increase in proteolytic activity, globulin degradation starts no earlier than day 2 to 3 after the beginning of imbibition (dai). Proteinases that intiate storage protein degradation in legume cotyledons seem to be de novo synthesized. Since protein biosynthesis begins as early as during the first hour of imbibition (dai) legume seeds should initially utilize amino acid sources other than storage protein degradation in the cotyledons to support protein formation in the axis and cotyledons. Using germinating vetch ( Vicia sativa L.) we started a thorough analysis of the temporal and histochemical pattern of storage protein degradation and cysteine proteinase activity in axis and cotyledons during germination and early seedling growth. The amount of protein does not significantly change in the embryonic axis and cotyledons during the two initial days of germination. Afterwards, total protein increases in the axis but decreases in the cotyledons. Similar to the cotyledons, the axis contains storage globulins in protein bodies. In the axis globulin degradation rapidly commences after the beginning of imbibition and it is nearly finished by 2 dai, whereas no significant globulin degradation occurs in the cotyledons. During this time there are no conductive tissue connections between the axis and the cotyledons. By the time protein reserves in the axis are exhausted after 2 dai conductive connections have been formed, and now globulin breakdown commences in the cotyledons. Independent of when globulin breakdown starts, vicilin degradation predominates in the beginning, and at first this globulin is locally degraded in those tissues in the regions of the embryo where growth and differentiation start. Molecular and biochemical analysis of five different cysteine proteinases confirmed that in cotyledons these enzymes are formed de novo at a time when globulin degradation becomes visible. Stored proteinases could also play a role in the rapid commencement of protein breakdown in the embryonic axis. The results suggest that during the first 2 dai protein biosynthesis in the axis is mainly supported by the degradation of internal protein reserves and that only after these have been exhausted globulin breakdown in the cotyledons takes over to provide amino acids to the growing axis.

Changes in ATP Content of Sorghum Seeds Imbibed in Aqueous Extracts of Germination‐Inhibitory Animal‐Waste Composts

AbstractThe changes of the ATP content in sorghum seeds imbibed in aqueous extracts of animal‐waste composts were studied to clarify the mode of action of the germination‐inhibitory composts. The seeds were imbibed in water or 1, 4 and 8 % extracts (w/v) of composts for 0, 1,2, 3, 4, 8, 16 and 24 h.ATP content in the non‐imbibed sorghum seeds was 0.182 n mol seed−1. The ATP content of seeds increased 2.6 fold during the first hour of imbibition. Statistically significant differences in the ATP content were observed between the treatments from 3 h of imbibition. The seeds imbibed in deionized water contained the highest ATP content at all imbibition durations. The ATP content decreased with the increase in concentration of the extracts. Significant linear correlations were observed between the ATP content and the increase of a‐amylase activity at 4 h (r = 0.75**), 16 h (r = 0.70*) and 24 h (r = 0.91**) of imbibition.The changes in the ATP content in seeds were observed prior to the increase of amylase activity. The reduction of ATP content is the first observable biochemical change in seeds caused by the germination‐inhibitory animal‐waste compost extracts. The ATP content of seeds could be considered as a sensitive indicator to detect the germination‐inhibitory composts.

Amide-Linked Indoleacetic Acid Conjugates May Control Levels of Indoleacetic Acid in Germinating Seedlings of Phaseolus vulgaris

We have shown that amide-linked IAA (indole-3-acetic acid) conjugates accumulated to high levels during maturation of bean seeds (K. Bialek and J.D. Cohen [1989] Plant Physiol 91: 775-779). In the present study, we were interested in the fate of these and other IAA conjugates during seed germination. The content of amide-linked conjugates of IAA in cotyledons declined dramatically during the first hours of imbibition. The rate of decline slowed markedly during the period of the resumption of axis growth. The level of amide-linked IAA conjugates in cotyledons remained relatively high after almost 1 week of germination. The decline of IAA conjugates in cotyledons was followed by a steady increase in the content of both free and amide-linked IAA in the embryonic axes. Amide-linked IAA conjugates were also present in the axes cultured on agar after the cotyledons were removed, which suggests that de novo production of these IAA conjugates occurs in the axis of germinating bean seedlings. A comparison of relative amounts of free and conjugated IAA in the axes of intact seedlings and axes cultured on agar showed lower levels of free IAA and higher levels of conjugated IAA in much slower growing isolated axes. These results suggest a more general role for IAA conjugates in the control of seedling growth than simply to serve as a seed storage form of auxin.

Some factors influencing electrolyte leakage from maize (Zea mays L.) kernels

AbstractEven though the embryo of a maize (Zea mays L.) kernel contributes relatively little to total kernel weight, it is a main source of electrolytes which leach from the kernel during imbibition. Ageing of maize kernels for 18 days at 40°C and a moisture content of about 15% results in an increase of electrolyte leakage which almost exclusively originates from the embryo. The effect of ageing is most apparent after prolonged periods of imbibition. Mechanical damage increases leakage early during imbibition, the effect of damage being considerably larger for aged than for unaged kernels. The large amount of electrolytes measured after the first hour of imbibition of undamaged kernels comes mainly from the pericarp. The electrolyte content of the pericarp is variety dependent and may interfere with quality testing by conductivity measurements.

Soya bean seed invigoration by ferrous sulphate: changes in lipid peroxidation, conductivity, tetrazolium reduction, DNA and protein synthesis

The invigorating effect of 0.04 M ferrous sulphate on the germination of soya bean seeds was investigated by examining changes in lipid hydroperoxides during the first hour of imbibition. Lipid hydroperoxides declined significantly in seed axes over the first hour of imbibition along with a reduced electrolyte leakage, and an enhanced tetrazolium staining in seeds over a 24 hour period. No differences were evident between treated seed axes and controls as regards absolute levels of incorporation of H3 thymidine and H3 leucine into DNA and protein, respectively. However, the percentage of H3 leucine incorporated, relative to uptake, was significantly greater than that for untreated axes. It is suggested that the invigorating effect of ferrous sulphate is due to the dismutation of lipid peroxides and the quenching of free radicals.

Heat shock proteins in Sorghum bicolor and Pennisetum americanum I. genotypic and developmental variation during seed germination

Abstract The capacity to synthesize heat shock proteins (HSPs) during seed germination of sorghum (Sorghum bicolor) and pearl millet (Pennisetum americanum) has been examined. HSP synthesis is detectable in a thermotolerant genotype of sorghum during the first hour of imbibition of the seed under high temperature stress. A non‐coordinate control of HSP synthesis during germination was revealed. Genotypic differences were manifest in the stage of germination at which the ability to synthesize HSPs was first apparent and this related to the thermosensitivity of that genotype.