Seed and Pod Wall Development in Pisum sativum, L. in Relation to Extracted and Applied Hormones

Developing fruits of Pisum sativum, L., cv. ‘Alaska’,contain relatively large amounts of hormones, mainly concentratedin the embryos and liquid endosperm. A close relationship canbe demonstrated between changes in extractable amounts of gibberellins(mainly GA₂₀), auxins (methyl 4-chloroindol-3yl acetate andprobably 4-chloroindol-3yl acetic acid), and abscisic acid,and changes in growth rates of both the pod wall and seeds.Growth of the pod wall appears to depend largely on hormonessupplied by the seeds. Marked changes in the germination capacity of the maturing seedsare closely associated with changes in extractable amounts ofmethyl-4-chloroindol-3yl acetate and abscisic acid. It is believedthat high concentrations of these substances in the embryo,rather than any restriction imposed by the testa, may preventprecocious germination of the seeds     

Phytohormone Profiling During Tuber Development of Chinese Yam by Ultra-high performance Liquid Chromatography–Triple Quadrupole Tandem Mass Spectrometry

Changes in agronomic characters and the profile of various endogenous phytohormones during tuber development were studied in Dioscorea opposite (Chinese yam) cv. Guihuai 16. Tuber development exhibited a sigmoidal growth pattern according to the changes in tuber agronomic characters. The growth cycle of yam tuber could be divided into three stages: initiation stage, enlargement stage, and maturation stage. Moreover, the enlargement stage could be separated into three phases—slow growth phase, rapid growth phase, and late growth phase. Endogenous changes in phytohormones were associated with developmental changes in the tubers. The pulses of bioactive gibberellins (such as GA₃ and GA₄) were measured in tubers. The highest contents of GA₃ and GA₄ were reached 90 days after field planting, corresponding to the beginning of the rapid growth phase of tuber enlargement. Changes in trans-zeatin (tZ), jasmonic acid (JA), indole-3-acetic acid (IAA), and abscisic acid (ABA) levels were also observed, and seemed to be related to tuber enlargement at different phases. Continuous increases in JA and tZ contents accompanied tuber enlargement. Transient pulses of both IAA and ABA contents were also observed at the start of tuber rapid growth. Additionally, a second peak level of IAA was detected at the tuber maturation stage. These results suggest GAs play a key role at the beginning of the tuber rapid growth stage, and there is a close relationship between whole tuber enlargement and the contents of JA and tZ. Moreover, it is suggested that IAA and ABA also may be linked to the beginning of tuber rapid growth, and IAA also seems to be correlated to late tuber maturation.     

Seed dormancy and germination: the role of abscisic acid and gibberellins and the importance of hormone mutants

Over the past decades many studies have aimed at elucidating the regulation of seed dormancy and germination. Many hypotheses have been proposed and rejected but the regulatory principle behind changes in dormancy and induction of germination is still a black box. The majority of proposed mechanisms have a role for certain plant hormones in common. Abscisic acid and the gibberellins are the hormones most frequently suggested to control these processes. The development of hormone-deficient mutants made it possible to provide direct evidence for the involvement of hormones in germination and dormancy related processes.In the present paper an attempt is made to assess the role of abscisic acid and gibberellins in the transitions between dormant and non-dormant states and germination. First a conceptual framework is presented in which the different states of dormancy and germination are defined in order to contribute to a solution of the semantic confusion about these terms that has existed since the beginning of seed physiology.It is concluded that abscisic acid plays a pivotal role during the development of primary dormancy and gibberellins are involved in the induction of germination. Changes in sensitivity to these hormones occur during changes in dormancy. Both synthesis of and responsiveness to the hormones are controlled by natural environmental factors such as light, temperature and nitrate.     

Influence of Seed Pre-treatments with Plant Growth Regulators on Metabolic Alterations of Germinating Maize Embryos Under Stressing Temperature Regimes

The germination performance of maize seeds (Zea mays L. cv.Partap-1) pre-treated individually with the substituted phthalimideAC 94,377 (1-(3-chlorophthalimido)-cyclohexanecarboxamide),GA₄₊₇ and ABA was markedly improved under sub- and supra-optimaltemperature regimes. ABA was especially stimulatory at the sub-optimaltemperature. Metabolic alterations in the germinating embryosof treated seeds revealed an increased accumulation of solublesugars and proteins compared with the controls under stressingtemperatures. The activities of acid phosphatase, invertase,catalase and peroxidase were seemingly related to the alleviationmetabolism. It is suggested that gibberellins and abscisic acidmay have positive regulatory effects in triggering the systemfor stress alleviation. Germination, Zea mays, temperature, growth regulators, embryos, metabolism     

Tuberization in Potato at High Temperatures: Responses to Gibberellin and Growth inhibitors

The responses of potato plants (Solanum tuberosum L., cv. Sebago)to high temperatures (32 day/28 C night or 32/18 °C) andgibberellin are similar, in that they promote haulm growth andsuppress tuber production, whereas low temperatures (22/18 °C)abscisic acid and CCC have the opposite effect, promoting tuberproduction and reducing the growth of the haulms. The inhibitoryeffect of the high temperatures on tuber production, under aphotoperiod of 14 h, was almost completely reversed in theseexperiments by the application of CCC, and partly reversed byABA. Single-leaf cuttings from plants grown at the various temperaturesand chemical treatments responded in the same way as the wholeplant. It is suggested that both haulm growth and tuber initiationare influenced by a common hormonal control, and that temperatureexerts its influence by altering the balance between the levelsof endogenous gibberellins and inhibitors. These substancesapparently act directly on the stolon tip, rather than throughtheir general influence on haulm growth. Solanum tuberosum L., potato, tuberization, temperature response, gibberellin, abscisic acid, 2-chloroethyltrimethylammonium chloride (CCC)     

Developing a model of plant hormone interactions

Plant growth and development is influenced by mutual interactions among plant hormones. The five classical plant hormones are auxins, cytokinins, gibberellins, abscisic acid and ethylene. They are small diffusible molecules that easily penetrate between cells. In addition, newer classes of plant hormones have been identified such as brassinosteroids, jasmonic acid, salicylic acid and various small proteins or peptides. These hormones also play important roles in the regulation of plant growth and development. This review begins with a brief summary of the current findings on plant hormones. Based on this knowledge, a conceptual model about interactions among plant hormones is built so as to link and develop an understanding of the diverse functions of different plant hormones as a whole in plants.Key words: abscisic acid, auxin, brassinosteroids, cytokinins, ethylene, gibberellins, jasmonic acid, salicylic acid, plant peptide hormones     

Sensitivity to Abscisic Acid and Osmoticum Changes During Embryogenesis of Alfalfa (Medicago sativa)

Developing embryos of alfalfa can be placed into nine stagesof development according to their morphological characteristics.The intact seeds do not germinate when removed from the podand placed on water until at least stage VI, and complete germinabilityis not achieved until the seeds are at the stage when they startto undergo maturation desiccation. Isolated embryos are germinableas early as stage III, and will germinate within 24 h on Murashigeand Skoog medium containing 3% sucrose. Osmoticum can inhibitembryo germination, but only proper osmotic conditions can maintaindevelopment in vitro; development does not occur at germination-inhibitingconcentrations of abscisic acid. The sensitivity to abscisicacid and osmoticum changes with stage of development. Early-stageembryos have the highest abscisic acid sensitivity and thisdeclines to the extent that mature dry embryos require a highconcentration (1?0 mol m^–3) to prevent their germination.Sensitivity of the embryos to osmoticum is maximum at stageVII of development. The combined inhibitory effect of abscisicacid and osmoticum on germination during development is greaterthan their individual effects. This combined effect is stage-dependent.Thus studies on the effects of abscisic acid and osmoticum onembryogenesis and associated synthetic events should be expectedto vary according to the sensitivity to these agents at differentstages of development. Key words: Medicago sativa, embryogenesis, abscisic acid, osmoticum, seed development     

Hormonal Control of Nuclease Level in Excised Avena Leaf Tissues1

In excised Avena leaves, kinetin and benzyladenine decreased,while abscisic acid and benzimidazole increased the over-allnuclease level. Significant effects were observed as early as2 h after treatment. Not all the nucleases of the Avena leafwere affected by the growth regulators. Changes in over-allnuclease activity were accounted for almost entirely by changesin the amount of a relatively purine-specific endo-ribonuclease,which produces 2',3'-cyclic phosphates as breakdown products.Slight changes induced by the growth regulators were also detectedin the amount of a sugar non-specific endo-nuclease which produces5'-nucleotides and has a relative specificity for adenylic acid.The level of an alkaline phosphodiesterase, an exo-nucleasewhich produces 5'-nucleotides, was not affected by any of thegrowth regulators tested. Gibberellic acid and indol-3yl-aceticacid did not influence the level of Avena nucleases.     

Biosynthesis and beneficial effects of microbial gibberellins on crops for sustainable agriculture

Soil microbes promote plant growth through several mechanisms such as secretion of chemical compounds including plant growth hormones. Among the phytohormones, auxins, ethylene, cytokinins, abscisic acid and gibberellins are the best understood compounds. Gibberellins were first isolated in 1935 from the fungus Gibberella fujikuroi and are synthesized by several soil microbes. The effect of gibberellins on plant growth and development has been studied, as has the biosynthesis pathways, enzymes, genes and their regulation. This review revisits the history of gibberellin research highlighting microbial gibberellins and their effects on plant health with an emphasis on the early discoveries and current advances that can find vital applications in agricultural practices.     

Effects of Far-red Light on the Hormonal Control of Side Shoot Growth in the Tomato

Side shoot growth in young tomato plants was almost completelysuppressed by a 5 min period of far-red light immediately followinga 16 h photoperiod from fluorescent tubes, whereas plants givenan identical photoperiod but lacking the far-red treatment branchedprofusely. The influence of far-red light on the degree of sideshoot suppression and the correlated changes in the levels ofauxins, gibberellins, cytokinins and abscisic acid is presentedand discussed in relation to current hypotheses of correlativeinhibition. It is suggested that far-red light causes increasedauxin synthesis in the apex and young leaves, which in turninduces the formation of abscisic acid in or near the axillarybuds, and it is this hormone which inhibits bud outgrowth. Therole of cytokinins and gibberellins remains uncertain but theyprobably act in a sequential manner, the gibberellins promotingbud growth following cytokinin-mediated release from apicaldominance.     

The role of hormonal balance in plant adaptation to flooding

The effect of flooding on the growth parameters and hormonal dynamics (anxins, abscisic acid, cytokinins, gibberellins, and ethylene) has been studied in a vegetation experiment on the leaves of wheat (Triticum aestivum L.) and oat (Avena sativa L.). Growth inhibition during flooding in both species was due to the accumulation of abscisic acid and ethylene, while the repair processes were due to the increased level of auxins, cytokinins, and gibberellins. The difference in the hormonal response in wheat and oat to flooding, in particular, the degree and timing of accumulation of abscisic and indoleacetic acids and different dynamics of the level of cytokinins and gibberellins, induced their different physiological response, which determined the level of their resistance. The growth control of cereals during flooding as well as the hormonal dynamics are proposed to rely on the strategy of plant ontogenetic adaptation.     

Studies of Growth and Flowering in Picea sitchensis (Bong.) Carr. 1. Effects of Growth Regulator Applications to Mature Scions on Seedling Rootstocks

Effects of growth regulator applications on the flowering of5-years-grafted mature scions of Picea sitchensis (Bong.) Carr.were assessed. Growth regulators were applied to the bud surfacein droplets of ethanol during July, August and September ina polythene house or glasshouse. A mixture of gibberellins A₄and A₇ applied alone, and in combination with gibberellins A₃and A₅, significantly increased numbers by up to seven timesfor male and by up to eight times for female strobili, gibberellinA, gave relatively the strongest response, and gibberellin A₄was inactive. Phosphon D and abscisic acid each reversed thepromotion of flowering by gibberellins, whilst kinetin and N,N-diphenylureahad no effect. The number of female strobili was negativelycorrelated with vegetative shoot length in the year after treatment. Under field conditions hormones were applied in July and Augustunder flaps of bark on the branches of 10-years-grafted maturescions. Gibberellin applications caused a 5-fold increase inflowering and N⁶-benzyladenine further increased the response.Naphth-lyl-acetic acid reduced female and increased male flowering.Bark removal near the base of the branch further enhanced hormone-inducedstrobilus production. The usefulness of these findings for thebreeding of Picea sitchensis is discussed.     

Abscisic acid,phaseic acid and gibberellin contents associated with dormancy and germination in barley

Analyses of abscisic acid (ABA), ent -kaurenoids and gibberellins (GAs) showed that there were major changes in the contents of these compounds associated with germination of after-ripened barley ( Hordeum vulgare cv. Schooner and cv. Proctor) grain but not in hydrated dormant grain. Embryos from dormant and after-ripened dry grain contained similar amounts of ABA, of ent -kaurenoids and of GAs, determined by gas chromatography-mass spectrometry-selected ion monitoring. In embryos of after-ripened grain, ABA content decreased rapidly after hydration and ABA appeared to be metabolized (inactivated) to phaseic acid (PA) rather than diffusing into the endosperm or the surrounding medium as previously thought. Similar changes in ABA occurred in hydrated dormant grain during germination in darkness. Accumulation of ent -kaurenoids and GAs, including GA_1, the first biologically active GA in the early 13-hydroxylation biosynthetic pathway, occurred to a much greater extent in after-ripened than in dormant grain and these changes occurred mainly after 18 h of hydration when ABA had already decreased and germination was occurring. The block in ent -kaurenoid and GA synthesis in dormant grain appeared to occur prior to ent -kaurene in the biosynthetic pathway. These results are consistent with the view that ABA is the primary effector of dormancy and that after-ripening involves the development of the ability to reduce the amount of ABA quickly following hydration. Accumulation of GAs does not appear to be causally related to loss of dormancy but it does appear to be related to germination.     

Hormonal Responses to Water Deficit in Cambial Tissues of Populus alba L.

Changes in the concentrations of bioactive gibberellins and abscisic acid in the cambial region of white poplar (Populus alba L.) were investigated in 1-year-old plants, to highlight how these phytohormone signals are modulated in response to water deficit. Plants were cultivated in pots outdoor and, at the time of maximum cambial growth (T ₀), irrigation was withdrawn for 8 days, inducing a mild water deficit, thus mimicking a condition that is recurrent in Mediterranean climates when white poplar attains its maximum growth rate. The water deficit was suspended by resuming irrigation (T _max) throughout a recovery period of 2 weeks (T _rec). Cambial tissues were sampled at T ₀, T _max, and T _rec. Significant changes of leaf and stem relative water content, leaf water potential, stomatal conductance, transpiration, carbon assimilation, stem shrinkage, and leaf number were induced by soil water shortage, which also negatively affected cambium development. Nevertheless, these responses were almost fully reversed following the resumption of irrigation. Water deficit induced the accumulation of large amounts of abscisic acid in cambial tissues, but the hormone was brought back to pre-stress levels after the recovery period. With regard to bioactive gibberellins, GA₁ was several folds more abundant than GA₄ and reached the greatest level in the plants recovering from the water status imbalance. The possible functions of gibberellins and abscisic acid in the response of cambial tissues to water deficit are discussed in view of the known physiological roles and molecular mechanisms of action of these hormonal signals.     

Seed Dormancy in Acer: CHANGES IN ENDOGENOUS CYTOKININS, GIBBERELLINS AND GERMINATION INHIBITORS DURING THE BREAKING OF DORMANCY IN ACER SACCHARUM MARSH

The present studies on changes in the levels of cytokinins,gibberellins, and germination inhibitors during stratificationof Acer saccharum sceds suggest that the breaking of dormancyis a phasic process. Stratification at 5°C led to a markedincrease in the butanol-soluble cytokinins after 20 d. Furtherchilling resulted in a loss of cytokinin. The majority of thedetectable cytokinin activity co-chromatographed with zoatin.Similarly, at day 40, acidic gibberellin-like substances increasedand declined with further chilling. A loss of acidic germinationinhibitors was also detected during stratification. The acidicfraction was shown to contain abscisic acid (ABA) by its behaviouron GLC and isomerization with ultra-violet light. Determinationsof endogenous levels of ABA by combined GLC and isotope dilutionmethods indicated a loss of 97.9 per cent ABA during stratification.The data suggest that the breaking of seed dormancy at low temperatureinvolves the initiation of an ordered sequence of events thatinclude the changes in growth hormones necessary to determinethe course of development for the removal of dormancy.     

Effects of Applied Growth Regulators on Pod Growth and Seed Protein Composition in Pisum sativum L.

Plants of Pisum sativum L. raised from seed of an isogenic lineselected from cv. Greenfeast were grown under glasshouse conditions.The plant growth regulators naphthalene-acetic acid, benzyl-adenine,abscisic acid and gibberellic acid (GA₃) were administered todeveloping fruits by daily injections into the pedicels of podsbetween 2 d and 32 d after full bloom, thereby spanning thetime of maximum protein synthesis. Changes were observed ingrowth rates and dry weights of pods at maturity. Total proteincontent per cotyledon increased in naphthalene-acetic acid,benzyladenine and abscisic acid treatments. Legumin increasedin response to naphthalene-acetic acid and benzyladenine whilevicilin increased in response to abscisic acid. The albumincontent was not affected. Gibberellic acid (GA₃) caused no changesin total protein content or in levels of individual proteinfractions. The level of legumin was further increased by applicationof a one to one mixture of naphthalene-acetic acid and benzyladenine;this treatment also resulted in a marked increase in the albuminfraction but a considerable decrease in vicilin content. Theresults imply that hormones play a role in regulating proteinsynthesis and accumulation in Pisum. Key words: Hormones, Seed, Protein, Composition     

Regulation of Submergence-induced Enhanced Shoot Elongation in Oryza sativa L.

Rice (Oryza sativa L.) is the only cereal that can be cultivatedin the frequently flooded river deltas of South-East and SouthAsia. The survival strategies used by rice have been studiedquite extensively and the role of several phytohormones in theelongation response has been established. Deep-water rice cultivarscan diminish flooding stress by rapid elongation of their submergedtissues to keep up with the rising waters. Other rice cultivarsmay react by mechanisms of submergence tolerance. Aerenchymaand aerenchymatous adventitious roots are formed that facilitateoxygen diffusion to prevent anaerobic conditions in the submergedtissues. This paper discusses the molecular aspects of the mechanismthat leads to shoot elongation (leaves of seedlings and internodes),the regulation of which involves metabolism of, and interactionsbetween, ethylene, gibberellins and abscisic acid. Finally,the importance of new techniques in future research is assessed.Current molecular technology can reveal subtle differences ingene activity between tolerant and non-tolerant cultivars, andidentify genes that are involved in the regulation of submergenceavoidance and tolerance.     

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     

Relationships of endogenous plant hormones to accumulation of grain protein and starch in winter wheat under different post-anthesis soil water statusses

Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought or waterlogging, endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, four winter wheat (Triticum aestivum L.) varieties differing in grain protein content, Heimai 76, Wanmai 38, Yangmai 10 and Yangmai 9, were subjected to drought (SRWC = 4550%, DR), waterlogging (WL) and moderate water supply (SRWC = 7580%, CK), beginning from 4 days post-anthesis (DPA) to maturity. On the 10 (grain enlargement stage) and 20 (grain filling stage) DPA, endogenous abscisic acid (ABA), gibberellins (GA₁₊₃), indole-3-acetic acid (IAA) and zeatin riboside (ZR) were determined in sink and source organs of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in four varieties. The ABA levels were much higher under DR and WL than under CK. Compared with CK, GA₁₊₃ levels in whole-plant under DR and WL changed a little at 10 DPA, but markedly decreased under DR and WL at 20 DPA. Changes of endogenous IAA level under DR and WL exhibited a complicated pattern, depending on organs and growth stages. Particularly at the 20 DPA, the mean levels of IAA in roots, leaves and grains decreased significantly under DR and WL. In comparison with CK, ZR levels in all organs significantly decreased under DR and WL at both stages. The correlation analyses between yields and contents of starch and protein in grains and levels and ratios of four hormones in source and sink organs indicated that the changes in yield and content of grain starch and protein under DR and WL were associated with the reduced IAA, ZR and GA₁₊₃ levels and elevated ABA level in plants, especially in grains. It was proposed that the changed levels of endogenous hormones under post-anthesis DR and WL might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.     

From Storage Compartment to Lytic Organelle: The Metamorphosis of the Aleurone Protein Storage Vacuole

Protein storage vacuoles are found in a variety of tissues butare especially abundant in the storage organs of fruits andseeds. In this review, we focus on the protein storage vacuolesof cereal aleurone. In the mature grain, these organelles arerepositories for reserve nitrogen, carbon and minerals. Followingimbibition, protein storage vacuoles of cereal aleurone changefrom storage compartments to lytic organelles. Changes in proteinstorage vacuole structure and enzymatic activity during thistransition are discussed. It is emphasized that protein storagevacuoles are poised for reserve mobilization, and that gibberellinperception by the aleurone cell initiates a signalling cascadethat promotes acidification of the vacuole lumen and activationof enzymes and transporters.Copyright 1998 Annals of BotanyCompany Protein storage vacuole, cereal aleurone, gibberellin, abscisic acid, protein body, endosperm reserves.