兰州百合鳞茎发育及低温解除休眠过程中内源激素的变化

以兰州百合为试材,研究了鳞茎发育过程中以及2、6、10℃条件下保湿贮藏101 d内母鳞茎与新鳞茎中内源激素的变化。结果表明：鳞茎发育过程中内源ABA含量以及母鳞茎的GA₃与ZR含量增加,而内源IAA含量以及新鳞茎的GA₃与ZR含量下降。低温贮藏期间,母鳞茎与新鳞茎的GA₃、IAA含量均有升高过程,而ABA含量呈下降趋势;新鳞茎的ZR含量呈下降趋势,母鳞茎的ZR含量也有升高过程。低温处理初期的34 d内,内源激素变化最为显著。不同贮藏温度相比较,ABA含量差异不大,GA₃含量随温度升高而下降。在富含淀粉的新鳞茎中,GA₃和ABA表现出极显著的负相关关系,而在淀粉含量较低的母鳞茎中GA₃和ABA无相关性。通径分析结果表明,母鳞茎与新鳞茎的物质代谢机制不同,母鳞茎的物质变化受内源GA₃的调控,新鳞茎主要是ABA作用的结果。     

Gibberellins do not act against abscisic acid in the regulation of bulb dormancy of Allium wakegi Araki

Abscisic acid (ABA) is involved in bulb dormancy of Alliumwakegi Araki. We examined the antagonistic role of gibberellins(GAs)against ABA in the regulation of this dormancy. The concentrations of ABA andGAs in the basal leaf sheaths or bulbs of A. wakegi cv.Kiharawase were investigated during growth in the field and postharveststorage.The concentration of ABA in the basal leaf sheaths began to increase about onemonth before they began to swell, reached a maximum shortly after bulbharvesting, and decreased during postharvest storage. The plants showed bulbdormancy accompanied with the change in ABA concentration. GA1,GA3, GA4, GA12, GA15, GA19, and GA20 were identified in the basal leaf sheaths of A. wakegi from Kovats retention indices (KRI) andfull-scan mass spectra by gas chromatography - mass spectrometry (GC-MS)analysis. The concentrations of all classes of GAs in the basal leaf sheathsestimated by the dwarf rice micro-drop assay increased transitorily shortlybefore they began to swell, and decreased rapidly during bulb development. Bulbdormancy had already been induced when the concentration of the GAs becamemaximum. All the GAs in the bulbs remained at a low level during postharveststorage, when bulbs were gradually released from dormancy. The concentrationsof GA1+3, GA4, GA15, and GA20 inthe bulbs increased after sprouting of the bulbs planted in moist vermiculite.Hence, the state of bulb dormancy is considered to be independent of the GAconcentrations of in the basal leaf sheaths or bulbs of A.wakegi.     

Necessity of high temperature for the dormancy release of Narcissus tazetta var. chinensis

Winter dormancy has been extensively studied in many plants, while much less information is available for summer dormancy. Narcissus tazetta var. chinensis is characterized by a prolonged period of summer dormancy during the annual cycle. In the present study, we characterized the nature of dormancy in the controlled growth conditions and investigated the effects of temperature and ethylene on dormancy release. Cessation of growth and senescence of aerial tissues occurred even under conditions favorable for growth, suggesting an endo-dormancy process. Bulbs failed to sprout when they were exposed to low storage temperatures, while high temperature treatment preceding low storage temperatures, or heating interruption during low storage temperatures, could make bulbs sprouting. These results suggest that high temperatures are necessary for endo-dormancy release. Ethylene application during a later storage stage showed an obvious accelerative effect on bulb sprouting, whereas ethylene application during the middle stage had no effect on sprouting. The biological progression of dormancy was further studied through cytological and physiological analyses. Under natural conditions, the ethylene level was reduced to trace amounts with the transition and progression of dormancy. A transient peak in ethylene release was found when the plugged plasmodesmata (PD) began to re-open and flower initiation began. The most common PD possessed electron-dense deposits in endo-dormancy. These data indicate that endo-dormancy ends when flower initiation begins and ethylene peak occurs. Ethylene application had no effect on dormancy release, while it hastened sprouting only after the release from endo-dormancy by high temperature.     

MRI can reveal metabolic changes in lily bulbs in vivo during dormancy release

The factors influencing dormancy release in lily bulbs strongly affect commercialization success, but the mechanism of dormancy release is still unclear. Magnetic resonance imaging (MRI) can detect changes in morphology and water status in a living plant bulb and aid in investigating release factors. To evaluate whether MRI could be used to detect intra-bulb metabolic changes during the dormant period in Oriental Lilies (Lilium ??Sorbonne??), a series of MRI and sugar concentration measurements were performed weekly on bulbs stored for 11 weeks at 4°C. The image quality of intra-bulb structure obtained using T ₁-weighted imaging was superior to that obtained using T ₂-weighted imaging and had a higher signal-to-noise ratio (0.97±0.01). Magnetization transfer ratio values for the bud and basal plate declined during the first eight weeks of cold storage (P>0.05), and were well correlated with concentration of soluble sugar in the bud (R ²=0.95) and basal plate (R ²=0.93). Thus, MRI can serve as a valuable tool for observation and analysis of dynamic morphological and metabolic changes in vivo during dormancy release. This information is potentially useful as a guide in the improvement of horticultural product quality.     

Morphogenetic potential and in vitro micropropagation of endangered plant species Leucojum aestivum L. and Lilium rhodopaeum Delip.

Summary The present work deals with the in vitro methods for rapid propagation, and morphogenetic potential of the rare and endangered bulb species Leucojum aestivum L., Amaryllidaceae, and Lilium rhodopaeum Delip., Liliaceae. The morphogenetic potential of different plant organs (bulb, stem, leaves and ovaries) was studied. Leaves of Leucojum aestivum L. and basal parts of the bulb in Lilium rhodopaeum Delip. possess the highest regeneration activity. Murashige and Skoog (MS) medium + 1 mg/l 6-benzylaminopurine (BAP) + 1 mg/l kinetin and Linsmaier and Skoog (LS) medium + 0.5 mg/l 1-naphthaleneacetic acid (NAA) + 0.1 mg/l kinetin were favourable for direct organogenisis from these explants. A stimulating effect of alow gamma-irradiation dose (5 Gy) upon the quantity and growth intensity of the bulbs formed by the explants in in vitro conditions is observed.     

Flowering pathway is regulated by bulb size in Lilium longiflorum (Easter lily)

Lilium longiflorum (Easter lily) vegetative propagation occurs through production of underground bulbs containing apical and axillary meristems. In addition, sexual reproduction is achieved by flowering of elongated shoots above the bulb. It is generally accepted that L. longiflorum has an obligatory requirement for vernalisation and that long day (LD) regime hastens flowering. However, the effect of bulb size and origin, with respect to axillary or apical meristems on flowering, as well as the interactions between these meristems are largely unknown. The aim of this study was to explore the effect of bulb size, vernalisation and photoperiod on L. longiflorum flowering. To this end, we applied vernalisation and photoperiod treatments to the different bulb sizes and used a system of constant ambient temperature of 25 °C, above vernalisation spectrum, to avoid cold‐dependent floral induction during plant growth. Vernalisation and LD hasten flowering in all bulbs. Large, non‐vernalised bulbs invariably remained at a vegetative stage. However, small non‐vernalised bulbs flowered under LD conditions. These results demonstrate for the first time that cold exposure is not an obligatory prerequisite for L. longiflorum flowering, and that an alternative flowering pathway can bypass vernalisation in small bulbs. We suggest that apical dominance interactions determine the distinct flowering pathways of the apical and axillary meristems. Similar floral induction is achieved in propagated bulblets from scaling. These innovative findings in the field of geophyte floral induction represent valuable applicative knowledge for lily production.     

Involvement of abscisic acid (ABA) in bulb dormancy of Allium wakegi Araki I. Endogenous levels of ABA in relation to bulb dormancy and effects of exogenous ABA and fluridone

Allium wakegi plants exposed to long days (LD, 14 h-photoperiod) developed bulbs, which were dormant from the 30th to the 125th day of LD, but those grown under natural short days (SD) did not develop bulbs. The contents of abscisic acid (ABA) in both whole bulbs and buds of the bulbs increased in LD, reaching a maximum at the 60th day of LD and decreasing thereafter, but those in basal leaf sheaths (this part corresponds to a bulb after bulb development) and buds did not increase in SD. The ABA content was related to the depth of bulb dormancy. Application of 500 M ABA to bulbs for 24 h significantly delayed sprouting, but that of 5 or 50 M ABA had little or no effect. Application of 25 or 125 M fluridone to the soil just before exposure to LD bleached new expanding leaves and reduced bulb size, but had no effect on the development of bulb scales that characterize bulb formation. The bulbs formed under such conditions sprouted earlier than those of control plants. The levels of endogenous ABA in bulbs, buds of the bulbs, leaf blades, and roots were reduced by fluridone application. These results indicate that ABA plays an important role in bulb dormancy of Allium wakegi.     

Differentiation in Lilium bulbscales grown in vitro. Effects of activated charcoal, physiological age of bulbs and sucrose concentration on differentiation and scale leaf formation in vitro

Organ differentiation and growth of tissue cultured bulbscales of Lilium auratum Lindl. was investigated. Benzyladenine stimulated bulb and bulbscale differentiation but inhibited root formation. Addition of activated charcoal to the medium negated the effect of BA on differentiation, while the growth of bulbs was markedly stimulated. Organ formation was also influenced by the physiological age of bulbs. From bulbscales of a 3-week-old bulb, a large number of bulbs and roots was formed but callus was not produced. A high sucrose concentration (90 g/1) reduced the subsequent sprouting after planting in soil. Scale leaf formation was also regulated. Sucrose (30 g/1) stimulated scale leaf formation but 90 g/1 were inhibitory.     

The effects of storage condition on starch metabolism and regeneration potentials of twin-scales and inflorescence stem explants of <Emphasis Type="Italic">Narcissus tazetta</Emphasis>

Summary The natural propagation rate of Narcissus is very slow. In vitro micropropagation of Narcissus is more efficient than conventional propagation for rapidly building up aseptic stocks of varieties, especially for the establishment of new cvs. and the production of pathogen-free stock material. In the present study, Narcissus tazetta cv. ‘Ziva’ bulbs were used as the source of mother plants. The bulbs were kept at 30°C in a dark chamber until the start of the experiments. Prior to explant preparation, the bulbs were subjected to a cold treatment at 15°C in the dark for 6 wk to break dormancy. Twin-scales and inflorescence stem discs were isolated from aseptic bulb parts and were used as the initial explants. The polar orientation affected the regeneration of the inflorescence stem. Storage duration at 30°C followed by cold treatment were found to affect starch levels, adenosine diphosphate glucose pyrophosphorylase (AGPase) activities, and regeneration potentials. Starch levels were reduced significantly during a 10 mo. storage period at 30°C in both twin-scales and inflorescence stem disc explants. Regeneration was followed by an efficient acclimatization system with 98–99% survival. More than 500 highly uniform young bulbs were propagated from one mother bulb in a 12 mo. period.     

Bulbil production in Narcissus: the effect of temperature and duration of storage on bulb unit development and subsequent propagation by twin-scaling

The growth of bulb components and carbohydrate content of Narcissus bulbs was followed during storage at 5–30 ^oC, and the productivity of twin-scale propagules cut from bulbs after these storage treatments was studied. Growth of daughter bulb unit components was greatest during storage at 9–15 ^oC, and greatly inhibited at 30 ^oC. Concentrations of soluble sugars were highest following 30 ^oC storage, and higher in intermediate bulb scales than in outer or inner scales. Bulbil production on twin-scales was greatest on propagules cut from the intermediate scales, and in bulbs previously stored at 15 or 30 ^oC.     

Exogenous ethylene inhibits sprout growth in onion bulbs

Background and Aims

Exogenous ethylene has recently gained commercial interest as a sprouting inhibitor of onion bulbs. The role of ethylene in dormancy and sprouting of onions, however, is not known.

Methods

A cultivar (Allium cepa ‘Copra’) with a true period of dormancy was used. Dormant and sprouting states of onion bulbs were treated with supposedly saturating doses of ethylene or with the ethylene-action inhibitor 1-methylcyclopropene (1-MCP). Initial sprouting was determined during storage at 18 °C by monitoring leaf blade elongation in a specific size class of leaf sheaths. Changes in ATP content and sucrose synthase activity in the sprout leaves, indicators of the sprouting state, were determined. CO₂ and ethylene production of onion bulbs during storage were recorded.

Key results

Exogenous ethylene suppressed sprout growth of both dormant and already sprouting onion bulbs by inhibiting leaf blade elongation. In contrast to this growth-inhibiting effect, ethylene stimulated CO₂ production by the bulbs about 2-fold. The duration of dormancy was not significantly affected by exogenous ethylene. However, treatment of dormant bulbs with 1-MCP caused premature sprouting.

Conclusions

Exogenous ethylene proved to be a powerful inhibitor of sprout growth in onion bulbs. The dormancy breaking effect of 1-MCP indicates a regulatory role of endogenous ethylene in onion bulb dormancy.Key words: Bulb dormancy, Allium cepa, onion, sprout growth, ethylene, CO₂ production, respiration, 1-methylcyclopropene     

Identification of free mannose and partial characterization of a mannose-6-phosphate isomerase from Lilium longiflorum bulbs

The existence of free mannose in storage bulbs of Lilium longiflorum Thunb, was established using preparative high performance liquid chromatography, gas chromatography and gas chromatography-mass spectroscopy. Free mannose was not detected in developing (importing) bulb tissues. Mannose, a relatively rare hexose in plant tissue, probably arises from the hydrolysis of glucomannan, a hemicellulosic carbohydrate polymer known to be present in Lilium storage tissues. A calculation of total mannose residues per bulb (prior to versus after reserve hydrolysis and export) indicated that mannose is metabolized, probably in sucrose biosynthesis. A mannose-6-phosphate isomerase (EC 5.3.1.8) was isolated from Lilium bulbs and purified 155-fold with 29% yield. The molecular weight of the enzyme was estimated by gel filtration to be 64 kDa, and the K_m for mannose-6-phosphate was 0.42 m M . It is concluded that glucomannan is functioning as a reserve carbohydrate in Lilium storage tissues and that the mannose-6-phosphate isomerase is responsible for the entry of mannose into the sucrose biosynthetic pathway.     

Pathogenicity of Fusarium oxysporum to Easter lily, narcissus and gladiolus

Isolates of Fusarium oxysporum from roots, bulbs and stems of Easter lilies (Lilium longiflorum) differed widely in pathogenicity and also, apparently, in tissue specificity. Virulent isolates caused a typical basal rot and root rot (but not a wilt) in which the mycelium advanced intercellularly through the scales and basal plates. Mildly pathogenic isolates became established in mature or senescent outer scales, at first producing only superficial effects, but further growth of mycelium occurred as the outer scales died and sometimes continued until the dead tissues were permeated and chlamydospores were formed. The underlying scales were then colonized. The modes of pathogenicity and survival in Easter lily were compared with those of the F. oxysporum formae causing bulb rots of gladiolus and narcissus. It is suggested that advance of hyphae by penetration between the cells of the vascular parenchyma, which is common in isolates causing rots in bulbs and corms, represents a stage in the evolution of the truly vascular habit among fusaria.     

Effect of Methyl Jasmonate on Morphology and Dormancy Development in Lily Bulblets Regenerated In Vitro

Scales of lily bulbs are swollen petioles. Lily scale fragments cultured in vitro regenerate bulblets consisting of scales that may or may not carry a leaf blade. The bulblets are dormant and require a cold treatment to sprout. We added the gaseous plant growth regulator methyl jasmonic acid (MeJA) in the headspace of the tissue-culture container and studied the effect on plantlet morphology (scale/leaf-blade formation) and dormancy development in three lilies, Lilium speciosum “Rubrum No. 10,” L. longiflorum “Snow Queen,” and the Asiatic hybrid “Connecticut King.” Methyl jasmonic acid strongly reduced leaf-blade formation in Lilium longiflorum and Connecticut King. This was a specific effect as scale formation was affected much less. The specific inhibition of leaf-blade formation was not observed in Lilium speciosum. In this lily, high concentrations of methyl jasmonic acid (MeJA) inhibited leaf-blade and scale formation to similar extents. Methyl jasmonic acid reduced dormancy development in all three lilies, with the largest effect observed in Connecticut King. In this Asiatic hybrid, almost all bulblets that had regenerated at 300 or 1000 μl l⁻¹ MeJA in the headspace, did not require a dormancy-breaking treatment to achieve sprouting after planting in soil. Previously, it has been found in lily that treatments that reduce leaf-blade formation promote dormancy development. The present findings with MeJA do not agree with this. In the three lilies, the various parameters that were studied—regeneration, scale weight, leaf-blade weight, and dormancy development—were very differently affected by MeJA.     

Photoperiod and Temperature Affect Sprouting of Onion bulbs (Allium cepa L.)

The effects of photoperiod and temperature on sprouting wereinvestigated using three cultivars of onion which exhibit differentresponses to daylength during bulb growth. Two photoperiods(8 h and 14 h) and two constant temperatures (15 C and 20 C)were used. Two cultivars showed enhanced sprouting and leafemergence in short days, and one sprouted poorly in all conditions.In long days, some plants showed growth of new bulbs withinthe old one, without sprouting. Photomorphogenesis, photoperiodism, Allium cepa L, onion, dormancy, bulb sprouting     

Endogenous levels of abscisic Acid and decanoic Acid in dutch iris bulbs and the influence of abscisic Acid and decanoic Acid on iris meristems cultured in vitro

Abscisic acid (ABA) and decanoic acid inhibited shoot elongation and floral development of Dutch iris (Iris hollandica Hoog. cv Ideal) meristems cultured in vitro. No synergism with respect to inhibition of leaf growth between ABA and decanoic acid was observed. With monthly harvest dates, from July 10, 1981 to October 10, 1981, there was a progressive decrease in endogenous level of free ABA in `Ideal' iris bulbs. Bulbs subjected to a full set of the usual preplanting storage conditions flowered, on average, 46 days after planting versus 194 days after planting for bulbs planted directly after harvest. ABA levels at harvest were 4- to 5-fold those after the preplanting storage treatment. In general, ABA levels did not correlate well with the length of time from planting until flowering of iris bulbs. Endogenous decanoic acid levels did not follow any pattern with respect to harvest date or postharvest treatment. After the postharvest high temperature treatment, there was about a 3-fold increase in nonscale decanoic acid concentration. Decanoic acid levels, in nonscale tissue, remained high after each of the other postharvest treatments. It is concluded that there is no good evidence to support the contention that either ABA or decanoic acid is directly involved in iris bulb dormancy.