Lettuce Achenes Research Articles

Time-course transcriptome landscape of achene development in lettuce

Lettuce (Lactuca sativa L.), which belongs to the large Asteraceae (Compositae) family, breeds by sexual reproduction and produces seeds. Actually, lettuce seeds are achenes, which are defined as fruits. However, few studies have described the morphological characteristics of the lettuce achenes, and genes essential for achene development are largely unknown in lettuce. To investigate the gene activity during achene development and determine the possible mechanisms that influence achene development in lettuce, we performed a time-course transcriptome analysis of lettuce achenes. A total of 27,390 expressed genes were detected at the five achene development stages. We investigated the gene expression patterns during achene development and identified the enriched biological processes at the corresponding stages. Kyoto Encyclopedia of Genes and Genomes and Gene Ontology analyses revealed a variety of transcriptomic similarities and differences at different achene development stages. Further, transcription factors and phytohormones were found to play important roles during achene development. Finally, we proposed a working model to illustrate the gene expression modules and possible molecular mechanisms underlying achene development. Our time-course transcriptome data also provide a foundation for future functional studies to reveal the genetic control of achene development in lettuce.

Chemical constitution and allelopathic effects of Curcuma zedoaria essential oil on lettuce achenes and tomato seeds

Chemical constitution and allelopathic effects of Curcuma zedoaria essential oil on lettuce achenes and tomato seeds

Atividade alelopática de óleos essenciais de plantas medicinais na germinação e vigor de aquênios de alface

In recent years, essential oils have gained commercial interest in the agricultural area, mainly for their allelopathic, insecticidal, antifungal, antimicrobial and antioxidant properties, and, also for their natural compounds, which have generally displayed low toxicity, relatively low cost and rapid degradation in the environment. Medicinal plants have emerged as potential suppliers of essential oils because of their ethnopharmacological utility. The aim of this study was to evaluate the allelopathic potential of essential oils extracted from fresh leaves of lemon grass ( Cymbopogon citratus ), wild basil ( Ocimum gratissimum L.) and sweet basil ( Ocimum basilicum L.) with regard to their major constituents (citral, eugenol and cineol, respectively) in different application forms (direct contact and the effect of volatile constituents) on the germination and vigor of lettuce seeds (cultivar Regina SF 3500). The effects of the oils and their major components were evaluated with regard to the variables: first germination count, total germination, GVI (germination velocity index), seedling dry weight and average lengths of shoots and lettuce roots. The essential oils from lemon grass and basil displayed allelopathic potentials on seed germination and vigor of lettuce achenes that can be assigned to their respective major constituents citral and eugenol. On the other hand, the allelopathic effect of the essential oil from basil was a consequence of the combined effect of all the components, regardless the application method.

Allelopathic activity of medicinal plant essential oils on seed germination and vigor of lettuce achenes

Allelopathic activity of medicinal plant essential oils on seed germination and vigor of lettuce achenes

Molecular aspects of the antagonistic interaction of smoke-derived butenolides on the germination process of Grand Rapids lettuce (Lactuca sativa) achenes.

Smoke-derived compounds provide a strong chemical signal to seeds in the soil seed bank, allowing them to take advantage of the germination niche created by the occurrence of fire. The germination stimulatory activity of smoke can largely be attributed to karrikinolide (KAR(1) ), while a related compound, trimethylbutenolide (TMB), has been shown to have an inhibitory effect on germination. The aim of this study was to characterize the interaction of these potent fire-generated compounds. Dose-response analysis, leaching tests and a detailed transcriptome study were performed using highly KAR(1) -sensitive lettuce (Lactuca sativa cv 'Grand Rapids') achenes. Dose-response analysis demonstrated that the compounds are not competitors and TMB modulates germination in a concentration-dependent manner. The transcriptome analysis revealed a contrasting expression pattern induced by the compounds. KAR(1) suppressed, while TMB up-regulated ABA, seed maturation and dormancy-related transcripts. The effect of TMB was reversed by leaching the compound, while the KAR(1) effect was only reversible by leaching within the first 2h of KAR(1) treatment. Our findings suggest that the compounds may act in concert for germination-related signaling. After the occurrence of fire, sufficient rainfall would contribute to post-germination seedling recruitment by reducing the concentration of the inhibitory compound.

Germination activity of smoke residues in soils following a fire

A simple and rapid bioassay was implemented to detect the germination activity of extracts from soils in pre/post-burn conditions. Soil samples taken from burnt, unburnt and adjacent plots at depths of 0–2, 2–4, 4–6 and 6–8 cm before and after burning mesic grassland in South Africa were analysed for germination activity over an eight-week period. Soil samples were extracted using dichloromethane and bioassayed using Grand Rapids lettuce ( Lactuca sativa L.) achenes (seeds). The Grand Rapids lettuce seeds exhibited greater germination percentages when treated with extracts from burnt soil compared to the other plots. The magnitude of the germination activity declined with time since the burn. The Grand Rapids lettuce seeds also exhibited significantly higher germination when treated with unburnt soil extracts compared to the control (distilled water) which indicates the existence of other factors controlling germination in unburnt soil. Germination activity in the adjacent plots decreased with time. These findings indicate that the germination activity of the smoke derived from burning plant-material diffuses into the soil and its persistence declines with time. Considering that the soil seed bank contains viable seeds, at a moderate depth, and that they are initially unaffected by the heat of the fire, then smoke residues following a fire can influence the germination and recruitment of plant species that are responsive to smoke-derived compounds and are represented in the germinable soil seed bank.

Smoke-water-induced changes of expression pattern in Grand Rapids lettuce achenes

AbstractAerosol smoke and smoke-water can break dormancy and promote seed germination of many plant species. In this study we investigated changes in gene expression after imbibition of light-sensitive Lactuca sativa L. cv. ‘Grand Rapids’ achenes with dilute smoke-water compared to water control samples kept in the dark or continuous light, using the fluorescent differential display technique. Although no difference was detected in the smoke-water versus water control samples germinated in light, smoke-water treatment resulted in the differential display of several expressed sequence tags (ESTs) when compared to water control samples kept in the dark. The most pronounced fragments isolated correspond to known genes related to germination, with functions in cell wall expansion, regulation of translation, the cell division cycle, carbohydrate metabolism and abscisic acid (ABA) regulation. Real-time polymerase chain reaction (PCR) validation revealed that the transcript abundance of the genes, HVA22, short-chain dehydrogenase/reductase and late embryogenesis abundant protein, are upregulated after smoke treatment when compared to control achenes kept in the light. The results indicate that smoke has a dual effect. On the one hand, the smoke can induce genes that may be linked to ABA action, whereas, on the other hand, it elicits a faster germination rate by inducing a similar pattern in gene expression as light treatment. Smoke effects could be manifested mainly through the induction of the cell division cycle, cell wall extension and storage mobilization.

Germination and emergence of prickly lettuce (Lactuca serriola L.) and its susceptibility to selected herbicides

Three-year trials were conducted to study germination and emergence of prickly lettuce (Lactuca serriola L.) achenes, increments of shoot dry matter and susceptibility of the weed to selected herbicides. The germination rates of achenes at10°C (92%),20°C (97%) and30°C (95%) did not indicate any significant differences within 20 days from sowing. The highest percentage emergence of prickly lettuce achenes was determined after their sowing into a depth of1 mm. Differences from the variants of sowing onto the soil surface (0 mm), into a depth of 10 and20 mm were significant. There were no differences in the emergence rates from a depth of 10 and20 mm. The highest increments of shoot dry matter were observed when prickly lettuce plants were grown for 4–7 weeks after sowing at20°C. The effect of selected herbicides on prickly lettuce plants treated at the stage of 2–3 true leaves was evaluated on the basis of a change in the content of shoot dry matter. A significant decrease in dry matter against the control was recorded in all variants after herbicide application. The effect (expressed by a lower dry matter content) was significantly higher after the combination amidosulfuron + iodosulfuron-methyl + mefenpyr-diethyl (10 + 2.5 + 25 g/ha) was used than after the application of tribenuron (10.85 g/ha) and picolinafen + cyanazine (120 g + 480 h). The effect of amidosulfuron (22.5 g/ha) was significantly higher than in the variants treated with tribenuron, picloram + clopyralid (16.75 + 66.75 g/ha), clopyralid (90 g/ha) and picolinafen + cyanazine (150 + 600 g/ha). The best effects were produced by herbicides containing amidosulfuron and iodosulfuron as active ingredients.  

Fiber optic studies of light gradients and spectral regime within Lactuca sativa achenes

Light gradients and spectral regime were measured in Lactuca sativa L. cv. Grand Rapids achenes using fiber optic microsensors. The distribution of scattered light across lettuce achenes was linear for 660 and 730 nm and non‐linear for 450 nm light. Spectra for scattered light within intact achenes also showed a non‐linear increase with wavelength. The preferential attenuation of blue light by the pericarp and seed explains in part the relative ineffectiveness of blue light with respect to red in triggering germination of lettuce. Calculated action spectra for phytochrome‐stimulated germination agree closely in the red with experimentally derived action spectra; however, there is little agreement within the blue.

Metabolism of (±) 2‐[14C]‐abscisic acid in Lactuca sativa achenes

Achenes ofLactuca sativa L. cv. Grand Rapids were treated with (±) 2‐[14C]‐abscisic acid (ABA) at 105 ‐ or 2‐106 M for 6, 12, 24, 48 or 96 h in darkness at 24°C. They were then extracted in 80% ethanol. Two acidic diethyl ether phases which contained the free acids and the acids released after mild alkaline hydrolysis respectively, were analyzed as well as the radioactivity which remained in the final aqueous phase. For treatment durations between 6 and 96 h, the major part of the radioactivity was found in the free phase, in the form of ABA. For treatment durations up to 48 h, no radioactivity was detected at the Rf of phaseic acid or dihydrophaseic acid (free and hydrolysed phases). After 96 h culture on 105 M ABA, dihydrophaseic acid was present, but only in very small quantities. Two ABA metabolites were detected. One was characterized as β‐d‐glucopyranosyl abscisate since its Rf was the same as that of an authentic sample in three different solvent systems and also since it released ABA on mild alkaline hydrolysis. It increased steadily with time and represented the main metabolite. The other metabolite found in the aqueous phase after mild alkaline hydrolysis and extraction with ether at pH 3 was a very polar compound, resistant to alkaline hydrolysis in the presence of concentrated ammonia and to methylation. It was, however, metabolized by apple embryo, yielding essentially dihydrophaseic acid and an ester which released dihydrophaseic acid on mild alkaline hydrolysis. These results indicate that under the conditions tried, the metabolism of [14C]‐ABA by lettuce achenes leads almost exclusively to the formation of conjugates, oxidative metabolism of ABA being almost non‐existent. Separate analysis of the integuments and of the endosperm plus embryo after culture of whole achenes for 48 h in the presence of 105 M [14C]‐ABA showed that ABA metabolism occurred only in the endospermembryo tissue.

Structural Alterations in Isolated Endosperms of Lactuca sativa L. Achenes

Endosperm tissue of lettuce (Lactuca sativa L.) achenes germinating in the dark was isolated from the embryo after appropriate time periods of imbibition in the dark and was incubated in water or in gibberellic acid solution in the dark. It was found that endosperms which were dissected from achenes during the first to the eighth hours of imbibition do not show any structural alteration even after 24 h of incubation either in water or in GA(3) while endosperms excised after 9 hours of imbibition show moderate modifications of micropylar area cells if incubated in water for 24 h. Endosperms isolated after 8 hours of imbibition show great structural alterations of their micropylar cells if incubated for the same period in gibberellic acid solution. These results indicate (a) that the presence of the embryo is necessary for a long period for the manifestation of structural modifications of the isolated endosperm; and (b) that the two areas of lettuce endosperm (i.e. micropylar vs lateral) are different.

Lettuce achene germination and seedling growth on alkali chloride salts

Lettuce achenes germinated on different alkali chloride salts manifested significant percentages of germination, thus demonstrating that neither the cations nor the anion were toxic to this aspect of achene activity. However, seedling growth was adversely affected by Rb+ compared with that observed on Na+, K+, and glass-distilled water. Evidece is presented which indicates that Rb+ adversely affected seedling growth by having interfered with the normal endogenous K+ physiology of the growing seedlings.

Gibberellic Acid-induced Structural Alterations in the Endosperm of Germinating Lactuca sativa L. Achenes

Summary Exogenously applied gibberellic acid induces structural alterations in the micropylar region of the endosperm in Grand Rapids lettuce ( Lactuca sativa L.) achenes prior to radicle protrusion. Besides the pattern of storage material degradation and vacuole formation, both timing and localization of endosperm alterations are similar to the previously reported phytochrome-mediated ones. These data favor the concept that gibberellic acid and phytochrome promote lettuce achene germination, at least in the later stages, through a similar channel.

Lettuce Endosperm Structural Changes During Germination under Different Light, Temperature, and Hydration Conditions

The endosperm structure of dark-germinating Grand Rapids lettuce (Lactuca sativa L.) achenes was examined by light microscopy under different germination conditions. Achenes imbibed in darkness at 25 C show significant structural modifications in a restricted area of the endosperm, opposite the radicle tip, before radicle emergence. These preemergence changes, similar to those observed in light-requiring Grand Rapids lettuce achenes after phytochrome activation, are mainly characterized by the mobilization of storage materials and the vacuolation of the cytoplasm Achenes imbibed under conditions not permitting the completion of germination (continuous far-red light, high temperature, and appropriate osmotic solution) do not show any structural change in their endosperm cells. We conclude that cytoplasmic modification of the endosperm cells in the micropylar region is necessary for the completion of germination in lettuce achenes, in addition to the necessity for decrease in embryo water potential.

Colchicine-light effects on growth and mitotic behaviour in germinating lettuce achenes.

Root and shoot growth were severely suppressed in colchicine-pretreated lettuce achenes germinated in the dark and under illumination of 150 lux. Abnormal nuclear morphology rather than normal-appearing restitution nuclei was evident in these drug-pretreated achenes, there being no evidence of normal mitotic behaviour or cytokinetic activity in the root and shoot tissues examined. Root extension and lateral root meristem differentiation were evident in colchicine-pretreated achenes germinated under an illumination of 3000 lux, normal-appearing anaphase figures and cytokinetic activity being evident in both the primary root apices and lateral root meristems. Thus, the growth and mitotic behaviour of germinating colchicine-pretreated lettuce achenes were observed to be influenced significantly by the environmental light intensity in which germination occurred.

Phytochrome control of skotodormancy release in Grand Rapids lettuce achenes

Light‐requiring Grand Rapids lettuce (Lactuca sativa L.) achenes develop skotodormancy when imbibed in darkness for 7 days at 25°C. Redried skotodormant achenes maintain this type of dormancy upon subsequent rehydration. At 25°C full germination of skotodormant achenes can be induced by continuous and intermittent red light illumination as well as by several brief red irradiations given daily. One brief (10 min) red light irradiation can partly break skotodormancy at 20°C, while at lower temperatures the same treatment results in full induction of germination. Phytochrome control of the release from skotodormancy is proven by a) the dependence of the germination response on the relative sequence of red and far‐red light in cyclic irradiations, and b) the reversion of red action by subsequent far‐red irradiation. The time course of germination of skotodormant achenes treated with intermittent red light depends upon the length of dark interval between the light pulses. Germination is considerably delayed compared to that of non‐skotodormant ones, induced by a single brief red light treatment. This fact in combination with the requirement, over a long period of time, of Pfr action for full manifestation of germination, indicates that skotodormancy is a deeper form of dormancy. It is concluded that the germination of lettuce achenes may always be subjected to phytochrome control.

Effect of Light Intensity on Anaphase Activity in Root Apices of Colchicine-pretreated Lettuce Achenes (Lactuca sativa L.)

Summary Anaphase activity was observed in the primary root apices of colchicine-pretreated lettuce achenes germinated under 75 μmol m-2s-1 light intensity. This aspect of mitotic activity was also evident in the lateral root meristems which developed at times in the drug-pretreated achenes germinated under this light intensity. Neither anaphase activity nor lateral root meristem development was evident in the colchicine-pretreated achenes germinated in the dark or under 5 μmol m-2s-1 light intensity. Use of the same light source for providing both the 5 and 75 μmol m-2s-1 light intensity environments points to the significance of the environmental light intensity in influencing anaphase activity in root apices of colchicine-pretreated lettuce achenes.

Largactil and Hydroxylamine Induced Geotropic Disorientation in Lettuce (Lachica sativa L.)

Summary Lettuce achenes germinated in the light and dark on the neuroleptic drug largactil and the inorganic amine hydroxylamine hydrochloride manifested disorientation of normal root and shoot geotropisms. The root apices of the achenes germinated on this drug and inorganic amine were freely suspended in the air whereas the cotyledons remained lying on the physical substratum. Thus, largactil and hydroxylamine hydrochloride apparently adversely affected the same endogenous physiological processes) which govern normal root and shoot geotropisms in germinating lettuce achenes.

Dark-induced Anomalous Hypocotyl Growth in Colchicine-treated Lettuce Seedlings

Central nervous system (CNS) depressant drugs such as barbiturates and tranquillizers have been observed: ( a ) to depress cell multiplication in different types of animal cells growing in culture (Dawson, 1972; Jackson, 1975); (b) to interfere with the normal germination and growth behaviour of angiosperm seedlings and pollen grains (Kordan, 1977a, ft, 1978, 1979a, ft; Kordan and Mumford, 1978, 1979); and (c) to inhibit transpiration in excised barley leaves (Ramiandrasoa-Luong et al., 1979). Although gaseous oxygen is not listed in the medical literature as being a CNS depressant agent, hyperbaric oxygenation in clinical anaesthetic practice has been observed to exert toxic effects under certain conditions, the basic mechanism of oxygen toxicity not being understood (Ledingham, 1971). Hyperbaric oxygen has been observed to exert greater adversity of action on radicle and hypocotyl growth than on cotyledonary growth in germinating lettuce seedlings (Borthwick and Robbins, 1928). Colchicine, a weak anaesthetic and CNS depressant drug (Jackson, 1975) that also causes metaphase arrest in most animal and plant cells (Sharma and Sharma, 1972; Jackson, 1975), also exerts greater adversity of action on radicle and hypocotyl growth than on cotyledonary growth in germinating lettuce seedlings, this phenomenon being the subject of this brief communication. Sixteen 'Pyrex' unspouted crystallizing dishes (94x50 mm) were each lined on the bottom with Whatman No. 1 (9 cm diam.) filter-paper discs. The paper in eight dishes was wetted thoroughly with glass-distilled water and in the other eight dishes with 1 per cent (w/v) colchicine (BDH Chemicals Ltd., Poole). Fifty lettuce achenes {Lactuca sativa L. cv. Grand Rapids) were placed in each crystallizing dish, each dish was covered with a 'Pyrex' Petri dish lid and sealed with 'Parafilm'. Eight dishes were placed in an 18 h light (25-26 °C) and 6 h dark (21-22 °C) daily cycle and the other eight dishes were placed in continuous darkness (26-27 °C). On day 3 all germinated and ungerminated achenes in two dishes from each of the glass-distilled water and colchicine treatments in the light and dark environments were washed thoroughly with glass-distilled water and transferred to glass-distilled water on filter paper in^sealed crystallizing dishes in their respective light and dark environments for seven more days. All treatments were harvested for examination on day 10. High percentages of achene germination were evident in all treatments in both the light and dark environments (Table 1). Washing one set of the lightand dark-germinated seedlings with glass-distilled water and transferring them to glass-distilled water for 7 additional days did not bring about any apparent differences in their growth behaviour from that manifested by the 10-day-old unwashed seedlings in the duplicate treatments (Table 1) (Plate 1 a-h). Thus, the washing procedure neither impaired nor enhanced the growth behaviour of the seedlings compared with that of the unwashed seedlings. Radicle but not cotyledonary growth was completely inhibited in all lightand darkgerminated colchicine-treated seedlings (Table 1) (Plate lc, d, g, h). The cotyledons of

Germination inhibition activity of a naturally occurring lignan fromAegilops ovata L. in green and infrared light

The naturally occurring lignan, monoepoxylignanolide (MEL) fromAegilops ovata L., inhibits germination of lettuce achenes (seeds) in incandescent light but not in the dark. The ‘action spectrum’ after preincubation of MEL in darkness shows inhibition in the regions of 399 nm and 712–804 nm, but after pretreatment with incandescent light inhibition is seen at 500–577 nm and 712–804 nm. The infrared inhibition by MEL is not reversible by red light. The pretreatment of MEL with incandescent light gives rise to a photoproduct which, together with MEL itself, inhibits the germination of lettuce achenes in the dark.