Endogenous Ethylene Concentration Research Articles

Ethephon-Induced Ethylene Enhances Protein Degradation in Source Leaves, but Its High Endogenous Level Inhibits the Development of Regenerative Organs in Brassica napus.

To investigate the regulatory role of ethylene in the source-sink relationship for nitrogen remobilization, short-term effects of treatment with different concentrations (0, 25, 50, and 75 ppm) of ethephon (2-chloroethylphosphonic acid, an ethylene inducing agent) for 10 days (EXP 1) and long-term effects at 20 days (Day 30) after treatment with 100 ppm for 10 days (EXP 2) on protein degradation and amino acid transport in foliar sprayed mature leaves of Brassica napus (cv. Mosa) were determined. In EXP 1, endogenous ethylene concentration gradually increased in response to the treated ethephon concentration, leading to the upregulation of senescence-associated gene 12 (SAG12) expression and downregulation of chlorophyll a/b-binding protein (CAB) expression. Further, the increase in ethylene concentration caused a reduction in protein, Rubisco, and amino acid contents in the mature leaves. However, the activity of protease and expression of amino acid transporter (AAP6), an amino acid transport gene, were not significantly affected or slightly suppressed between the treatments with 50 and 75 ppm. In EXP 2, the enhanced ethylene level reduced photosynthetic pigments, leading to an inhibition of flower development without any pod development. A significant increase in protease activity, confirmed using in-gel staining of protease, was also observed in the ethephon-treated mature leaves. Ethephon application enhanced the expression of four amino acid transporter genes (AAP1, AAP2, AAP4, and AAP6) and the phloem loading of amino acids. Significant correlations between ethylene level, induced by ethephon application, and the descriptive parameters of protein degradation and amino acid transport were revealed. These results indicated that an increase in ethylene upregulated nitrogen remobilization in the mature leaves (source), which was accompanied by an increase in proteolytic activity and amino acid transport, but had no benefit to pod (sink) development.

Ethephon-Induced Ethylene Enhances Starch Degradation and Sucrose Transport with an Interactive Abscisic Acid-Mediated Manner in Mature Leaves of Oilseed rape (Brassica napus L.).

The leaf senescence process is characterized by the degradation of macromolecules in mature leaves and the remobilization of degradation products via phloem transport. The phytohormone ethylene mediates leaf senescence. This study aimed to investigate the ethephon-induced ethylene effects on starch degradation and sucrose remobilization through their interactive regulation with other hormones. Ethephon (2-chloroethylphosphonic acid) was used as an ethylene-generating agent. Endogenous hormonal status, carbohydrate compounds, starch degradation-related gene expression, sucrose transporter gene expression, and phloem sucrose loading were compared between the ethephon-treated plants and controls. Foliar ethephon spray enhanced the endogenous ethylene concentration and accelerated leaf senescence, as evidenced by reduced chlorophyll content and enhanced expression of the senescence-related gene SAG12. Ethephon-enhanced ethylene prominently enhanced the endogenous abscisic acid (ABA) level. accompanied with upregulation of ABA synthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED3), ABA receptor gene pyrabactin resistance 1 (PYR1), and ABA signaling genes sucrose non-fermenting 1 (Snf1)-related protein kinase 2 (SnRK2), ABA-responsive element binding 2 (AREB2), and basic-helix-loop-helix (bHLH) transcription factor (MYC2).) Ethephon treatment decreased starch content by enhancing expression of the starch degradation-related genes α-amylase 3 (AMY3) and β-amylase 1 (BAM1), resulting in an increase in sucrose content in phloem exudates with enhanced expression of sucrose transporters, SUT1, SUT4, and SWEET11. These results suggest that a synergistic interaction between ethylene and ABA might account for sucrose accumulation, mainly due to starch degradation in mature leaves and sucrose phloem loading in the ethephon-induced senescent leaves.

Salicylic acid differently impacts ethylene and polyamine synthesis in the glycophyte Solanum lycopersicum and the wild-related halophyte Solanum chilense exposed to mild salt stress.

This study aimed to determine the effects of exogenous application of salicylic acid (SA) on the toxic effects of salt in relation to ethylene and polyamine synthesis, and to correlate these traits with the expression of genes involved in ethylene and polyamine metabolism in two tomato species differing in their sensitivity to salt stress, Solanum lycopersicum cv Ailsa Craig and its wild salt-resistant relative Solanum chilense. In S. chilense, treatment with 125 mM NaCl improved plant growth, increased production of ethylene, endogenous salicylic acid and spermine. The production was related to a modification of expression of genes involved in ethylene and polyamine metabolism. In contrast, salinity decreased plant growth in S. lycopersicum without affecting endogenous ethylene, salicylic or polyamine concentrations. Exogenous application of salicylic acid at 0.01 mM enhanced shoot growth in both species and affected ethylene and polyamine production in S. chilense. Concomitant application of NaCl and salicylic acid improved osmotic adjustment, thus suggesting that salt and SA may act in synergy on osmolyte synthesis. However, the beneficial impact of exogenous application of salicylic acid was mitigated by salt stress since NaCl impaired endogenous SA accumulation in the shoot and salicylic acid did not improve plant growth in salt-treated plants. Our results thus revealed that both species respond differently to salinity and that salicylic acid, ethylene and polyamine metabolisms are involved in salt resistance in S. chilense.

Transgenic analysis reveals LeACS-1 as a positive regulator of ethylene-induced shikonin biosynthesis in Lithospermum erythrorhizon hairy roots.

The phytohormone ethylene (ET) is a crucial signaling molecule that induces the biosynthesis of shikonin and its derivatives in Lithospermum erythrorhizon shoot cultures. However, the molecular mechanism and the positive regulators involved in this physiological process are largely unknown. In this study, the function of LeACS-1, a key gene encoding the 1-aminocyclopropane-1-carboxylic acid synthase for ET biosynthesis in L. erythrorhizon hairy roots, was characterized by using overexpression and RNA interference (RNAi) strategies. The results showed that overexpression of LeACS-1 significantly increased endogenous ET concentration and shikonin production, consistent with the up-regulated genes involved in ET biosynthesis and transduction, as well as the genes related to shikonin biosynthesis. Conversely, RNAi of LeACS-1 effectively decreased endogenous ET concentration and shikonin production and down-regulated the expression level of above genes. Correlation analysis showed a significant positive linear relationship between ET concentration and shikonin production. All these results suggest that LeACS-1 acts as a positive regulator of ethylene-induced shikonin biosynthesis in L. erythrorhizon hairy roots. Our work not only gives new insights into the understanding of the relationship between ET and shikonin biosynthesis, but also provides an efficient genetic engineering target gene for secondary metabolite production in non-model plant L. erythrorhizon.

MODELLING BIOLOGICAL VARIATION IN THE SKIN BACKGROUND COLOUR OF 'JONAGOLD' APPLES DURING CONTROLLED ATMOSPHERE STORAGE

Skin background colour is a very important quality aspect in the grading of ‘Jonagold’ apples, with consumers usually preferring fruit with a green background colour. However, apple handlers are usually faced with large fruit-to-fruit variability of background colour within a population of fruit. In this study, a stochastic modelling approach is used to describe how the initial fruit-to-fruit variability in the background colour of ‘Jonagold’ apples present at harvest, propagates throughout the postharvest chain. Two hundred fruit were harvested and stored at 1 or 4°C, under different controlled atmosphere (CA) conditions for six months. The fruit were taken out of storage every two months, and the background colour and the ethylene production of individual fruit were measured. At the end of the six months storage, the fruit were placed in shelf life conditions for 15 days, during which skin background colour and ethylene production were measured every five days. A mathematical model was developed to describe the postharvest loss of the skin greenness of apples during CA storage, by assuming that the loss is principally due to chlorophyll breakdown, the rate of which is dependent on the endogenous ethylene concentration within the fruit. The stochastic model parameters in the model were identified, and by treating these parameters as fruitspecific parameters, the model could describe more than 93% of the data for the individual fruit. By considering these fruit-specific parameters as stochastic parameters, the Monte Carlo method was used to describe the propagation of the fruit-to-fruit variability of the background colour of ‘Jonagold’ apples within a population. The model developed in this study can be used to predict how the initial fruit-to-fruit variability within a batch of apple will propagate throughout the postharvest chain.

Managing biological variation in skin background colour along the postharvest chain of ‘Jonagold’ apples

Skin background colour is an important quality aspect in the grading of ‘Jonagold’ apples, with consumers usually preferring fruit with a green background colour. However, apple handlers are usually faced with large fruit-to-fruit variability of background colour within a population of fruit. In this study, a stochastic modelling approach was used to describe how the initial fruit-to-fruit variability in the background colour of ‘Jonagold’ apples present at harvest, propagates throughout the postharvest chain. Two hundred and twenty ‘Jonagold’ apple fruit were harvested and stored at 1°C or 4°C, under different controlled atmosphere (CA) conditions for 6 months, followed by 2 weeks exposure to shelf-life conditions, during which the background colour and ethylene production of the individual fruit were measured. A kinetic model was developed to describe the postharvest loss of skin greenness, by assuming that the loss was principally due to chlorophyll breakdown, the rate of which was dependent on the endogenous ethylene concentration. Stochastic model parameters were identified, and by treating these parameters as fruit-specific, the model could account for more than 95% of the variability of the data. By treating the stochastic model parameters as random factors, the Monte Carlo method was used to model and describe the propagation of the fruit-to-fruit variability of the background colour within a population of fruit. The model developed in this study might allow better management of variability in quality along the postharvest chain, by predicting how the initial fruit-to-fruit variability within a batch of apples will propagate throughout the postharvest chain, as a function of storage and shelf-life conditions.

Effect of low temperatures on pulp browning and endogenous abscisic acid and ethylene concentrations in peach (Prunus persica L.) fruit during post-harvest storage

SummaryChanges in the severity of pulp browning, endogenous abscisic acid (ABA) and ethylene concentrations, and related gene expression in peach (Prunus persica L. ‘Bayuecui’) fruit stored at the biological freezing-point temperature (BFT; 1ºC), at 4ºC, or at room temperature (20ºC; as a control) were investigated.The results showed that fruit stored at room temperature showed climacteric changes in ethylene and ABA concentrations and in levels of expression of the corresponding ethylene synthetase genes (PpACS1, PpACO1) and the gene for a key enzyme of ABA synthesis (PpNCED), concomitant with a significant decrease in fruit firmness and an increase in juice yield. Meanwhile, two sucrose synthase genes (PpSUS1 and PpSUS2) were expressed at relatively low levels. However, fruit firmness decreased slightly and chilling injury (CI) increased significantly 40 d after storage (DAS) at 4ºC, with a significant accumulation of proline [from 8.33 µg g–1 (at t = 0 d) to 9.125 µg g–1 (at t = 40 d)]. In contrast, fruit firmness decreased slowly and pulp browning increased slightly 80 DAS at the BFT ( 1ºC), with a lower accumulation of proline than in fruit stored at 4ºC. The concentrations of soluble sugars and titratable acidity decreased during storage at 1ºC, 4ºC, or 20ºC, but there was a peak of soluble sugars at a late stage of storage at the BFT ( 1ºC). The fruit browning index was significantly and positively correlated (R 2 = 0.967) with ABA concentration. The decrease in ABA concentration in cold-stored fruit (at both 1ºC and 4ºC) inhibited ethylene production. Moreover, there was no significant correlation between CI in fruit and ethylene production. In conclusion, the decrease in ABA concentration reduced ethylene concentrations and inhibited the development of pulp browning, which resulted in an improved taste, but crisper fruit, when fruit were stored at the BFT (–1ºC).

Towards flexible management of postharvest variation in fruit firmness of three apple cultivars

Stochastic modeling provides a useful tool in managing biological variation in the postharvest chain. In the current study, the fruit-to-fruit variability in the postharvest firmness of apples was modeled. Apples from three cultivars (‘Jonagold’, ‘Braeburn’, and ‘Kanzi’) were harvested at different levels of maturity, and stored at different temperatures and controlled atmosphere (CA) conditions. By using a kinetic model describing firmness breakdown as a function of time, temperature, controlled atmosphere conditions and endogenous ethylene concentration, the main stochastic variables were identified as the initial firmness and the rate constants for firmness breakdown and ethylene production. Treating these variables as random model parameters, the Monte Carlo method was used to simulate the propagation of the fruit-to-fruit variability in flesh firmness within a batch of apples during storage under different CA conditions and subsequent shelf-life exposure. The model was validated using independent data sets from apples picked in a different season. The model developed in this study can be used to predict the probability of having apples of certain firmness after long term storage for different scenarios of temperatures and CA conditions.

PTR-ToF-MS, A Novel, Rapid, High Sensitivity and Non-Invasive Tool to Monitor Volatile Compound Release During Fruit Post-Harvest Storage: The Case Study of Apple Ripening

In the present study, the potential of PTR-ToF-MS for addressing fundamental and technical post-harvest issues was tested on the non-destructive and rapid monitoring of volatile compound evolution in three apple cultivars (‘Golden Delicious’, ‘Braeburn’ and ‘Gold Rush’) during 25 days of post-harvest shelf life ripening. There were more than 800 peaks in the PTR-ToF-MS spectra of apple headspace and many of them were associated with relevant compounds. Besides the ion produced upon proton transfer, we used the ion at mass 28.031 (C2H 4 + ) produced by charge transfer from residual O 2 + as a monitor for ethylene concentration. ‘Golden Delicious’ apples were characterised by higher ethylene emission rates than ‘Gold Rush’ and ‘Braeburn’, and quantitative comparison has been supported by two segment piecewise linear model fitting. Ester evolution during post-harvest ripening is strongly dependent on endogenous ethylene concentration levels. For ‘Golden Delicious’ and ‘Braeburn’, sesquiterpenes (alpha-farnesene) exhibited a fast response to ethylene emission followed by a rapid decline after the endogenous ethylene maximum peak. Carbonyl compounds displayed a different time evolution as compared to esters and terpenes and did not show any evident relationship with ethylene. Methanol and ethanol concentrations during the entire storage period did not change significantly. We show how multivariate analysis can efficiently handle the large datasets produced by PTR-ToF-MS and that the outcomes obtained are in agreement with the literature. The different volatile compounds could be simultaneously monitored with high time resolution, providing advantages over the more established techniques for the investigation of VOC dynamics in fruit post-harvest storage trials.

Effects of antagonists and inhibitors of ethylene biosynthesis on maize root elongation

During the first days of development, maize roots showed considerable variation in the production of ethylene and the rate of elongation. As endogenous ethylene increases, root elongation decreases. When these roots are treated with the precursor of ethylene aminocyclopropane-1-carboxylic acid (ACC), or inhibitors of ethylene biosynthesis 2-aminoethoxyvinyl glycine (AVG) or cobalt ions, the root elongation is also inhibited. Because of root growth diminishes at high or reduced endogenous ethylene concentrations, it appears that this phytohormone must be maintained in a range of concentrations to support normal root growth. In spite of its known role as inhibitor of ethylene action, silver thiosulphate (STS) does not change significantly the root elongation rate. This suggests that the action of ethylene on root elongation should occur, at least partially, by interaction with other growth regulators.

Endogenous Ethylene and Color Development in the Skin of ‘Pink Lady’ Apple

To elucidate the temporal relationship between endogenous ethylene and color development, changes in ethylene concentration, fruit color, pigments, and flavonoids were monitored at different intervals during the development and ripening of ‘Pink Lady’ apple (Malus × domestica Borkh.), commencing from 60 days after full bloom (DAFB) in 2002 to 2003, and 7 DAFB in the 2003 to 2004 season. Concentrations of chlorogenic acid, phloridzin, catechin, epicatechin, and quercetin glycosides were significantly higher (P ≤ 0.05) during the early stages (7−60 DAFB) compared with the later stages (≥60 DAFB) of fruit growth. During fruit development, concentrations of phloridzin, catechin, epicatechin, and quercetin glycosides decreased to low and stable levels. However, the concentration of anthocyanin (cyanidin 3-galactoside) increased during maturation and ripening (≥168 DAFB), coinciding with a corresponding increase in percent red blush and endogenous ethylene concentration. Positive and significant correlations were found between ethylene and color development and between ethylene and total anthocyanin, but not the other flavonoid compounds. Ethylene therefore appears to be a key factor regulating anthocyanin biosynthesis and color development in ‘Pink Lady’ apple. However, the accumulation of other classes of flavonoids such as catechin, epicatechin, phloridzin, chlorogenic acid, and quercetin glycosides seems to be regulated independently of ethylene during fruit development and ripening.

Effects of ethylene and abscisic acid upon heterophylly in Ludwigia arcuata (Onagraceae).

In this study, we examined the effects of ethylene and abscisic acid (ABA) upon heterophyllous leaf formation of Ludwigia arcuata Walt. Treatment with ethylene gas resulted in the formation of submerged-type leaves on terrestrial shoots of L. arcuata, while treatments with ABA induced the formation of terrestrial-type leaves on submerged shoots. Measurement of the endogenous ethylene concentration of submerged shoots showed that it was higher than that of terrestrial ones. In contrast, the endogenous ABA concentration of terrestrial shoots was higher than that of submerged ones. To clarify interactions of ethylene and ABA, simultaneous additions of these two plant hormones were examined. When L. arcuata plants were treated with these two plant hormones, the effects of ABA dominated that of ethylene, resulting in the formation of terrestrial-type leaves. This suggests that ABA may be located downstream of ethylene in signal transduction chains for forming heterophyllous changes. Further, ethylene treatment induced the reduction of endogenous levels of ABA in tissues of L. arcuata, resulting in the formation of submerged-type leaves. Thus the effects of ethylene and ABA upon heterophyllous leaf formation are discussed in relationship to the cross-talk between signaling pathways of ethylene and ABA.

Fruitlet abscission of mango in relation to ethylene

SummaryThe role of ethylene in mango (Mangifera indica L.) fruitlet abscission was investigated by determining endogenous ethylene concentrations in intact and about-to-abscise fruitlets and their pedicels, and the effects of exogenous applications of ethephon and inhibitors of ethylene biosynthesis. About-to-abscise fruitlets and pedicels at pinhead, pea and marble stages had higher endogenous ethylene production than intact tissues in ‘Kensington Pride’ and ‘Glen’ (191% and 66% more ethylene in ‘Kensington Pride’ in 2001, 53.5% and 101% in ‘Glen’ in 2000, and 135% and 93% in 2001). Exogenous application of ethephon at fruit set, accelerated fruitlet abscission compared with control. Fruitlet abscission was increased with increased rates of ethephon applied during 1999 and 2000. Exogenous spray of ethylene inhibitors at pre-anthesis stage increased fruitlet retention. Spray of STS or CoSO4 (200.mg l–1) resulted in the highest fruitlet retention (7.7 and 7.6 fruit per panicle) compared with control (4.9 fruit per panicle). These results suggested that ethylene is involved in mango fruitlet abscission.

Ethylene emission and responsiveness to applied ethylene vary among Poa species that inherently differ in leaf elongation rates.

A plant's ability to produce and respond to ethylene is essential for its vegetative growth. We studied whole-shoot ethylene emission and leaf growth responses to applied ethylene in four Poa spp. that differ inherently in leaf elongation rate and whole-plant relative growth rate. Compared with the fast-growing Poa annua and Poa trivialis, the shoots of the slow-growing species Poa alpina and Poa compressa emitted daily 30% to 50% less ethylene, and their leaf elongation rate was more strongly inhibited when ethylene concentration was increased up to 1 microL L(-1). To our surprise, however, low ethylene concentrations (0.02-0.03 microL L(-1)) promoted leaf growth in the two slow-growing species; at the same concentrations, leaf elongation rate of the two fast-growing species was only slightly inhibited. All responses were observed within 20 min after ethylene applications. Although ethylene generally inhibits growth, our results show that in some species, it may actually stimulate growth. Moreover, in the two slow-growing Poa spp., both growth stimulation and inhibition occurred in a narrow ethylene concentration range, and this effect was associated with a much lower ethylene emission. These findings suggest that the regulation of ethylene production rates and perception of the gas may be more crucial during leaf expansion of these species under non-stressful conditions and that endogenous ethylene concentrations are not large enough to saturate leaf growth responses. In the two fast-growing species, a comparatively higher ethylene endogenous concentration may conversely be present and sufficiently high to saturate leaf elongation responses, invariably leading to growth inhibition.

Effects of herbivory on internal ethylene production and sex expression in Cucurbita texana

Abstract1. Field‐grown Cucurbita texana was used in a study to determine if stress ethylene from damaged leaves promotes changes in sex expression.2. Internal ethylene concentrations were experimentally enhanced by inserting an ethylene‐filled syringe into the hollow chamber of an internode seven nodes from the growing tip of a branch. Branches enhanced with ethylene produced significantly more pistillate buds than control branches and experienced greater bud abortion later in floral development.3. The timing and magnitude of Diabrotica beetle leaf damage was simulated using a paper‐hole puncher (15% removed from all leaves). Simulated herbivory was applied to new growth every 3 days throughout the growing season.4. Endogenous ethylene concentrations recovered from the internode adjacent to the growing tip were significantly greater in damaged plants than undamaged plants 1 day after damage to new growth during the second and third week of the experiment, and 2 days after damage during the fourth and fifth week. By the sixth week, no significant differences were evident.5. Damaged plants produced fewer pistillate buds than undamaged plants, indicating that stress ethylene from simulated herbivory does not induce femaleness. A second messenger that suppresses pistillate bud production may be produced during damage.

FRUIT CANOPY POSITION EFFECTS ON QUALITY AND STORAGE RESPONSE OF 'TAROCCO' ORANGES

Quality characteristics of mature 'Tarocco' oranges harvested from the northern, southern and interior part of tree canopy was investigated over 10 weeks of storage at 9°C plus 1 week of simulated marketing period at 21°C. No significant differences in fruit mass loss and decay percentage were observed after 5 or 10 weeks of cold storage. After simulated marketing period (SMP) mass loss was significantly higher in fruit from northern part of tree canopy. Differences in mass loss between fruit from interior and southern parts were insignificant. Decay percentage was significantly lower in southern fruit with minimal differences between northern and interior fruit. h * colour values were significantly higher in fruit from interior canopy. After SMP differences in h * colour were insignificant. Fruit canopy position did not affect endogenous ethylene concentration. At harvest and after 10 weeks of cold storage respiration rate was higher in northern fruit, lower in southern fruit and intermediate in fruit from the interior part of canopy. After SMP differences in respiration rates were not significant. Freshly harvested fruit from the external southern side of the tree had higher soluble solids concentration (SSC) and lower acid levels, resulting in higher SSC: acid ratio and improved taste in comparison to fruit from northern and interior parts of canopy. By the end of SMP these differences tended to level out. At harvest ethanol level in the juice was significantly higher in fruit from southern part of canopy. By the end of cold storage and after SMP a sharp increase in ethanol concentration was detected in all samples, with no significant differences in relation to canopy position. SMP resulted in off-flavour development, presumably due to the high levels of ethanol in the juice.

A Model For the Lowering of Plant Ethylene Concentrations by Plant Growth-promoting Bacteria

It was previously shown that a number of plant growth promoting rhizobacteria contain an enzyme, 1-aminocyclopropane-1-carboxylate deaminase, that catalyses the cleavage of 1-aminocyclopropane-1-carboxylate, the immediate precursor of ethylene in plants. Moreover, experimental evidence indicated that the activity of this enzyme was the key factor in the ability of plant growth promoting rhizobacteria to stimulate the elongation of plant roots. In the model presented in this manuscript we address the question of how the bacterial enzyme 1-aminocyclopropane-1-carboxylate deaminase, with a low affinity for 1-aminocyclopropane-1-carboxylate, can effectively compete with the plant enzyme 1-aminocyclopropane-1-carboxylate oxidase, which has a high affinity for the same substrate, 1-aminocyclopropane-1-carboxylate, with the result that the plant's endogenous ethylene concentration is reduced. It is argued that the simplest explanation for the observed biological activity of plant growth promoting rhizobacteria relates to the relative amounts of 1-aminocyclopropane-1-carboxylate deaminase and 1-aminocyclopropane-1-carboxylate oxidase in the system under consideration. For plant growth promoting rhizobacteria to be able to lower plant ethylene levels, the 1-aminocyclopropane-1-carboxylate deaminase level should be at least 100- to 1000-fold greater then the 1-aminocyclopropane-1-carboxylate oxidase level. This is likely to be the case, provided that the expression of 1-aminocyclopropane-1-carboxylate oxidase has not been induced.

The role of endogenous ethylene in the expansion of Helianthus annuus leaves.

The possible role of ethylene in leaf expansion of the primary leaves of sunflower plants (Helianthus annuus) was studied. Our lowest application of ethephon promoted expansion of primary leaves. Higher concentrations of ethephon, and a range of concentrations of 1-aminocyclopropane-1-carboxylic acid, increased endogenous ethylene concentration and caused a reduction in the area of the primary leaves. The inhibition in leaf expansion induced by ethephon and 1-aminocyclopropane-1-carboxylic acid was reversed by pretreating the plants with an inhibitor of ethylene action, namely silver thiosulphate. Treating leaves with lower concentrations of aminoethoxyvinylglycine reduced ethylene production and stimulated leaf expansion. This effect of aminoethoxyvinylglycine could be nullified by pretreating the plants with 1-aminocyclopropane-1-carboxylic acid. Treatment with silver thiosulphate enhanced leaf expansion. This indicates that endogenous ethylene normally plays a significant role in leaf expansion. Flooded and gravistimulated plants produced more ethylene and had smaller leaves. This could suggest that the increased ethylene is the main cause of the slowed leaf growth, however, only in some cases were we able to partially reverse the effect of flooding with silver thiosulphate. This indicates that there are probably many factors, in addition to increased ethylene, that inhibit leaf expansion in flooded and gravistimulated plants.

Laser-driven Photoacoustic Spectroscopy: What We Can Do with it in Flooding Research

flow-through systems that avoid the need for enclosing excised plant parts in small volumes for head-space analysis. In this way, artifacts introduced by various accumulation techniques can be avoided and ethylene production monitored at short intervals in air or other gas mixtures as it flows out of a cuvette enclosing all or part of an intact plant. The principles of this technique are described. Three case studies demonstrate the application of photoacoustic spectroscopy in flooding research. These studies concentrate on accurate measurement of endogenous ethylene concentrations in submerged shoots and roots, root ethylene production under subambient oxygen pressures and the simultaneous measurement of ethylene production and leaf growth. In addition, the qualitative and quantitive methods previously used to measure the gaseous plant hormone ethylene are briefly reviewed. Finally, the future prospects of photoacoustic spectroscopy in flooding research are discussed. © 1997 Annals of Botany Company

An Ethylene-Mediated Increase in Sensitivity to Auxin Induces Adventitious Root Formation in Flooded Rumex palustris Sm.

The hormonal regulation of adventitious root formation induced by flooding of the root system was investigated in the wetland species Rumex palustris Sm. Adventitious root development at the base of the shoot is an important adaptation to flooded conditions and takes place soon after the onset of flooding. Decreases in either endogenous auxin or ethylene concentrations induced by application of inhibitors of either auxin transport or ethylene biosynthesis reduced the number of adventitious roots formed by flooded plants, suggesting an involvement of these hormones in the rooting process. The rooting response during flooding was preceded by increased endogenous ethylene concentrations in the root system. The endogenous auxin concentration did not change during flooding-induced rooting, but a continuous basipetal transport of auxin from the shoot to the rooting zone appeared to be essential in maintaining stable auxin concentrations. These results suggest that the higher ethylene concentration in soil-flooded plants increases the sensitivity of the root-forming tissues to endogenous indoleacetic acid, thus initiating the formation of adventitious roots.