Increased Ethylene Levels Research Articles

Increasing SnRK1 activity with the AMPK activator A-769662 accelerates seed germination in rice

Sucrose non-fermenting-1-related protein kinase 1 (SnRK1) plays a key role in rice germination. The small molecule drug, A-769662, activates AMP-activated protein kinase, a mammalian homolog of SnRK1. However, it is unknown whether A-769662 activates SnRK1, thereby affecting germination. SnRK1 in desalted extracts from germinating rice seeds was strongly activated by adding A-769662 in vitro. Applying 50 or 100 μM A-769662 accelerated germination and increased the root length, shoot length, and seedling fresh weight. 50 μM A-769662 treatment increased the catalytic activity and phosphorylation of SnRK1 during germination. Transcriptome analysis and biochemical validation were performed to investigate the mechanism whereby A-769662 treatment promoted rice germination. A-769662 treatment promoted starch hydrolysis by increasing the expression and activity of amylase and inhibited starch biosynthesis by decreasing the expression of OsAGPL2, OsAGPS2a, Wx, and SSIIa. The abscisic acid (ABA) level and gene expression of ABA-induced transcription factors, including OsNF-YC9, OsNF-YC12, OsWRKY24, OsPYL8, OsMKKK62, and OsMKKK63, which reduced the inhibition of germination by ABA were decreased under 50 μM A-769662 treatment. The increased expression of the OsACO3 and OsACO5 genes and increased ethylene levels under A-769662 treatment, which counteracted the inhibition of ABA on germination and, thus, promoted germination. These results demonstrate the activation of A-769662 on SnRK1 and further reveal the regulatory mechanism of A-769662 in rice seed germination and nutrient remobilization.

Balancing of hormonal biosynthesis and catabolism pathways, a strategy to ameliorate the negative effects of heat stress on reproductive growth.

In pea (Pisum sativum L.), moderate heat stress during early flowering/fruit set increased seed/ovule abortion, and concomitantly produced fruits with reduced ovary (pericarp) length, and fewer seeds at maturity. Plant hormonal networks coordinate seed and pericarp growth and development. To determine if these hormonal networks are modulated in response to heat stress, we analyzed the gene expression patterns and associated these patterns with precursors, and bioactive and inactive metabolites of the auxin, gibberellin (GA), abscisic acid (ABA), and ethylene biosynthesis/catabolism pathways in young developing seeds and pericarps of non-stressed and 4-day heat-stressed fruits. Our data suggest that within the developing seeds heat stress decreased bioactive GA levels reducing GA growth-related processes, and that increased ethylene levels may have promoted this inhibitory response. In contrast, heat stress increased auxin biosynthesis gene expression and auxin levels in the seeds and pericarps, and seed ABA levels, both effects can increase seed sink strength. We hypothesize that seeds with higher auxin- and ABA-induced sink strength and adequate bioactive GA levels will set and continue to grow, while the seeds with lower sink strength (low auxin, ABA, and GA levels) will become more sensitive to heat stress-induced ethylene leading to ovule/seed abortion.

Early histological, hormonal, and molecular changes during pineapple (Ananas comosus (L.) Merrill) artificial flowering induction

Natural flowering can cause serious scheduling problems in the pineapple (Ananas comosus) industry and increase harvest costs. Pineapple flowering is thought to be triggered by increased ethylene levels and artificial forcing of pineapple flowering is a common practice to promote flowering synchronisation. However, little is known about the early hormonal and molecular changes of pineapple flowering induction and development. Here, we aimed to analyse the molecular, hormonal, and histological changes during artificial pineapple flowering by Ethrel®48 treatment. Histological analyses of the shoot apical meristem, leaf gibberellic acid (GA3), and ethylene quantification were carried out during the first 72h after Ethrel®48 treatment. Expression profiles from ethylene biosynthesis (AcACS2 and AcACO1), gibberellin metabolism (AcGA2-ox1 and AcDELLA1), and flower development (FT-like gene (AcFT), LFY-like gene (AcLFY), and a PISTILLATA-like gene (AcPI)) genes were analysed during the first 24h after Ethrel®48 treatment. Differentiation processes of the shoot apical meristem into flower buds were already present in the first 72h after Ethrel®48 treatment. Ethrel®48 lead to a reduction in GA3 levels, probably triggered by elevated ethylene levels and the positive regulation AcGA2-ox1. AcLFY activation upon Ethrel®48 may also have contributed to the reduction of GA3 levels and, along with the up-regulation of AcPI, are probably associated with the flower induction activation. AcFT and AcDELLA1 do not seem to be regulated by GA3 and ethylene. Decreased GA3 and increased ethylene levels suggest an accumulation of AcDELLA1, which may display an important role in pineapple flowering induction. Thus, this study shows that molecular, hormonal, and histological changes are present right after Ethrel®48 treatment, providing new insights into how pineapple flowering occurs under natural conditions.

Ethylene is not involved in adaptive responses to flooding in the Amazonian wild rice species Oryza grandiglumis

The Amazonian wild rice Oryza grandiglumis has two contrasting adaptation mechanisms to flooding submergence: a quiescence response to complete submergence at the seedling stage and an escape response based on internodal elongation to partial submergence at the mature stage. We investigated possible factors that trigger these responses. In stem segments excised from mature O. grandiglumis plants, complete submergence only slightly promoted internodal elongation with increased ethylene levels in the internodes, while partial submergence substantially promoted internodal elongation without increased ethylene levels in the internodes. Incubation of non-submerged stem segments under a continuous flow of humidified ethylene-free air promoted internodal elongation to the same extent as that observed for partially submerged segments. Applied ethylene had little effect on the internodal elongation of non-submerged segments irrespective of humidity conditions. These results indicate that the enhanced internodal elongation of submerged O. grandiglumis plants is not triggered by ethylene accumulated during submergence but by the moist surroundings provided by submergence. The growth of shoots in O. grandiglumis seedlings was not promoted by ethylene or complete submergence, as is the case in O. sativa cultivars possessing the submergence-tolerant gene SUB1A. However, because the genome of O. grandiglumis lacks the SUB1A gene, the quiescence response of O. grandiglumis seedlings to complete submergence may be regulated by a mechanism distinct from that involved in the response of submergence-tolerant O. sativa cultivars.

Cadmium-induced ethylene production and responses in Arabidopsis thaliana rely on ACS2 and ACS6 gene expression.

BackgroundAnthropogenic activities cause metal pollution worldwide. Plants can absorb and accumulate these metals through their root system, inducing stress as a result of excess metal concentrations inside the plant. Ethylene is a regulator of multiple plant processes, and is affected by many biotic and abiotic stresses. Increased ethylene levels have been observed after exposure to excess metals but it remains unclear how the increased ethylene levels are achieved at the molecular level. In this study, the effects of cadmium (Cd) exposure on the production of ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid (ACC), and on the expression of the ACC Synthase (ACS) and ACC Oxidase (ACO) multigene families were investigated in Arabidopsis thaliana.ResultsIncreased ethylene release after Cd exposure was directly measurable in a system using rockwool-cultivated plants; enhanced levels of the ethylene precursor ACC together with higher mRNA levels of ethylene responsive genes: ACO2, ETR2 and ERF1 also indicated increased ethylene production in hydroponic culture. Regarding underlying mechanisms, it was found that the transcript levels of ACO2 and ACO4, the most abundantly expressed members of the ACO multigene family, were increased upon Cd exposure. ACC synthesis is the rate-limiting step in ethylene biosynthesis, and transcript levels of both ACS2 and ACS6 showed the highest increase and became the most abundant isoforms after Cd exposure, suggesting their importance in the Cd-induced increase of ethylene production.ConclusionsCadmium induced the biosynthesis of ACC and ethylene in Arabidopsis thaliana plants mainly via the increased expression of ACS2 and ACS6. This was confirmed in the acs2-1acs6-1 double knockout mutants, which showed a decreased ethylene production, positively affecting leaf biomass and resulting in a delayed induction of ethylene responsive gene expressions without significant differences in Cd contents between wild-type and mutant plants.

“Rock-Ad”, a new wild rocket (Diplotaxis tenuifolia) mutant with late flowering and delayed postharvest senescence

Wild rocket (Diplotaxis tenuifolia) is a leafy herb in salads and cooked dishes originating in the Mediterranean basin. The leaves contain many nutrients, plus beneficial phytochemicals such as flavonoids and glucosinolates. Rocket suffers from two major limitations: early bolting during growth and leaf yellowing after harvest, both of which affect both yield and market quality. We have used ethyl methanesulfonate (EMS) to induce mutation in wild rocket, and selected a mutant line (registered as cv. “Rock-Ad”), which has a two week delay in flowering time compared to current commercial cultivars. “Rock-Ad” plants began to flower when more than 50% of commercial plants had flowered. Storage properties of the mutant were also better than the commercial cultivar. In storage, after simulation of shipment by sea, there was no yellowing in young “Rock-Ad” leaves, chlorophyll levels were higher, fewer flower buds developed, and hydrophilic antioxidant levels decreased less than the commercial cultivar. Holding leaves in 5kPa CO2 in air decreased yellowing and decay significantly in both cultivars compared to air storage, while exposure to 2.23μmolL−1 ethylene increased yellowing and decay. When ethylene and CO2 were applied together (5kPa and 2.23μmolL−1, respectively), yellowing and decay decreased in both cultivars compared to air storage. 1-MCP treatment reduced yellowing and decay in leaves of the commercial variety, but had no effect on leaves of “Rock-Ad”. The respiration rate of the leaves increased after 7 days of storage in both cultivars, but was significantly higher in leaves of the commercial cultivar, and 1-MCP significantly moderated this increased respiration. Although treatment with 1-MCP led to increased ethylene levels on the first day after harvest, during storage, ethylene levels decreased in all treatments and cultivars.

The F-Box Protein OsFBK12 Targets OsSAMS1 for Degradation and Affects Pleiotropic Phenotypes, Including Leaf Senescence, in Rice

Leaf senescence is related to the grain-filling rate and grain weight in cereals. Many components involved in senescence regulation at either the genetic or physiological level are known. However, less is known about molecular regulation mechanisms. Here, we report that OsFBK12 (an F-box protein containing a Kelch repeat motif) interacts with S-ADENOSYL-l-METHIONINE SYNTHETASE1 (SAMS1) to regulate leaf senescence and seed size as well as grain number in rice (Oryza sativa). Yeast two-hybrid, pull-down, and bimolecular fluorescence complementation assays indicate that OsFBK12 interacts with Oryza sativa S-PHASE KINASE-ASSOCIATED PROTEIN1-LIKE PROTEIN and with OsSAMS1. Biochemical and physiological data showed that OsFBK12 targets OsSAMS1 for degradation. OsFBK12-RNA interference lines and OsSAMS1 overexpression lines showed increased ethylene levels, while OsFBK12-OX lines and OsSAMS1-RNA interference plants exhibited decreased ethylene. Phenotypically, overexpression of OsFBK12 led to a delay in leaf senescence and germination and increased seed size, whereas knockdown lines of either OsFBK12 or OsSAMS1 promoted the senescence program. Our results suggest that OsFBK12 is involved in the 26S proteasome pathway by interacting with Oryza sativa S-PHASE KINASE-ASSOCIATED PROTEIN1-LIKE PROTEIN and that it targets the substrate OsSAMS1 for degradation, triggering changes in ethylene levels for the regulation of leaf senescence and grain size. These data have potential applications in the molecular breeding of rice.

Suppression of ethylene levels promotes morphogenesis in pepper (Capsicum annuum L.)

Ethylene and polyamines (PAs) are two phytohormones that play important roles during in vitro morphogenesis of several plant species. The interaction between ethylene and PAs has been of interest because both have S-adenosylmethionine as a precursor. To study the influence of ethylene and PAs on in vitro morphogenesis of an ornamental pepper, we added an ethylene scavenger, PAs, a PA inhibitor, and compounds that affect ethylene biosynthesis and activity to the regeneration medium. Regeneration frequencies increased in response to treatment with ethylene inhibitors (aminoethoxyvinylglycine and silver thiosulfate) and an ethylene scavenger (mercury perchlorate). Treatment with the ethylene precursor 1-aminocyclopropane-1-carboxylic acid reduced the regeneration frequency, increased callus formation, and increased ethylene levels; similar results were obtained in response to treatment with the PA inhibitor methylglyoxal-bis(guanylhydrazone). By contrast, treatment with PAs (particularly spermidine and spermine) decreased ethylene levels, increased the regeneration frequency, and increased shoot bud formation. These results suggest a coordinated regulation of ethylene and polyamines because the suppression of ethylene levels using ethylene inhibitors, polyamines, or mercury perchlorate increased the in vitro regeneration frequency and morphogenic responses of Capsicum annuum L.

Factors contributing to the regulation of thermoinhibition in Tagetes minuta L.

Thermoinhibition in Tagetes minuta achenes is tightly and rapidly regulated with regard to its imposition and release, with both processes occurring within 2-3h. Germination at high temperatures is almost exclusively regulated by the embryo, while the pericarp appears to play only a minor role. Thermoinhibition in T. minuta could not be alleviated by any single plant growth regulator application, but a combination of treatments that both reduced ABA levels and increased ethylene levels were able to restore germination at supraoptimal temperatures. This suggests a role for both ethylene and ABA in the imposition of thermoinhibition in this species.

Headspace ethylene accumulation effects on secondary metabolite production in Vaccinium pahalae cell culture

The influence of headspace ethylene on anthocyanin, anthocyanidin, and carotenoid accumulation was studied in suspension cultures of Vaccinium pahalae. Exogenous application of ethrel (an ethylene-releasing compound) significantly reduced growth and secondary metabolite production, whereas incorporation of 5.0 or 10.0 mg l-1 CoCl2 or NiCl2 effectively reduced ethylene accumulation and improved product accumulation, but AgNO3was toxic to cells. This study showed an overall negative impact of increased ethylene levels in the vessel headspace on phytochemical production in ohelo cell cultures.

Cytokinin effects on root growth and possible interactions with ethylene and indole‐3‐acetic acid

Etiolated pea seedlings (Pisum sativum L. cv. Weibull's Marma) were used to investigate the effects of exogenous cytokinins on root growth. Benzylaminopurine (BAP) added to the growth solution inhibited the elongation and formation of lateral roots and stimulated swelling of the root tips. Similar effects were obtained with zeatin. The effects were obtained over a wide concentration range down to 0.01 μM. Growth responses appeared only after treatment for several hours, and the duration of treatment had an important influence on the degree of the effects. BAP caused a moderate increase in ethylene production as measured in excised 10‐mm‐long root tips. Lowering ethylene production by treatment with cobalt ions counteracted both the inhibition and swelling caused by BAP. Treatment with silver ions also reversed the effect to some extent, indicating that ethylene is involved in the response of the roots to BAP. To further study the involvement of the increased ethylene production in the elongation and swelling response, the effects were compared with those obtained after application of 1‐aminocyclopropane‐1‐carboxylic acid (ACC) in relation to the ethylene produced from this compound. This comparison showed that the increase in ethylene production caused by BAP was too low to explain the response of the roots. However, ACC treatment caused a considerable lowering of the content of indole‐3‐acetic acid (IAA) in the root tips, whereas BAP did not; instead, BAP increased the amount of IAA per root tip. It is concluded that cytokinins influence growth processes in roots via several mechanisms. A synergistic interaction between endogenous IAA, maintained at a high level by the cytokinin treatment, and the increased ethylene levels appears to explain most of the cytokinin effects during the first day of treatment.

Does gibberellic acid inhibit 2,4-dichlorophenoxyacetic acid-induced ethylene production in Cucurbita pepo L. seedlings?

Summary The development of the swelling of the hypocotyl base induced in C pepo by 2,4-D was closely correlated with a marked increase in endogenous ethylene production and, although 2,4-D treatment was continuous for periods up to 8d, hypocotyl swelling was complete and 2,4-D-stimulated ethylene production had ceased within 5d and 3d respectively. The cobaltous ion, an inhibitor of ethylene biosynthesis, supplied in conjunction with 2,4-D, inhibited both hypocotyl swelling and ethylene production, but GA3, although suppressing 2,4-D-induced hypocotyl swelling, had no inhibitory effect on the levels of ethylene produced. It is concluded that increased ethylene levels, produced in response to 2,4-D treatment, are responsible for the abnormal growth patterns in hypocotyls of C pepo, but although GA prevents this response to ethylene, it does not do so by suppressing ethylene production.

Ethylene, Cellulase, 2,4-D, and Summer Fruit Drop of Navel Orange in Florida

Abstract Secondary-fruit yellowing (SFY) of navel orange [Citrus sinensis (L.) Osbeck], a major cause of summer fruit drop, was induced artificially by girdling the stem 5 to 10 cm from the fruit. Girdling from 26 to 28 May 1982 increased ethylene levels at the stylar end and induced SFY in 90% of treated fruit. Girdling at other times, or at 30 to 45 cm from the fruit, however, caused minor SFY, particularly if leaves were present between the fruit and girdled area, indicating some material is produced by the leaves that reduces the incidence of SFY. Increase of ethylene levels and cellulase activity in the abscission zone of the secondary fruit prior to increases in the abscission zone of the primary fruit indicate that secondary-fruit abscission leads to primary fruit abscission. Water stress or changes in nonstructural carbohydrate levels within the leaves induced by branch sawing did not cause SFY. Application of 2,4-dichlorophenoxyacetic acid (2,4-D) prior to or during induction lessened the severity of SFY and significantly decreased ethylene levels at the stylar end of the fruit.

Effects of Auxins and Cytokinins on Ethylene Evolution and Growth of Rose Callus Tissue in Sealed Vessels1

Abstract Ethylene evolution from callus tissue of rose (Rosa hybrida L.) grown in air tight vessels was enhanced by the presence of auxin and cytokinin in the culture medium. Increased ethylene levels did not adversely affect the fresh weight gain of rose callus tissue.

The Role of Endogenous Auxins and Ethylene in the Formation of Adventitious Roots and Hypocotyl Hypertrophy in Flooded Sunflower Plants (Helianthus annuus)

AbstractThe role of ethylene and auxins in flood‐induced adventitious root formation and hypocotyl hypertrophy in sunflower (Helianthus annuus L. cv. Russian) plants was studied. Flooding without aeration (F) resulted in a steady increase in ethylene in hypocotyls, and flooding with aeration (FA) caused a transient increase. Low light intensity increased ethylene levels but decreased adventitious root formation. Treatment of shoots with benzyladenine (BA) increased ethylene content in non‐flooded (NF) but not in F or FA shoots.Twenty‐four hours of flooding brought about a rise of endogenous indole‐acetic acid (IAA) in hypocotyls. 14C‐IAA applied to the shoot accumulated more in F and FA hypocotyls than in NF hypocotyls, and BA reduced this accumulation. There was less IAA metabolism in F and FA than in NF hypocotyls.Tri‐iodo benzoic acid (TIBA) applied to the hypocotyls of F plants inhibited root production. Benzyladenine (BA) applied to the leaves had similar effect but was not effective when supplied to the shoot apex. BA did not inhibit flood‐induced hypocotyl hypertrophy. Ethrel did not affect adventitious root formation in NF plants but did increase hypocotyl thickening.It is concluded that flood‐induced adventitious root formation is stimulated primarily by an accumulation of auxins in the hypocotyls. Increases in ethylene might cause this auxin build up. Hypocotyl hypertrophy is presently thought to be the result of an interaction of auxin and ethylene with ethylene being the major factor.

Ethylene and tension wood formation in Eucalyptus gomphocephala

Eucalyptus gomphocephala A.DC seedlings grown horizontally for 103 days had less terminal shoot elongation and higher internal and emanated ethylene levels in the basal portion of the stem than seedlings grown vertically under otherwise identical conditions. Horizontal seedlings had greater radial growth in the upper stem half than in the lower half of the basal portion of the stem. Upper halves contained 60–80 percent tension wood by volume, lower halves 0–10 percent tension wood. Radial growth in vertical seedlings was symmetrical, and they contained negligible tension wood. Upper halves of the basal portion of the stem of horizontal seedlings had greater amounts of internal and emanated ethylene than lower halves and vertical seedling halves. Ethylene differences between random halves of vertical seedlings were smaller than differences between upper and lower halves of horizontal seedlings. The data suggest an association between increased ethylene levels and tension wood formation.

Cobalt and Plant Development

Co(2+) promoted elongation of hypocotyl segments of light-grown cucumber (Cucumis sativus) seedlings. Time course and dose response data are presented and interactions with IAA, gibberellin, cyclohexanol, and cotyledons described. Segments without cotyledons responded to Co(2+) only if grown in gas-tight vessels with IAA added. When bases of cotyledons were ringed with an inhibitor of auxin transport, Co(2+) caused no growth promotion in the hypocotyl. Co(2+) prevented lateral swelling of hypocotyls treated with supraoptimal IAA. Removal of ethylene from the atmosphere reduced the Co(2+) response, but Co(2+) did not counteract the inhibitory effect of increased ethylene levels. These results are consistent with the hypothesis that Co(2+) promotes hypocotyl elongation by inhibiting ethylene production. The hypothesis was confirmed by a direct demonstration that Co(2+), at growth-promoting concentrations, powerfully inhibited ethylene production in the cucumber hypocotyl.

Stress Ethylene Production in Apple Shoots1

Abstract Increases in internal ethylene concentrations occurred after attached and detached apple (Malus domestica, Borkh. cv. Winesap) shoots were placed in a horizontal position. Ethylene was higher in the underside of the shoot, and decreased linearly in a basipetal direction along the axis. Bent and horizontally-oriented detached shoots did not increase in ethylene at 20°C, but increased to identical levels at 30°, suggesting that responses to the 2 types of stress were identical. Although gravitational stress alone increased ethylene levels, an experiment designed to separate bending stress from gravitational stress was inconclusive because rotation decreased shoot ethylene levels.