Ethylene biosynthesis and respiration in strawberry fruit treated with diazocyclopentadiene and IAA

Diazocyclopentadiene (DACP), an inhibitor of ethylene action, was used to investigate the role of ethylene receptor(s) in regulating ethylene biosynthesis and respiration in strawberry fruit. DACP stimulated ethylene production of fruit at all stages of maturity. This stimulation was mainly due to an increase in ACC content in the tissue without significantly changing ACC oxidase activity. DACP did not induce any change in respiration in fruit at various stages of maturity except the early green stage (green I). We also investigated the possible interaction of DACP and IAA in ethylene production. Results indicated that all treatments increased ethylene production compared to the control although the absolute ethylene production differed in the order IAA plus DACP > only DACP > only IAA > control. IAA stimulated ethylene production without change of ACC oxidase activity at 1 day after treatment in strawberry fruit at pink stage. Results suggest that ethylene biosynthesis in nonclimacteric strawberry fruit at various stages of maturity may be regulated by ethylene receptor(s) with inhibition of ethylene production. DACP may release this inhibitory effect, and resulting in increasing ethylene production. Results also indicated that respiration may not be regulated by an ethylene receptor in strawberry fruit at most stages of maturity. DACP and IAA showed interaction in regulation of ethylene production which was caused by an increase in ACC content, not ACC oxidase activity.     

Recovery of ethylene biosynthesis in diazocyclopentadiene (DACP)-treated tomato fruit

Diazocyclopentadiene (DACP), a competitive ethylene action inhibitor binds irreversibly to the ethylene receptor to reduce tissue responses to ethylene. Tomato fruit (Lycopersicon esculentum Mill cv lsquo;Rondellorsquo;) were treated with DACP at the mature green stage. Ethylene biosynthesis and respiration rate were depressed. Color changes from green to red were delayed. Compared to the control, ACC content increased and ACC oxidase activity in vivo decreased in DACP-treated fruit. Thus, decrease of ethylene production caused by DACP treatment was due to the reduction of ACC oxidase activity. The decline in ripening subsequently recovered after DACP treatment. Results from the Northern analysis for gene expression of ACC synthase and ACC oxidase, showed that expression of both genes declined in DACP-treated fruit, and then recovered. Therefore the recovery of ethylene production was due to the recovery in gene expression and activity of ACC oxidase. We conclude that the effects of DACP on ethylene biosynthesis are on expression of ACC synthase and ACC oxidase genes, and/or regulation of ACC oxidase activity.     

Compounds Interacting with the Ethylene Receptor in Plants

Abstract: Some of the compounds binding to the ethylene receptor induce an ethylene response, but others prevent it. The compounds preventing an ethylene response have been developed into a means for protecting plants against ethylene and extending the life of some plant material. 1-Methylcyclopropene (1-MCP), a compound now commercially available under the names EthylBloc and SmartFresh™, is currently being used on flowers, fruit and vegetables with great success. In ethylene sensitive flowers, among other responses, it prevents senescence and abscission of plant organs; in fruit and vegetables it slows down the ripening process. Other similar compounds are now being developed for a range of methods of application.     

Evidence for a novel phosphopantetheinyl transferase domain in the polyketide synthase for enediyne biosynthesis

The polyketide synthase associated with the biosynthesis of enediyne-containing calicheamicin contains a putative phosphopantetheinyl transferase (PPTase) domain. By cloning and expressing the C-terminal region of the polyketide synthase and in vitro phosphopantetheinylation assay, we found that the PPTase domain exhibits preferred substrate specificity towards acyl and peptidyl carrier proteins in fatty acid and non-ribosomal peptide synthesis over its cognate partner. We also found evidence suggesting that the PPTase domain adopts a pseudo-trimeric structure, distinct from the pseudo-dimeric structure of type II PPTases. The results revealed a novel type of PPTase with unique structure and substrate specificity, and suggested that the polyketide synthase probably acquired the PPTase domain from a primary metabolic pathway in evolution.     

Inhibitory effect of diazocyclopentadiene on the development of superficial scald in Granny Smith apple

In this work, diazocyclopentadiene (DACP), an ethylene action inhibitor was used to test if ethylene is involved in the development of superficial scald of apple. Apples (Malus domestica Borkh., c.v. Granny Smith) were pre-stored at 0°C for a month before DACP treatment. After treatment, fruit were stored at 0°C for a further 17 weeks before being transferred to room temperature for a week. The incidence of superficial scald, contents of -farnesene and conjugated triene in fruit skin were analysed. Ethylene production, respiration rate, flesh firmness and soluble solids content of fruit were determined. Results indicated that superficial scald is related to chilling injury. DACP delayed ripening, and dramatically inhibited the development of superficial scald in Granny Smith apple by lowering -farnesene and conjugated triene contents. Ethylene might promote -farnesene synthesis presumably by binding to the ethylene receptor(s).     

Growth inhibition of pollen tubes by blocking the aromatic or branched-chain amino acid pathways of biosynthesis

A number of organic molecules that appear to block the ethylene receptor have been discovered recently. For example, on irradiation with visible light, diazocyclopentadiene (DACP), gives rise to some potent but as yet unidentified inhibitor compounds. Some synthetic cyclopropenes have been shown to bind to the ethylene receptor and prevent the physiological action of ethylene for extended periods. Cyclopropene (CP). 1-methylcyclopropene (1-MCP) and 3,3-dimethylcyclopropene (3,3-DMCP) have been shown to prevent ethylene effects in a number of plants. As low a concentration as 0.5 nl l⁻¹ of 1-MCP is sufficient to protect carnation ( Dianthus caryophyllus ) flowers for several days against ethylene, and 0.7 nl l⁻¹ 1-MCP or CP will prevent the ripening of banana ( Musa sapientum ) for 12 days at 24°C. Some plant organs require higher concentrations of these inhibitors. Complete inhibition of ethylene effects in pea seedlings requires treatment with 40 n1 1⁻¹ of 1-MCP. These novel inhibitors appear to be suitable for many commercial applications including extending the vase life of cut flowers and the display life of potted plants. Since 1-MCP apparently is non-toxic at concentrations that are active, it may in future be available for regulating the ripening of fruits and preventing the deleterious effects of ethylene in vegetables.