Changes in 1-(malonylamino)cyclopropane-1-carboxylic acid content in wilted wheat leaves in relation to their ethylene production rates and 1-aminocyclopropane-1-carboxylic acid content

Effects of Flooding and Endogenous Hormone on the Formation of Knee Roots in Taxodium ascendens

Taxodium ascendens is a typical tree species with high flood tolerance, and it can generate knee roots in the wetlands. This study investigated the number and size of knee roots and the soil flooding conditions. Furthermore, we also measured physiology, biochemical responses, and the anatomical structure of knee roots and underground roots at different developmental stages. This study aimed to understand the adaptation mechanism of T. ascendens to flooding stress and the formation mechanism of the knee roots. The results showed that the formation of knee roots was significantly affected by the soil water table (P < 0.05). The middle water table was more conducive to the formation of knee roots. In the middle water table, the 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase activity were significantly lower in the knee roots than in the underground roots. The knee roots at the young-aged stage showed the highest ACC oxidase activity among the development stages of the knee roots. The ethylene release rate was significantly higher in the knee roots than in the underground roots (P < 0.05). Indole-3-acetic acid (IAA) content first increased, then decreased with knee root development. The periderm cells at the apex of the knee roots were dead and had many intercellular spaces, which was beneficial for the growth of T. ascendens. In conclusion, the middle water table induced the ethylene and IAA production, which promoted the formation of knee roots, which improved roots ventilation and flooding tolerance of T. ascendens. The results obtained can provide information about mechanisms of knee roots formation and provide scientific evidence for the afforestation and management under wetland conditions.

Pyrazinamide and derivatives block ethylene biosynthesis by inhibiting ACC oxidase

Ethylene is an important phytohormone that promotes the ripening of fruits and senescence of flowers thereby reducing their shelf lives. Specific ethylene biosynthesis inhibitors would help to decrease postharvest loss. Here, we identify pyrazinamide (PZA), a clinical drug used to treat tuberculosis, as an inhibitor of ethylene biosynthesis in Arabidopsis thaliana, using a chemical genetics approach. PZA is converted to pyrazinecarboxylic acid (POA) in plant cells, suppressing the activity of 1-aminocyclopropane-1-carboxylic acid oxidase (ACO), the enzyme catalysing the final step of ethylene formation. The crystal structures of Arabidopsis ACO2 in complex with POA or 2-Picolinic Acid (2-PA), a POA-related compound, reveal that POA/2-PA bind at the active site of ACO, preventing the enzyme from interacting with its natural substrates. Our work suggests that PZA and its derivatives may be promising regulators of plant metabolism, in particular ethylene biosynthesis.

Regulation by Carbon Dioxide of Wound-induced Ethylene Biosynthesis in the Peel of Citrus Fruit

The effect of carbon dioxide (CO2) on wound-induced ethylene biosynthesis in flavedo discs of mature orange fruits (Citrus sinensis L. Osbeck) is investigated. Wounding induced a marked and rapid increase on the rate of ethylene production, the content of 1-aminocyclopropane-1-carboxylic acid (ACC) and on the in vivo ACC oxidase (ACO) activity. Incubation of flavedo discs in a 15% CO2 atmosphere suppressed activation of these processes. Wound-induced ethylene production was inhibited by CO2 in a concentration-dependent manner but ACO activity was enhanced at concentrations between 1% and 5%. Kinetic analysis of the interaction between CO2 and ACO activity indicated that high CO2 acted as a noncompetitive inhibitor. Removal of CO2 after 24 h incubation did not restore normal rates of ethylene production. CO2 partially counteracted the increase in ethylene production and ACO activity induced by a pretreatment with an ethylene action inhibitor (STS, silver thiosulfate). This suggested that part of CO2 action on ethylene biosynthesis might be due to interfering ethylene action. Collectively, the results indicated that ACS activity appeared to be the major regulatory step by which CO2 suppresses wound-induced ethylene production. ACO was differentially modulated by CO2, which is being stimulated at low concentrations and inhibited at high concentrations.

Note. The ripening of Prunus persica fruits with a dominant flat allele Nota. Maduración de frutos de Prunus persica con un alelo dominante de la forma achatada

The changes of peaches ( Prunus persica, L.) with a predominant flat allele were studied during their ripening on the tree. Physicochemical and physiological parameters were analyzed between days 101 and 121 after fruit set. During this period, the weight ranged from 65 g (corresponding to fruit growth stage III) up to a stabilized weight of 90 g when the fruit was ripe. The color changes that characterized fruit ripening began to appear on day 112 after fruit set, with a decrease in the hue angle value both in the skin and pulp. Firmness diminished along the experience from 6.75 to 3.03 Monet units in ripe state. Ripened fruit was also characterized by a soluble solid content of 13.43 °Brix and 0.178% malic acid as titratable acidity. The ripeness index increased throughout maturation from 25.41 at the outset to 44.42 on day 112 after fruit set, and 75.45 at the end of the experiment. The fruit showed a clear climacteric behavior with increased ethylene production and respiration rate. The onset in both processes started on day 112 after fruit set, reached a maximum on day 116, and decreased thereafter. Changes in the content of free and conjugated 1-aminocyclopropane-1-carboxy lic acid (ACC) were coincident with those of ethylene evolution throughout ripening. In regard to polyamine levels, putrescine showed a peak slightly later than that of ethylene and ACC.

Induced drought tolerance through wild and mutant bacterial strain Pseudomonas simiae in mung bean (Vigna radiata L.)

The present study focused on the overproducing mutant of a plant growth promoting rhizobacterium (PGPR) Pseudomonas simiae strain AU (MTCC-12057) for significant drought tolerance in mung bean plants. Five mutants namely AU-M1, AU-M2, AU-M3, AU-M4 and AU-M5 were made after treatment of wild type strain with N-methyl-N-nitro-N-nitrosoguanidine. Mutant strain AU-M4 was recorded for enhanced ACC deaminase (ACC-D) activity, indole acetic acid (IAA) production and inorganic phosphate (Pi) solubilization compared to wild strain and other four mutant strains under drought condition. AU-M4 showed higher phosphate solubilization index (8.17) together with higher ACC-D activity (98 nmol/mg/h) and IAA concentration (69.35 µg/ml) compared with the wild type P. simiae strain AU ACC-D activity (79 nmol/mg/h) and IAA concentration (38.98 µg/ml) respectively. In this report, we investigated the effect of both wild and mutant type bacterial strain on mung bean plants under drought stress. Results showed that mutant AU-M4 and wild type strain AU inoculated plants exhibited superior tolerance against drought stress, as shown by their enhanced plant biomass (fresh weight), higher water content, higher proline accumulation and lower osmotic stress injury. Mutant AU-M4 and wild strain AU inoculated plants reduced the ethylene level by 59 and 45% respectively, compared to the control under stress condition. Furthermore, bacterial inoculated plants showed enhanced induced systemic drought tolerance by reducing stomata size and net photosynthesis resulting higher water content in mung bean plants that may help in survival of plants during drought condition. To mitigate the effects of drought stress, use of PGPR will be needed to ensure sufficient production of food from crop plants. Taking current leads available, concerted future research is needed in this area, particularly on field evaluation with application of potential microorganisms.

An overview of preharvest factors influencing mango fruit growth, quality and postharvest behaviour

Mango, a tropical fruit of great economic importance, is generally harvested green and then commercialised after a period of storage. Unfortunately, the final quality of mango batches is highly heterogeneous, in fruit size as well as in gustatory quality and postharvest behaviour. A large amount of knowledge has been gathered on the effects of the maturity stage at harvest and postharvest conditions on the final quality of mango. Considerably less attention has been paid to the influence of environmental factors on mango growth, quality traits, and postharvest behaviour. In this paper, we provide a review of studies on mango showing how environmental factors influence the accumulation of water, structural and non-structural dry matter in the fruit during its development. These changes are discussed with respect to the evolution of quality attributes on the tree and after harvest. The preharvest factors presented here are light, temperature, carbon and water availabilities, which can be controlled by various cultural practices such as tree pruning, fruit thinning and irrigation management. We also discuss recent advances in modelling mango function on the tree according to environmental conditions that, combined with experimental studies, can improve our understanding of how these preharvest conditions affect mango growth and quality.

Changes in ACC and conjugated ACC levels following controlled atmosphere storage of nectarine

Low temperature disorders of nectarines are thought to be expressions of chilling injury. Chilling injury is a form of stress usually associated with increased synthesis of ethylene and its immediate precursor, aminocyclopropane-1-carboxylic acid (ACC). However, other mechanisms for the development of chilling injury have been proposed. To help determine the nature of the processes leading to chilling injury in nectarines (Prunus persica) and how the gaseous composition of the storage atmosphere effects the development of low temperature disorders, levels of ACC and conjugated ACC were measured in fruit of the cv. Arctic Snow. These compounds were measured in fruit ripened at 20°C immediately after harvest, in fruit on removal from cold storage and in fruit ripened at 20°C following cold storage. During storage, fruit were kept at 0°C in the 4 following atmospheres: air; air + 15% CO2; air + 15 µL/L ethylene; and air + 15% CO2 + 15 µL/L ethylene. Concentrations of ACC remained low in all treatments and no significant changes in ACC levels due to added ethylene or CO2 were observed. Concentrations of conjugated ACC were about 10-times that of ACC and again were not influenced by the composition of the storage atmosphere. No significant changes in either ACC or conjugated ACC were observed until after flesh bleeding, the major symptoms of low temperature disorder expressed in these fruit, had begun to appear. It was concluded that disorders in nectarines stored at low temperatures are not a stress response involving a disruption of ethylene metabolism but may be associated with differential changes in the metabolism of enzymes associated with normal ripening.

In vitro germination of Striga hermonthica and Striga aspera seeds by 1-aminocyclopropane-1-carboxylic acid

Treatment of conditioned seeds of four isolates of Striga hermonthica and one isolate of Striga aspera with various concentrations of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), caused complex stimulation of germination patterns. GR 24, the strigol analogue served as a positive control and its stimulatory activity was comparable to that of ACC. When conditioned Striga seeds were treated with negative control that did not contain ACC, the stimulatory effect was lost. Overall, the germination data suggested a hormonal mode of action by ACC, which involves indirect stimulation of biosynthesis of ethylene that then triggers seed germination. The various mechanisms that have been proposed for the chemical and biological oxidation of ACC to generate ethylene are discussed.

Role of ethylene and abscisic acid in physicochemical modifications during melon ripening

Hormonal metabolism associated with fruit ripening in two cantaloupe muskmelon cultivars, Talma and Manta, has been studied. The ethylene crisis began on day 33 after fruit set, reaching the maximum values of internal ethylene concentration and ethylene production rate on day 35 after fruit set. This was the optimum moment for consumption as shown by the higher content in soluble solids, ripening index, sensory analysis, and color parameter values. The b parameter and the b/a quotient values in peel were good indicators of the maturity stage, the optimum moment for harvesting being about day 33 after fruit set (when autocatalytic ethylene synthesis has begun), with values of 20 and 5 for the b parameter and b/a quotient, respectively. In both cultivars, free 1-aminocyclopropane-1-carboxylic acid (ACC) content increased until day 35 after fruit set and conjugated ACC increased in postclimacterium. The increase in both ACC-synthase and ACC-oxidase activities together could be responsible for the climacteric ethylene production. Significant differences in the abscisic acid evolution in Talma and Manta cultivars were reached, and also a possible stimulation of ethylene by this hormone could be established.

Differential regulation of the tomato ETR gene family throughout plant development

Ethylene perception in plants is co-ordinated by multiple hormone receptor candidates sharing sequence commonalties with prokaryotic environmental sensor proteins known as two-component regulators. Two tomato homologs of the Arabidopsis ethylene receptor ETR1 were cloned from a root cDNA library. Both cDNAs, termed LeETR1 and LeETR2, were highly homologous to ETR1, exhibiting approximately 90% deduced amino acid sequence similarity and 80% deduced amino acid sequence identity. LeETR1 and LeETR2 contained all the major structural elements of two-component regulators, including the response regulator motif absent in LeETR3, the gene encoding tomato NEVER RIPE (NR). Using RNase protection analysis, the mRNAs of LeETR1, LeETR2 and NR were quantified in tissues engaged in key processes of the plant life cycle, including seed germination, shoot elongation, leaf and flower senescence, floral abscission, fruit set and fruit ripening. LeETR1 was expressed constitutively in all plant tissues examined. LeETR2 mRNA was expressed at low levels throughout the plant but was induced in imbibing tomato seeds prior to germination and was down-regulated in elongating seedlings and senescing leaf petioles. NR expression was developmentally regulated in floral ovaries and ripening fruit. Notably, hormonal regulation of NR was highly tissue-specific. Ethylene biosynthesis induced NR mRNA accumulation in ripening fruit but not in elongating seedlings or in senescing leaves or flowers. Furthermore, the abundance of mRNAs for all three LeETR genes remained uniform in multiple plant tissues experiencing marked changes in ethylene sensitivity, including the cell separation layer throughout tomato flower abscission.

Phytochrome-controlled ethylene biosynthesis of intact etiolated bean seedlings

Intact etiolated bean (Phaseolus vulgaris L. cv. Limburgse vroege) seedlings were illuminated with red light (10.5 W·m(-2)) for 10 min. After different time intervals ethylene production, and contents of 1-aminocyclopropane-1-carboxylic acid (ACC) and 1-(malonylamino)cyclopropane-1-carboxylic acid were measured. The red-light-induced decrease of ethylene production in 8-d-old intact etiolated bean seedlings was fast, strong and long-lasting ad was mediated through the phytochrome system. This effect appeared to be strictly age-dependent, as it could not be detected in plants younger than 6 d or older than 11 d.The capacity for the conversion of ACC to ethylene was not affected by red light. The inhibitory effect of the light treatment on ethylene production could be related to a reduced free-ACC content. This reduction was a consequence of a temporary non-reversible increase of ACC malonylation and a long-lasting, for a certain time reversible, inhibition of ACC synthesis. The effect of a brief irradiation with red light on the decrease of ethylene production and free-ACC content was completed after about 2 h. Reversibility by far-red, however, persisted for at least 3 h, and was lost between 3 and 6 h.

Malonyl-coenzyme A:isoflavone 7-O-glucoside-6"-O-malonyltransferase from roots of chick pea (Cicer arietinum L.)

A malonyltransferase which catalyzes the malonylation of isoflavone 7-O-glucosides in position 6 of the glucose moiety using malonyl-coenzyme A as acyl donor has been purified 157-fold from 4-day-old roots of chick pea (Cicer arietinum L.). The enzyme showed a pH optimum of 8.0 and a molecular weight of 112,000. The Km for malonylcoenzyme A was 48 microM and, for the chick pea isoflavones biochanin A and formononetin, 36 and 24 microM, respectively. Various other isoflavone, flavone, and flavonol 7-O-glucosides and chalcone 4'-O-glucosides were much poorer substrates. Flavonol 3-O-glucosides and isoflavone 4'-O-glucosides were not malonylated by the malonyltransferase.

The enzymatic malonylation of 1-aminocyclopropane-1-carboxylic acid in homogenates of mung-bean hypocotyls

Homogenates of hypocotyls of light-grown mung-bean (Vigna radiata (L.) Wilczek) seedlings catalyzed the formation of 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) from the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) and malonyl-coenzyme A. Apparent Km values for ACC and malonyl-CoA were found to be 0.17 mM and 0.25 mM, respectively. Free coenzyme A was an uncompetitive inhibitor with respect to malonyl-CoA (apparent Ki=0.3 mM). Only malonyl-CoA served as an effective acyl donor in the reaction. The D-enantiomers of unpolar amino acids inhibited the malonylation of ACC. Inhibition by D-phenylalanine was competitive with respect to ACC (apparent Ki=1.2 mM). D-Phenylalanine and D-alanine were malonylated by the preparation, and their malonylation was inhibited by ACC. When hypocotyl segments were administered ACC in the presence of certain unpolar D-amino acids, the malonylation of ACC was inhibited while the production of ethylene was enhanced. Thus, a close-relationship appears to exist between the malonylation of ACC and D-amino acids. The cis- as well as the trans-diastereoisomers of 2-methyl- or 2-ethyl-substituted ACC were potent inhibitors of the malonyltransferase. Treatment of hypocotyl segments with indole-3-acetic acid or CdCl2 greatly increased their content of ACC and MACC, as well as their release of ethylene, but had little, or no, effect on their extractable ACC-malonylating activity.

Relationship between the malonylation of 1-aminocyclopropane-1-carboxylic acid and D-amino acids in mung-bean hypocotyls

In sections from hypocotyls of dark-grown mung-bean (Vigna radiata L.) seedlings, D-phenylalanine and D-methionine (D-met) inhibited the formation of 1-(malonylamino)cyclopropane-1-carboxylic acid from exogenously administered 1-aminocyclopropane-1-carboxylic acid (ACC), resulting in an increase in free ACC content and stimulation of ethylene production, whereas their L-enantiomers had little or no such effect. When the hypocotyls were administered D-Met, it was mainly metabolized to N-malonylmethionine and N-malonylmethionine sulfoxide, and this malonylation process was inhibited to a greater extent by ACC and D-amino acids (phenylalanine and serine) than by L-amino acids. These results indicate that malonylation of D-amino acids and of ACC are intimately interrelated.