Production of ethylene by excised segments of plant tissue prior to the effect of wounding

Plant-Plant Communication: Is There a Role for Volatile Damage-Associated Molecular Patterns?

Damage-associated molecular patterns (DAMPs) are an ancient form of tissue-derived danger or alarm signals that initiate cellular signaling cascades, which often initiate defined defense responses. A DAMP can be any molecule that is usually not exposed to cells such as cell wall components, peptides, nucleic acid fragments, eATP and other compounds. DAMPs might be revealed upon tissue damage or during attack. Typically, DAMPs are derived from the injured organism. Almost all eukaryotes can generate and respond to DAMPs, including plants. Besides the molecules mentioned, certain volatile organic compounds (VOCs) can be considered as DAMPs. Due to their chemical nature, VOCs are supposed to act not only locally and systemically in the same plant but also between plants. Here, we focus on damage-induced volatiles (DIVs) that might be regarded as DAMPs; we will review their origin, chemical nature, physiochemical properties, biological relevance and putative function in plant-plant communications. Moreover, we discuss the possibility to use such airborne DAMPs as eco-friendly compounds to stimulate natural defenses in agriculture in order to avoid pesticides.

Protecting cotton crops under elevated CO2 from waterlogging by managing ethylene

Soil waterlogging and subsequent ethylene release from cotton (Gossypium hirsutum L.) tissues has been linked with abscission of developing cotton fruits. This glasshouse study investigates the effect of a 9-day waterlogging event and CO2 enrichment (eCO2, 700 parts per million (ppm)) on a fully linted cultivar 'Empire' and a lintless cotton mutant (5B). We hypothesised that cotton performance in extreme environments such as waterlogging can be improved through mitigating ethylene action. Plants were grown at 28:20°C day:night temperature, 50-70% relative humidity and a 14:10 light:dark photoperiod under natural light and were exposed to waterlogging and eCO2 at early reproductive growth. Ethylene synthesis was inhibited by spraying aminoethoxyvinylglycine (830ppm) 1 day before waterlogging. Waterlogging significantly increased ethylene release from both cotton genotypes, although fruit production was significantly inhibited only in Empire. Aminoethoxyvinylglycine consistently reduced waterlogging-induced abscission of fruits, mainly in Empire. Limited damage to fruits in 5B, despite increased ethylene production during waterlogging, suggested that fruit abscission in 5B was inhibited by disrupting ethylene metabolism genetically. Elevated CO2 promoted fruit production in both genotypes and was more effective in 5B than in Empire plants. Hence 5B produced more fruits than Empire, providing additional sinks (existing and new fruit) that enhanced the response to CO2 enrichment.

Endogenous Ethylene Concentration Is Not a Major Determinant of Fruit Abscission in Heat-Stressed Cotton (Gossypium hirsutum L.)

We investigated the role of ethylene in the response of cotton to high temperature using cotton genotypes with genetically interrupted ethylene metabolism. In the first experiment, Sicot 71BRF and 5B (a lintless variant with compromised ethylene metabolism) were exposed to 45°C, either by instantaneous heat shock or by ramping temperatures by 3°C daily for 1 week. One day prior to the start of heat treatment, half the plants were sprayed with 0.8 mM of the ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG). In a subsequent experiment, Sicot 71BRF and a putatively heat-tolerant line, CIM 448, were exposed to 36 or 45°C for 1 week, and half the plants were sprayed with 20 μM of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, (ACC). High temperature exposure of plants in both experiments was performed at the peak reproductive phase (65-68 days after sowing). Elevated temperature (heat shock or ramping to 45°C) significantly reduced production and retention of fruits in all cotton lines used in this study. At the termination of heat treatment, cotton plants exposed to 45°C had at least 50% fewer fruits than plants under optimum temperature in all three genotypes, while plants at 36°C remained unaffected. Heat-stressed plants continued producing new squares (fruiting buds) after termination of heat stress but these squares did not turn into cotton bolls due to pollen infertility. In vitro inhibition of pollen germination by high temperatures supported this observation. Leaf photosynthesis (Pn) of heat-stressed plants (45°C) measured at the end of heat treatments remained significantly inhibited, despite an increased leaf stomatal conductance (gs), suggesting that high temperature impairs Pn independently of stomatal behavior. Metabolic injury was supported by high relative cellular injury and low photosystem II yield of the heat-stressed plants, indicating that high temperature impaired photosynthetic electron transport. Both heat shock and ramping of heat significantly reduced ethylene release from cotton leaf tissues measured at the end of heat treatment but modulating ethylene production via AVG or ACC application had no significant effect on fruit production or retention in heat-stressed cotton plants. Instead, high temperature accelerated fruit abortion by impairing pollen development and/or restricting leaf photosynthesis.

Signaling events in the hypoxic induction of alcohol dehydrogenase gene in Arabidopsis

Expression of the alcohol dehydrogenase gene (ADH) of Arabidopsis is induced during hypoxia. Because many plants increase their ethylene production in response to hypoxic stress, we examined in this report whether ethylene is involved in the hypoxic induction of ADH in Arabidopsis. We found that the hypoxic induction of ADH can be partially inhibited by aminooxy acetic acid, an inhibitor of ethylene biosynthesis. This partial inhibition can be reversed by the addition of 1-aminocyclopropane-1-carboxylic acid, a direct precursor of ethylene. In addition, the hypoxic induction of the ADH gene is also reduced in etr1-1 and ein2-1, two ethylene insensitive mutants in ethylene-signaling pathways, whereas the addition of exogenous ethylene or an increase in cellular ethylene alone does not induce ADH under normoxic conditions. Kinetic analyses of ADH mRNA accumulation indicated that an ethylene signal is required for the induction of ADH during later stages of hypoxia. Therefore, we conclude that ethylene is needed, but not sufficient for, the induction of ADH in Arabidopsis during hypoxia.

Endogenous ABA maintains shoot growth in tomato independently of effects on plant water balance: evidence for an interaction with ethylene

To examine whether the reduced shoot growth of abscisic acid (ABA)-deficient mutants of tomato is independent of effects on plant water balance, flacca and notabilis were grown under controlled-humidity conditions so that their leaf water potentials were equal to or higher than those of well-watered wild-type plants throughout development. Most parameters of shoot growth remained markedly impaired and root growth was also greatly reduced. Additional experiments with flacca showed that shoot growth substantially recovered when wild-type levels of ABA were restored by treatment with exogenous ABA, even though improvement in leaf water potential was prevented. The ability of applied ABA to increase growth was greatest for leaf expansion, which was restored by 75%. The ethylene evolution rate of growing leaves was doubled in flacca compared to the wild type and treatment with silver thiosulphate to inhibit ethylene action partially restored shoot growth. The results demonstrate that normal levels of endogenous ABA are required to maintain shoot development, particularly leaf expansion, in well-watered tomato plants, independently of effects on plant water balance. The impairment of shoot growth caused by ABA deficiency is at least partly attributable to ethylene.

The promoter of LE-ACS7, an early flooding-induced 1-aminocyclopropane-1-carboxylate synthase gene of the tomato, is tagged by a Sol3 transposon

Many terrestrial plants respond to flooding with enhanced ethylene production. The roots of flooded plants produce 1-aminocyclopropane-1-carboxylic acid (ACC), which is transported from the root to the shoot, where it is converted to ethylene. In the roots, ACC is synthesized by ACC synthase, which is encoded by a multigene family. Previously, we identified two ACC synthase genes of tomato that are involved in flooding-induced ethylene production. Here, we report the cloning of LE-ACS7, a new tomato ACC synthase with a role early during flooding but also in the early wound response of leaves. The promoter of LE-ACS7 is tagged by a Sol3 transposon. A Sol3 transposon is also present in the tomato polygalacturonase promoter to which it conferred regulatory elements. Thus, Sol3 transposons may affect the regulation of LE-ACS7 and may be involved in the communication between the root and the shoot of waterlogged tomato plants.

Analysis of LE-ACS3, a 1-aminocyclopropane-1-carboxylic acid synthase gene expressed during flooding in the roots of tomato plants

The plant hormone ethylene is produced in response to a variety of environmental stresses. Previous work has shown that flooding or anaerobic stress in the roots of tomato plants caused an increase in the production of the ethylene precursor 1-aminocyclopropane-1-carboxylate (ACC) in the roots, due to flooding-induced activity of ACC synthase (EC 4.4.1.14). RNA was extracted from roots and leaves of tomato plants flooded over a period of 48 h. Blot analysis of these RNAs hybridized with probes for four different ACC synthases revealed that the ACC synthase gene LE-ACS3 is rapidly induced in roots. LE-ACS2 is also induced, but at later times. The genomic clone for LE-ACS3 was isolated and sequenced. At all time points, the probe from the LE-ACS3 coding region hybridized to two bands in the RNA blots. Hybridization using the first and third introns of LE-ACS3 separately as probes indicate that flooding may inhibit processing of the LE-ACS3 transcript. Sequence homology analysis identified three putative cis-acting response elements in the promoter region, corresponding to the anaerobic response element from the maize adh1 promoter, the root-specific expression element from the cauliflower mosaic virus 35S promoter and a recognition element for chloroplast DNA binding factor I from the maize chloroplast ATP synthase promoter.