Biological control of parthenium (Parthenium hysterophorus): the Australian experience

ABSTRACT

Parthenium is a Weed of National Significance in Australia. Biological control of parthenium in Australia commenced in 1977 and since then nine insect species and two rust fungi have been introduced and established. Seven of them are widespread, however the time taken for field establishment varied widely between various agents, ranging from one to 15 years. Among them, the stem-galling Epiblema moth, the stem-boring Listronotus weevil, the seed-feeding Smicronyx weevil and the root-feeding Carmenta moth occur in all parthenium-infested areas at high population densities. The leaf-feeding Zygogramma beetle occurs only in central and southern Queensland, and not in northern Queensland. The parthenium summer rust occurs seasonally in central and northern Queensland, while the parthenium winter rust is more widespread in southern Queensland than in central Queensland, but does not occur in north Queensland. The sap-feeding Stobaera planthopper and the leaf-mining Bucculatrix moth established and are widespread, but their damage levels remain very low. The stem-galling Conotrachelus weevil and the stem-boring Platphalonidia moth are believed to be established, but at very low abundance. Biological control has resulted in significant reductions in the abundance and impact of parthenium in Australia. As a result, the area infested with parthenium in central Queensland has declined since the mid-1990s. Due to the absence of many of the effective agents in southern and south-eastern Queensland, agents from central Queensland are being redistributed there. Additionally, based on Australian success, many of these agents have also been introduced into other countries around the world.     

EDTA enhanced heavy metal phytoextraction: metal accumulation,leaching and toxicity

Synthetic chelates such as ethylene diamine tetraacetic acid (EDTA) have been shown to enhance phytoextraction of some heavy metals from contaminated soil. In a soil column study, we examined the effect of EDTA on the uptake of Pb, Zn and Cd by Chinese cabbage (Brassica rapa), mobilization and leaching of heavy metals and the toxicity effects of EDTA additions on plants. The most effective was a single dose of 10 mmol EDTA kg^–1 soil where we detected Pb, Zn and Cd concentrations that were 104.6, 3.2 and 2.3-times higher in the aboveground plant biomass compared to the control treatments. The same EDTA addition decreased the concentration of Pb, Zn and Cd in roots of tested plants by 41, 71 and 69%, respectively compared to concentrations in the roots of control plants. In columns treated with 10 mmol kg^–1 EDTA, up to 37.9, 10.4 and 56.3% of initial total Pb, Zn and Cd in soil were leached down the soil profile, suggesting high solubility of heavy metals-EDTA complexes. EDTA treatment had a strong phytotoxic effect on the red clover (Trifolium pratense) in bioassay experiment. Moreover, the high dose EDTA additions inhibited the development of arbuscular mycorrhiza. The results of phospholipid fatty acid analyses indicated toxic effects of EDTA on soil fungi and increased environmental stress of soil microfauna.     

Larval parasitism by native insects on the introduced stem-galling moth Epiblema strenuana Walker (Lepidoptera: Tortricidae) and its implications for biological control of Parthenium hysterophorus (Asteraceae)

Abstract  The significance of natural enemies in the failure or reduced effectiveness of weed biological control agents remains largely unknown. Larval and pupal parasitism by native insects in the stem-galling moth Epiblema strenuana was studied in north Queensland, 4 (1986–87) and 16 (1998–99) years after its introduction as a biological-control agent for Parthenium hysterophorus . Specific questions answered in this study are: (i) Has parasitism increased over the years?; (ii) Are the levels of parasitism influenced by the host plant phenology?; and (iii) What are the potential implications of current parasitism levels for the effectiveness of E. strenuana ? There was no increase in the parasitoid species assemblage over the years. In 1986–87, Antrocephalus sp. and Bracon sp. were the most predominant species. The combined larval and pupal parasitism was low (2.6%) and there was no seasonal difference in the parasitism levels. In 1998–99 Bracon sp. was the most prevalent species. Parasitism by Bracon sp. in 1998–99 was several times higher (22.9%) than the combined larval and pupal parasitism in 1986–87. However, parasitism by Bracon sp. remained low (6.5–8.2%) at the beginning of the parthenium-growing season, and reached peak levels (49–53%) only at the end of the season. Parasitism by Bracon sp. was also significantly lower in rosettes (7.2%) than in flowering plants (22.8%). Galling can have a negative impact on the weed only when initiated at the rosette stage. In 1998–99 lower levels of parasitism early in the season when most plants are in the rosette stage suggest that the impact of parasitism on the effectiveness of the gall insect may not be significant.     

Post introductory risk assessment studies on Zygogramma bicolorata (Coleoptera: Chrysomelidae), a classical biological control agent of Parthenium hysterophorus (Asteraceae) in India

Zygogramma bicolorata Pallister (Coleoptera: Chrysomelidae), a biological control agent of Parthenium hysterophorus L. (Asteraceae), was feeding on leaves of Helianthus annuus in India, raising concerns of its host range. Based on the age grading technique, it was shown that the majority of Z. bicolorata on sunflower plants at any time were reproductively immature. This establishes that Z. bicolorata does not pose any risk to sunflower in India.     

Chemically enhanced phytoextraction of risk elements from a contaminated agricultural soil using Zea mays and Triticum aestivum: performance and metal mobilization over a three year period

Enhanced phytoextraction using EDTA for the remediation of an agricultural soil contaminated with less mobile risk elements Cd and Pb originating from smelting activities in Príbram (Czech Republic) was assessed on the laboratory and the field scale. EDTA was applied to the first years crop Zea mays. Metal mobilization and metal uptake by the plants in the soil were monitored for two additional years when Triticum aestivum was planted. The application ofEDTA effectively increased water-soluble Cd and Pb concentrations in the soil. These concentrations decreased over time. Anyhow, increased concentrations could be still observed in the third experimental year indicating a low possibility of groundwater pollution after the addition of EDTA during and also after the enhanced phytoextraction process under prevailing climatic conditions. EDTA-applications caused phytotoxicity and thereby decreased biomass production and increased Cd and Pb uptake by the plants. Phytoextraction efficiency and phytoextraction potential were too low for Cd and Pb phytoextraction in the field in a reasonable time frame (as less than one-tenth of a percent of total Cd and Pb could be removed). This strongly indicates that EDTA-enhanced phytoextraction as implemented in this study is not a suitable remediation technique for risk metal contaminated soils.     

Enhanced Phytoremediation of Crude Oil-Polluted Soil by Four Plant Species: Effect of Inorganic and Organic Bioaugumentation

A field experiment investigating the removal and/or uptake of Polycyclic Aromatic Hydrocarbons (PAHs) and specific metals (As, Cd, Cr) from a crude oil polluted agricultural soil was performed during the 2013 wet season using four plant species: Fimbristylis littoralis, Hevea brasilensis (Rubber plants), Cymbopogom citratus (Lemon grass), and Vigna subterranea (Bambara nuts). Soil functional diversity and soil-enzyme interactions were also investigated. The diagnostic ratios and the correlation analysis identified mixed petrogenic and pyrogenic sources as the main contributors of PAHs at the study site. A total of 16 PAHs were identified, 6 of which were carcinogenic. Up to 42.4 mg kg^?1 total PAHs was recorded prior to the experiments. At 90 d, up to 92% total PAH reduction and 96% As removal were achieved using F. littoralis, the best performing species. The organic soil amendment (poultry dung) rendered most of the studied contaminants unavailable for uptake. However, the organic amendment accounted for over 70% of the increased dehydrogenase, phosphatase, and proteolytic enzymes activities in the study. Overall, the combined use of soil amendments and phytoremediation significantly improved the microbial community activity, thus promoting the restoration of the ecosystem.     

Biology and Host Specificity of the Stem Galling Weevil Conotrachelus albocinereus Fiedler (Col.: Curculionidae), a Biocontrol Agent for Parthenium Weed Parthenium hysterophorus L. (Asteraceae) in Queensland, Australia

The stem-galling weevil Conotrachelus albocinereus Fiedler has been investigated as a potential biological control agent against parthenium weed ( Parthenium hysterophorus L.) in Australia. Adults were tested in multiple-choice feeding and oviposition tests on 56 plant species in 51 genera. No feeding or oviposition was recorded on any non-target plant except annual ragweed ( Ambrosia artemisiifolia L.), a closely related weed. Field releases of the weevil in Queensland, Australia, commenced in 1995 and establishment has been recorded at several sites.     

Enhanced phytoextraction: I. Effect of EDTA and citric acid on heavy metal mobility in a calcareous soil

Phytoextraction, the use of plants to extract heavy metals from contaminated soils, could be an interesting alternative to conventional remediation technologies. However, calcareous soils with relatively high total metal contents are difficult to phytoremediate due to low soluble metal concentrations. Soil amendments such as ethylene diaminetetraacetate (EDTA) have been suggested to increase heavy metal bioavailability and uptake in aboveground plant parts. Strong persistence of EDTA and risks of leaching of potentially toxic metals and essential nutrients have led to research on easily biodegradable soil amendments such as citric acid. In our research, EDTA is regarded as a scientific benchmark with which degradable alternatives are compared for enhanced phytoextraction purposes. The effects of increasing doses of EDTA (0.1,1,10 mmol kg(-1) dry soil) and citric acid (0.01, 0.05, 0.25, 0.442, 0.5 mol kg(-1) dry soil) on bioavailable fractions of Cu, Zn, Cd, and Pb were assessed in one part of our study and results are presented in this article. The evolution of labile soil fractions of heavy metals over time was evaluated using water paste saturation extraction (approximately soluble fraction), extraction with 1 M NH4OAc at pH 7 (approximately exchangeable fraction), and extraction with 0.5 M NH4OAc + 05 M HOAc + 0.02 M EDTA at pH 4.65 (approximately potentially bioavailable fraction). Both citric acid and EDTA produced a rapid initial increase in labile heavy metal fractions. Metal mobilization remained constant in time for soils treated with EDTA, but a strong exponential decrease of labile metal fractions was noted for soils treated with citric acid. The half life of heavy metal mobilization by citric acid varied between 1.5 and 5.7 d. In the following article, the effect of heavy metal mobilization on uptake by Helianthus annuus will be presented.     

Current Status of the Stem-boring Weevil Listronotus setosipennis (Coleoptera: Curculionidae) Introduced Against the Weed Parthenium hysterophorus (Asteraceae) in Australia

Effects of the stem-boring weevil Listronotus setosipennis (Coleoptera: Curculionidae) on different growth stages of the weed Parthenium hysterophorus (Asteraceae) was evaluated in a glasshouse and field cages, and its field prevalence in Queensland, Australia was assessed. In the glasshouse, L. setosipennis reduced the plant height by 51%, number of leaves by 78%, flower production by 63% and plant biomass by 54% in rosette stage plants. Damage by L. setosipennis in rosette stage plants in the field cage reduced the primary stem height by 26% and flower production by 38%, but the impact on total plant height, basal stem width, root length, number of branches, root biomass and total plant biomass was not significant. In both glasshouse and field cages, the impact of L. setosipennis on preflowering and flowering stages of parthenium was not significant. L. setosipennis was recorded in 48% of the parthenium-infested sites (n=132) sampled and 16% of the sites showed high to very high levels of incidence. L. setosipennis was more prevalent on alluvial and black soils than on clay and sandy soils. L. setosipennis is a promising biocontrol agent for regions with prolonged dry periods and erratic rainfall pattern.     

Phytoremediation of lead (Pb) and Arsenic (As) by Melastoma malabathricum L. from Contaminated Soil in Separate Exposure

This study was conducted to investigate the uptake of lead (Pb) and arsenic (As) from contaminated soil using Melastoma malabathricum L. species. The cultivated plants were exposed to As and Pb in separate soils for an observation period of 70 days. From the results of the analysis, M. malabathricum accumulated relatively high range of As concentration in its roots, up to a maximum of 2800 mg/kg. The highest accumulation of As in stems and leaves was 570 mg/kg of plant. For Pb treatment, the highest concentration (13,800 mg/kg) was accumulated in the roots of plants. The maximum accumulation in stems was 880 mg/kg while maximum accumulation in leaves was 2,200 mg/kg. Only small amounts of Pb were translocated from roots to above ground plant parts (TF < 1). However, a wider range of TF values (0.01–23) for As treated plants proved that the translocation of As from root to above ground parts was greater. However, the high capacity of roots to take up Pb and As (BF > 1) is indicative this plants is a good bioaccumulator for these metals. Therefore, phytostabilisation is the mechanism at work in M. malabathricum's uptake of Pb, while phytoextraction is the dominant mechanism with As.     

Enhanced phytoextraction: II. Effect of EDTA and citric acid on heavy metal uptake by Helianthus annuus from a calcareous soil

High biomass producing plant species, such as Helianthus annuus, have potential for removing large amounts of trace metals by harvesting the aboveground biomass if sufficient metal concentrations in their biomass can be achieved However, the low bioavailability of heavy metals in soils and the limited translocation of heavy metals to the shoots by most high biomass producing plant species limit the efficiency of the phytoextraction process. Amendment of a contaminated soil with ethylene diamine tetraacetic acid (EDTA) or citric acid increases soluble heavy metal concentrations, potentially rendering them more available for plant uptake. This article discusses the effects of EDTA and citric acid on the uptake of heavy metals and translocation to aboveground harvestable plant parts in Helianthus annuus. EDTA was included in the research for comparison purposes in our quest for less persistent alternatives, suitable for enhanced phytoextraction. Plants were grown in a calcareous soil moderately contaminated with Cu, Pb, Zn, and Cd and treated with increasing concentrations of EDTA (0.1, 1, 3, 5, 7, and 10 mmol kg(-1) soil) or citric acid (0.01, 0.05, 0.25, 0.442, and 0.5 mol kg(-1) soil). Heavy metal concentrations in harvested shoots increased with EDTA concentration but the actual amount of phytoextracted heavy metals decreased at high EDTA concentrations, due to severe growth depression. Helianthus annuus suffered heavy metal stress due to the significantly increased bioavailable metal fraction in the soil. The rapid mineralization of citric acid and the high buffering capacity of the soil made citric acid inefficient in increasing the phytoextracted amounts of heavy metals. Treatments that did not exceed the buffering capacity of the soil (< 0.442 mol kg(-1) soil) did not result in any significant increase in shoot heavy metal concentrations. Treatments with high concentrations resulted in a dissolution of the carbonates and compaction of the soil. These physicochemical changes caused growth depression of Helianthus annuus. EDTA and citric acid added before sowing of Helianthus annuus did not appear to be efficient amendments when phytoextraction of heavy metals from calcareous soils is considered.     

Enhanced accumulation of Cd in castor (Ricinus communis L) by soil-applied chelators

Phytoextraction has been identified as one of the most propitious methods of phytoremediation. This pot experiment were treated with varying amounts of (ethylenediamine triacetic acid) EDTA 3–15, (Nitriloacetic acid) NTA 3–10, (Ammonium citrate) NH₄ citrate 10 – 25 mmol and one mg kg^–1Cd, filled with 5 kg soil. The addition of chelators significantly increased Cd concentration in soil and plant. The results showed that maximum Cd uptake was noted under root, shoot and leaf of castor plant tissue (2.26, 1.54, and 0.72 mg kg^–1) under EDTA 15, NTA 10, and NH₄ citrate 25 mmol treatments respectively, and in soil 1.08, 1.06 and 0.52 mg kg^–1 pot^–1 under NH₄ citrate 25, NTA 10 and EDTA 15 mmol treatments respectively, as against to control (p < 0.05). Additions of chelators reduction biomass under the EDTA 15 mmol as compared to other treatments, However, Bioconcentration factor (BCF), translocation factor (TF) and remediation factor (RF) were significantly increased under EDTA 15 and NH₄ citrate 25 mmol as against control. Our results demonstrated that castor plant proved satisfactory for phytoextraction on contaminated soil, and EDTA 15 and NH₄ citrate 25 mmol had the affirmative effect on the Cd uptake in the artificial Cd-contaminated soil.     

4种植物对133Cs和88Sr污染土壤的修复研究

以露地盆栽的苏丹草、向日葵、芥菜、萝卜4种植物为对象,研究它们对土壤中不同浓度(0、2.5、5.0、10.0、20.0、40.0mg/kg)133Cs、88Sr的吸收积累状况,并比较它们对133Cs、88Sr污染土壤的修复效率。结果显示:(1)4种植物单株生物量在各浓度处理下均表现为向日葵>萝卜>芥菜>苏丹草,但它们对133Cs的吸收能力为萝卜>苏丹草>向日葵>芥菜,单株133Cs累积量为向日葵>萝卜>苏丹草>芥菜,单株88Sr累积量表现为萝卜、向日葵>苏丹草>芥菜,而且4种植物对88Sr的吸收能力均强于133Cs。(2)萝卜在除10.0mg/kg133Cs外的各处理中富集系数均大于1,对土壤中133Cs的吸收能力较强;苏丹草在除5.0mg/kg133Cs处理外的转运系数均大于1,其余3种植物在各处理中的转运系数均低于1;88Sr在萝卜体内从根系向上转运到地上部分的能力明显高于其它3种植物,芥菜、向日葵次之。(3)4种植物对88Sr在体内向上的迁移转运能力均大于133Cs。研究表明,向日葵单株对133Cs、88Sr污染土壤的修复效率最高,萝卜次之,且向日葵和萝卜分别因其生物量和吸收能力优势而对被污染土壤中的133Cs和88Sr具有更强的提取能力。     

Comparative Evaluation of Metal Phytoremediation Potential of Trees,Grasses, and Flowering Plants from Tannery-Wastewater-Contaminated Soil in Relation with Physicochemical Properties

This study reports a comparative account of metal accumulation in the trees, grasses, and flowering plants from agricultural fields contaminated with tannery wastewater. Soil physico-chemical properties along the pollution gradient and soil depth were analyzed. Monitoring and assessment of the plants growing on contaminated sites revealed that the accumulation of Cr in the aboveground part of the trees ranged from 1.87 to 34.44 μg g^?1 dw with maximum concentration in Dendro-calamus strictus (34.44 μg g^?1 dw). Chrysanthemum coronarium and Tagetes erecta showed better accumulation of Cr than other flowering plants. Separate field experiments were conducted on the contaminated area. The shoots of Vetiveria zizanoides (532 mg 4 m^?2) and Cymbopogan winterianus (535.46 mg 4 m^?2) have shown almost similar removal potential of Cr, with maximum removal potential in the roots of C. winterianus (1206.43 mg 4 m^?2). Seasonal flowering plants (i.e., C. coronarium) have shown better accumulation of Cr than T. erecta. The results indicate that the plants of V. zizanoides, C. coronarium, and C. winterianus are suitable for phytoremediation of contaminated sites and trees can successfully be used for phytostabilization.     

Influence of Soil Chemistry and Plant Physiology in the Phytoremediation of Cu,Mn, and Zn

Different anthropogenic sources of metals can result from agricultural, industrial, military, mining and urban activities that contribute to environmental pollution. Plants can be grown for phytoremediation to remove or stabilize contaminants in water and soil. Copper (Cu), manganese (Mn) and zinc (Zn) are trace essential metals for plants, although their role in homeostasis in plants must be strictly regulated to avoid toxicity. In this review, we summarize the processes involved in the bioavailability, uptake, transport and storage of Cu, Mn and Zn in plants. The efficiency of phytoremediation depends on several factors including metal bioavailability and plant uptake, translocation and tolerance mechanisms. Soil parameters, such as clay fraction, organic matter content, oxidation state, pH, redox potential, aeration, and the presence of specific organisms, play fundamental roles in the uptake of trace essential metals. Key processes in the metal homeostasis network in plants have been identified. Membrane transporters involved in the acquisition, transport and storage of trace essential metals are reviewed. Recent advances in understanding the biochemical and molecular mechanisms of Cu, Mn and Zn hyperaccumulation are described. The use of plant-bacteria associations, plant-fungi associations and genetic engineering has opened a new range of opportunities to improve the efficiency of phytoremediation. The main directions for future research are proposed from the investigation of published results.     

The Effect of EDTA Addition on the Phytoremediation Efficiency of Pb and Cr by Echinochloa crus galii (L.) Beave and Associated Potential Leaching Risk

Metal-contaminated soils constitute a serious environmental problem with adverse consequences for human health. This study was conducted to determine phytoextraction efficiency of Echinochloa crus galii for Pb and Cr and the EDTA-assisted (0. 2.5, 5, 10 mmol kg^?1) phytoextraction and the potential for leaching of the metals during the phytoextraction process. The results revealed that the bioconcentration factors of roots of the plant were relatively higher than the bioconcentration factors of the shoot. Thus, the plant species of E. crus galii would be applicable for Pb and Cr phytostabilization. Addition of EDTA had virtually a significant effect on uptake of the metals by the plant and elevated Pb and Cr concentrations in plant organs as compared with the control. Optimum phytoextraction was observed when 5 mmol kg^?1 EDTA was added in a single dosage 60 days after the plant cultivation and consequently soil Pb and Cr concentration decreased with the passage of time.     

Effects of GA3 on Plant Physiological Properties,Extraction, Subcellular Distribution and Chemical Forms of Pb in Lolium perenne

The effects of growth-promoting hormone gibberellic acid 3 (GA₃) on physiology, Pb phytoextraction, and metal detoxification mechanisms in Lolium perenne were studied. Results showed that addition of GA₃ alone at lower doses (1 or 10 μM) facilitated antioxidant defense of L. perenne under Pb stress, decreased the toxicity of Pb in plant shoot by increasing the proportion of Pb in cell wall, hence significantly enhanced photosynthesis and plant growth, as well as Pb uptake and accumulation in L. perenne (P < 0.05). However, these indicators showed the opposite changes when treated with GA₃ at a higher dose (100 μM). Of the total Pb in plant shoot, 36–51% was associated with cell wall, and 31–40% was soluble fraction, while 41.4–49.7% was NaCl extractable, 24.6–35.4% HAc extractable followed by other fractions. These findings suggest that Pb fixation by pectates and proteins in cell wall and sequestration in vacuole are responsible for Pb detoxification in plant, and the GA₃ at 1 μM appears to be optimal for enhancing Pb phytoextraction by L. perenne from Pb polluted soils.     

Status, invasiveness and environmental threats of three tropical American invasive weeds (Parthenium hysterophorus L., Ageratum conyzoides L., Lantana camara L.) in India

Invasive weeds have threatened the integrity of ecosystems throughout the world. They affect not only the species diversity of native areas but also their biological integrity. In India, a number of invasive exotic weeds have been reported but some viz. Parthenium hysterophorus, Lantana camara and Ageratum conyzoides, especially those from tropical America are troublesome and have caused adverse ecological, economic and social impact. These weeds can be seen growing in different landscapes but are luxuriantly localized in unattended forests and cultivated areas. Parthenium hysterophorus (Asteraceae, commonly known as congress grass) is perhaps the most troublesome and noxious weed of urban and rural India. Besides rapidly colonizing areas replacing the native vegetation, it is also known to cause a number of human health problems such as skin allergy, rhinitis and irritation to eyes of the residents in the vicinity. Likewise, it causes fodder scarcity in addition to being unpalatable and toxic to livestock. Lantana camara (Verbenaceae), another serious tropical American pest, has encroached upon large areas of land, especially the forests where it has virtually replaced the forest floor vegetation and reduced tree growth. Also because of its bushy and spreading type of growth it obstructs forest operations. The third weed, Ageratum conyzoides (Asteraceae, Billy goat weed) has invaded agricultural fields. It interferes with crops and causes yield reductions of major staple crops of India. When it invades rangeland areas, it out competes native grasses causing scarcity of fodder. These weeds have similar growth strategies such as fast growth rates, short life-cycles, greater reproductive potential, high competitive abilities and allelopathy that make them successful invaders of native habitats. Mechanical, chemical, biological and cultural control tactics have failed individually, though integrated approaches combining all these approaches along with community participation and proper land management have been relatively successful. This paper presents various aspects of biology, ecology, hazards and control measures of these weeds.     

Sulfuric Acid and Gibberellic Acid (GA3) Treatment Combined with Exposure to Cold Temperature Modulates Seed Proteins during Breaking of Dormancy to Germination in Tilia miqueliana

The Protein Journal - Tilia miqueliana produces woody seeds that exhibit deep dormancy. In this study, we used cell biology methods, including Paraffin section determination and Coomassie brilliant...     

A Possible Role for Indoleacetic Acid, Low Temperature, and Phospholipid Metabolism in the Induction of GA(3) Responsiveness in GA(3) Insensitive (Rht3-Containing) Dwarf Wheat Aleurone

Preincubation of dwarf, Rht3-containing deembryonated seed for 4 hours in 342 nanomolar indoleacetic acid (IAA) induced maximum sensitivity to GA₃. In addition, the 4-hour IAA pretreatment caused a 2-fold increase in total phospholipids which coincided identically on a temporal basis with the induced GA₃ sensitivity. Changes in absolute levels of individual phospholipids and their acyl groups were recorded and compared with the changes observed in several Rht-containing aleurone tissues which were induced to develop GA₃ sensitivity by exposure to low temperature (5°C). Several distinct similarities between all tissues were recorded as they develop GA₃ sensitivity. One parameter, the percentage phospholipid composition, was quite similar in all tissues after they had become maximally sensitive to GA₃, suggesting that there is at least one membrane phospholipid composition which is particularly responsive to GA₃. The results indicate that (a) the basis of the GA₃ insensitivity of the Rht mutation resides in an aberrant phospholipid/fatty acid composition and/or metabolism; (b) exposure to low temperature (5°C) for 20 hours or longer, or 342 nanomolar IAA for 4 hours or longer reverses or corrects the genetic lesion, enabling the tissue to adopt a GA₃ responsive membrane composition. Finally, an hypothesis is discussed which indicates that IAA may play a controlling role in the mobilization of endospermal reserves, at least in Rht3-containing wheat aleurone.