Approach to Physiological Functions of Ethrel in the Ripening of Cotton Boll

Both leaf and boll of cotton can absorb ethrel and the acceptor releases ethylene rapidly. Ethrel absorbed by leaves can release ethylene in bolls, whereas that absorbed by bolls cannot release ethylene in leaves. Bolls treated with ethrel has two peaks in ethylene releasing. The first peak appears about two days after treatment, and the second appears before the splitting of boll. The control has only one peak in ethylene releasing which appears eight days later than the second peak of the bolls treated with ethrel. This coincides with the fact that ethrel enables bolls to split seven to ten days earlier. The releasing of ethylene by cotton bolls is closely related to temperature, and is accelerated with increasing temperature no matter cotton bolls are treated with ethrel or not.     

Involvement of Hydrogen Peroxide in Cotton Leaf Abscission Induced by Thidiazuron

Journal of Plant Growth Regulation - Thidiazuron (TDZ) has been extensively applied as chemical defoliant in cotton production, but the physiological mechanisms for its defoliating activity are...     

乙烯利对菜豆叶枕外植体脱落和离区纤维素酶合成的影响

以乙烯利处理菜豆叶枕外植体,能显著提高对抗的脱落及其离区纤维酶的活力。蛋白质和核酸合成的抑创剂环己酰亚胺和放线菌素Ｄ,对乙烯利促进的脱落与离区纤维素酶活力不仅有明显的抑制作用,而且具有严格的时间顺序。提示乙烯利促进脱落的生理效应与其诱导高区纤维素酶合成时基因表达的转录和翻译过程有密切关系。此外,外植体经乙烯利处理后再分别不同时间加ＩＡＡ,并根据测定其抑制乙烯利诱导的纤维素酶活力变化,与不同时间加放线菌素Ｄ的实验结果相同,推断ＩＡＡ对乙烯利促进脱落的拮抗作用可能是在乙烯利诱导纤维素酶合成的转录过程。     

Role of IAA-Oxidase in Abscission Control in Cotton

The potential role of indoleactic acid (IAA)-oxidase as an in vivo abscission regulating system in the cotton (Gossypium hirsutum L.) cotyledonary explant was investigated. Phenols (usually monophenols), which are cofactors of cotton IAA-oxidase in vitro, accelerated abscission. Phenols (usually orthodihydroxyphenols), which inhibit cotton IAA-oxidase in vitro, inhibited abscission. Inhibition or stimulation of abscission was accomplished by phenols both with and without IAA. Results were similar when treatments were applied as lanolin pastes to the cut petiole ends or as solutions in which explants were submerged. An abscission accelerating phenol stimulated the decarboxylation of IAA-1-¹⁴C by explants and an abscission inhibiting phenol inhibited the decarboxylation of IAA-1-¹⁴C.     

Auxin Transport as Related to Leaf Abscission during Water Stress in Cotton

Plant water deficits reduced the basipetal transport of auxin in cotyledonary petiole sections taken from cotton (Gossypium hirsutum L.) seedings. A pulse-labeling technique was employed to eliminate complications of uptake or exit of ¹⁴C-indoleacetic acid from the tissue. The transport capacity or the relative amount of radioactivity in a 30-minute pulse which was basipetally translocated was approximately 30% per hour in petioles excised from well watered seedlings (plant water potentials of approximately -4 to -8 bars). No cotyledonary leaf abscission took place in well watered seedlings. Plant water potentials from -8 to -12 bars reduced the transport capacity from 30 to 15% per hour, and although the leaves were wilted, cotyledonary abscission did not increase appreciably at these levels of stress. The threshold water potential sufficient to induce leaf abscission was approximately -13 bars and abscission increased with increasing stress while the auxin transport capacity of the petioles remained relatively constant (15% per hour). The basipetal transport capacity of well watered petioles tested under anaerobic conditions and acropetal transport tested under all conditions were typically less than basipetal transport under the most severe stress conditions. Cotyledonary abscission took place during and 24 hours after relief of stress with little or no abscission taking place 48 hours after relief of stress. Although the water potential returned to -4 bars within hours after rewatering the stressed plants, partial recovery of the basipetal transport capacity of the petioles was not apparent until 48 hours after rewatering, and at least 72 hours was required to return the transport capacity to near normal values. These data support the view that decreased levels of auxin reaching the abscission zone from the leaf blade influence the abscission process and further suggest that the length of time that the auxin supply is maximally reduced is more critical than the degree of reduction.     

Nucleolar Activity in Differentiating Cotton Fibres is Related to the Position of the Boll on the Plant

Significant differences in nucleolar size at early stages ofcotton fibre development have been observed between bolls ofdifferent fruiting branches. Cutting off the apex or removalof the leaf subtending the cotton boll 6 d before floweringor emasculation followed by an addition of GA₃ resulted in asignificant decrease of the nucleolar size. Excising half ofthe roots had no influence on the nucleolar activity. The differencesin nucleolar size between bolls of the first and fifth fruitingbranches remained significant except in the case where the leafsubtending the boll was removed. Key words: Cotton fibres, nucleolus, gibberellin     

Identification and Characterisation of Cotton Boll Wall-Specific Gene Promoters for Future Transgenic Cotton Varieties

Current transgenic cotton varieties constitutively express transgenes encoding anti-pest proteins to protect against plant damage caused by insect attack. However, restricting the spatial expression of transgenes to the tissues in which their products are required is likely to improve crop performance and reduce environmental impacts. Therefore, we sought to identify native gene promoters that would restrict transgene expression to the boll wall of the cotton plant. Six abundant mRNAs that accumulated preferentially in the boll wall were identified, and the gene promoters of two of these mRNAs were identified, isolated and characterised. The promoters of a proline-rich protein gene (GhPRP3) and a chalcone synthase gene (GhCHS1) were demonstrated to drive boll wall-preferential expression of a reporter gene in a transient transformation system. In silico analyses of the GhPRP3 and GhCHS1 promoters identified numerous previously identified cis-acting regulatory elements (CAREs) as well as the presence of three novel shared CAREs. The identification and characterisation of these promoters provides an important step in the development of the next generation of transgenic plants.     

Electron-Microscope Observation on the Pollen Development of Male Sterility Wheat Induced by Ethrel

The pollen development of male sterility wheat induced by Ethrel was studied in comparison with that of normal wheat by transmission and scanning electron-microscope. The results obtained are summarized as follows: 1. The primary morphological changes of abortive wheat pollen after treatment with Ethrel took place in the vacuole stage. The materials of cytoplasm were rarefied. All kinds of the cell organelles and vacuoles became degenerated and disorganized. Inside a small number of cell nuclei, chromatin granules coagulated irregularly. The number and the activity of the Ubisch bodices became reduced evidently. 2. In the mature stage, the differences between the treated wheat and normal wheat became even more striking. The normal pollens were spherical in sharp, and full of starch granules. The treated pollen were monstrous. There was a large empty vacuole in every abortive pollen cell, in which the starch granules were smaller and fewer than these in the normal ones. The nuclei and cytoplasm in some of the abortive pollens were degenerated, leaving only the cell walls. 3. Under scanning electron microscope, it was discovered that the normal wheat pollen were spherical or oval. The germinated pores jutted. The round-openings of the pores could be clearly seen. The abortive pollen induced by Ethrel looked like some shrunken balls, and became deformed and were blocked up. 4. On discussion of the mechanism of the Ethrel-induced male sterility in wheat, the authors suggest that special attention should be paid to the changes of the Ubisch bodies and the vacuoles.     

Involvement of Abscisic Acid in Ethylene-Induced Cotyledon Abscission in Cotton Seedlings

Cotton (Gossypium hirsutum L. cv LG102) seedlings raised from seeds exposed to 100 [mu]M norflurazon (NFZ) during imbibition contained reduced levels of free abscisic acid (ABA) and were visibly achlorophyllous. Exposure of untreated cotton seedlings to ethylene concentrations >1 [mu]L/L for 24 h resulted in cotyledon abscission. In contrast, exposure of NFZ-treated seedlings to concentrations of ethylene [less than or equal to]50 [mu]L/L elicited no cotyledon abscission. Application of ABA, an ABA analog, or jasmonic acid to NFZ-treated seedlings restored ethylene-induced abscission. Isolated cotyledonary node explants prepared from NFZ-treated seedlings exhibited an altered dose-response pattern of ethylene-induced petiole abscission. Endogenous levels of free IAA were unaltered in NFZ-treated seedlings. Ethylene treatment (50 [mu]L/L, 24 h) had no effect on free indoleacetic acid (IAA) levels in either control or NFZ-treated seedlings. Levels of conjugated (ester plus amide) IAA were substantially increased in NFZ-treated seedlings regardless of ethylene treatment. These results indicate that endogenous ABA plays an essential, but physiologically undefined, role in ethylene-induced cotyledon abscission in cotton.     

Patterns of Ethylene and Carbon Dioxide Evolution during Cotton Explant Abscission

The relationship between abscission and the evolution of ethylene and CO₂ was examined in explants and explant segments of cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-1) under both static and flow system conditions, and in the presence and absence of mercuric perchlorate. Explant excision was immediately followed by increased ethylene evolution (wound ethylene); senescence was also accompanied by increased ethylene evolution (senescence ethylene). One or two ethylene peaks were found to interrupt the low background rate of ethylene evolution during the period between excision and senescence. The first intermediate ethylene peak coincided with a rise in CO₂ evolution; however, precedence could not be established. No statistical correlations were discovered between either intermediate ethylene peak and abscission. The best statistical correlation was found between wound ethylene and abscission at 12 hr after excision. No positive correlations were found between senescence ethylene and abscission. Implications of these results for the understanding of the role of ethylene in explant abscission are discussed.     

棉花化学催熟与脱叶的生理基础

从棉铃开裂和棉叶脱落的生理过程、化学催熟剂和脱叶剂作用的生理机制、不同种类催熟剂和脱叶剂复配/混用的方式等方面介绍了棉花化学催熟与脱叶的生理基础以及影响催熟剂和脱叶剂作用效果的因素,并对这一领域的研究作了展望.     

Field Evaluation of Bt Cotton Crop Impact on Nontarget Pests: Cotton Aphid and Boll Weevil

Bt cotton plants expressing Cry1Ac protein have high specificity for the control of lepidopteran larvae. However, studies conducted in several countries have shown these plants have a differential impact on nontarget herbivores. The aim of this study was to compare the colonization rates and population abundance of the cotton aphid, Aphis gossypii Glover (Hemiptera: Aphididae) and the boll weevil, Anthonomus grandis Boheman (Coleoptera: Curculionidae), in plots of Bt (Nuopal) and non-Bt cotton (Delta Opal) in an experimental field in Brasilia, DF, Brazil. No difference was observed in the preference and colonization by winged aphids to plants from the two treatments. There was no significant difference in abundance of wingless aphids or in the production of winged aphids between treatments. Apparently, the parameters that control factors such as fecundity, survival, and dispersal were similar on both Bt and non-Bt plants. Monitoring of plants for coccinellids, a specialist predator of aphids, and ants that act on the dispersal of aphids among plants showed no significant difference between Bt and non-Bt plants, supporting the inference above. Regarding the effect on boll weevil, there was also no significant difference between treatments in the total number of fruiting structures attacked in each plot, the percentage of fruiting structures attacked per plant or on the number of weevils emerging from fruits with boll weevil damage from egg-laying, when damaged fruit samples were held in the laboratory. Based on these results, we conclude that there is no impact of Bt cotton crop expressing Cry1Ac on the nontarget herbivores tested under field conditions.     

Seasonal Dynamics of Bacterial Colonization of Cotton Fiber and Effects of Moisture on Growth of Bacteria within the Cotton Boll

A highly replicated 3-year field study was conducted to determine the seasonal patterns of bacterial colonization of cotton fiber from the time of dehiscence of the bolls (the point at which the bolls just begin to open) through harvest and commercial ginning. Bacterial numbers on fiber samples from 16 plots were determined by dilution pour plating with tryptic soy agar containing cycloheximide, and numbers of gram-negative bacteria were determined by plating on tryptic soy agar containing vancomycin and cycloheximide. Populations of bacteria varied from year to year, but in all three seasons the pattern of colonization was generally a pattern consisting of a rapid increase following opening of the bolls and a more or less stable number thereafter throughout the growing season. Gram-negative bacteria accounted for 50% or more of the recoverable bacterial population. We hypothesized that the luxuriant bacterial flora developed as a result of the availability of sufficient free water in the bolls to allow bacterial proliferation with the carbon sources remaining after fiber maturation. Therefore, laboratory experiments were conducted to determine the threshold moisture level allowing growth of bacteria on fiber in the bolls. Bacterial proliferation occurred when as little as 2% moisture was added to air-dried fiber. Using simulated bolls, we demonstrated bacterial growth resulting from dew formation on fiber held in controlled-humidity chambers.     

Influence of Reproduction on the Abscission Process of Cotton (Gossypium barbadense L.) Leaves

Abscission responses of debladed petioles of young and olderleaves were analysed during flowering, fruiting and post fruitingstages of development of G. barbadense plants. Identical abscissionexperiments were performed with materials collected from plantsmaintained in a vegetative condition by removal of flower buds. Inhibition of the abscission of debladed petioles by NAA wasgreater in debudded plants as compared to normal plants andthe extent of inhibition gradually declined during growth. Promotiveeffects of ethrel and abscisic acid were higher in normal plantsthan in debudded plants. The duration of auxin-inhibitablc stage-I of abscission wasextended in debudded plants and it gradually declined with theprogress of development. Debudded plants were characterizedby higher abscission inhibition during stage-I and lower abscissionpromotion during stage-II as a result of application of auxincompounds to the debladed petioles. Laminar tissues of debudded plants contained higher amountsof endogenous IAA and lesser amount of abscisions than did thoseof normal plants and in both cases the levels of these compoundschanged markedly during plant development. Decrease of total RNA content in the distal tissues of the abscissionzones was accompanied by increase in proximal tissues duringabscission in both normal and debudded plants. This tendencywas more pronounced in normally grown plants as compared todebudded plants.     

Seed Priming with Gibberellin Regulates the Germination of Cotton Seeds Under Low-Temperature Conditions

Journal of Plant Growth Regulation - Exogenous substances play an important role in the response of cotton to low-temperature conditions during the germination stage, but little is known about the...     

Movement and Endogenous Levels of Abscisic Acid during Water-Stress-induced Abscission in Cotton Seedlings

In an effort to investigate possible involvement of abscisic acid (ABA) in foliar abscission processes, its movement and endogenous levels were examined in cotyledons taken from cotton seedlings (Gossypium hirsutum L.) subjected to varying degrees of water deficit, a condition which initiates leaf abscission. Using a pulse-labeling technique to avoid complications of uptake and exit from the tissue, ABA-1-¹⁴C movement was observed in both basipetal and acropetal directions in cotyledonary petioles taken from well watered, stressed, and rewatered plants. The label distribution patterns obtained after 1 and 3 hours of transport under all situations of water supply were diffusive in nature and did not change when tested under anaerobic conditions. The transport capacity of the petioles ranged from 3.6 to 14.4% ABA-1-¹⁴C transported per hour at estimated velocities of 0 to 2 millimeters per hour. Comparison of basipetal and acropetal movement indicated a lack of polarity under all conditions tested. These low transport capacities and slow velocities of movement, when compared to the active transport systems associated with auxin movement, as well as the lack of anaerobic effects and polarity, suggest that ABA movement in cotton cotyledonary petiole sections is facilitated by passive diffusion. Increases in free and bound ABA in the lamina with increased water stress did not correlate with patterns of cotyledonary abscission. Thus, no evidence was found to suggest that ABA is directly involved in stress-induced abscission processes.     

Ascorbic Acid Turnover in Cotton Boll as Affected by Foliar Application of Sucrose

Excision of main stem leaf subtending the sympodium decreasedascorbic acid turnover in the developing boll (cotton fruit)on the first node of this sympodium in var. Suvin Gossypiumbarbadense L). Ascorbic acid turnover increased substantiallyin seed cotton and carpels of the boll when sucrose was appliedto the source leaf even though the main stem leaf remained excised.The role of ascorbic acid if any in boll growth appeared tobe linked with sucrose transport. Ascorbic acid, sympodial leaf, sucrose, boll     

棉花GA 20-氧化酶基因转毛白杨的研究

以毛白杨为材料,研究了超量表达赤霉素合成酶基因(GA20-氧化酶基因)对毛白杨根、茎和叶的生长以及组织结构的影响,结果显示,表达GA20-氧化酶基因能显著提高毛白杨茎的生长,但是对根系的生长带来负面影响.同时,超量表达GA20-氧化酶基因促进了毛白杨茎木质部的生长,抑制了韧皮部和皮层的生长.研究结果表明GA20-氧化酶基因在毛白杨遗传改良中具有一定的应用价值.