Water Stress Enhances Ethylene-mediated Leaf Abscission in Cotton

Self Cite

120

The effect of plant water deficit on ethylene production by intact plants was tested in three species, beans (Phaseolus vulgaris L.), cotton (Gossypium hirsutum L.) and miniature rose (Rosa hybrida L., cv Bluesette). Compressed air was passed through glass, plant-containing cuvettes, ethylene collected on chilled columns, and subsequently assayed by gas chromatography. The usual result was that low water potential did not promote ethylene production. When plants were subjected to cessation of irrigation, ethylene production decreased on a per plant or dry weight basis of calculation. No significant promotion of ethylene production above control levels was detected when water deficit-treated bean or cotton plants were rewatered. The one exception to this was for cotton subjected to a range of water deficits, plants subjected to deficits of -1.4 to -1.6 MPa exhibited a transient increase of ethylene production of 40 to 50% above control levels at 24 or 48 hours. Ethylene was collected from intact leaves while plants developed a water deficit stress of -2.9 megapascals after rewatering, and no significant promotion of ethylene production was detected. The shoots of fruited, flowering cotton plants produced less ethylene when subjected to cessation of irrigation. In contrast, the ability of bench drying of detached leaves to increase ethylene production several-fold was verified for both beans and cotton. The data indicate that detached leaves react differently to rapid drying than intact plants react to drying of the soil with regard to ethylene production. This result suggests the need for additional attention to ethylene as a complicating factor in experiments employing excised plant parts and the need to verify the relevance of shock stresses in model systems.interest because the ethylene could be responsible for senescence and abscission induced by water deficits (13,25,26).Although the promotion of ethylene synthesis by water deficits appears firmly established, there are a number of concerns. First, to have a convenient experimental system, water deficits have often been imposed rapidly by drying detached leaves or fruits (3-6, 16, 18, 24, 31). In contrast, under natural drought the soil water is depleted slowly and plants progress through a series of drying cycles during which #w3 falls during the day and rises at night as plants recover due to reduced evaporative demand (30). Second, the experimental measurement of ethylene has usually required that detached plant parts be concentrated in a sealed container from which air samples are withdrawn and analyzed for ethylene. The air supply in these containers has often been static which is of some concern because oxygen is needed for the conversion of ACC to ethylene (2) and CO2 can either promote or reduce the production of ethylene (33). Finally, there are a few reports in the literature where investigators failed to observe a promotion of ethylene release with water deficit treatment of intact plants (6,9,13,19).With the development of flowing air sys...

Section: Discussionmentioning

confidence: 99%

Does Water Deficit Stress Promote Ethylene Synthesis by Intact Plants?

Morgan¹,

He²,

Greef³

et al. 1990

Self Cite

120

“…Leaf (2,4,24). The relationship between ethylene production and abscission, both induced by water stress, has also been well established in cotton (11,15) and citrus (4). However, it has been indicated recently that these findings may be artifactual results obtained when working with detached tissues (19,20).…”

Section: Introductionmentioning

confidence: 99%

1-Aminocyclopropane-1-Carboxylic Acid Transported from Roots to Shoots Promotes Leaf Abscission in Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) Seedlings Rehydrated after Water Stress

Tudela¹,

Primo‐Millo²

1992

135

The effect of water stress and subsequent rehydration on 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity, ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in ACC synthase activity were observed. Neither increase in ACC content nor significant ethylene production were detected in leaves of water-stressed plants. After rehydration, a sharp rise in ACC content and ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after water stress than in nonstressed plants. Leaf (2,4,24). The relationship between ethylene production and abscission, both induced by water stress, has also been well established in cotton (11,15) and citrus (4). However, it has been indicated recently that these findings may be artifactual results obtained when working with detached tissues (19,20). These authors concluded that water stress alone cannot induce ethylene synthesis in intact plants.Citrus trees present a characteristic behavior of water stress-induced leaf abscission. When trees are subjected to water stress, leaves are injured but are not abscised. They remain attached until water stress is relieved (by rain or irrigation) and, soon afterwards, they are abscised (1). Similar behavior has been reported in cotton plants (15), which has led us to suggest that during water stress an abscissioninducing factor is synthesized in roots of citrus trees, and later it is transported to the aerial parts of the plant where it induces abscission. Ethylene is the natural regulator of abscission, and due to its gaseous nature, it may be that this abscission-inducing factor is ACC, the metabolic precursor of ethylene. Xylem transport of ACC from roots to shoots was first demonstrated by Bradford and Yang to induce epinasty in tomato plants subjected to anaerobic root stress (5, 6). Later, interorgan ACC transport was shown in several systems (3,9,12,18,21,23,28,29). However, no studies to test the relationship between water stress-induced abscission and xylem transport of ACC have been made. The aim of this work is to study this hypothesis. MATERIALS AND METHODS Plant MaterialEight-to 10-month-old Cleopatra mandarin (Citrus reshni TUDELA AND PRIMO-MILLO flux density, 120 Mmol-s-1 m2. RH was 95% during dark periods and oscillated between 60 and 95% during light periods. Plants were watered three times per week with 300 mL of half-strength modified Hoagland solution. Water Stress TreatmentsWater stress began at the start of the 16-h light period. Well-watered plants were taken from the pots and their roots washed with water. Then, the plants were placed in pots with dry sand for different periods under continuous light. In rehy...

“…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 Cotton plants have provided the materials for extensive abscission research, and ETH2 has been implicated in the regulation of this abscission many times over (1,8,9,19,21,24,26 In a flow system specifically designed for this work, the patterns of ETH and CO2 evolution accompanying abscission in control explants were established and then compared with those patterns in explants treated with IAA and ABA. Abscission of hormone-treated and untreated explants was compared in the presence and absence of MP.…”

Section: Introductionmentioning

confidence: 99%

“…Cotton plants have provided the materials for extensive abscission research, and ETH2 has been implicated in the regulation of this abscission many times over (1,8,9,19,21,24,26). Among the numerous proposals forwarded to explain the role(s) of ETH in abscission, several have been based on experiments with cotton explants: most notably the hypotheses that abscission may be controlled in part by increasing tissue sensitivity to the ETH already produced (1), and that absicssion may be controlled in part by reduced auxin transport resulting from increased ETH evolution (10).…”

mentioning

confidence: 99%

Patterns of Ethylene and Carbon Dioxide Evolution during Cotton Explant Abscission

Marynick¹

1977

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 Cotton plants have provided the materials for extensive abscission research, and ETH2 has been implicated in the regulation of this abscission many times over (1,8,9,19,21,24,26 In a flow system specifically designed for this work, the patterns of ETH and CO2 evolution accompanying abscission in control explants were established and then compared with those patterns in explants treated with IAA and ABA. Abscission of hormone-treated and untreated explants was compared in the presence and absence of MP. Patterns of ETH and CO2 evolution were also studied in segments of cotton explants and in individual explants. MATERIALS AND METHODSGeneral Explant Techniques. All experiments were performed with excised cotyledonary nodes of 14-day-old cotton seedlings (Gossypium hirsutum L. cv. Acala SJ-1) or with further subdivisions of this explant. Subdivision of a standard explant consisted of excising the petiole stumps and dividing them each into two segments 2 to 2.5 mm in length. The proximal segments contained the abscission zones with their surrounding tissues and were called abscission zone segments. The distal segments and the axes were referred to, respectively, as petiole stump segments and axial segments. On subdivision, each standard explant yielded two abscission zone segments, two petiole stump segments, and one axial segment. The standard growth regime and cotton explant procedures were followed with minor modifications (7,12,28). Briefly, the explants were supported in an upright position by a shallow layer (5 mm) of 1.5% agar covering the base of the explant chamber, approximately 10 g of pressure was applied to the petioles in testing for abscission, and abscised petioles were not removed from the explant chambers until all gas production data had been obtained. Agar droplets were omitted on all stem and petiole stumps unless otherwise indicated.Flow System, Chromatography, and Sampling. Most experiments were conducted in a flow system. Rates of ETH and CO2 evolution were determined from chromatographic analysis of gas samples withdrawn from the explant chambers (22,23). Instantaneous rates of gas evolution were calculated using the appropriate formula (22), and total amounts produced were estimated by cutting and weighing Xerox copies of the individual rate versus time graphs.The atmosphere of the flow system was Purafil-filtered ETHfree air. The flow system was similar to that described by Claypool and Keefer (14) for respiration studies.