Light and Shade Effects on Abscission and C-Photoassimilate Partitioning among Reproductive Structures in Soybean

Field experiments were conducted in 1981 and 1982 to study the effects of low-irradiance supplemental light on soybean (Glycine max [L.] Merr. cv Evans) flower and pod abscission. Cool-white and red fluorescent lights illuminated the lower part of the soybean canopy during daylight hours for 3 weeks late in flowering. At the same time, flowers and young pods on half the plants were shaded with aluminum foil. Flowers were tagged at anthesis and monitored through abscission or pod maturity.

Responses to red and white lights were similar. Supplemental light tended to reduce abscission and increase seed weight per node compared to natural light. Shading flowers and pods increased abscission and reduced seed weight per node. Number of flowers produced per node, individual seed weight, and seeds per pod were not affected by light or shade treatments.

Further studies examined the effects of shading reproductive structures on their capacity to accumulate ¹⁴C-photoassimilates. Individual leaves were pulse labeled with ¹⁴CO₂ 1, 2, and 4 weeks post anthesis. Flowers and pods in the axil of the labeled leaf were covered with aluminum foil 0, 24, 72, and 120 hours before pulsing.

Shading flowers and pods resulted in a 30% reduction in the relative amount of radiolabel accumulated from the source leaf. The reduction in ¹⁴C accumulation due to shading was evident regardless of the length of the shading period and was most pronounced when the shades were applied early in reproductive development. We conclude that light perceived by soybean flowers and young pods has a role in regulating both their abscission and their capacity to accumulate photoassimilates.

     

Temporal and Spatial Distribution of Auxin Response Factor Genes During Tomato Flower Abscission

Abscission facilitates growth and reproduction and improves plant defenses against pathogens. This tightly regulated process is triggered by environmental cues and hormones such as ethylene and auxin. Because auxin is crucial for abscission, auxin response factors (ARFs) may play important roles in this process. Here, we examined changes in gene expression during abscission in tomato, focusing on regulation of genes encoding ARFs. Specifically, we analyzed the pattern of ARF gene expression in tomato flower pedicel explants treated with ethylene, the ethylene blocker 1-methylcyclopropene (1-MCP), or auxin to determine how auxin and ethylene affect ARF gene expression. In addition, we examined the spatial and temporal distribution of IAA during abscission by examining transgenic tomato plants expressing an IAA-inducible promoter fused to the GUS reporter gene (the P5::GUS ‘Chico III’ line). Flower removal from the explants quickly induced abscission by ethylene, which was inhibited by exogenous auxin or 1-MCP. During early abscission, auxin (or 1-MCP) regulated the expression of various ARFs, including ARF1, 2, 3, 4, 5, 7, 8-1, 9, 11, 12, 13, 13-1, 14, and 17, whereas ethylene had the opposite effect on most of these genes. Further analysis shows that during this stage, auxin may mediate the expression of ARF8-1, 9, 11, 12, 13, 13-1, and 14, whereas ethylene may mediate ARF13-1. During the later stage of abscission, ARF2, 8, 10, 11, and 19 were upregulated, and 8-1, 12, 13, and 13-1 were downregulated, compared with nonabscising parts of plants. Fluorometric GUS analysis indicated that GUS activity in the abscission zone remained stable at 4 h and sharply decreased after 8 h until abscission was complete (32 h).     

大豆花荚败育期间的植物激素变化

大豆开花结荚期,不同发育阶段的幼蕾与花荚的脱落率不同,其中以花后5d内的幼荚脱落最严重。与败育花荚相比,正常花荚中的干物质积累量均较高。细胞分裂素(DHZRs,ZRs,iPA)含量也较高,花后3～5d的幼荚中表现更明显。脱落酸(ABA)则是以败育幼蕾及花后3～5d的幼荚中含量较高。不同发育阶段的大豆生殖器官中,正常开放花中的玉米赤霉烯酮(ZEN)含量最高。     

大豆花荚败育期间的植物激素变化

大豆开花结荚期,不同发育阶段的幼蕾与花荚的脱落率不同,其中以花后５ｄ内的幼荚脱落最严重。与败育花荚相比,正常花荚中的干物质积累量均较高。细胞分裂素（ＤＨＺＲｓ,ＺＲｓ,ｉＰＡ）含量也较高,花后３～５ｄ的幼荚中表现更明显。脱落酸（ＡＢＡ）则是以败育幼蕾及花后３～５ｄ的幼荚中含量较高。不同发育阶段的大豆生殖器官中,正常开放花中的玉米赤霉烯酮（ＺＥＮ）含量最高     

Ethylene perception inhibitor 1-MCP decreases oxidative damage of leaves through enhanced antioxidant defense mechanisms in soybean plants grown under high temperature stress

Ethylene is a stress hormone involved in early senescence and abscission of vegetative and reproductive organs under stress conditions. Ethylene perception inhibitors can minimize the impact of ethylene-mediated stress. The effects of high temperature (HT) stress during flowering on ethylene production rate in leaf, flower and pod and the effects of ethylene inhibitor on ethylene production rate, oxidative damage and physiology of soybean are not understood. We hypothesize that HT stress induces ethylene production, which causes premature leaf senescence and flower and pod abscission, and that application of the ethylene perception inhibitor 1-Methyl cyclopropene (1-MCP) can minimize HT stress induced ethylene response in soybean. The objectives of this study were to (1) determine whether ethylene is produced in HT stress; (2) quantify the effects of HT stress and 1-MCP application on oxidative injury; and (3) evaluate the efficacy of 1-MCP at minimizing HT-stress-induced leaf senescence and flower abscission. Soybean plants were exposed to HT (38/28 °C) or optimum temperature (OT; 28/18 °C) for 14 d at flowering stage (R2). Plants at each temperature were treated with 1-MCP (1 μg L⁻¹) gas for 5 h or left untreated (control). High temperature stress increased rate of ethylene production in leaves, flowers and pods, production of reactive oxygen species (ROS), membrane damage, and total soluble carbohydrate content in leaves and decreased photosynthetic rate, sucrose content, F_v/F_m ratio and antioxidant enzyme activities compared with OT. Foliar spray of 1-MCP decreased rate of ethylene production and ROS and leaf senescence traits but enhanced antioxidant enzyme activities (e.g. superoxide dismutase and catalase). In conclusion, HT stress increased ethylene production rates, caused oxidative damage, decreased antioxidant enzyme activity, caused premature leaf senescence, increased flower abscission and decreased pod set percentage. Application of 1-MCP lowered ethylene and ROS production, enhanced antioxidant enzyme activity, increased membrane stability, delayed leaf senescence, decreased flower abscission and increased pod set percentage. The beneficial effects of 1-MCP were greater under HT stress compared to OT in terms of decreased ethylene production, decreased ROS production, increased antioxidant protection, decreased flower abscission and increased pod set percentage.     

Periods of Shoot Chilling Sensitivity in Soybean Flower Development, and Compensation in Yield after Chilling

Soybeans [Glycine max (L.) Merr. cv. Ransom] grown at a constant25 °C were placed in a 12-h inductive photoperiod at twoweeks of age. Subgroups were shoot-chilled for one week at aconstant 10 °C during each of the first four weeks of floralinduction. Controls were photoinduced but not chilled. Chillingduring the first week of photoinduction inhibited productionof floral primordia, but did not increase the abscission rateof flowers and pods. Chilling during the second week did notaffect primordium production or abscission rate, but did causea significant increase in numbers of fused and malformed pods.Chilling during the third week caused loss of 77 per cent ofearly flowers and pods by abscission, while fourth week chillingcaused less severe losses by abscission. Inhibition of vegetativegrowth may have been responsible for primordium loss in first-weekplants, while disturbances in the development of flowers wereresponsible for the losses in the other chilling weeks. Althoughchilling during the first and third photoinduction weeks causeda significant reduction in early pod numbers, plants harvestedat 16 weeks of age showed no significant loss in seed yield.Low abscission rates late in pod filling and increased weightof individual seeds compensated for early losses of pods. Thesecompensatory responses to a chilling-induced loss of pods aresimilar to those reported for mechanically depodded soybeans. Glycine max (L.) Merr., soybean, temperature, chilling, floral initiation, anthesis, abscission, yield, compensation     

SlERF52 regulates SlTIP1;1 expression to accelerate tomato pedicel abscission

Abscission of plant organs is induced by developmental signals and diverse environmental stimuli and involves multiple regulatory networks, including biotic or abiotic stress-impaired auxin flux in the abscission zone (AZ). Depletion of auxin activates AZ ethylene (ETH) production and triggers acceleration of abscission, a process that requires hydrogen peroxide (H₂O₂). However, the interaction between these networks and the underlying mechanisms that control abscission are poorly understood. Here, we found that expression of tonoplast intrinsic proteins, which belong to the aquaporin (AQP) family in the AZ was important for tomato (Solanum lycopersicum) pedicel abscission. Liquid chromatography–tandem mass spectrometry and in situ hybridization revealed that SlTIP1;1 was most abundant and specifically present in the tomato pedicel AZ. SlTIP1;1 localized in the plasma membrane and tonoplast. Knockout of SlTIP1;1 resulted in delayed abscission, whereas overexpression of SlTIP1;1 accelerated abscission. Further analysis indicated that SlTIP1;1 mediated abscission via gating of cytoplasmic H₂O₂ concentrations and osmotic water permeability (P_f). Elevated cytoplasmic levels of H₂O₂ caused a suppressed auxin signal in the early abscission stage and enhanced ETH production during abscission. Furthermore, we found that increasing P_f was required to enhance the turgor pressure to supply the break force for AZ cell separation. Moreover, we observed that SlERF52 bound directly to the SlTIP1;1 promoter to regulate its expression, demonstrating a positive loop in which cytoplasmic H₂O₂ activates ETH production, which activates SlERF52. This, in turn, induces SlTIP1;1, which leads to elevated cytoplasmic H₂O₂ and water influx.

A SlERF52-SlTIP1;1 regulatory module accelerates pedicel abscission by increasing cytoplasmic hydrogen peroxide contents and osmotic water permeability.     

喷施细胞分裂素对豇豆花荚脱落率及花荚酶活性的影响

以4个豇豆(Vigna unguiculata Linn.)品种‘鄂豇豆6号’、‘鄂豇豆2号’、‘鄂豇豆7号’和‘美国地豆’为材料,在现蕾期叶面喷施植物细胞分裂素(CTK),于喷施后第7、14、28、42 d测定脱落花荚的多聚半乳糖醛酸酶(PG)和纤维素酶活性,并统计花荚脱落率和豇豆产量,研究CTK在豇豆生长发育过程中对花荚脱落的影响。结果显示,喷施CTK后,豇豆各品种的花荚脱落率均小于对照,豇豆产量均高于对照,且差异极显著(P0.01);喷施CTK后第14、28、42 d豇豆各品种脱落花荚的PG活性显著降低(P0.05);喷施CTK后第7 d各处理组脱落花荚的PG活性极显著降低(P0.01);喷施CTK后第7 d和第42 d豇豆各品种脱落花荚的纤维素酶活性显著降低(P0.05),喷施CTK后第14 d和第28 d各处理组脱落花荚的纤维素酶活性极显著降低(P0.01)。研究结果表明喷施CTK可调节脱落花荚的PG活性和纤维素酶活性,从而降低花荚脱落率,实现对豇豆产量的调控。     

Use of Mutants to Dissect the Role of Ethylene Signalling in Organ Senescence and the Regulation of Yield in Arabidopsis thaliana

The role of ethylene in regulating organ senescence in Arabidopsis has been investigated by studying the development of mutants that have an attenuated capacity to perceive the gas. The onset of leaf senescence and floral organ abscission was delayed in the ethylene-insensitive mutant etr1. The photosynthetic life span of rosette leaves was similarly extended in the gain-of-function mutant ers2, and this mutant also exhibited a delay in the timing of pod dehiscence primarily as a consequence of an extension in the final stages of senescence. A detailed analysis of yield revealed that whilst thousand grain weight was increased, by as much as 20 %, in etr1, ein4, and the loss-of-function mutant etr2, only the latter showed a significant increase in total weight of seeds produced per plant. The other studied mutants exhibited a reduction in total seed yield of almost 40 %. These observations are discussed in the context of the possible role of ethylene in regulating organ senescence and their significance in the breeding of crop plants with enhanced phenotypic characteristics.     

Ethylene- and dark-induced flower abscission in potted Plectranthus: Sensitivity,prevention by 1-MCP,and expression of ethylene biosynthetic genes

Prevention of ethylene- and shipping-induced flower abscission is necessary to maintain the quality of both cut flowers and potted plants during handling, transport and retail display. The aims of the present work were to determine the sensitivity of Plectranthus cultivars to applied ethylene, to alleviate ethylene- and shipping-induced flower abscission in intact potted plants using 1-methylcyclopropene (1-MCP), and to investigate the possible causes of dark-induced flower abscission. All cultivars were sensitive to ethylene in a concentration-dependent manner, and complete abscission occurred within 24 h with 1 and 2 μl l^− 1 ethylene. Unopened buds were more sensitive to applied ethylene, and exhibited greater abscission than open flowers. Ethylene synthesis remained below detection limits at all time points under control and continuous dark conditions. Dark treatment significantly increased flower abscission in Plectranthus cultivars, and like ethylene-induced flower abscission, this could be prevented by continuous 1-MCP treatment. Gene expression of ethylene biosynthetic enzymes ACS and ACO was examined as possible causes for the accelerated flower abscission observed in plants kept in continuous darkness. Expression patterns of ACS and ACO varied between different cultivars of Plectranthus. In some cases, increased expression of ACS and ACO led to increased flower abscission. Gene expression was higher in open flowers when compared to unopened flowers suggesting a cause for the observed preferential shedding of open flowers in some cultivars. Although the cause of dark-induced abscission in Plectranthus remains elusive, it can be effectively controlled by treatment with 1-MCP.     

Source/Sink relations of abscising and nonabscising soybean flowers

The partitioning of recently fixed ¹⁴C to setting and abscising flowers within the axillary raceme of `Clark' isoline E1t soybeans (Glycine max L. Merr) was examined as a function of time after anthesis of individual flowers. In such racemes, the first four flowers showed a 17% abscission while the next four flowers showed 47% abscission.

Source/sink relations of flowers I-IV (normally setting) were compared to those of flowers V-VIII (normally abscising) by pulse labeling source leaves with ¹⁴CO₂ and determining the radioactivity of individual flowers after a 4-hour chase period. The relative specific activity (RSA;% disintegrations per minute per% dry weight), sink strength (% disintegrations per minute), and its components, sink size (milligrams dry weight) and sink intensity (% disintegrations per milligram dry weight) were then calculated as a function of days after anthesis.

Sink intensity (i.e. the competitive ability to accumulate photoassimilate per unit mass) was very high prior to anthesis of both setting and abscising flowers. Sink intensity then became very low for the first 3 days following anthesis after which it recovered in normally setting flowers, but failed to recover in normally abscising flowers. It is concluded that soybean reproductive abscission is determined at or very near the day of anthesis.

     

New Clothes for the Jasmonic Acid Receptor COI1: Delayed Abscission,Meristem Arrest and Apical Dominance

In a screen for delayed floral organ abscission in Arabidopsis, we have identified a novel mutant of CORONATINE INSENSITIVE 1 (COI1), the F-box protein that has been shown to be the jasmonic acid (JA) co-receptor. While JA has been shown to have an important role in senescence, root development, pollen dehiscence and defense responses, there has been little focus on its critical role in floral organ abscission. Abscission, or the detachment of organs from the main body of a plant, is an essential process during plant development and a unique type of cell separation regulated by endogenous and exogenous signals. Previous studies have indicated that auxin and ethylene are major plant hormones regulating abscission; and here we show that regulation of floral organ abscission is also controlled by jasmonic acid in Arabidopsis thaliana. Our characterization of coi1-1 and a novel allele (coi1-37) has also revealed an essential role in apical dominance and floral meristem arrest. In this study we provide genetic evidence indicating that delayed abscission 4 (dab4-1) is allelic to coi1-1 and that meristem arrest and apical dominance appear to be evolutionarily divergent functions for COI1 that are governed in an ecotype-dependent manner. Further characterizations of ethylene and JA responses of dab4-1/coi1-37 also provide new information suggesting separate pathways for ethylene and JA that control both floral organ abscission and hypocotyl growth in young seedlings. Our study opens the door revealing new roles for JA and its interaction with other hormones during plant development.     

Does Pollination Induce Corolla Abscission of Cyclamen Flowers by Promoting Ethylene Production?

Very low ethylene production rates were measured in nonpollinated Cyclamen persicum Mill flowers, and no change in production was observed during the whole life span of the flower until death. Normal senescence was accompanied by a gradual discoloration and loss of turgor followed by wilting. Pollination induced a dramatic increase in ethylene evolution, culminating in a peak 4 days after pollination, and abscission of the corolla on that day. Silver-thiosulfate, an inhibitor of ethylene action, had no effect on longevity of unpollinated flowers, but completely nullified the effect of pollination on corolla abscission. Exposing unpollinated flowers to very high ethylene concentrations (50 microliters per liter) for 48 hours did not promote corolla abscission or senescence. 1-Aminocyclopropane-1-carboxylic acid, the immediate precursor of ethylene, increased ethylene production by unpollinated flowers more than 100-fold, but did not promote corolla abscission. 1-Aminocyclopropane-1-carboxylic acid did enhance corolla abscission of pollinated flowers. It is concluded that the main effect of pollination in inducing corolla abscission of cyclamen is by rendering the tissue sensitive to ethylene, apart from the promotion of ethylene production.     

Role of Ethylene Biosynthesis and Auxin Content and Transport in High Temperature-Induced Abscission of Pepper Reproductive Organs

High temperatures induced abscission of pepper (Capsicum annuum L. cv. Maor) reproductive organs at various developmental stages. The role of ethylene biosynthesis and auxin economy in high temperature-induced abscission is described. High temperatures somewhat increased ethylene production in the reproductive organs, but the highest temperature treatment, which was the most active in inducing reproductive organ abscission, decreased it. In contrast to ethylene, 1-aminocyclopropane-1-carboxylic acid levels increased significantly in response to high temperatures and correlated positively with the increase in temperature. High temperatures reduced indole-3-acetic acid levels and particularly auxin transport capacity in the reproductive organs. The data suggest that the reduction of auxin transport capacity is the major mechanism by which high temperatures induce reproductive organ abscission in pepper. Received September 27, 1996; accepted March 13, 1997     

Improved Postharvest Quality of Inflorescences of <Emphasis Type="Italic">fbp1::etr1-1</Emphasis> Transgenic <Emphasis Type="Italic">Burrageara</Emphasis> ‘Stefan Isler Lava Flow’

Flowers of the complex orchid hybrid Burrageara ‘Stefan Isler Lava Flow’ had been shown previously to react sensitively to ethylene. Via Agrobacterium tumefaciens, the mutant ethylene receptor ETHYLENE RESPONSE 1 (etr1-1) from Arabidopsis thaliana under the control of the flower-specific promoter FLOWER BINDING PROTEIN 1 (fbp1) from Petunia hybrida was transferred to Burrageara. One single-copy event was analyzed in this study aiming to investigate the expression of the fbp1::etr1-1 transgene in different plant and flower organs by quantitative RT-PCR and the reaction of flowers and inflorescences to ethylene. It was shown that the heterologous promoter led to high expression levels in the perianth of the orchid flowers compared to low levels in leaves and roots. The expression shift to the first whorl (sepals) described here corresponds to extended expression of endogenous B class MADS box homeotic genes in orchids in general. The transgenic plants grew and developed similar to the wild-type plants, except for slightly faster rooting in vitro and smaller flowers. Flower longevity was improved by 7 days in 10 ppm ethylene. Moreover, bud drop starting at day 5 of incubation of inflorescences in 10 ppm ethylene in the wild-type was efficiently prevented for at least 19 days in the fbp1::etr1-1 transgenic plants. The function of the tissue-specific promoter fbp1 and the mutant receptor etr1-1 was shown for the first time in a monocotyledonous plant.     

不同时期叶喷植物生长调节剂对大豆花荚脱落率及多聚半乳糖醛酸酶活性的影响

在大田条件下,以大豆品种‘合丰50＇为材料,比较研究了在V3（第3节龄期,三叶期）、R1（初花期）和R3（始荚期）期叶面喷施DTA-6、S_（3307）和TIBA三种植物生长调节剂对大豆花荚脱落率及多聚半乳糖醛酸酶活性的影响。结果表明：V3期叶喷TIBA、S_（3307）、DTA降低了大豆花荚脱落率,降低了大豆花荚和脱落花荚多聚半乳糖醛酸酶活性;R1期叶喷植物生长调节剂显著降低了大豆花荚及脱落花荚中多聚半乳糖醛酸酶活性,以DTA-6调控效果最佳,S_（3307）次之;R3期叶喷植物生长调节剂降低了大豆荚及落荚的多聚半乳糖醛酸酶活性,以DTA-6调控效果最佳,TIBA次之。综合分析表明,V3、R1和R3期叶面喷施植物生长调节剂能够降低大豆花荚脱落率及多聚半乳糖醛酸酶活性,对大豆花荚的脱落有一定的调控作用,有利于提高产量,其综合调控效果为,V3期：S_（3307）〉DTA-6〉TIBA〉CK;R1期：DTA-6〉TIBA〉S_（3307）〉CK;R3期：DTA-6〉TIBA〉S_（3307）〉CK。     

Studies on flower longevity in Digitalis

The flowers of Digitalis purpurea respond to pollination by rapid corolla abscission without any loss of corolla turgor, nor any significant loss of corolla constituents, relative to the corollas of unpollinated flowers of a similar age. The corollas of unpollinated flowers too eventually abscise, 6 d after the stigma opens, however, they do so with only a minimal loss of fresh weight or corolla constituents. Pollination causes an increase in ethylene production detectable within 1 h. Increased ethylene production occurs initially only from the upper portion of the style, later from the lower portion, and lastly, between 23 and 48 h after pollination, from the ovary plus calyx. The pollination response can be induced by exogenous ethylene, the degree of weakening of the corolla abscission zone being dependent upon the concentration and duration of the exposure period and on the stage of flower development. The regulation of ethylene biosynthesis and its involvement in the control of pollination-induced corolla abscission are discussed.