Abscission Of Reproductive Organs Research Articles

Low temperature decreased insecticidal protein contents of cotton and its physiological mechanism.

Low temperature delayed cotton growth, increased abscission of reproductive organs, and seriously reduced quality and yield. Moreover, failed or unstable performance of insecticidal resistance due to adverse environments have been reported. In order to study the impact of low temperature on the insecticidal protein contents at square stage in Bacillus Thuringenesis (Bt) transgenic cotton, different temperature regimes and durations were imposed on two Bt cotton cultivars, Sikang1 (the conventional cultivar, SK1) and Sikang3 (the hybrid cultivar, SK3). Low temperature stress exhibited a significant inhibitory effect on insecticidal protein expression in squares and leaves of Bt transgenic cotton plants, with insecticidal protein contents decreased up to 30% with decreasing temperature. In addition, the threshold temperature resulting in significant reduction of insecticidal protein contents symbolized a rising trend as stress duration extended, together with a greater reduction observed. Thus, at square stage, the detrimental influence of low temperature on Bt protein contents was closely related to the low temperature level and duration. The square Bt protein content was positively correlated with leaf Bt protein content, but was more sensitive to low temperature. Across the whole treatment duration in both years, square Bt protein level was significantly negatively correlated with malondialdehyde (MDA) contents, as well as the activities of catalase (CAT) and superoxide dismutase (SOD), indicating the negative effect of cold induced oxidative stress on Bt protein contents. The reduced Bt protein contents under low temperature were also related to altered N metabolism. Glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) activities, as well as soluble protein contents in squares reduced, and greater reduction was recorded with decreasing temperature. In contrast, the free amino acid contents, and peptidase and protease activities increased, and greater elevation was noted with decreasing temperature. These results suggested in Bt cotton production, it is necessary to be alert to low temperature disasters that may last for more than 24 hours and lower than 15-17°C during the square stage, which may lead to reduced insecticidal resistance causing serious economic losses.

Efecto del nitrógeno en la producción y abscisión de órganos reproductivos y rendimiento del frijol en función del nitrógeno.

The objective of this study was to determine the effect of nitrogen on the production and abscission of reproductive organs and dry bean yield. This research was carried out in Iguala, Guerrero, Mexico where the climate is hot and subhumid. The Michoacan 12A3 bean variety, was sown on November 17, 1989, and December 17, 1990, with irrigation (autumn), and June 1, 1990 and June 29, 1991, without irrigation (summer). Population density was 13.3 plants/m-2. Treatments of zero and 80 kg N ha-1 were applied in each experiment. Results indicated that in both sowing seasons N increased leaf area, production and abscission of reproductive organs, number of pods reaching physiological maturity, and seed yield. As compared to the control, the higher abscission of reproductive organs in plants with N limited a higher seed yield under this treatment. Bean production in autumn was higher than in the summer.

STRUCTURAL STUDIES ON NATURAL FLOWER AND FRUIT ABSCISSION IN OLEA EUROPAEA L.

The study of the abscission of reproductive organs in olive has received attention in the past decades, but mostly when trees were treated with fruit loosening agents. Less attention has been given to the course of natural flower and fruit drop, and the anatomy of the abscission process of the same organs is still waiting for a detailed study. We carried out preliminary anatomical investigations on the development of abscission zones. Anatomical modifications were also observed during the abscission process in the inflorescence structure, involving the cell wall of the competent cells and other histochemical modifications in the neighbouring tissues.

Inheritance of Heat Tolerance during Reproductive Development in Snap Bean (Phaseolus vulgaris L.)

The genetic basis for heat tolerance during reproductive development in snap bean was investigated in a heat-tolerant × heat-sensitive common bean cross. Parental, F1, F2, and backcross generations of a cross between the heat-tolerant snap bean breeding line `Cornell 503' and the heat-sensitive wax bean cultivar Majestic were grown in a high-temperature controlled environment (32 °C day/28 °C night), initiated prior to anthesis and continued through plant senescence. During flowering, individual plants of all generations were visually rated and scored for extent of abscission of reproductive organs. The distribution of abscission scores in segregating generations (F2 and backcrosses) indicated that a high rate of abscission in response to heat stress was controlled by a single recessive gene from `Majestic'. Abscission of reproductive organs is the primary determinant of yield under heat stress in many annual grain legumes; this is the first known report of single gene control of this reaction in common bean or similar legumes. Generation means analysis indicated that genetic variation among generations for pod number under heat stress was best explained by a six-parameter model that includes nonallelic interaction terms, perhaps the result of the hypothetical abscission gene interacting with other genes for pod number in the populations. A simple additive/dominance model accounted for genetic variance for seeds per pod. Dominance [h] and epistatic dominance × dominance [l] genetic parameters for yield components under high temperatures were the largest in magnitude. Results suggest `Cornell 503' can improve heat tolerance in sensitive cultivars, and heat tolerance in common bean may be influenced by major genes.

Effect of different concentrations of Figaron on production and abscission of reproductive organs, growth, and yield in soybean ( Glycine max L.)

Figaron (ethyl-5-chloro-3(1H)-indazolyl-acetate), a synthetic auxin, has been used in the past to abort surplus flowers in soybean. We examined the effects of Figaron on chlorophyll levels, photosynthetic rate, stomatal conductance, growth, flowering pattern, flower production, reproductive abscission and yield of soybeans grown in pots in 1999 and 2000. Concentrations of Figaron were 2 in 1999 and 3 in 2000. Plant height and leaf area in plants treated with 100 or 150 mg l −1 Figaron were statistically not different from those of controls. However, in both cultivars these parameters were significantly smaller in plants given 200 mg l −1 Figaron than in controls. Total chlorophyll content, rate of photosynthesis, and stomatal conductance in plants treated with 100 or 150 mg l −1 decreased initially, but after 12 days of Figaron application these parameters became higher than in controls. In both cultivars level of these parameters remained low in plants given 200 mg l −1. In the later stages of growth, total chlorophyll content, photosynthesis rate, and stomatal conductance decreased slightly in plants of both cultivars treated with 150 or 200 mg l −1 Figaron to levels below those of plants treated with 100 mg l −1 or control plants. Different concentrations of Figaron reduced flower production, however, 150 or 200 mg l −1 Figaron had the greatest effect in both cultivars. The percentage reduction in flower production increased with increasing concentrations of Figaron, leading to a decrease in the rate of reproductive abscission. On the other hand, in both cultivars the total number of pods was higher in plants treated with 150 or 200 mg l −1 Figaron than in those treated with 100 mg l −1 or the controls; this led to an increased percentage of unfilled pods and decreased the seed weight. Ultimately, the higher concentrations of Figaron (150 and 200 mg l −1) decreased soybean yield compared to plants in 100 mg l −1 and control.

The Effects of Figaron and Water Deficit on Seed Yield of Two Soybean Cultivars

In tropical and subtropical regions, soybean (Glycine max L.) often encounters a temporary water deficit in summer. Application of auxin during the reproductive period, when a water deficit and high temperature cause pod abscission, is expected to decrease pod abscission and thus increase seed yield. The present study was conducted in a greenhouse to assess the effects of Figaron (synthetic auxin) under various conditions of water deficiency in two soybean cultivars, Fukushirome and Miyagishirome. The plants were supplied with 500–, 300–, 200–, or 100–mL water per pot (5 L) three times a day. Figaron (lOOmgL–1) was sprayed 10 days after opening of the first flower. The rate of photosynthesis and transpiration were greatly decreased by water deficit in both cultivars. Application of Figaron slightly increased the rates of photosynthesis and transpiration irrespective of the water condition, though it temporarily decreased the rates during the initial few days after Figaron application. Figaron decreased the abscission of reproductive organs and increased the percentage of pod set, irrespective of the water condition, resulting in increase of seed yield. However, seed yield was severely decreased by water deficit, and application of Figaron could not fully overcome the decrease of yield caused by a severe water deficit.

Sink Characteristics of Reproductive Organs of Dwarf Bean in Relation to Likelihood of Abscission

In common with other grain legumes, dwarf bean (Phaseolus vulgaris L.) exhibits premature abscission of reproductive organs and concomitant reduction in harvestable yield potential. This problem was investigated by mapping 14C‐photosynthate partitioning to individual buds, flowers, and pods of dwarf bean plants growing in a controlled‐ environment cabinet. Experimental plants bore a single raceme for which probabilities of abscission at each reproductive site were determined beforehand with a separate batch of plants. Reproductive organs at proximal sites on the raceme had low probabilities of abscission and always received greater proportions of 14C‐photosynthate than did reproductive organs at distal sites with high abscission probabilities. The activity of reproductive organs as sinks in relation to their developmental stage and position on the raceme was also examined. Sink activity of reproductive organs was determined in this study as the percentage of total 14C‐activity imported by reproductive organs per dry weight of the organ expressed as a percentage of total dry weight of reproductive organs. Sink activities of reproductive organs could be ranked in the order buds > pods > flowers. Most importantly, it was clear that pods likely to abscise had reduced sink activity when at both the flower and bud stages compared with those likely to be retained. It is proposed that loss of sink activity by reproductive organs is a key event leading to their eventual abscission and an essential feature of the mechanism whereby pod number is controlled in grain legumes.

Cotton responses to simulated insect damage: Radiation-use efficiency, canopy architecture and leaf nitrogen content as affected by loss of reproductive organs

Key cotton pests feed preferentially on reproductive organs which are normally shed after injury. Loss of reproductive organs in cotton may decrease the rate of leaf nitrogen depletion associated with fruit growth and increase nitrogen uptake and reduction by extending the period of root and leaf growth compared with undamaged plants. Higher levels of leaf nitrogen resulting from more assimilation and less depletion could increase the photosynthetic capacity of damaged crops in relation to undamaged controls. To test this hypothesis, radiation-use efficiency (RUE = g dry matter per MJ of photosynthetically active radiation intercepted by the canopy) of crops in which flowerbuds and young fruits were manually removed was compared with that of undamaged controls. Removal of fruiting structures did not affect RUE when cotton was grown at low nitrogen supply and high plant density. In contrast, under high nitrogen supply and low plant density, fruit removal increased seasonal RUE by 20–27% compared to controls. Whole canopy measurements, however, failed to detect the expected variations in foliar nitrogen due to damage. Differences in RUE between damaged and undamaged canopies were in part associated with changes in plant and canopy structure (viz. internode number and length, canopy height, branch angle) that modified light distribution within the canopy. These structural responses and their influence on canopy light penetration and photosynthesis are synthetised in coefficients of light extinction ( k) that were 10 to 30% smaller in damaged crops than in controls and in a positive correlation between RUE −1 and k for crops grown under favourable conditions (i.e. high nitrogen, low density). Changes in plant structure and their effects on canopy architecture and RUE should be considered in the analysis of cotton growth after damage by insects that induce abscission of reproductive organs.

The Relationship Between Sugar‐Nitrogen Ratio and Reproductive Organs Abscission in Faba Bean (Vicia Faba L.)

AbstractThe changes of soluble sugar and total nitrogen content of vegetative organs in faba bean, sugar‐nitrogen ratio, abscission of reproductive organs and the relationship between sugar‐nitrogen ratio and abscission probability were studied using the faba bean cultivar Xichang Dabai. Plants were field grown in 1986, 1988 and 1990. The lands were separated into high yield land, middling yield land and low yield land according to grain yield at maturing stage. The soluble sugar content in vegetative organs (leaf + stem) was greatest from branching to floral initiation stages and pod‐set to filling grain stages, and distinctly decreased at the onset of bloom and maturing stages. The total N content was greatest at branching stage, and gradually decreased with growth. In general, the sugar and total N contents in high yield lands were greatest, followed by that in middling yield and low yield lands. The sugar‐nitrogen ratio varied depending on the soluble sugar content.Average yield on high yield lands, middling yield land and low yield land across 3 years were 5048.77 kg/ha, 3744.01 kg/ha and 2378.22 kg/ha, respectively. The total reproductive organs abscission exceeded 90 % of total flower buds. Abscission probability averaged across 3 yield lands and 3 years were 21.6 %, 84.0 % and 32.8 % in flower buds, flowers, and pods, respectively. Node 7–12 of canopy produced more flowers, and fewer flowers and pods were produced in the upper and lower regions. Photosynthate supply has been implicated in control of abscission. Faba bean reproductive organs abscission probability increased with the sugar‐nitrogen ratio of vegetative organs decreasing. It seemed that the soluble sugar content influenced significantly the shedding rate during flowering and pod‐growing stages.

High-temperature-acclimation potential of the common bean: can it be used as a selection criterion for improving crop performance in high-temperature environments?

The common bean ( Phaseolus vulgaris L.) is a heat-sensitive plant species in which excessive abscission of reproductive organs occur during hot weather. This results in ‘split sets’ and yield reductions, and, in extreme heat stress, plant produce few or no pods. We evaluated 74 bean genotypes in terms of leaf heat-tolerance ( ht) and leaf heat-acclimation potential ( hap), as expressed by heat killing-time ( hkt), the time in minutes needed to cause 50% ion leakage from leaf tissue heat stressed at 50°C. Leaf ht is defined as the leaf hkt of plants without prior conditioning at 37°C day/night temperature and leaf hap as the change in leaf ht following exposure of the plant at 37°C day/night for 24 h. Among 74 bean genotypes examined, leaf ht ranged from 5 to 30 min hkt, whereas leaf hap ranged from 35 to 130 min hkt. Positive significant correlations were observed between leaf hap and post-stres performance in plant dry-weight, pod set, pod weight and yield among bean genotypes. However, correlations were not significant between leaf ht and post-stress performance. A relationship between heat resistance—consisting of the combination of htand hap—and heat injury is proposed. Interpretation of the differential amounts of heat injury among genotypes having different hap, is discussed. We view leaf ht and leaf hap as two distinguishable phenomena. We suggest that, in breeding programs, hap may be the more important of the two, and should be evaluated as a selection criterion for improving crop performance in high-temperature environments.

HIGH TEMPERATURE RESPONSE IN BEAN-PHYSIOLOGICAL CONSIDERATIONS.

The common bean (Phaseolus vulgaris L.) is a heat-sensitive plant species in which excessive abscission of reproductive organs occurs during hot weather. This results in yield reductions, and, in extreme heat stress, plants produce few or no pods. We evaluated 74 bean genotypes in terms of leaf heat tolerance (HT) and leaf heat acclimation potential (HAP), as expressed by heat killing time (HKT), the time in minutes needed to cause a 50% electrolyte leakage from leaf tissue heated at 50°C Leaf HT is defined as the leaf HKT of plants without prior conditioning at 37°C day/night temperature and leaf HAP as the change in leaf HT following exposure of the plant to 37°C day/night for 24-h. Among 74 bean genotypes examined leaf HT ranged from 5 to 30 min HKT, whereas leaf HAP ranged from 35 to 130 min HKT. Positive significant correlations were observed between leaf HAP and post-stress performance in photosynthetic activities, plant dry weight, pod set, pod weight and yield among bean genotypes. Correlations, however, were not significant between leaf HT and post-stress performance.A relationship between heat resistance, consisting of the combination of HT and HAP, and heat injury is proposed. Interpretation of the differential amounts of heat injury among genotypes having different HAP, is discussed. We view leaf HT and leaf HAP as two distinguishable phenomena. We suggest that in breeding programs HAP may be the more important of the two, and should he evaluated as a selection criterion for improving crop performance in high temperature environments.

FLOWER AND POD ABSCISSION IN SNAP BEAN AS INFLUENCED BY INFLORESCENCE POSITION, RACEME NODE, IRRIGATION AND PLANT DENSITY

Abscission and/or retention of flowers and pods formed on inflorescences arising from mainstem nodes 6 (terminal) and 2 (first trifoliolate leaf) of Oregon 1604 snap bean (Phaseolus vulgaris L.) were studied during the 1978 and 1979 seasons to determine the effects of irrigation and plant population. Inflorescences at these two nodes account for the majority of the yield produced in this determinate cultivar. The influence of high (−0.06 MPa) and low (−0.25 MPa) soil water potential and plant density were also assessed. High and low plant densities were 45 vs. 18 in 1978, and 54 vs. 33 plants m−2 in 1979. Percent flower and pod abscission was signficantly less under high (62%) than low (74%) irrigation at node 6 in 1978, and at node 2 in 1978 (48 vs. 71) and 1979 (37 vs. 60). Although plant density had no effect at node 6, percent abscission at node 2 was significantly less under low than high plant density in both years. An acropetal increase in percent abscission occurred within the inflorescence at node 6, with a value of 45% at the proximal, first raceme node, and from 65 to 86% at the most distal, third raceme node. The acropetal pattern of abscission was less marked in inflorescences at node 2. A sharp rise in reproductive abscission was observed in 1978 after a 3-d period when maximum daily temperatures exceeded 34 °C. This early rise in abscission (which did not occur in the cooler 1979 season) was reduced by high irrigation (nodes 6 and 2) and low plant density (node 2). Abscission of flowers at the white bud stage or at anthesis was relatively low. The major portion of reproductive organs were shed after anthesis. High irrigation delayed abscission at both main-stem nodes, thus increasing the proportion of organs which abscised as pods. Low plant density also postponed abscission of reproductive organs at node 2, but had less effect at node 6.Key words: Phaseolus vulgaris L., anthesis, first bloom

Reproductive responses of cowpea (Vigna unguiculata (L.) Walp.) to heat stress. II. Responses to night air temperature

The influence of high night temperature and drought on the abscission of reproductive organs were studied with cowpea (Vigna unguiculata (L.) Walp. cv. ‘California Blackeye No. 5’) in controlled environments. Floral development of cowpeas at 33/22°C day/night temperature appeared to be normal. However, at 33/30°C day/night temperature all flowers abscissed within 48 h after anthesis due to male sterility resulting from abnormal pollen development and anther indehlscience. By moving plants between growth chambers with high and moderate night temperatures, it was demonstrated that the stage of floral development most sensitive to high night temperature occurred 5–7 days before anthesis. This corresponds with the stage just after the release of the tetrads from the microscope mother cell sac. Plants subjected to drought were smaller, and at the lower night temperature drought resulted in less seed production but this was due to fewer reproductive nodes and the percent abscission of reproductive organs was not influenced by drought. Observations were made on the effects of high temperatures on reproductive growth of six cowpea strains grown under field conditions. Complete abscission of flowers was observed during hot weather under field conditions followed by pod set approximately 6 days after decrease in night temperature. These data are consistent with the observations on cowpeas in growth chambers which demonstrated that high night temperatures can cause male sterility and complete abscission of flowers.

Reproductive responses of cowpea (Vigna unguiculata (L.) Walp.) to heat stress. I. Responses to soil and day air temperatures

Abstract Cowpea (Vigna unguiculata (L.) Walp.) plants are characterized by occasional excessive abscission of reproductive organs which result in low numbers of pods per unit area and consequently low seed yields. The possibility that heat stress may cause this excessive abscission was examined. Interactive effects of different soil and two day air temperatures on growth and reproductive performance of cowpea cultivar ‘California Blackeye No. 5’ were determined in controlled environments. Emergence was slow, and the seedlings were stunted at constant soil temperatures equal to or lower than 23°C. Seedlings at 18°C soil temperature exhibited nitrogen deficiency, and they developed bigger and more numerous nodules on their roots. The different soil and air temperatures did not influence the duration from emergence to appearance of the first floral bud or to anthesis. The duration from anthesis to maturity of individual pods was six days longer with the cooler day air temperature, but it was not influenced by the different soil temperatures. Plants produced more pods at 27/19°C than at 33/19°C day/night air temperature; however, the variation in number of pods was associated with variation in the number of reproductive nodes per plant. Levels of flower abscission were not excessive in any of the environments, and plants at 33/19°C air temperature exhibited less percent flower abscission than plants at 27/19°C air temperature. The seeds produced at 33/19°C air temperature were misshapen. Normal and misshapen seeds exhibited high percent emergence when sown at a depth of 2.5 cm at all soil temperatures studied, whereas 5-cm sowing depth resulted in poor emergence at high soil temperatures with misshapen seeds exhibiting less percent emergence than normal seeds.

A Collection Receptacle for Field Abscission Studies in Common Bean1

A non tagging, non destructive, continuous, and inexpensive method was developed to evaluate abscission of reproductive organs in dry beans (Phaseolus vulgaris L.) under field conditions. Abscission collection receptacles (ACR) were built, using saran screen (1.5 × 2.0 mm mesh) and 2.5 × 5.0 cm redwood stock. Receptacles were placed in the field over a 1.25 m segment of row, and the floor was carefully fitted around competitively growing plants at the 2 to 3 true leaf stage. The method was tested on dry bean cvs., ‘Tuscola,’ ‘NEP II,’ and ‘Black Turtle Soup,’ selected because of their contrasting growth and flowering habits. Reproductive organs were collected every 4 days and taken to the laboratory where the data were quantified. Samples required 3 min per ACR. Abscission could be broken down into flower and pod drop components. Pod abscission accounted for most of the shedding of reproductive organs. The abscission of pods under 10 mm accounted for 64 to 82% of all reproductive structures abscised. The ACR was useful to study the seasonal patterns of flowering, abscission, and pod retention of genotypes. Differences in these parameters were detected among the three cultivars studied in this experiment. Low coefficients of variation associated with data collection indicated a good degree of precision in the experiments. Compared to unenclosed plants, the ACR had no significant effect on growth, vigor, yield, and yield components of enclosed plants.

Physiology of Injury Caused by Lygus hesperus1

Injury caused by Lygus hesperus Knight is due principally to the enzymatic digestion of the plant’s tissue by polygalacturonase secreted during feeding. A limited amount of mechanical injury may result from feeding. L. hesperus is unable to synthesize indoleacetic acid and is also unable to secrete plant hormones in its saliva after having ingested these hormones in its diet. The type of damage associated with feeding, i.e., necrosis, abscission of reproductive organs, “blasting,” “cat facing,” or reduction of vegetative growth, depends upon the size of the organ fed upon and the specific site of feeding. If feeding results in the destruction of specific hormone producing sites, the resultant damage is in accord with the known physiological responses of plants to hormonal manipulation.