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- Author or Editor: Barbara D. Webster x
Abstract
Anatomical changes which take place in conjunction with abscission of cantaloupe fruits (Cucumis melo L. cv. Powdery Mildew Resistant No. 45) include cell separation and cell collapse. Structural modifications in abscission zone cell walls are accompanied by histochemical changes which include losses of pectins and insoluble polysaccharides. Development of a separation cavity is consistently correlated with physiologically defined stages of fruit maturity, and the time of abscission coincides with the peak of the respiratory climacteric. Anatomical and histochemical changes similar to those in cantaloupe also take place in honeydew fruits (Cucumis melo L. cv. Honeydew). However, the abscission zone of honeydews is not structurally well defined, changes are limited to certain parenchyma cells, and the honeydew fruits do not normally abscise. It is suggested that the most desirable growth regulator for use on cantaloupes to accelerate and unify the time of fruit ripening would be one which did not coincidentally accelerate abscission.
During the initiation of pollen exine wall formation in Vigna, localized accumulations of membranes in the microspore cortex coincide with sites which during further development reflect the lumina of me reticulate exine, and with apertural sites. Multi-membrane bodies are prominent in the cytoplasm, especially subtending aperture sites. Multi-membrane structures continue to be present as pollen wall development proceeds, notably during the early patterning stages. Labelling with the endomembrane-specific fluorochrome DiOC6 does not conclusively lead to membrane identification. However, electron micrographs illustrate elaborate membrane systems during stages when the most obvious developmental activity is initiation of the microspore wall. This suggests that there may be a causal relationship between endomembranes and exine pattern formation.
Abstract
In the article “Effects of Water Stress on Pollen of Phaseolus vulgaris L.”, by Xiu Ying Shen and Barbara D. Webster (J. Amer. Soc. Hort. Sci. 111:807–810, September 1986), on p. 808, the last sentence before Results and Discussion should read: “The term microspore refers to the uninucleate structures released from tetrads after meiosis. The term pollen grain refers to the above structures after mitosis of the microspore nucleus and formation of the vegetative (tube) and generative cells.”
Abstract
The surface meshwork of tissue, commonly referred to as the “net,” of fruit of Cucumis melo L. cv. PMR-45 is an elaborate system of lenticels. Lenticellar tissue is derived from a subepidermal periderm. Cork cells, which comprise the complementary tissue of lenticels, protrude through the surface fissures which develop as the fruit enlarges. It is suggested that cork cells of the net and of the periderm contribute to resistance to mechanical injury of the fruit; that gaseous exchange is facilitated by lenticellar net development; and that resistance to disease is enhanced by the presence of a surface cuticle and by the development of cork cells with suberized walls.
Abstract
Pollen of plants of Phaseolus vulgaris L. ‘Red Mexican’ is affected adversely by water stress. The critical stress period occurs 10-13 days after emergence, during the transition from the vegetative to the reproductive phase of development. The transition phase is characterized by the presence of tiny green buds (>0.5-2.0 mm in length), bearing anthers that contain tetrads or free microspores. Pollen abortion of plants stressed during the transition phase is significantly higher than that of pollen from nonstressed plants or from those stressed during later phases of reproductive development. The percentage of pollen germination and total pollen production also are reduced in transition phase-stressed plants. Exine development is abnormal. This abnormal development is particularly interesting because the exine is regarded as so genetically stable that it is regularly used for species identification. Results of these experiments raise questions about the infallibility of identifications, since an environmental stress (such as water) imposed at a critical time of gametophytic development can markedly alter exine patterning.
Abstract
The ultrastructure of floral abscission zone cells of Phaseolus vulgaris L. cv. Dark Red Kidney was studied in order to relate changes in fine structure to known changes in morphology and physiology of the foliar abscission zone of Phaseolus and to the fine structure of floral abscission zones of other plants. Major structural changes in cell walls are similar in abscission zones of senescing leaves and post-anthesis flowers but the rapidity of cellular changes is greatly accelerated in the latter. Inclusions typically found in floral abscission zone cells of Solanaceous plants are not present in Phaseolus floral abscission zone cells. Cellular changes are evaluated in terms of their potential relationship to the abscission process.
Abstract
The humidity of the atmosphere profoundly affects every aspect of morphogenesis and the practical importance of this has provided the impetus for extensive research, particularly in agriculture. Maximov’s (13) excellent monograph delineates the effects of various moisture regimes on growth, structure and composition of crop plants, and Wangerman’s (23) review focuses on effects of water supply and humidity on plants which can regulate their water content and those which cannot. These and other reviewers have been quick to point out that effects of relative humidity are frequently confounded by interrelationships with other factors, including particularly temperature, light and soil moisture. Thus the analysis of morphological and histochemical effects of atmospheric humidity per se is frequently difficult.
Abstract
No significant differences in bean seed yield of field grown ‘Dark Red Kidney’ beans were observed in plants treated at the green or white bud stage or in full bloom with (2-chloroethyl)phosphonic acid (ethephon) at concentrations ranging from 300 to 2400 ppm. Plants treated with 300 and 600 ppm ethephon produced and retained more flowers and matured 7-10 days earlier than untreated plants. Treatment with 1200 and 2400 ppm reduced flower production and delayed pod maturity.
The drought-adapted, disease-resistant tepary bean (Phaseolus acutifolius A. Gray. var. acutifolius) is of great value as a potential gene donor of useful traits to the common bean (P. vulgaris L.). Analyses of flowering and fruiting patterns of tepary indicate that anthesis and abscission of reproductive structures within a raceme follow well-defined spatial and temporal patterns. Flowering occurs acropetally, and the probability of flowering decreases with distance from the most basal bud of the raceme. The probability of bud or pod abortion increases with distance from the basal bud, and the rate of abortion is highest in buds and pods proximal to the apex. Buds that never reach anthesis abort in the green-bud stage of development and aborting fruits cease development within the first 25% increase in pod length. In nonaborting fruits, the rate of seed abortion is 6%. A marked increase in abscission of all buds and fruits at all raceme nodes occurs before cessation of flowering.
Abstract
The number of pollen grains in anthers of Phaseolus vulgaris L. was estimated using a Coulter Counter, an electrical particle-counting device. Nine green buds were collected randomly from 3 plants grown in a growth chamber. From each bud, one anther at a time was excised and placed in liquid Ν for 3 sec. Pollen grains were transferred from the anthers into a drop of 0.3 M NaCl on a glass slide. The saline-pollen grain mixture was cleaned of all debris, and pollen was washed into a beaker containing the same solution. This procedure was repeated for the remaining 9 anthers of each bud. The total number of pollen grains per bud was determined using a Coulter Counter.