Differential effects of elevated ultraviolet-B radiation on the photochemical and reproductive performances of dicotyledonous and monocotyledonous arid-environment ephemerals

Four dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet-B (UV-B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV-B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV-B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV-B radiation.     

Features of the hmg 1 subfamily of genes encoding HMG-CoA reductase in potato

3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) catalyzes a key step in isoprenoid metabolism leading to a range of compounds that are important for the growth, development and health of the plant. We have isolated 7 classes of genomic clones encoding HMGR from a potato genomic library. Comparison of nucleic acid sequences reveals a high degree of identity between all seven classes of clones and the potato hmg 1 gene described by Choi et al. (Plant Cell 4: 1333, 1992), indicating that all are members of the same subfamily in potato. A representative member (hmg 1.2) of the most abundant class of genomic clones was selected for further characterization. Transgenic tobacco and potato containing the -glucuronidase (GUS) reporter gene under the control of the hmg 1.2 promoter expressed GUS activity constitutively at a low level in many plant tissues. High levels of GUS activity were observed only in the pollen. GUS assays of isolated pollen, correlations of GUS activity with the HMGR activity of anthers, hmg 1.2 promoter deletion studies, and segregation analysis of the expression of hmg 1.2::GUS among the R₂ pollen of R₁ progeny plants demonstrated that the hmg 1.2 promoter controls pollen expression.     

Successful expression in pollen of various plant species of in vitro synthesized mRNA introduced by particle bombardment

Gold particles coated with -glucuronidase (GUS) mRNA with a 5 cap structure that had been synthesized in vitro were introduced, by use of a pneumatic particle gun, into pollen grains of lily (Lilium longiflorum), freesia (Freesia refracta) and tulip (Tulipa gesneriana). A fluorometric assay for the GUS activity indicated that in vitro synthesized GUS mRNA introduced into these pollen cells by particle bombardment was successfully expressed. GUS activity in extracts of the bombarded lily pollen became detectable fluorometrically within 30 min after bombardment, peaked at 6 h, then gradually decreased. This activity changed as a function of the developmental stage of the pollen cell of lily.     

OVULE PACKAGING IN STOCHASTIC POLLINATION AND FERTILIZATION ENVIRONMENTS

The modular morphology of plants has important consequences for reproductive strategies. Ovules are packaged in discrete structures (flowers) that usually vary stochastically in pollen capture and ovule fertilization, because of the vagaries of pollen transfer by external agents. Different ovule packaging schemes may use limited reproductive resources more or less effectively, so that some number of ovules per flower may be optimal, given the prevailing probabilities of ovule fertilization. I derive a phenotypic model for ovule number per flower that maximizes the expected total ovule fertilizations on a plant when pollination and fertilization vary randomly among individual flowers. This model predicts that, except for small or inexpensive flowers, ovules should be “oversupplied” relative to the mean receipt of pollen tubes, so that pollen limitation of seed set should be common. Published data are congruent with this prediction. Additional hypotheses on the relation of ovule packaging to floral cost, plant size, and variance in pollen receipt are suggested by the model, but few data exist to evaluate these hypotheses.     

New evidence for the systematic significance of acylated spermidines and flavonoids in pollen of Higher Hamamelidae

New distributional recores of hydroxycinnamoyl spermidines (HCS), including novel trisubstituted HCSs and flavonol glycosides, in pollen of Higher Hamamelidae are presented. The 51 taxa analyzed by HPLC and TLC included members of the families Fagaceae (Castanoideae, Fagoideae, Quercoideae), Betulaceae, Juglandaceae, Myricaceae, Hamamelidaceae, Rosaceae, and Buxaceae (Simmondsia). The results support generic concepts in the Higher Hamamelidae derived from morphological and chloroplast DNA data and support a close evolutionary relationship between the Higher Hamamelidae and the Rosidae.     

Allergenic and antigenic proteins released in the apertural sporoderm during the activation process in grass pollen grains

A combination of transmission electron microscopy with immunocytochemical methods was used to localize antigenic and allergenic proteins during the maturation and activation processes of Poaceae pollen grains. The intine undergoes a series of modifications that play a decisive role in these processes. Allergenic and antigenic proteins were detected particularly in the intine of activated in vitro grass pollen grains. Labelling of antigenic proteins was more abundant and less specific than that of allergenic proteins. At the time of hydration, the operculum was lifted up, the intine was swollen and labelling of allergenic proteins appeared highly localized in the Zwischenkörper. No significant labelling was observed when the Zwischenkörper gelatinized. Immunolocalization of allergenic proteins in the activated Zwischenkörper indicated the presence of proteins related to activation of the pollen grains. This confirms that the intine function is involved in the processes of pollen tube formation and fertilization, and also suggests the possible mechanism activated in the pollen grains when allergenic proteins reach the mucosa of sensitive subjects.     

Notes on the colour of pollen

The spectral reflection of pollen in 67 plant species out of 28 families was measured by means of mass recording of pollen grains. Various types of spectral reflection curves were found, but 75% belonged to two categories: 1. Human-yellow pollen with strong reflection in the green and red, and low reflection in the ultraviolet and blue range of wavelengths. 2. Human-whitish pollen with strong reflection in the green and red and additional reflection of shorter wavelengths. It is shown that it is important to have information about the mode of the visual pollen display — crypsis or colour contrast against the corolla, pollen advertisement, or concealment — and the visual capabilities of the presumed pollinators in order to be able to discuss the signalling function of pollen colours.     

Airborne grass pollen in Granada (Spain)

We have carried out a study on the annual and daily pollen concentrations from Gramineae over four consecutive years in the atmosphere of Granada (Spain). Samples of pollen grains were collected by the volumetric method with the aid of a Burkard sporetrap. Gramineae, according both to their high sensitizing capacity and to data from allergologists, are responsible for many pollinoses diagnosed in this area. In this work, daily pollen levels from April to July are monitored and the variations identified are interpreted in relation to meteorological conditions. Results indicated that the highest airborne concentrations of Gramineae pollen were found in May and June, although the beginning and intensity of pollination have been variable during these 4 years.     

A study on pollen grains ofCrocus cartwrightianus (Iridaceae)

Crocus cartwrightianus andC. cartwrightianus cv.albus pollen have been studied from structural and ultrastructural points of view and the germination assayed in vivo and in vitro.C. cartwrightianus pollen is regularly shaped and sized, has a low percentage of anomalous grains and has a high germination rate in vitro, whileC. cartwrightianus cv.albus is less regularly shaped with some variation in size and has a high percentage of anomalous grains and a low germination percentage in vitro. Ultrastructural observations have revealed, in the pollen of both the taxa, the presence of a thin elongated vegetative nucleus and a generative cell surrounded by a thin membrane. However,C. cartwrightianus pollen shows a thicker intine, andC. cartwrightianus cv.albus shows numerous pollen germination anomalies which are in common withC. sativus.