Consequences of whole genome duplication for 2n pollen performance

The vegetative cell of the angiosperm male gametophyte (pollen) functions as a free-living, single-celled organism that both produces and transports sperm to egg. Whole-genome duplication (WGD) should have strong effects on pollen because of the haploid to diploid transition and because of both genetic and epigenetic effects on cell-level phenotypes. To disentangle historical effects of WGD on pollen performance, studies can compare 1n pollen from diploids to neo-2n pollen from diploids and synthetic autotetraploids to older 2n pollen from established neo-autotetraploids. WGD doubles both gene number and bulk nuclear DNA mass, and a substantial proportion of diploid and autotetraploid heterozygosity can be transmitted to 2n pollen. Relative to 1n pollen, 2n pollen can exhibit heterosis due to higher gene dosage, higher heterozygosity and new allelic interactions. Doubled genome size also has consequences for gene regulation and expression as well as epigenetic effects on cell architecture. Pollen volume doubling is a universal effect of WGD, whereas an increase in aperture number is common among taxa with simultaneous microsporogenesis and pored apertures, mostly eudicots. WGD instantly affects numerous evolved compromises among mature pollen functional traits and these are rapidly shaped by highly diverse tissue interactions and pollen competitive environments in the early post-WGD generations. 2n pollen phenotypes generally incur higher performance costs, and the degree to which these are met or evolve by scaling up provisioning and metabolic vigor needs further study.

Microspore growth and anther staging in barley anther culture

Nuclear growth, microspore cell growth and cell cycle stage were examined in microspores of anthers of Hordeum vulgare L. cv. Klages taken from florets of the middle of the spike as per anther staging methods. Although there was wide variation in nuclear size at all stages of the cell cycle, mean nuclear size appeared to be a good indicator of cell cycle stage for microspores within anthers. Microspore cell size increased considerably during Gl of the cell cycle. Anthers bearing microspores cytologically characterized as in the mid-uninucleate stage, which have proven to yield high levels of callus production, were determined to be in G1 of the cell cycle and were regularly found in spikes taken from tillers in which the base of the flag leaf had emerged 0 to 3 cm above the penultimate leaf.

Analysis of growth of tetraploid nuclei in roots of Vicia faba

Growth of nuclei of a marked population of cells was determined from G1 to prophase in roots of Vicia faba. The cells were marked by inducing them to become tetraploid by treatment with 0.002% colchicine for 1 hr. Variation in nuclear volume is large; it is established in early G1 and maintained through interphase and into prophase. One consequence of this variation is that there is considerable overlap between volumes of nuclei of different ages in the cell cycle; nuclear volume, we suggest, cannot be used as an accurate indicator of the age of the cell in its growth cycle. Nuclei exhibit considerable variation in their growth rate through the cell cycle. Of the marked population of cells, about 65% had completed a cell cycle 14--15 hr after they were formed. These tetraploid nuclei have a cell cycle duration similar to that of fast cycling diploid cells of the same roots. Since they do complete a cell cycle, at least 65% of the nuclei studied must come from rapidly proliferating cells, showing that variability in nuclear volumes must be present in growing cells and cannot be attributed solely to the presence, in our samples, of non-cycling cells.

GROWTH OF NUCLEI IN METHYLXANTHINE INDUCED BINUCLEATE CELLS OF VICIA FABA

Primary roots of Vicia faha L. were treated with solutions of two methylxanthines, 3-isobutyl-1-methylxanthine (IBMX) and 8-ethoxycaffeine (8-EOC). Binucleate cells were formed and, using this marked sub-population, nuclear growth was studied. In a 12 h period of interphase, nuclei did not grow, their mean volume decreased slightly, by 5.3% in IBMX induced binucleate cells and by 11.3% in 8-EOC induced binucleate cells. In the next 2 h, nuclear volume increased. By 15-17 h after IBMX treatment, about 75% of the binucleate cells had divided; none of the binucleate cells in 8-EOC treated roots had divided even by 21 h. Mean volume of prophase nuclei was lower in uni- and binucleate cells of IBMX treated roots than in normal roots. Sister nuclei of binucleate cells rarely had identical volumes. The difference between the mean volume of the larger and smaller nucleus of each pair of interphase nuclei ranged from 74 μm3, in a sample whose mean nuclear volume was 545 ± 131 μm3, to 178 μm3, when mean nuclear volume was 707 ± 284 μm3. The mean difference between prophase sister nuclei was 190 μm3 and the overall mean volume was 1320 ± 297 μm3. In some way, sister nuclei of binucleate cells are unequal and the mitosis from which they were formed was differential. The results are discussed in terms of nucleo-cytoplasmic interactions.