HAPLOIDY IN HAPLOPAPPUS GRACILIS (N = 2)

Analysis of meiosis in a haploid (monoploid) sporophyte of Haplopappus gracilis (n = 2) showed a nonrandom distribution of chromosomes at anaphase I. Chromosomes A and B were associated at various prophase I stages in 34 % of the microsporocytes. Presumably, this association persisted long enough to disrupt random distribution in a portion of those meiocytes showing such an association. Pollen stainability of 26.5 % in the haploid was in agreement with the normal expectation. However, this number resulted from a nonrandom chromosome distribution. The usual method of predicting fertility of haploids, 1/21, is not accurate for monoploids with low chromosome numbers, and more functional methods are proposed. ALTHOUGH HAPLOID sporophytes have been reported for a substantial number of angiosperm genera and families (Kimber and Riley, 1963), there is a paucity of data concerning distribution frequencies of their chromosomes at anaphase I of meiosis. There are several reasons for this. Many workers are interested primarily in bivalent formation in polyhaploids or monoploids because this gives considerable understanding of genome relationships in the former and of the amount of duplication in the latter. The high chromosome number of many species requires large sample sizes to obtain all probable distributions, and the high numbers also may interfere with numerical determinations. Further complicating the situation is the reported lack of clear metaphase plates in some species. During an analysis of seedling karyotypes from a population of hybrids between the standard and Mexican chromosome races of Haplopappus gracilis, two monoploids were detected among 1,063 plants examined. Both monoploids came from seeds of one plant, and each had the Mexican chromosome A (Jackson, 1973). Haplopappus gracilis is an ideal organism for several kinds of monoploid analysis. The chromosome number is n = 2 in the standard race, the post-pachytene stages are easily studied, and cytokinesis does not occur until after the second meiotic division (Jackson, 1957, 1959). Furthermore, the spindle may be observed under phase contrast optics with suitable fixation and staining so that metaphase and anaphase stages may be determined unambiguously. MATERIALS AND METHODS-Seeds from Marfa, Texas, were germinated in a mixture of tap and distilled water and then transplanted to water'Received for publication 24 July 1974. Supported by the Institute for Research of Texas Tech University. expanded solid peat pots when they were ca. 10 mm long. They were maintained under conditions of high humidity and light for at least 3 days until the roots became established. The pots were then wrapped in aluminum foil and kept in a growth chamber until roots had emerged from the peat and karyotypes had been determined. The peat pots were then transferred to soil in 6in. clay pots, and the plants were grown to maturity in a growth chamber. One plant died shortly after flowering because of improper watering so that meiotic analyses were confined to one plant. Immature heads for cytological study were fixed in a mixture of 3:1 ethanol-propionic acid and stored at 0 C until used. Root tips were pretreated for 3 hr in a .0001 M solution of 1-bromonaphthalene and then placed in 4:1 ethanolpropionic acid fixative. All root tips were hydrolyzed for 15 min in 15 % H Cl and then washed in 4:1 fixative before squashing and staining. Staining of both meiotic and mitotic chromosomes was by the usual squash method. The stain used was FLP orcein (Jackson, 1973) which allowed observation of the spindle under suitable fixation and phase contrast optics. Pollen grains were stained with Buffalo Black B in the same acid and water mixture as the orcein. Those pollen grains with the stain distributed uniformly throughout the cytoplasm were considered fertile. RESULTS-The somatic chromosome number in the monoploid plants was 2 in root, leaf, and floral tissue in both plants (Fig. 1). No diploid cells were noted in any somatic tissue examined. This is in contrast to haploid-diploid tissues found in this species by Lima-de-Faria and Jaworski (1964). Meiotic analysis was confined initially to anaphase I (152 cells) and prophase II (330 cells) stages. As there was no statistically significant difference between chromosome distribution patterns at the two stages, the data were combined