A unique pollen wall mutation in the family Compositae: ultrastructure and genetics.

During a routine screening of pollen fertility in the n = 2 chromosome race of Haplopappus gracilis, a spineless pollen wall mutation was discovered that renders the otherwise functional pollen grains completely unrecognizable as Compositae pollen. Normal Haplopappus pollen is characterized by an outer layer, the ektexine, consisting of large spines supported by a roof (tectum), which in turn is supported by collumellae that are joined basally. A large cavity (cavea) stretches from aperture to aperture and separates columellae bases from the final ektexine unit, the foot layer. The spines, tectum, columellae, and columellae bases are filled with perforations (internal foramina), while the foot layer is without them. Immediately underlying the foot layer is a thickened, lamellate, disrupted, internal foramina-free second exine layer, the endexine. In contrast, the mutant pollen ektexine is a jumble of components with randomly dispersed spines as the only clearly definable unit. The endexine layer is similar to the endexine in normal pollen. The mutation apparently disrupts only the organization of ektexine units, and mutant pollen appears to be without the caveae and foot layer characteristic of normal pollen. In genetic tests, the mutant allele is recessive. There is a simple Mendelian pattern of inheritance of the mutant gene, and its phenotype is under sporophytic control.

Hexamethyldisilazane as a drying agent for pollen scanning electron microscopy.

Use of hexamethyldisilazane (HMDS) as a final dehydrating solution provides robust, undistorted secondary electron images of a variety of angiosperm and gymnosperm pollen grains, including those considered to be susceptible to collapse in the scanning electron microscope. Ease of handling, low cost, lack of specialized equipment, minimal expenditure of time, and high rate of success are factors that favor HMDS over other drying agents for preparing pollen grains for scanning electron microscopy.

Subcellular localization of isocitrate lyase in nongreen tissue culture cells.

Density gradient centrifugation and electron microscopy were used to establish that isocitrate lyase present in Rosa cv. Paul's Scarlet cells was located in the mitochondria and not other membrane fractions. The enzyme may be important in glycine and serine synthesis. A comparison between the enzymic activity of isocitrate lyase and the amount of glycine and serine synthesized during logarithmic growth indicated that the activity was great enough to account for all of the carbon entering these amino acids during that stage of growth.

Primitively columellaless pollen: a new concept in the evolutionary morphology of angiosperms.

Comparative study of pollen of the ranalean complex has revealed a remarkable, hitherto unrecognized characteristic of primitive angiosperm pollen, namely, its complete lack of columellae. Pollen with such exine has been desnated atectate anid taxa in the Magnoliaceae. Degenzeriaceae, Eupomatiaceae, Annonraceae, and possibly Himantandraceae and Nymphaeaceae have pollen which is considered to be primitively columellaless.