Crozier Formation in Byssochlamys Nivea

Abstract

Crozier formation in Byssochlamys nivea was studied by means of scanning electron microscopy (SEM) and light microscopic techniques. The continuous recording of crozier formation by time lapse cinematography combined with karyological analyses revealed an important deviation from the classical scheme of crozier formation. In B. nivea the divisions of the two nuclei during crozier formation are not simultaneous (conjugate). First, the nucleus in the crook region divides followed by septum formation, and then the nucleus in the basal region undergoes nuclear division followed by septum formation. The three-dimensional arrangement of crozier chains was analyzed by SEM. Subsequent croziers are turned against each other at an angle of 120?. There are two modes of crozier chain branching: formation of one crozier, each, from the penultimate cell and from the fused terminal cell, and simultaneous formation of the two croziers from the penultimate cell. Crozier formation is a prominent feature in the dikaryotic stage of the majority of higher Ascomycetes. The classical scheme is based on Claussen's observations of the development of Pyronema confluens Pers. ex Tul. and other Discomycetes (Claussen, 1912). Later work on other fungi, e.g., Saccobolus kerverni (Crouan) Boud. (Carroll, 1968), Pyronema domesticum (Sow. ex Gray) Sacc. (Hung and Wells, 1971) and Neurospora crassa Shear & Dodge (Raju, 1980) seemed to confirm the general validity of the pattern of crozier formation derived from studies of Pyronema confluens. In all cases, however, data were obtained from sections of fixed material since the croziers usually are hidden within the developing fruiting bodies. As a consequence, the time course and details of crozier formation had to be reconstructed from different croziers in various developmental stages. In all such investigations there was incomplete information as a result. In our paper, crozier formation is analyzed in a more primitive organism, Byssochlamys nivea Westling, than P. confluens and others. In this ascomycete, the croziers and, later on, the asci, are surrounded by very scanty, loose welts of hyphae. To suppress even this presumably primitive form of a peridium, a suitable nutrient medium which allowed normal ascus formation without any cover of hyphae was developed. Crozier formation could then be studied by timelapse cinematography of living material combined with other techniques to reveal the karyology. As a result we have traced a complete course of crozier chain formation obtained from individual crozier initials. Important deviations from the classical scheme of crozier development were found.