Articles
CYTOLOGICAL INVESTIGATIONS IN MIDDAY FLOWERS (AIZOACEAE) REVEAL HIGH DNA CONTENTS IN DIFFERENT SOMATIC TISSUES AND POTENTIAL OCCURRENCE OF UNREDUCED MALE GAMETES
Article number
1087_59
Pages
437 – 444
Language
English
Abstract
Breeding, possibly including polyploidization, in the midday flowers (Aizoaceae) genera Lampranthus and Delosperma is of interest for developing novel drought tolerant bedding plants.
However, cytological knowledge on these plants is scarce.
Flow cytometric investigations on different genotypes of Lampranthus and Delosperma revealed that most organs of these plants predominantly consist of endoreduplicated cells with up to five different DNA contents (2C-32C). Endoreduplication (endocycling) is a process involving one or several rounds of nuclear DNA synthesis without chromosomal and cellular division.
The highest proportions of endoreduplicated cells were detected in petaloid staminodes and mature succulent leaves (up to 95%), whereas only relatively low percentages were found in young leaves and roots (≈23-56%). A comparison of greenhouse and in vitro grown plant organs in respect of their endoreduplication patterns only showed marginal differences.
How endocycling affects in vitro shoot regeneration and/or chromosome doubling through antimitotic agents remains to be clarified.
Further observations on midday flowers of these genera revealed that pollen grains of identical genotypes had various diameters, possibly indicating spontaneous production of unreduced male gametes (2n pollen). In addition microscopic analyses showed that exceptionally large pollen grains also contained larger sperm nuclei.
Flow cytometric measurements of pollen nuclei isolated from germinated tricellular grains resulted in the detection of 1C (haploid), 2C and even low percentages of 3C particles.
Ongoing microscopic analyses of microsporogenesis, microgametogenesis and the appearance of gametes in pollen tubes should clarify the question whether the detected 2C and 3C signals were caused by unreduced male gametes or physically connected pollen nuclei (male germ units).
However, cytological knowledge on these plants is scarce.
Flow cytometric investigations on different genotypes of Lampranthus and Delosperma revealed that most organs of these plants predominantly consist of endoreduplicated cells with up to five different DNA contents (2C-32C). Endoreduplication (endocycling) is a process involving one or several rounds of nuclear DNA synthesis without chromosomal and cellular division.
The highest proportions of endoreduplicated cells were detected in petaloid staminodes and mature succulent leaves (up to 95%), whereas only relatively low percentages were found in young leaves and roots (≈23-56%). A comparison of greenhouse and in vitro grown plant organs in respect of their endoreduplication patterns only showed marginal differences.
How endocycling affects in vitro shoot regeneration and/or chromosome doubling through antimitotic agents remains to be clarified.
Further observations on midday flowers of these genera revealed that pollen grains of identical genotypes had various diameters, possibly indicating spontaneous production of unreduced male gametes (2n pollen). In addition microscopic analyses showed that exceptionally large pollen grains also contained larger sperm nuclei.
Flow cytometric measurements of pollen nuclei isolated from germinated tricellular grains resulted in the detection of 1C (haploid), 2C and even low percentages of 3C particles.
Ongoing microscopic analyses of microsporogenesis, microgametogenesis and the appearance of gametes in pollen tubes should clarify the question whether the detected 2C and 3C signals were caused by unreduced male gametes or physically connected pollen nuclei (male germ units).
Authors
P. Braun, T. Winkelmann
Keywords
Delosperma, Lampranthus, endoreduplication, endocycling, flow cytometry, polyploidization
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