Chromosomes under the Microscope

The photographs shown below are from from Landolt (1996), pp. 129-136.
 
 

 Wolffiella and Wolffia Chromosomes

Wolffiella hyalina, 8640  (2n = 40)	Wolffiella lingulata, 7292  (2n = 50)	Wolffia columbiana, 8018  (2n = 50)

The above are brightfield micrographs show mitotic chromosome spreads stained with orcein, a dye.  These images are the work of Dr. Krystyna Urbanska, ETH, Zurich.
 

Spirodela and Lemna Chromosomes

a  Spirodela polyrrhiza, 7551 (2n = 40),         b  Lemna gibba, 7245 (2n = 84)

The above are fluorescence micrographs of mitotic chromosome spreads stained with a DAPI, a fluorescent dye that binds to DNA.  They are the work of G. Geber, published in Landolt's book.
 

Chromosome Counts

A extensive literature survey assembled by Elias Landolt (1986, pages 134-135) shows that the chromosome counts in duckweed differ widely among species, even between different species of the same genus and different isolates (clones) of the same species.  For example, isolates of three widely studied Lemna species, L. gibba, L. minor and L. trisulca, are reported to have widely varying numbers of chromosomes (see above).

DNA Content of Duckweed Chromosomes

The chromosomes are the smallest in Spirodela and the largest in Wolffia (average 1.7 um).  See the table below.  It is a mystery why the largest duckweed species should have the smallest chromosomes, while the smallest duckweeds have the largest ones.
 

DNA Content of the Chromosomes of Lemnaceae and Pistia

Species	2n	pg DNA	pg DNA /  1 C	pg DNA /  chromsome
Pistia stratiotes	28	1.08 /  4C	0.25	0.036
Spirodela polyrrhiza 7110	80	1.19 /  8C	0.15	0.015
Spirodela punctata 7461	46	1.48 /  4C	0.37	0.032
Lemna minor 7115	126	5.82 / 12C	0.49	0.046
Wolffiella oblonga 79 (7166)	42	3.02 /  4C	0.76	0.072
Wolffia arrhiza 7347	42	6.53 /  4C	1.63	0.155

C = one chromosome set, from the Ph.D. thesis of  Günter Geber, Vienna, Austria  (published in Landolt, 1986, p. 137), using the garden pea (Pisum sativum) as a standard.
 
 

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Revised:  January 9, 2002