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On the origin of the ovule: some key events and their impact

100%

Herr J. M.

Acta Biologica Cracoviensia. Series Botanica. Supplement

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1999

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tom 41

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nr 1

2

On the origin of the ovule: some key events and their impact

100%

Herr J. M.

Acta Biologica Cracoviensia. Series Botanica

|

2000

|

tom 42

|

nr 2

Of the several theories for the origin of the ovule advanced in this century, based largely on fossil evidence, the telome concept and double integument theory are accepted as the most plausible. Derivation of the integument through fusion of sterile telomes is the salient feature. For all theories, a common point of agreement is that the entire nucellus is a megasporangium. Evidence from both Paleozoic and extant ovules indicates that some of the integumentary telomes were fertile; that the nucellus is a sporangiophore of fertile telome origin; and that among all features cited to characterize ovules, the unique nature of the megaspores alone is definitive. Changes in the megaspore that extended the period of nutrient absorption over the course of female gametophyte development were probably achieved in a Late Devonian population of progymnosperms, indicating a monophyletic origin for seed plants. Ancient primitive features in ovule structure recur in genetically transformed plants and in natural populations of advanced taxa as well. In ovules of the bel1-3 mutant of Arabidopsis thaliana, a single integument takes the form of two or three columnar axes structurally similar to the integumentary axes of Devonian ovules. A single homeotic recessive gene derived by mutation of its dominant allele expresses this departure from the typical bitegmic form. The phenomenon suggests that expression of primitive form may be suppressed over the course of ovule evolution and later reinstated by homeotic gene mutation.

3

Endosperm development in Arabidopsis thaliana [L.] Heynh

100%

Herr J. M.

Acta Biologica Cracoviensia. Series Botanica

|

1999

|

tom 41

According to many reports, the endosperm of Arabidopsis thaliana (L.) Heynh. follows Nuclear-type development whereby the primary endosperm nucleus divides without cytokinesis, ultimately to produce a peripheral, multinuclear endosperm tissue. However, some features of endosperm development in seeds collected from populations in central South Carolina reveal striking differences from the Nuclear type of other Brassicaceae. Nuclei produced by the first division of the central or slightly chalazal primary endosperm nucleus quickly migrate to opposite poles on the longitudinal axis, where the chalazal nucleus immediately becomes enshrouded with dense cytoplasm. Divisions from that point onward are free-nuclear and frequent in the micropylar portion, which enlarges markedly as it becomes multinucleate. The chalazal endosperm is sometimes positioned in a different focal plane as a result of curvature of the immature seed toward amphitropous form. It does not enlarge appreciably and accumulates only 2-8 nuclei before it gradually degenerates, persisting until digested during maturation of the developing embryo. Thus, the functional endosperm is produced primarily by the micropylar chamber.

Ograniczanie wyników

2 Acta Biologica Cracoviensia. Series Botanica

1 Acta Biologica Cracoviensia. Series Botanica. Supplement

3 Herr J. M.

1 2000

2 1999

On the origin of the ovule: some key events and their impact

On the origin of the ovule: some key events and their impact

Endosperm development in Arabidopsis thaliana [L.] Heynh