Embryo Excision Research Articles

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. III. Cytology, breeding behavior, fertility, and morphology of autotriploids

Mature triploid seed from reciprocal (2n = 4x × 2n = 2x) crosses in Triticum monococcum was minute and shrivelled because of endosperm collapse and therefore failed to germinate. This necessitated the excision of embryos from successful pollinations and their growth in vitro to ensure subsequent germination so as to obtain viable and vigorous autotriploids. A comparison of these triploids with their diploid and tetraploid progenitors revealed that cell size, kernel weight, and pistil size increased with an increase in ploidy level. However, unlike other species, optimum expression was observed in these triploids for plant height, tillering, size of spikes, number of spikelets/spike, and leaf size. Earliness, althoughenhanced in tetraploids relative to diploids, was delayed in the triploids. Mean numbers of univalents, bivalents, and trivalents per microsporocyte were 2.65, 2.60, and 4.38, respectively. Only chains (93.5%), which formed V-shaped metaphase I (MI) configurations, frying pan (5.0%), and Y-shaped (1.5%) trivalent associations occurred. On the average, two reciprocal exchanges occurred per bivalent and trivalent. Trivalents corriented randomly at MI. At anaphase I, all sets of three homologues segreated randomly to the two poles, lagging univalents always divided equationally, and only meiocytes with such chromosomes formed micronuclei. The reasons for similarities and differences in meiotic behaviour of T. monococcum triploids with those of other species are discussed. Confirmation of the conclusions drawn with respect to the cytology of the triploids was obtained from similar cytological observations with primary single trisomics. These triploids produced euploids, primary single trisomics as well as some double and triple trisomics all of which differed phenotypically from diploids. Triticum monococcum, like most diploid species, is highly intolerant of aneuploidy. Possible reasons for the differences in levels of tolerance of aneuploidy in species like T. monococcum and those like Petunia hybrida, which are highly tolerant of aneuploidy, are discussed. Pollen fertility was high and seed fertility was very low. Reasons for the latter as well as the high fertility in species that are highly tolerant of aneuploidy and allotriploids are discussed.Key words: Triticum monococcum, autotriploid, trisomic, cytology, breeding behavior, fertility, morphology.

Genetic and cytogenetic analyses of the A genome of Triticum monococcum. I. Cytology, breeding behaviour, fertility, and morphology of induced autotetraploids

Autotetraploids were colchicine-induced in Triticum monococcum and, upon comparison to their diploid progenitor, possessed the following characteristics: (i) their cells were on the average 20.8% larger; (ii) plant height was reduced by 15% and tillering by 37.5%; (iii) spikes, 1000-kernel weight, pistil size (length (L)/weight (W), and leaf size (L/W) were 53.9, 51.2, 80/57.1, and 60/26.4% larger, respectively; and (iv) they were 12.4% earlier in heading. Observed mean numbers of univalents, bivalents, trivalents (linear, convergent, and indifferent coorientations), and quadrivalents (convergent and parallel alignments only) per microsporocyte at metaphase I were 0.62, 9.86, 0.23, and 1.74, respectively; 65.4% of all meiocytes possessed bivalents and (or) quadrivalents and produced balanced meiotic products; 34.6% also possessed univalents and (or) trivalents and, therefore, produced balanced and unbalanced meiotic products. The actual 70.9% balanced meiotic products falls within the calculated range of 65.4–81.3%. Our tetraploids breed true. Evidence and reasons for this are discussed. The fertility of our tetraploids was high (79.8%). Irregular chromosome behaviour during meiosis may play a decisive role in determining the fertility level. Genic factors may also be involved. Methods of improving fertility and whether chromosomal factors alone are responsible for tetraploid fertility levels are discussed. Mature seed from reciprocal 2n = 4x × 2n = 2x crosses was shrivelled because of endosperm collapse and did not germinate. Thus, embryo excision and culturing on artificial medium was required to obtain viable autotriploids.Key words: Triticum monococcum, autotetraploid, cytology, breeding behavior, fertility, morphology.

Membrene turnover in imbibed and dormant embryos of the wild oat (Avena fatua L.)

A comparative study of protein synthesis has been carried out with embryos excised from dormant (D) and non-dormant (ND) caryopses of the wild oat. Although D embryos imbibed in water or ND embryos imbibed in abscisic acid do not germinate, they incorporate [(14)C]leucine into TCA-insoluble material for the first 48 h as readily as embryos that do germinate (ND embryos imbibed in water, or D embryos imbibed in gibberellic acid). Pulsechase experiments with [(14)]leucine show that in both D and ND embryos the proteins associated with the membranes undergo turnover. The rates of decay of incorporated radioactivity are similar in both dormant and germinating embryos up to 98 h following embryo excision. Fractionation of the membrane proteins in SDS-polyacrylamide gels indicates that the different polypeptides have different rates of turnover. It is concluded that membrane proteins in imbibed D embryos are in a state of constant turnover, and that this is a part of the replacement processes necessary to maintain the integrity of hydrated cells. The continuation of such synthetic events could account for long term survival of dormant Avena fatua in the imbibed state.

Thyroxine effects upon the mitotic activity of the medulla oblongata after unilateral excision in embryos of the frog

The right half of the hindbrain of Rana pipiens embryos was removed at stage 16 in order to determine whether thyroxine would influence regeneration of the deleted half. Thyroxine was found to accelerate the mitotic activity of the ependyma of both the right regenerating and left intact halves. However, this activity did not enhance restitution of the deleted half. Thyroxine-treated embryos experienced peaks of mitotic activity between stages 24 and 25. The decline which followed reached levels lower than those of controls by stage I. Findings in this study suggest that at embryonic stages exogenous thyroxine merely accelerates mitotic activity in neurons ready or nearly ready to divide and that upon termination of division an overall decline in proliferation occurs due to growth and synthetic processes occurring in daughter cells.

Occurrence of an inhibitor in wheat endosperm as revealed by embryo transplantation in irradiated seeds

Seeds (caryopses) of durum wheat var. Cappelli were soaked in water for 24 hr at 20°C to soften them enough for excision of embryos with scutellum. After irradiation of half of the soaked seeds (2–10 kr of X-rays), embryos were excised from both irradiated and unirradiated seeds and the following transplantations were made: (1) unirradiated embryo on irradiated endosperm, EM ( u) /EN ( i) and (2) unirradiated embryo on unirradiated endosperm, EM ( u) /EN ( u) (homotransplant, to serve as control). In 1962 and 1963, using seeds of the crops of 1961 and 1962 respectively, it was demonstrated that endosperms of after-ripened seeds stimulated growth in the EM ( u) /EN ( l) seedlings. Evidence was found that this stimulatory effect results from the destruction—or inactivation—by radiation of an inhibitor present in the endosperm of after-ripened seeds. The inhibitor is not present, in detectable amounts, in the endosperm of seeds during the total period of dormancy (first three months or more after harvest). The results are discussed in relation to the general problem of growth responses, including stimulation, in irradiated seeds.

Regeneration of the brachial spinal cord after unilateral excision in embryos of Rana pipiens.

Regeneration of the brachial spinal cord after unilateral excision in embryos of Rana pipiens.

The restitution of the medulla oblongata following unilateral excision in embryos of the frog.

Journal of Experimental ZoologyVolume 135, Issue 3 p. 403-423 Article The restitution of the medulla oblongata following unilateral excision in embryos of the frog† Thomas Ferguson, Thomas Ferguson Department of Zoology, State University of Iowa, Iowa City, IowaSearch for more papers by this author Thomas Ferguson, Thomas Ferguson Department of Zoology, State University of Iowa, Iowa City, IowaSearch for more papers by this author First published: August 1957 https://doi.org/10.1002/jez.1401350302Citations: 5 † Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Zoology in the State University of Iowa, August, 1955. Thanks are due to Dr. Jerry J. Kollros for serving as chairman of this investigation. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume135, Issue3August 1957Pages 403-423 RelatedInformation

Size changes in primary brachial motor neurones following limb excision in amblystoma embryos

Size changes in primary brachial motor neurones following limb excision in amblystoma embryos