MUTATIONS:

Many anomalous somatic embryos were detected such as fused ones, some lacking or with poorly developed cotyledons, others with supernumerary cotyledons, and also embryos with fused cotyledons (cupuliform cotyledons) (Pescador et al, 2008).

The gene mutant of arabidopsis, characterized by a variable degree of inclined cell division planes, presented marked zygote phenotypical alterations. Arabidopsis thaliana (L.) Heynh. mutant plants for normal organization of shoot apical meristems as the shootmeristemless (stm), wuschell (wus) and gurke (gk) present profound phenotypical changes. Two other functionally redundant genes CUP-SHAPED COTYLEDON 1  (CUC1) and  2 (CUC2), are also necessary for the separation of the cotyledon primordia and for the formation of a functional shoot apical meristem in arabidopsis. Embryos with fused cotyledons and absence of cotyledons lacking shoot apical meristem are similar to what was found in some of the somatic embryos of Acca sellowiana (Pescador et al, 2008).

The ease by which somatic embryogenesis is induced in Acca sellowiana would largely result from the relatively high level of 2,4- D present in the culture medium. Deleterious effects of  2,4-D on the in vitro chromosomal feature such as endoreduplication, aneuploidy and polyploidy have been observed in several cases (Pescador et al, 2008).

In fact, 2,4-D can change the conformation of the PIN protein, negatively interfering with the efflux of IAA, and altering the normal establishment of the apical-basal somatic embryos axis. At least two arabidopsis mutants for auxin signaling (bdl and mp) were shown to block the formation of the central and basal regions of the embryo and these defects could be traced back to the two-cell stage where the apical cell divides horizontally rather than vertically. Comparative hormonal studies performed with corresponding zygotic and somatic 2,4-D-formed embryo stages of Acca sellowiana showed profound differences in their ABA, IAA and cytokinins endogenous levels (Pescador et al, 2008).

BIBLIOGRAPHY:

1. PESCADOR, R. KERBAUY, G. VIVIANI, D.  &  KRAUS, J. Anomalous somatic embryos in Acca sellowiana (O. Berg) Burret (Myrtaceae). Rev. bras. Bot. [online]. 2008, vol.31, n.1 [cited  2011-05-20], pp. 155-164 . Available from: <http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-84042008000100014&lng=en&nrm=iso>. ISSN 0100-8404.  doi: 10.1590/S0100-84042008000100014.