Agriculture Reference
In-Depth Information
3.4.2 Growth Regulators
The requirement of growth regulators and culture medium in terms of kind and
concentration may vary with each and every plant system. Generally, there is an
agreement that the source and amount of total nitrogen as well as combination of a
cytokinin and an auxin is necessary for pollen embryogenesis and pollen callusing
in several woody plants (Chaturvedi et al.
2003
; Chen
1986
; Nair et al.
1983
). It has
been reported in most members of Solanaceae, that addition of an auxin to the in-
duction medium is not a pre-requisite for anther response, but the addition of auxins
and cytokinins alone or in combination is crucial for microspore-derived embryo
induction in majority of the plants, especially the recalcitrant ones (Maheshwari
et al.
1982
). The type and concentration of auxins seem to determine the pathway of
microspore development (Ball et al.
1993
), with 2, 4-D inducing callus formation,
and indole-3-acetic acid (IAA) and Napthaleneacetic acid (NAA) promoting direct
embryogenesis (Armstrong et al.
1987
; Liang et al.
1987
). Gibberellins and abscisic
acid have been occasionally added to the media.
Growth regulators, especially, auxins are widely used for induction of gyno-
genesis and their optimum concentrations have been reported to vary consider-
ably from species to species (San Noeum and Gelebart
1986
). In sunflower,
gynogenesis occurs only when 2,4-D or NAA is added to the medium (Gelebart
and San Noeum
1987
). As observed in many species, a combination of auxin and
cytokinin was also reported to be useful for gynogenesis in allium species (Alan
et al.
2003
) and mulberry (Thomas et al.
1999
). In mulberry, gynogenic haploids
are also produced on BA or Kinetin medium (Lakshmi Sita and Ravindran (
1991
).
These researchers observed gynogenesis in
ab initio
ovary cultures of mulberry.
Thomas et al. (
1999
) obtained maximum gynogenic response when excised ova-
ries from inflorescence segments of mulberry were cultured on MS supplemented
with BAP (8.5 µM) + 2,4-D (4.5 µM), followed by transferring them to MS + 2,4-D
(4.5 µM) + Glycine (6660 µM) + Proline (1738 µM).
3.4.3 Growth Additives
The supplement of other substances, such as free amino acids (glutamine, proline,
glycine), biotin, myo-inositol, casein hydrolysate, coconut water, silver nitrate (eth-
ylene antagonist) and polyvinylpyrrolidone has been reported to enhance gynogenic
response (Reinert and Bajaj
1977
; Powell
1990
; Achar
2002
). Moreover, the ad-
dition of exogenous aliphatic polyamines (PAs) to the culture medium has been
found to increase the number of pollen-derived embryos in potato (Tiainen
1992
),
in some Indian wheat cultivars (Rajyalakshmi et al.
1995
), cucumber (Ashok kumar
et al.
2004
and Chiancone et al.
2006
). Polyamines such as putrescine, cadaverine,
spermidine and spermine are low molecular mass polycations which are involved
in in vitro organogenesis and embryogenesis (Bagni and Tassoni
2001
; Kumar et al.
1997
). Similarly, the use of additives has also been reported in unfertilized ovary
cultures. Thomas et al. (
1999
) obtained maximum gynogenic response in mulberry
