Rooting and establishment of plantlets from longitudinal half plumule of mature embryo in vitro
--Pranab Gayen, Jasbir Kaur Madan and K. R. Sarkar

Recovery of mature, fertile plants from the in vitro culture of maize shoot apical meristem is known (Bommineni et al., Plant Cell Tissue Organ Cult. 19:225-234, 1989). There is also a report about recovery of two mature, fertile plants from the single embryonic axis of immature embryo through microsurgery in vitro (Bommineni, MNL66:98, 1992). We have now obtained success in recovering plantlets from longitudinally bisected embryo and plumule parts of the mature embryo of maize.

Mature seeds of the inbred MG209 were soaked for 60 h and the embryos scooped out from the seed. The embryos were then sterilized for 4-5 min in 0.1% mercuric chloride and washed three times with sterile water. A single medial longitudinal incision was made through the embryonic axis with the help of a sterile razor blade under sterile conditions. The two halves of the embryo or of the plumule only (excluding the radicle part from the middle of the hypocotyl) were separated and placed along the slant of the medium, keeping approximately half of the cut surface inserted into the medium and with the plumule side facing the top of the test tube (placement-A). The medium was comprised of the usual MS salts plus casein hydrolysate (1g/l), inositol (100mg/l), sucrose (3%) and agar (0.7%) with IAA (2mg/l) or without rooting hormone.;

In another set (placement-B) two types of explants were placed vertically on the medial surface with the same composition of media. Data on root initiation and plantlet establishment after 10 days of inoculation under white fluorescent light are presented in Table 1. Significant difference in rooting was observed between media with or without rooting hormone. Placement-A was better than placement-B over the two types of media. Half plumules produced normal plantlets; however, half embryos registered a greater degree of success. In placement-B, roots formed were weaker and the number of roots less than in placement-A.

Table 1. Rooting and plantlet establishment from embryonic axis and plumule half of maize.
                                        
Placement A Placement B
a
b
c
d
a
b
c
d
Media without rooting hormone Half-embryo 62 34 39 32 48 12 22 20
Half-plumule 58 21 35 30 43 9 16 13
Media with rooting hormone Half-embryo 59 47 53 49 50 19 27 24
Half-plumule 64 46 50 45 60 21 26 19
a=No. of half embryos/plumules cultured
b=No. of embryos/plumules rooted after 4 days
c=No. of embryos/plumules rooted after 10 days
d=No. of transferrable plantlets with proper root and shoot growth

Placement-A - Explants placed along the surface of the medial slant
Placement B - Explants vertically inserted into the medium


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