Microinjection and Macroinjection - Plant regeneration from transformed protoplasts, still remains a problem. Therefore cultured tissues, that encourage the continued development of immature structures, provide alternate cellular targets for transformation.

These immature structures may include immature embryos, meristems, immature pollen, germinating pollen, isolated ovules, embryogenic suspension cultured cells, etc. The main disadvantage of this technique is the production of chimeric plants with only a part of the plant transformed.

However, from this chimeric plant, transformed plants of single cell origin can be subsequently obtained. Utilizing this approach, transgenic chimeras have actually been obtained in oilseed rape (Brassica napus).

DNA macroinjection employing needles with diameters greater than cell diameter has also been tried. In rye (Secale cereale), a marker gene was macroinjected into the stem below the immature floral meristem, so as to reach the sporogenous tissue (De la Pena et al., 1987) leading to successful production of transgenic plants.

Unfortunately, this technique could not be successfully repeated with any other cereal, when tried in several laboratories. Therefore, doubt is expressed about the validity of earlier experiments conducted with rye (Potrykus, 1991).