Transient and stable expression of gfp gene
Segments of cotton hypocotyls were used for co-cul-
ture with the Agrobacterium and sampled at different
time points, then checked for the GFP expression un-
der the UV light. After co-culture with Agrobacterium,
transient expressions in cotton hypocotyls were visible
as early as 42 h after infection and reached maximum
levels on day 3 (Fig. 1-A, B). The majority of the cells
showing transient expression were close to the wounded
edge. Interestingly, most explants showed a ring of
transient GFP activity around the primary vascular struc-
ture 42 h after co-culture (Fig. 1-A). Stronger fluores-
cence was observed on day 3 in the vascular region
(Fig. 1-B). Agrobacterium emitted dull, pale green fluo-
rescence as observed under our fluorescence
microscope; however, this was quite distinct from the
bright green fluorescence of GFP-expressing cotton
cells which was consistent with the results described
by Sunilkumar and Rathore (2001). The transient ac-
tivity was predominant at the cut surface in the
hypocotyls, and very few of the transient transforma-
tion events were observed in the unwounded parts of
hypocotyls in the epidermal cells (Fig. 1-C). The re-sults on transient transformation of hypocotyl cells sug-gest that Agrobacterium-mediated transfering of T-DNA
into cotton genome is highly efficient. Although some
earliest transient GFP activity was seen in the epider-
mal cells, only a few cell division activity was detected
in these cells, approximately 0.25% stable expression
rate was obtained in this study (Fig. 1-D).