However, the importance of other cis-acting elements found to be essential for ribosome shunting in protoplasts and in vitro, namely, the stem section 1 [13], [16], [16] and the shunt landing site [2], [17], was not tested in planta.
In the present study, the stem section with one node was identified as the most suitable type of explant as it allowed the highest transformation frequency compared with root, internode and leaf.
However, the primary sequences building the stem section 1 in RTBV (Fig. 1) do not appear to bear any significant homology to the yeast retrotransposon sequence.
We measured the wall thickness of the parenchyma cells in the mature stem sections (E4I1 internode); the value for control plants was 4.21 ± 0.52 μm, compared with 1.85 ± 0.50 μm for the PvMYB4-OX transgenics (Student t-test E-value p = 6.0E-20 6.0E-20
To obtain this behavior in an ultrasonic step horn one can either, (i) couple the longitudinal and torsional modes of the horn by incorporating a ring of diagonal slits in the thick base section or, (ii) place helical flutes in the thin stem section to degenerate the longitudinal mode into a modified behavior with a longitudinal torsional motion.
Therefore, biochemical and molecular studies of intrusive growth of primary phloem fibres should be conducted in this stem section, corresponding to up to 3 days of growth.
Adventitious roots are absent in the specimens and stem sections of Yiduxylon, the outer cortex is Sparganum-type, and the angle of frond attachment is not so wide, whereas the stem diameter is generally less than 20 mm and the complex fronds consist of two orders of long pinnae with many large pinnules.
This labelling was punctate and appeared to be intracellular, similar to that observed in sieve elements in stem sections (Fig. 3B, D, F, H, J; 4F).
The structure of the vascular cambium in the hemp stem can thus be deduced by examination of secondary tissue patterns as seen in the stem cross-section (e.g. Larson 1994 and citations therein).
The total number of primary phloem fibres in the stem cross-sections of 67-day-old plants sharply increased from 1556 ± 201 at 10 mm from the SAM up to 6118 ± 392 at a distance of 60 mm from the SAM (Table 1).
