Search Results
The kinetics and efficiency of uptake of minerals (ammonium, nitrate, phosphate, potassium, calcium and magnesium) by roots of three tropical orchid genera (Aranda, Dendrobium and Oncidium) were studied and compared. Mericloned plantlets of these three orchids were cultured in solid Vacin and Went medium. The pattern of mineral uptake by orchids of these three orchid genera was similar. There was a preferential uptake of ammonia over nitrate. Rapid nitrate uptake by roots began only after 3 weeks in culture. Initial uptake of potassium, calcium and magnesium were rapid but the residual levels of these minerals either remained constant (Mg, PO4) or increased (K, Ca) after the 4th week. The % of uptake for ammonium nitrate, phosphate, potassium, calcium and magnesium over 9 weeks of culture was 60-76%, 24-28%, 12.8-27%, 17–30%, 17-26% respectively for the three orchid genera. A good correlation between growth of plantlets and uptrake was observed.
Three Korean cultivars, Pungkak, Kalmi, and Subi, were crossed with PI 201234, which has resistance to P. capsici. A backcross breeding program was initiated to incorporate the Phytophthora resistance into the Korean cultivars, but the level of resistance decreased as the backcross round increased. Highly resistant plants occurred frequently in the BC1F2 populations but were rare in the BC2F1 populations. Resistant plants selected in BC1F3 populations had nearly enough recovery of the growth and fruit characteristics of the Korean recurrent parents. Crosses were made between resistant selections in each BC1F2 population. The F1 hybrids showed a considerably increased level of resistance.
In order to regenerate explants of Brassica campestris ssp. pekinensis, known to be one of the most difficult crops to regenerate via organogenesis, three different explants, cotyledon, hypocotyl, and leaf, were cultured on MS basal medium supplemented with several plant growth regulators. In the medium containing NAA at 0.5 mg/L and BAP at 3.0 mg/L, the shoot regeneration, when hypocotyl was used as explant, was found to be quite effective. In the case of cotyledon, the most suitable combination of plant growth regulators was NAA at 1.0 mg/L and BAP at 3.0 mg/L. Treatment of AgNO3 (1.0 mg/L) for shoot regeneration gave positive results in general. Zeatin at 2.0 mg/L was very effective in shoot induction of leaf explant, especially when combined with BAP at 2.0 mg/L, NAA at 1.0 mg/L, and AgNO3 at 0.5 mg/L. A system to produce transgenic plants in Brassica spp. has also been developed using hypocotyl and cotyledonary-petiole segments and shoot-tips. An explants from 4-day-old seedlings were inoculated with an Agrobacterium tumefaciens strain containing a disarmed tumor-inducing plasmid pTiT37-SE carrying a chimaeric bacterial gene encoding hygromycin and kanamycin resistance, along with other genes of interests. The explants were co-cultured for 2 to 6 days before transfer to hygromycin and kanamycin selection media. Shoots regenerated directly from the explants in 1 to 4 weeks and were excised, transferred to shoot elongation medium, rooted in root induction medium, and planted in soil. Genetic transformation was confirmed by kanamycin or hygromycin resistance, GUS activities, and Southern blotting.
The uptake of nitrate and ammonium by a terrestial (Bromheadia finlaysonia) and an epiphytic (Dendrobium hybrid) orchid in solution culture has been studied. The rates of nitrate and ammonium were relatively linear, with higher rate of uptake for ammonium. The rates of nitrate uptake in terrestial and epiphytic orchids were 0.4 and 0.9 μmole gm fw-1 hr-1 respectively and they were considerably lower than those of most major crops. SEM studies show that the velamen of Bromheadia was 2 cells thick whereas that of Dendrobium was 8-10 cells thick. It is unlikely that the velamen is the major factor in restricting influx of nitrate or ammonium. Nitrate reductase (NR) and glutamine synthetase (GS) were present in roots and leaves of both orchids. NR was high in roots but low in leaves. The reverse was for GS. The activities of NR and GS was low but high enough to account for the rate of nitrate or ammonium uptake. It appears that the movement of ions across the transfer junction at the exodermis plays a major regulatory role in ion uptake by orchid root.