Xue-Yuan Li

Overexpression of the Arabidopsis gai gene in apple significantly reduces plant size

Genetic engineering is an attractive method to obtain dwarf plants in order to eliminate the extensive use of growth retardants in horticultural crop production. In this study, we evaluated the potential of using the Arabidopsisgai (gibberellic acid insensitive) gene to dwarf apple trees. The gai gene under 35S promoter was introduced in the apple rootstock A2 and the cultivars Gravenstein and McIntosh through Agrobacterium-mediated transformation. One transgenic clone was recovered for Gravenstein and McIntosh, and several transgenic clones for A2, confirmed by Southern blot analysis. Two weak bands were detected by Southern blot analysis in all the untransformed controls, possibly indicating the existence of the internal GAI gene in apple. Most of the transgenic plants showed reduced growth in vitro. Growth analyses in the greenhouse showed a clear reduction in stem length, internode length and node number for the dwarf clones. The normal phenotype of some transgenic clones appears to be associated with silencing of the introduced gai gene, confirmed by RT–PCR analysis. In general, transgenic clones showed reduced rooting ability, especially for the extremely compact ones.

Changes of leaf water potential and endogenous cytokinins in young apple trees treated with or without paclobutrazol under drought conditions

Abstract Leaf water potential and endogenous cytokinins in xylem sap of young apple trees treated with or without paclobutrazol (PBZ) under drought stress conditions were investigated. Three drought and rewatering cycles were used in the experiments and leaf water potential was measured every 2–4 days during the experimental period (39 days). Zeatin (Z) and zeatin riboside (ZR) from the xylem sap in the trunks were measured during the drought periods. The results showed that leaf water potential of the plants decreased significantly when drought was applied, while for the PBZ treatment the reduction of leaf water potential was significantly less in all the three drought cycles, particularly in the first and second cycles. The concentrations of Z and ZR in xylem sap of the drought treated plants decreased significantly in the first drought cycle. In the second cycle, Z continued to decrease but ZR did not change significantly by day 4 but increased at day 8 for both treatments compared with the control. In the third cycle, there was no difference in Z concentration between the drought treatment alone and the control, but Z increased significantly for the PBZ treatment. ZR increased significantly for the drought and drought plus PBZ treatments compared with the control in the third cycle.

Optimisation of growing conditions for the apple rootstock M26 grown in RITA containers using temporary immersion principle

The use of bioreactors may provide an efficient and economic tool for mass clonal propagation of plants if technical problems can be solved. In this paper, we report the results of experiments aimed at optimising conditions for apple rootstock M26 grown in RITA containers using the temporary immersion principle. We tested different types and sizes of explants, different concentrations of plant growth regulators (BAP, kinetin and IBA) in the multiplication and elongation phases, and medium exchange during the shoot elongation period. The results show that the higher concentrations of cytokinins were required during the shoot multiplication phase, while the lower concentrations were better during the shoot elongation phase. Hyperhydricity was increased with increasing concentration in of cytokinins during both shoot multiplication and shoot elongation phases. The best shoot production in terms of shoot number and shoot quality was obtained using 4.4 μmol BAP and 0.5 μmol IBA during the shoot multiplication phase and 1.1 μmol BAP and 0.25 μmol IBA during the shoot elongation phase. Medium exchange twice during the shoot elongation phase resulted in higher shoot production compared with no exchange of the medium. However, it also resulted in increased hyperhydricity. Immersion frequency of 16 times per day gave a higher multiplication rate and longer shoots than 8 times per day. The explant size of 0.5 cm or 1 cm resulted in a significantly higher shoot production rate compared with that of 1.5 cm, but shoot length and hyperhydricity were not affected by the explant size. Shoot cultures from the liquid media rooted normally in the RITA containers with more than 90% rooting and the rooted plantlets acclimatised well in the greenhouse.

The rooting ability of the dwarfing pear rootstock bp10030 (pyrus communis) was significantly increased by introduction of the rolb gene

Abstract The pear rootstock BP10030 ( Pyrus communis ) is dwarf, frost hardy and compatible with most pear varieties, but very difficult to propagate due to its poor rooting ability. In order to improve its rooting ability, we transformed this rootstock with the rol B gene. Six transgenic clones were obtained and named 1-6. PCR and Southern hybridisation confirmed that all the transgenic clones contained the rol B and npt II genes, but only two of them contained the gus gene. The in vitro rooting results showed that the transgenic clones rooted from 67 to 100% without auxin, while the untransformed control did not root at all on the hormone free rooting medium. To further confirm the increased rooting ability of these clones, cutting experiments were carried out on four transgenic clones (1-4) and the untransformed control in the greenhouse. The rooting percentage ranged from 71 to 100 for the transgenic clones and only five for the untransformed control. Moreover, the root number was also greatly increased ranging from 11 to 17 for the transgenic clones, but only 3 for the untransformed control. Another important alteration by the insertion of the rol B gene was the root morphology. For the transformed clones, the roots were distributed evenly on the cut surface, but only on one side of the cut surface of the untransformed control. Growth analysis in the greenhouse, conducted on four transgenic clones (1-4) and the untransformed control, showed that three of the transgenic clones had a shortened stem length. The transgenic clones did not show any other visual alteration in shoot phenotype compared with the untransformed control plants.

Integration of the rolA gene into the genome of the vigorous apple rootstock A2 reduced plant height and shortened internodes

Summary The aim of this work was to dwarf the vigorous apple rootstock A2 by insertion of the rolA gene. To optimize conditions for a successful transformation, regeneration tests were carried out. The use of sucrose in the regeneration medium gave higher regeneration frequency than sorbitol in some cases and the shoot number per regenerated leaf was higher at 10 |j.M TDZ compared with 2.5 |j.M TDZ on the sucrose medium. Two transgenic clones, verified by PCR and Southern analysis, have been obtained on the sucrose medium together with 2.5 |j.M TDZ and 1.0 or 2.5 |j.M NAA and wounding by forceps. The two clones, named LAI and LA2, contained both the rolA and nptll genes. The results of in vitro rooting showed that LAI had a lower rooting percentage and a reduced root number per rooted shoot than the untransformed control shoots and the clone LA2 on the rooting medium containing 5 |JLM IBA. Growth analysis revealed that both transgenic clones had a reduced plant height and a shortened internode length compared with the control plants. However, the node number and the stem diameter were significantly larger for clone LAI than clone LA2 and the control plants.