Auxin deprivation induces a developmental switch in maize somatic embryogenesis involving redistribution of microtubules and actin filaments from endoplasmic to cortical cytoskeletal arrays.

A developmental switch from non-polar pre-embryogenic units to polarized transition units in maize embryogenic callus is caused by auxin deprivation from the culture medium. This switch is accompanied by cytoskeletal rearrangements in embryogenic cells. An immunofluorescence study revealed prominent endoplasmic microtubules and actin filament meshworks radiating from the nuclear surfaces in pre-embryogenic cells growing on medium supplemented with auxin. On the other hand, parallel-organized cortical microtubules and cortical actin filament networks are inherently associated with polarized embryogenic cells of transition units growing on medium without auxin. These results indicate that fine-tuning of the dynamic equilibrium between endoplasmic and cortical cytoskeletal arrays is important for progress in somatic embryogenesis.

High-resolution two-dimensional electrophoresis separation of proteins from metal-stressed rice (Oryza sativa L.) leaves: drastic reductions/fragmentation of ribulose-1,5-bisphosphate carboxylase/oxygenase and induction of stress-related proteins.

Employing high-resolution two-dimensional electrophoresis (2-DE), we studied changes in the rice leaf protein patterns, in response to applied heavy and alkaline metals, important environmental pollutants in our surroundings. Drastic changes in 2-DE protein patterns after treatment with copper, cadmium, and mercury, over control were found, including changes in the morphology of the leaf segments. Changes in the major leaf photosynthetic protein, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO, both suppression and fragmentation), and induction of proteins are reported. A total of 33 proteins, which were highly reproducible in repeated experiments, were visually identified as changed over the control, and taken for N-terminal or internal amino acid sequencing. Among these, nine proteins were N-terminally blocked, and six proteins could not be sequenced. Most of the proteins showed homology to RuBisCO protein, and some to defense/stress-related proteins, like the pathogenesis related class 5 protein (OsPR5), the probenazole-inducible protein (referred to as the OsPR10), superoxide dismutase, and the oxygen evolving protein. Results presented here strongly indicate a highly specific action of some of these metals in disturbing the photosynthetic machinery, as evidenced by prominent reductions/fragmentation of the major photosynthetic protein, RuBisCO, and resulting in stress.

High efficiency Agrobacterium-mediated gene transfer to flax.

Using an Agrobacterium tumefaciens binary vector (pAL4404, pBI131), we have demonstrated the transfer of the ß-glucuronidase gene into the flax (Linum usitatissimum L.) cultivar Glenelg after selection for kanamycin resistance. The transformed lines were obtained by inoculation and subsequent regeneration of hypocotyl segments. The callus that formed on the cut surfaces of the hypocotyl segments was isolated three weeks after infection and was subsequently subcultured to yield shoots. This procedure generated a large number of transgenic shoots over a relatively short period of time. The transformation efficiencies obtained were the highest reported so far for this plant species.

Growth of zygotic flax embryos in vitro and influence of kinetin.

Embryos of flax (Linum usitatissimum L. cv. Viera) may be cultured in vitro from the globular stage of their development to germination. Kinetin added to the culture medium at the concentration of 5×10-8 mol/l accelerates embryo development, including the transition from greater expansion in width to greater expansion in length during the heart stage.