Long-term expression of the uidA gene in Gladiolus plants under control of either the ubiquitin, rolD, mannopine synthase, or cauliflower mosaic virus promoters following three seasons of dormancy

UidA silencing did not occur following three seasons of dormancy for 23 independently transformed lines of Gladiolus plants carrying the bar- uidA fusion gene under control of either the cauliflower mosaic virus 35S (CaMV 35S), ubiquitin ( UBQ3), mannopine synthase ( mas2), or rolD promoters. The highest levels of GUS (beta-glucuronidase) expression were observed in callus, shoots, and roots of plants carrying the bar- uidA fusion gene under control of the CaMV 35S promoter and in shoots and roots of greenhouse-grown plants that contained the rolD promoter. There was no major difference in GUS expression when plants carrying the fusion gene driven by either the CaMV 35S, mas2, or UBQ3 promoters were grown in vitro as compared to growth in the greenhouse, although plants containing the rolD promoter expressed at 4- to 11-fold higher levels in shoots and roots, respectively, when grown in the greenhouse. The levels of GUS expression in greenhouse-grown plants were higher in roots than shoots for all four promoters. Of the 21 plants analyzed, 20 contained one to three copies of the bar- uidA fusion gene. Of the 23 plants analyzed, 11 had rearrangements of the transgene, but without apparent effects on levels of GUS expression.

Effective resistance to potyvirus infection conferred by expression of antisense RNA in transgenic plants

Approximately 660 nt including the carboxy-terminal portion of the bean yellow mosaic potyvirus (BYMV) coat protein gene, complete 3' noncoding sequence and a short poly(A) tract were introduced to produce antisense RNA in transgenic Nicotiana benthamiana. Original (R0) transformants were selfed, and homozygous second generation (R2) populations challenged with infected sap, purified virus, or viral RNA. One transgenic line of 10 examined was extremely resistant to infection by mechanical inoculation of 100 micrograms/ml BYMV or 50 micrograms/ml BYMV RNA (the highest concentrations tested); no virus could be detected in inoculated leaves of this line. Nine other lines were systemically infected when inoculated with BYMV or BYMV RNA, with initial symptoms indistinguishable from those in nontransgenic plants. One of these lines subsequently developed reduced symptoms and then symptomless, virus-free leaves (complete recovery from BYMV infection), while other lines produced leaves with reduced symptoms and reduced virus titer compared to the controls (partial recovery). No transgenic lines had resistance to infection, nor recovery from symptom expression, following inoculation with pepper mottle or turnip mosaic potyviruses. Antisense RNA from 3' regulatory regions can confer multiple degrees of resistance to potyviruses, including extreme resistanc to infection, presumably by interference in virus replication.

Evaluation of DAPI as a fluorescent probe for DNA in viable Petunia protoplasts

4',6-Diamidino-2-phenyl-indole (DAPI), is a fluorescent probe that specifically and quantitatively stains DNA. Electroporation of viable Petunia protoplasts in the presence of DAPI revealed integral fluorescence that was similar for both the electroporated and fixed protoplasts, indicating quantitative staining of DNA. DAPI fluorescence was localized in the nuclei of viable protoplasts of Petunia. Protoplasts had a short term viability of 56-65% of the control (non-electroporated, unstained) protoplasts as determined by fluorescein diacetate staining 24 hr following electroporation in the presence of DAPI. The majority (84% of the number originally cultured) of these protoplasts subjected to electroporation were able to form a cell wall, but most did not form microcalli because they were blocked in cell division. The three week plating efficiency for protoplasts exposed to DAPI was 4% of the original number of protoplasts initially cultured compared to 30% for the control. DAPI should not be used as a fluorescent probe for plant protoplasts when the protoplasts are cultured for sustained growth because the levels of DAPI required to obtain quantitative staining of the DNA resulted in inhibition of the cell cycle. DAPI may, however, be used as a fluorescent DNA probe for short term (24 hr) studies.

Stable transformation of maize: the impact of feeder cells on protoplast growth and transformation efficiency

The importance of cell culture conditions, including the use of feeder cells, on protoplast growth and transformation in maize (Zea mays L.) was investigated. Total GUS activity, measured two days after transformation, was five-fold higher in protoplasts cultured on feeder cells compared to those grown in the absence of feeder cells. Since the specific activity of GUS was only slightly higher in the transformed protoplasts plated over feeder cells, the stimulation in transient gene expression resulted mainly from the improved environment provided by the feeder system. For stable transformation, either PEG treatment or electroporation of protoplasts was used to introduce the neo gene. When PEG was used, over 85% of the putative transformants (resistant to kanamycin) contained the neo gene. The combination of PEG transformation and the optimized cell culture protocol using feeder cells enabled the selection of about 100 stably transformed lines per gFW of cells. Electroporation was less efficient.

Embryogenic callus formation from maize protoplasts

Maize (Zea mays L.) protoplasts have been obtained which divide rapidly and produce a callus that differentiates to form somatic embryos. The somatic embryos can be induced to form roots and small leaf-like structures. The genotype was the hybrid A188xBlack Mexican Sweet. Protoplasts were prepared from an embryogenic suspension culture derived from a Type II callus which had been selected from Type I callus produced by immature zygotic embryos. The basal medium for the suspension culture was N6 (C.C. Chu et al., 1975, Scientia Sinica 18, 659-668). The 2,4-dichlorophenoxyacetic acid concentration of the suspension culture was critical for subsequent protoplast growth and was optimal at 4.0 mg.l. Protoplasts had to be cultured in a low-osmoticum medium (0.3 M mannitol) for subsequent cell divisions to occur. The protoplasts have been transformed transiently with the gene chloramphenicol acetyltransferase (CAT) containing the 35S promoter obtained from cauliflower mosaic virus (CaMV-35S).

Microcallus growth from maize protoplasts

Maize (Zea mays L.) protoplasts obtained from Type I and Type II calli from several genotypes were shown to be capable of synthesizing cell walls and forming small clusters of cells. The medium used also supported cluster formation from protoplasts obtained from root tips. The effects of various additions to the medium (such as casein hydrolysate, coconut water, amino acids, sugars, phytohormones, nitrate, calcium, and dimethylsulfoxide as well as pH variations on cellcluster formation were determined. The method of culture (protoplasts plated in agarose or supported in alginate beads in liquid medium) as well as several components of the medium were found to be critical for microcallus formation. Protoplasts obtained from embryogenic Type I callus and cultured in the medium of C. Nitsch and J.P. Nitsch (1967, Planta 72, 355-370) modified by various additions (NN 67-mod medium) were affected most by various sugars, casein hydrolysate, coconut water, and a combination of the auxins napthalene-1-acetic acid (2 mg/l) and 2,4-dichlorophenoxyacetic acid (0.1 mg/l), and the cytokinin N(6)-benzylaminopurine (0.5 mg/l). Cluster size in the agarose culture system was from 0.1 to 0.5 mm diameter and in the alginate culture system, up to 2.0 mm diameter.

Dopamine biosynthesis at different stages of plant development in Papaver somniferum

Latex and cell-free extracts of various organs and stages of plant and capsule development in Papaver somniferum, the opium poppy, synthesized dopamine, an alkaloid precursor, from 14C-dopa. The 1000 g X 30 min supernatant from latex of the pedicel-capsule junction converted more dopa than latex supernatant from the upper capsule or lower pedicel regions, although there was more protein in the latex from the capsule. Percent conversion of pedicel-capsule latex into dopamine was maximum in unopened flower buds and decreased within 14 days after flowering. Dopamine biosynthesis in latex and cell-free extracts also varied with the stage of organ development. Extracts from capsule tissue converted more labeled dopa into dopamine than did extracts from pedicels, leaves from vegetative plants at the rosette stage, leaves from flowering plants, or pedicels connected to capsules.