No abstract

No abstract

Direct DNA delivery via microprojectile bombardment has become an established approach for gene transfer into peanut (Arachis hypogaea L.). To optimize our transformation protocol and to simultaneously explore the function of a heterologous promoter whose activity is developmentally regulated, embryogenic cultures from three peanut cultivars were bombarded with two plasmid constructs containing a uidA gene controlled by either a soybean vegetative storage protein gene promoter or a cauliflower mosaic virus 35S promoter. We found that GUS transient expression was useful to predict stable transformation and confirmed that image analysis could provide a quick and efficient method for semi‐quantitation of transient expression. One hundred and sixty hygromycin‐resistant cell lines were recovered from and maintained on selective medium, and those tested by Southern blot analysis showed integration of the foreign gene. Over 200 transgenic plants were regenerated from 38 cell lines. More than 100 plants from 32 cell lines flowered and 79 plants from 19 cell lines produced pods. Over 1000 R1 seeds were harvested. Analysis of expression in primary transgenic plants showed that GUS expression driven by the vspB promoter was modulated by chemical and positional information.

A significant correlation among chromosome number, chloroplast number and pollen grain size was observed using interspecific hybrids (2n = 30, 60), Arachis hypogaea (2n = 40), A. stenosperma (P1338280) (2n = 20), A. batizocoi (PI 468329) (2n = 20) and A. viUosulicarpa Hoehne (PI 336984) (2n = 20), representing four ploidy groups. Both chloroplast number in guard cells and pollen grain size were found to be positively correlated with ploidy, and provided a reliable method to distinguish diploid, triploid, tetraploid and hexaploid plants from each other regardless of their taxonomic backgrounds. These methods in combination with root-tip chromosome counts enabled us to confirm ploidy determinations on all three tissue layers, L1, L2 and L3 (guard cells, microsporocytes and root meristematic cells, respectively), and to detect the chimeric nature of some colchicine-treated tissue culture-derived plants. Screening pollen grains by size and the detection of highly stainable and viable, 30-chromosome pollen grains have enhanced the use of tripIoid hybrids in peanut breeding programs.