A non-destructive, simple and accurate method of determining the relative growth rate (RGR) of the packed cell volume (PCV) of plant suspension cells in one Erlenmeyer flask at any time during the incubation period is described. The Erlenmeyer flask was tilted and the length of the chord formed by the surface of the packed cells across the bottom of the flask was measured. The chord length and the log PCV were correlated in a calibration line. The method enables the RGR during the exponential growth phase to be calculated by multiplying the slope of the linear part of the curve of the chord length in time with the slope of the calibration line. In order to investigate other growth parameters and to analyse the accuracy of the method statistically, a four-parameter function for the chord length and a computer program were used.The RGR during the exponential growth phase of cell suspensions of Solanum tuberosum and Haplopappus gracilis appeared to be independent of the PCV of the inoculum. The method appeared to be sufficiently accurate.
Agrobacterium rhizogenes transformed and control roots of the tetraploid potato cv. Bintje were compared. Transformed roots were obtained after infection by A. rhizogenes 15834 or 1855. Both in leaf and stem segments, more roots were formed at the basal side of the segments, indicative for a polarity in root formation. As compared to control roots the transformed roots are characterized by smaller and more densely stained cells, a zone of cell division, and smaller statoliths. These characteristics are correlated with vigorous growth, high branching incidence and diminished geotropism. The plant regeneration procedure according to Ooms et al.[1] was modified. The transformed roots required less 2,4-D than control roots for the induction of shoot-competent calli. The callus and shoot induction phases were reduced from 8 and 6 weeks to 3 and 3 weeks, respectively. Upon induction, 25%, 58% and 61% of the root clones originating from tuber, stem and leaf, respectively, produced shoots, whereas all of the control roots produced shoots. Shoot outgrowth occurred on liquid MS medium in the absence of hormones.
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