Callus Suspension Cultures of Ipomea batates Poir. cv. White Star were grown in an airlift bioreactor. A machine vision system was used to monitor nondestructively callus growth during a 10 day culture period. Growth data obtained with this system included the overall reactor population and population estimates for the 200-1200-microm fractions at 200-microm intervals. A model of callus growth was developed to explain the mechanics of callus enlargement. The model was based on the assumptions that (1) the calli could not subdivide or shrink, (2) there was a fixed percentage of the initial population for each fraction that was nonviable, and (3) growth rates did not vary with time during the culture period. It was determined that the growth rates and nonviable ratios decreased as fraction size increased.
This work has demonstrated the aseptic, automated harvest of somatic embryos from a bioreactor suspension culture. Machine vision, emulating the selection criteria of an experienced biologist, classified embryos as harvestable or non-harvestable as they flowed through a 3 mm glass conduit. Embryos classified as harvestable were separated in a sealed harvest chamber. The system harvested 60% of the embryos at a rate of 2.4 embryos/h and incorrectly harvested less than 1% of the non-harvest objects. The low harvest rate precludes the applicability of this technique to research and commercial tissue culture laboratories. The suspension feed-rate, culture population density and culture homogeneity were identified as the most important factors influencing embryo harvest rate. The performance of this technique on more densely populated cultures was projected using anticipated improvements in suspension feedrate. It was concluded that, under the conditions of this analysis, the harvester would be of limited value in a commercial propagation environment but could be beneficial to many research labs working with plant somatic embryos.
Ulex europaeus is a much‐branched shrub with small, narrow, spine‐tipped leaves and axillary thorn shoots. The origin and development of axillary shoots was studied as a basis for understanding the changes that occur in the axillary shoot apex as it differentiates into a thorn. Axillary bud primordia are derived from detached portions of the apical meristem of the primary shoot. Bud primordia in the axils of juvenile leaves on seedlings develop as leafy shoots while those in the axils of adult leaves become thorns. A variable degree of vegetative development prior to thorn differentiation is exhibited among these secondary thorn shoots even on the same axis. Commonly the meristems of secondary axillary shoots initiate 3–9 bracteal leaves with tertiary axillary buds before differentiating as thorns. In other cases the meristems develop a greater number of leaves and tertiary buds as thorn differentiation is delayed. The initial stages in the differentiation of secondary shoot meristems as thorns are detected between plastochrons 10–20, depending on vigor of the parent shoot. A study of successive lateral buds on a shoot shows an abrupt conversion from vegetative development to thorn differentiation. The conversion involves the termination of meristematic activity of the apex and cessation of leaf initiation. Within the apex a vertical elongation of cells of the rib meristem initials and their immediate derivatives commences the attenuation of the apex which results in the pointed thorn. All cells of the apex elongate parallel to the axis and proceed to sclerify basipetally. Back of the apex some cortical cells in which cell division has persisted longer differentiate as chlorenchyma. Although no new leaves are initiated during the extension of the apex, provascular strands are present in the thorn tip. Fibrovascular bundles and bundles of cortical fibers not associated with vascular tissue differentiate in the thorn tip and are correlated in position with successive incipient leaves in the expected phyllotactic sequence, the more developed bundles being related to the first incipient leaves. Some secondary shoots displayed variable atypical patterns of meristem differentiation such as abrupt conversion of the apex resulting in sclerification with limited cell elongation and small, inhibited leaves. These observations raise questions concerning the nature of thorn induction and the commitment of meristems to thorns.
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