Ultrastructural Localization of Polygalacturonase in Ethylene-Stimulated Abscission of Tomato Pedicel Explants

Polygalacturonase (PG) is crucial in plant organ abscission process. This paper investigated the cellular and subcellular localization of PG in ethylene-stimulated abscission of tomato pedicel explants. Confocal laser scanning microscopy of abscission zone sections with the fluorescent probe Cy3 revealed that PG was initially accumulated in parenchyma cells in cortical and vascular tissues after 8 h of ethylene treatment and then extended throughout the abscission zone when the abscission zone separated at 24 h after ethylene treatment. At the subcellular level, transmission electron microscopy with immunogold staining showed that PG showed abundant accumulation in the cortical and vascular tissues at 8 h after ethylene treatment, and the distribution area extended to the central parenchyma cells at 16 h after ethylene treatment. In addition, PGs were observed in the distal and proximal parts of the tomato pedicel explants throughout the abscission process. The results provided a visualized distribution of PG in the pedicel abscission zone and proved that PG was closely related to abscission.

Variation for genetic recombination among tomato plants regenerated from three tissue culture systems

Shoot morphogenesis was compared among two tomato inbred lines, two mutant lines, and their eight reciprocal F1 hybrids in three tissue culture systems. The number of shoots per explant was greatest on tomato pedicel explants, intermediate on cotyledon calli, and poor on micropropagated shoot tips. Genetic recombination rates of F1 hybrid plants regenerated from three tissue culture systems were analyzed by backcrossing the regenerated plants with mutant parents and comparing the observed crossover frequencies with those expected based on control plants raised from seed. Increased recombination rates and map distance were observed among plants from micropropagated shoot tips (18.8%), cotyledon calli (17.3%), and pedicel explants (13.5%) between the markers sunny (sy) and baby leaf syndrome (bls), which flank the centromere on chromosome 3. Conversely, decreased recombination rates and map distance were observed between bls and the locus solanifolia (sf), which is more distal to the centromere on the same arm of chromosome 3 as bls. Increased recombination rates and map distance among plants from micropropagated shoot tips, cotyledon calli, and pedicel explants were also observed between the loci white virescence (wv) and anthocyanin reduced (are) on chromosome 2.Key words: genetic recombination, tomato, Lycopersicon esculentum, pedicel explants, micropropagation, callus culture, plant regeneration.