Paraquat herbicide is toxic to animals, including humans, via putative toxicity mechanisms associated to microsomal and mitochondrial redox systems. It is also believed to act in plants by generating highly reactive oxygen free radicals from electrons of photosystem I on exposure to light. Paraquat also acts on non-chlorophyllous plant tissues, where mitochondria are candidate targets, as in animal tissues. Therefore, we compared the interaction of paraquat with the mitochondrial bioenergetics of potato tuber, using rat liver mitochondria as a reference. Paraquat depressed succinate-dependent mitochondrial Delta(psi), with simultaneous stimulation of state 4 O2 consumption. It also induced a slow time-dependent effect for respiration of succinate, exogenous NADH, and N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD)/ascorbate, which was more pronounced in rat than in potato mitochondria. However, with potato tuber mitochondria, the Delta(psi) promoted by complex-I-dependent respiration is insensitive to this effect, indicating a protection against paraquat radical afforded by complex I redox activity, which was just the reverse of to the findings for rat liver mitochondria. The experimental set up with the tetraphenyl phosphonium (TPP+)-electrode also indicated production of the paraquat radical in mitochondria, also suggesting its accessibility to the outside space. The different activities of protective antioxidant agents can contribute to explain the different sensitivities of both kinds of mitochondria. Values of SOD activity and alpha-tocopherol detected in potato mitochondria were significantly higher than in rat mitochondria, which, in turn, revealed higher values of lipid peroxidation induced by paraquat.

Somatic embryogenesis is a valuable tool for plant breeding. In recent years, different aspects related to somatic embryogenesis (SE) induction in tamarillo have been studied at our laboratory. In this work, results concerning the establishment of a protocol for cloning an adult tamarillo tree through SE are presented. Attempts to induce SE in tamarillo from various explants directly taken from an adult tree were unsuccessful and only calli with no embryogenic potential were initiated. To overcome the lack of potential of adult tissues for SE, an indirect approach was attempted in which shoots from an adult tree were first established in vitro and then wounded leaves were used for SE induction. A low rate of embryogenic tissue formation was obtained (19.4%), but it was in the range of initiation rates from leaf explants of in vitro cloned plantlets of different tamarillo cultivars (red, orange and yellow) that originated from a single seedling (13.3-54.4%). High variation in SE initiation among juvenile controls could not be explained by different organogenetic potential, as no significant differences in shoot proliferation or rooting ability during micropropagation could be detected. Subcultures of embryogenic lines from the adult tree allowed us to obtain a large amount of embryogenic tissue that, after 8 weeks on a PGR-free medium, gave an average of 111 plants per gram of fresh mass of embryogenic tissue. A RAPD comparative analysis of somatic embryo-derived plantlets and the donor tree confirmed that the plantlets had no variation in the DNA regions amplified by 12 primers. These results open the way for large-scale cloning of elite tamarillo trees through SE.

Arbutus unedo grows spontaneously around the Mediterranean basin. The species is tolerant to drought and has a strong regeneration capacity following fires making it interesting for Mediterranean forestation programs. Considering the sparse information about the potential of this fruit tree to be propagated in vitro, a project to clone selected trees based on their fruit production was initiated a few years ago. The role of several factors on A. unedo propagation was evaluated. The results showed that 8.9 μm kinetin gave the best results although not significantly different from those obtained with benzyladenine or zeatin. The inclusion of thidiazuron or 1-naphthaleneacetic acid promoted callus growth and had deleterious effects on the multiplication rate. The genotype of the donor plants is also a factor interfering with the multiplication. The results also indicated that the conditions used for multiplication influenced the behavior of shoots during the rooting phase.

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