PECTIN METHYLESTERASE ISOFORMS IN TOMATO (LYCOPERSICON-ESCULENTUM) TISSUES - EFFECTS OF EXPRESSION OF A PECTIN METHYLESTERASE ANTISENSE GENE

We have identified two major groups of pectin methylesterase (PME, EC 3.1.1.11) isoforms in various tissues of tomatoes (Lycopersicon escule ntum). These two groups exhibited differential immuno-cross-reactivity with polyclonal antibodies raised against tomato fruit PME or flax ca llus PME and differences in their accumulation patterns in tissues of wild-type and transgenic tomato plants expressing a PME antisense gene . The group I isoforms with isoelectric points (pIs) of 8.2, 8.4, and 8.5 are specific to fruit tissue, where they are the major forms of PM E activity. The group II PME isoforms, with pi values of 9 and above, are observed in both vegetative and fruit tissues. The group I isoform s cross-react with polyclonal antibodies raised to a PME isoform purif ied from fruit, whereas the group II isoforms cross-react with antibod ies to a PME purified from flax callus. Expression of a fruit-specific PME antisense gene impairs accumulation of the group I PME isoforms, with no apparent effect on the accumulation of the group II PME isofor ms. The absence of any noticeable effects on growth and development of transgenic plants suggests that the group I PME isoforms are not invo lved in plant growth and development and may play a role under special circumstances such as cell separation during fruit ripening.