FIG. 7.

Model of the influence of mitochondrially derived malate on tomato fruit starch, soluble sugar content, post-harvest shelf life, and bacterial infection. Data are presented on the basis of analysis of transgenics lines described in (55). Mitochondrial malate dehydrogenase (MDH) lines [(A); increased malate]; fumarase lines [(B); decreased malate]. The same ripening and postharvest sequence is presented for both transgenic sets. (i) Alterations in mitochondrial redox status are transmitted, either within the same cell type or from adjacent tissues, to the plastid via the malate valve as described by (302). (ii) Altered plastidial redox status results in a decreased (MDH lines) or enhanced (fumarase lines) redox-activation state of AGPase and concomitant starch synthesis (as well as similar changes in the activation state of the plastidial MDH); whether this is mediated by the Trx or the NTRC pathway (Fig. 4) is currently unknown. (iii) This leads to redox-mediated alterations in pigment biosynthesis during ripening. (iv) Starch is rapidly broken down, leading to a decreased soluble solid content in red-ripe fruit in the MDH lines and an increased soluble solid content in the fumarase lines. (v) Potentially as a result of differences in cellular osmolarity, the transgenic sets oppositely display an increased water loss and wrinkling (MDH lines) or a decreased water loss and wrinkling (fumarase lines) that appears to be cell wall independent. (vi) These changes in water loss and wrinkling correlate positively to the rate of opportunistic pathogen infection in the transgenic sets, while the MDH lines are increasingly susceptible to Botrytis cincerea infection. To see this illustration in color, the reader is referred to the web version of this article at www.liebertpub.com/ars