Van Der Merwe MJ, Osorio S, Moritz T, Nunes-Nesi A, Fernie AR
Decreased mitochondrial activities of malate dehydrogenase and fumarase in Solanum lycopersicum lead to altered root growth and architecture via diverse mechanisms

Plant Physiology: 2008 149:653-669

Abstract
Transgenic tomato (Solanum lycopersicum) plants in which either mitochondrial malate dehydrogenase or fumarase were antisense inhibited have previously been characterized to exhibit altered photosynthetic metabolism. Here we demonstrate that these manipulations also resulted in differences in root growth with both transgenics being characterized by a dramatic reduction of root dry matter deposition and respiratory activity but opposite changes with respect to root area. A range of physiological, molecular and biochemical experiments were carried out in order to determine whether changes in root morphology were due to altered metabolism within the root itself, alterations in the nature of the transformants root exudation, consequences of alteration in the efficiency of photoassimilate delivery to the root or a combination of these factors. Grafting experiments in which the transformants were reciprocally grafted to wild type controls suggested that root length and area were determined by the aerial part of the plant but that biomass was not. Despite the transgenic roots displaying alteration in the expression of phytohormone associated genes evaluation of the levels of the hormones themselves revealed that, with the exception of gibberellins, they were largely unaltered. When taken together these combined experiments suggest that root biomass and growth are retarded by root-specific alterations in metabolism and giberrellin contents. These data are discussed in the context of current models of root growth and biomass partitioning.

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