van der Merwe MJ, Osorio S, Moritz T, Nunes-Nesi A, Fernie AR
Decreased mitochondrial activities of malate dehydrogenase and fumarase in tomato lead to altered root growth and architecture via diverse mechanisms
Plant Physiology: 2009 149:653-669

Abstract
Transgenic tomato (Solanum lycopersicum) plants in which eithermitochondrial malate dehydrogenase or fumarase was antisenseinhibited have previously been characterized to exhibit alteredphotosynthetic metabolism. Here, we demonstrate that these manipulationsalso resulted in differences in root growth, with both transgenicsbeing characterized by a dramatic reduction of root dry matterdeposition and respiratory activity but opposite changes withrespect to root area. A range of physiological, molecular, andbiochemical experiments were carried out in order to determinewhether changes in root morphology were due to altered metabolismwithin the root itself, alterations in the nature of the transformants'root exudation, consequences of alteration in the efficiencyof photoassimilate delivery to the root, or a combination ofthese factors. Grafting experiments in which the transformantswere reciprocally grafted to wild-type controls suggested thatroot length and area were determined by the aerial part of theplant but that biomass was not. Despite the transgenic rootsdisplaying alteration in the expression of phytohormone-associatedgenes, evaluation of the levels of the hormones themselves revealedthat, with the exception of gibberellins, they were largelyunaltered. When taken together, these combined experiments suggestthat root biomass and growth are retarded by root-specific alterationsin metabolism and gibberellin contents. These data are discussedin the context of current models of root growth and biomasspartitioning.

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