Lon1 is an ATP-dependent protease and chaperone located in the mitochondrial 
matrix in plants. Knockout in Arabidopsis (Arabidopsis thaliana) leads to a 
significant growth rate deficit in both roots and shoots and lowered activity of 
specific mitochondrial enzymes associated with respiratory metabolism. Analysis 
of the mitochondrial proteomes of two lon1 mutant alleles (lon1-1 and lon1-2) 
with different severities of phenotypes shows a common accumulation of several 
stress marker chaperones and lowered abundance of Complexes I, IV, and V of 
OXPHOS. Certain enzymes of the tricarboxylic acid (TCA) cycle are modified or 
accumulated, and TCA cycle bypasses were repressed rather than induced. While 
whole tissue respiratory rates were unaltered in roots and shoots, TCA cycle 
intermediate organic acids were depleted in leaf extracts in the day in lon1-1 
and in both lon mutants at night. No significant evidence of broad steady-state 
oxidative damage to isolated mitochondrial samples could be found, but peptides 
from several specific proteins were more oxidized and selected functions were 
more debilitated in lon1-1. Collectively, the evidence suggests that loss of 
Lon1 significantly modifies respiratory function and plant performance by small 
but broad alterations in the mitochondrial proteome gained by subtly changing 
steady-state protein assembly, stability, and damage of a range of components 
that debilitate an anaplerotic role for mitochondria in cellular carbon 
metabolism.