( ( plastid ( DNA content ) ) ( decreased . ) )
(ROOT (S (NP (JJ plastid) (NN DNA) (NN content)) (VP (VBD decreased)) (. .)))
plastid DNA content decreased.
(ROOT (S (PP (IN Like) (NP (NN mitochondria))) (, ,) (NP (NNS plastids)) (VP (VBP contain) (NP (PRP$ their) (JJ own) (NN dna))) (. .)))