Respiration Rate and Adenosine Triphosphate Formation in Tissues4

When leaves of Nicotiana tabacum L. var. Xanthi were inoculatedwith TMV, local lesion formation gave enhanced ATP concentrationaccompanied by increased respiration. Phosphorus metabolismin healthy and infected leaves was investigated either by floatingleaf tissue on ³²P₁-phosphate buffer or by allowing intact leavesto take up ³²P₁-phosphate buffer through the petioles. Bothmethods gave increased ³²P₁ incorporation into inorganic andorganic acid-soluble phosphorus fractions of the infected leaf.Comparison of the specific activity of ³²P₁-phosphate buffersupplied with the specific activity of the -phosphate groupof ATP demonstrated that 50 per cent of the ATP in the healthyleaf compared with over 78 per cent of the ATP in the infectedleaf was metabolically active in respiration. As the ATP concentrationin the infected leaf is much greater than that in the healthyleaf, this means that the amount of ATP being utilized and resynthesizedas a result of respiratory metabolism in the infected leaf ismore than twice that in the healthy leaf. Pulse-labelling experimentsdemonstrated that the rate of ATP turnover was very similarin healthy and infected leaves; therefore the increased respirationin the infected leaf results from the larger ATP pool with aturnover rate of ATP similar to that in the healthy leaf. Withtobacco callus tissue cultures infected by TMV, where infectiondoes not result in local-lesion formation, phosphorus metabolismwas unaltered in the infected tissue. It is concluded that necroticlocal-lesion formation results from increased availability ofATP at sites of ATP utilization, and this is aggravated by over-productionof ATP in the infected leaf.