TESTING THE RELATIONSHIP BETWEEN LEAF MITOCHONDRIAL ACTIVITY AND LEAF DENSITY BY USING A TETRAZOLIUM COLORIMETRIC ASSAY

Abstract

The leaf economic spectrum (LES) is a universal pattern describing the intercorrelation of many leaf traits underlying plant structural and physiological function. Dry leaf mass per unit area (LMA) is one of the main descriptor traits for the LES and reflects leaf density, the amount of mass allocated to cellular structure. Despite having a high epistemological impact for plant functional ecology, the underlying cellular trade-offs or coordination for the LES remain unknown. Here, we derive and use a triphenyl-tetrazolium chloride (TCC) colorimetric assay to determine mitochondrial activity through spectroscopic methods to produce empirical evidence at the cellular level. We found a negative relationship between LMA and leaf mitochondrial activity per mass across species. That is, plants that allocate more resources to tissue density had lower metabolic rates per mass. The relationship between dry leaf mass per unit volume (LMV) and leaf mitochondrial activity was also negative, but the models did not fit as strongly as in using LMA. We believe these two negative relationships are caused by the trade-off between cellular space and cellular building structure. This study not only provided empirical evidence, at the cellular level of the negative relationship between mitochondrial activity and leaf density, but also validates the efficacy of the tetrazolium test on leaves to measure leaf mitochondrial activity in an easy, ready, and available way.