Solute accumulation and electrical membrane potential in Agrobacterium tumefaciens-induced crown galls in Kalanchoë daigremontiana leaves
Leaves of Kalanchoë daigremontiana were infected with Agrobacterium tumefaciens strain C58 in order to determine the relative contributions of energy-dependent ion uptake to the observed higher solute concentrations in crown-gall tissue compared with unaffected tissue. The tumor tissue exhibited the following characteristics with respect to unaffected tissue: the content of most solutes was much higher: Na+, K+, Cl–, soluble Pi, total N, protein, soluble amino acids, and soluble sugars. Yet NH−4 and starch content was less. Malate did not fluctuate in a typical CAM rhythm and was lower. The respiration rate on a cytoplasmic volume basis was similar. Photosynthetic rates were much lower. The cytoplasmic ATP concentration was even less, while that of NAD(P)H was higher. Electrical membrane potential was lower (− 184 mV tumor vs. − 223 mV control) and was composed of a higher energy-independent component (− 125 vs. − 98 mV) and a smaller energy-dependent component (− 59 vs. − 125 mV). The response of the membrane potential upon addition of neutral, acidic and basic amino acids including the opines octopine and nopaline was similar in both tissue types. It is suggested that the stronger accumulation of solutes in tumor vs. mesophyll cells cannot be due to thermodynamically more favourable conditions at the plasmalemma, but more probably to a hormone-regulated solute transport across the tonoplast.