Organic acid and sugar contents in sugarcane stem apoplast solution and their role as carbon source for endophytic diazotrophs

We have identified aconitate, malate, and citrate organic acids as well as sucrose, glucose, and fructose sugar compounds from the apoplast solution of the stem of the sugarcane cultivars NiF-8 and RK86-129. The content of all the compounds varied with the cultivars, growth stages, and internode portions. Aconitate showed the highest content among the organic acids and sucrose was the predominant sugar compound. Moreover, Gluconoacetobacter diazotrophicus ATTCC 49037 and Herbaspirillum rubrisubalbicans PA18 differed in their ability to utilize sucrose or aconitate as sole carbon source. The G. diazotrophicus strain preferred sucrose to aconitate while H. rubrisubalbicans preferred aconitate to sucrose as carbon source.