Although several histone variants have been studied in both animal and plant organisms, little is known about their distribution during processes that involve alterations in chromatin function, such as differentiation, dedifferentiation and hormone treatment. In this study we evaluated the ratio of each histone variant in each of the four core histone classes in the three developmental zones of maize (Zea mays L.) root and in callus cultures derived from them, in order to define possible alterations either during plant cell differentiation or dedifferentiation. We also evaluated core histone variant ratios in the developmental zones of roots treated with auxin and gibberellin in order to examine the effects of exogenously applied plant hormones to histone variant distribution. Finally, immunohistochemical detection was used to identify the root tissues containing modified forms of core histones and correlates them with the physiological status of the plant cells. According to the results presented in this study, histone variant ratios are altered in all the cases examined, i.e. in the developmental zones of maize root, in callus cultures derived from them and in the developmental zones of roots treated either with auxin or gibberellin. We propose that the alterations in linker histone variant ratios are correlated with plant cell differentiation and physiological status in each case.