ARABIDOPSIS THALIANA AS A MODEL SYSTEM FOR THE STUDY OF THE EFFECT OF INOCULATION BY AZOSPIRILLUM BRASILENSE Sp-245 ON ROOT HAIR GROWTH

Seedlings of Arabidopsis thaliana, Columbia ecotype, were used in vitro to analyze root hair growth response to inoculation by the plant-growth-promoting rhizobacterium, Azospirillum brasilense Sp-245. Root hair length was measured at physiologically-identical stages of root growth. In seedlings inoculated with A. brasilense, root hairs were more than twice the length of those of the non-inoculated control. This effect was consistent, reproducible and independent of N or C sources in the growth medium (although root growth was significantly suppressed in C-starved seedlings). Root hair growth promotion was similar in media with or without 1 % sucrose. Although root hair length of non-inoculated seedlings growing in the presence of various amounts of potassium nitrate (0-20 mM) was affected, it was significantly lower than that caused by inoculation with A. brasilense. We propose that A. brasilense inoculation affects the size of individual root hairs of Arabidopsis plants in vitro.