Four root mutants, diageotropica (dgt), and altered root architecture (ara) 1, 2, and 3, were used to study root architecture and better understand the process by which root architecture is determined. Adventitious root formation, tissue response to auxin, nutritional response, and starch accumulation in the leaves were tested in ara 1 and ara 2. The expression of the DGT gene was studied in dgt. Ara 3 was removed from the experimental procedures once it was discovered that multiple mutations are present within ara 3 that are unrelated to the altered root architecture.
Ara 1 and ara 2 hypocotyl and cotyledon explants were exposed to a range of different concentrations of auxin (naphthalene acetic acid, NAA) for two weeks and adventitious root formation was quantified. Ara 1 showed a slightly increased sensitivity to auxin within cotyledons, while ara 2 exhibited virtually no response in either cotyledons or hypocotyls. Ara 2 was crossed with an AC wild type tomato line expressing the DR5:GUS auxin-response reporter to incorporate the construct into the ara 2 background. DR5:GUS revealed normal amounts of auxin present within the root. The ara 2 mutation is therefore likely to be involved in auxin transport or signaling. Nutrition response and starch accumulation was studied in ara 1. High starch levels were discovered within the leaves at all light exposure times, while removing sucrose from the media affected root growth in ara 1 less
profoundly than wild type. It is therefore likely that the ara 1 mutation is involved in carbohydrate biosynthesis.
Dgt expression was only observed in wild type AC tomato due to difficulties in transforming the dgt mutant. DGT expression was highest within the root tip and the pericycle cell layer from which lateral roots occur, indicating the importance of the DGT protein in lateral root initiation.