Root growth and proline content in drought sensitive and tolerant maize (Zea mays L.) seedlings under different water potentials

The effect of substrate water potential (ψW) in root growth and proline content of maize seedlings of Tuxpeño Sequía C0 (TSC0) and Tuxpeño Sequía C8 (TSC8), sensitive and resistant to drought respectively, were evaluated. Seventy two hours old seedlings, with 5 cm root length, were maintained for 24 h in vermiculite at ψW between −0.03 and −2.35 MPa. Root length, fresh and dry weight, number of lateral roots and proline content were evaluated. Root enlargement of TSCO was significantly higher than TSC8 at −0.03 MPa, but the response was opposite at low substrate ψW. The number of lateral roots was reduced in 23% in TSC8 at the lowest substrate ψW (−2.35 MPa) but it was not significantly affected in TSC0. A higher proline content was quantified in the cell division root region than in differentiation root region in both maize populations (5.64 and 6.96 umol 100 mg−1 of dry weight in TSC0 and TSC8, respectively); and ψW between −0.65 and −2.35 MPa induced a drastic and significant increase of proline content in both populations. The statistical interaction between maize population, substrate ψW, and root region was highly significant (P≤0.0039) for proline content. The results demonstrated that eight cycles of recurrent selection of Tuxpeño for drought tolerance induced a reduction of the number of secondary roots and proline content in the differentiation root region, but a proline increase in the cell division region when root seedling grow under no restrictive water conditions (ψW=−0.03 MPa), beside recurrent selection modified root reaction to low substrate ψW by accumulation of dry matter and proline.