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Effects of substrate water potential in root growth of Agave salmiana Otto ex Salm-Dyck seedlings

Abstract:

The objective of this study was to test the hypothesis that root of maguey (Agave salmiana Otto ex Salm-Dyck) seedlings reacts during the first 24 h to low substrate water potential (ψW), by anatomical modifications. Three-4 cm root length seedlings were planted in vermiculite for 24 h at ψW between -0.03 and -2.35 MPa. Root dimensions, proline content and anatomy were evaluated. Substrate ψW between -0.65 and - 2.35 MPa did not significantly affect longitudinal root growth. However, proline content significantly increased from 1.6 to 2.1 μmoles mg-1. Significant reductions of transverse root area (41 %), thickness of mucilage covering the epidermis (47 %), thickness of epidermis (between 15 and 46 %), area of the parenchyma (between 35 and 41 %) and number of vessels (up to 28 %) were observed with ψW of -2.35 MPa. In contrast, thickness of xylem wall, diameter of xylem vessels and the number of cells of the cortex of the differentiation root region significantly increased (64, 17, and 97 %, respectively). The anatomical changes associated with low substrate ψW indicate a net increase of root apoplatic paths; structures involved in water conduction increased their diameter under low substrate ψW conditions and anatomical changes occurred during the first 24 h of water stress.