Two cultivars of Digitaria eriantha (cold-sensitive cv. Sudafricana and cold-resistant cv. Mejorada INTA) were exposed to cold stress (5 A degrees C) for 0, 6, 24, or 72 h, and compared in terms of leaf and root growth, recovery period, shoot and leaf anatomy, and levels of chlorophyll, auxin (indole-3-acetic acid, IAA) and cytokinins (CKs). In Sudafricana, cold treatment caused reduced growth, slight changes in chlorophyll level, reduced levels of IAA and CK iso-pentenyladenine (iP), and reduced leaf dry weight (DW) and fresh weight (FW) during the recovery period. Anatomical damage was observed in chloroplasts, main stem, and axillary buds. Ultrastructural study showed reduced numbers of starch grains in chloroplasts of the bundle sheath and mesophyll. In Mejorada, cold treatment had no significant effect on growth or chlorophyll level. Leaf DW and FW quickly returned to normal levels during the recovery period. Anatomy of ground meristem was affected, but ultrastructure of bundle sheath and mesophyll chloroplasts was not. The cold tolerance of cv. Mejorada appears to be related to the stability of chlorophyll and CK levels, increase of IAA, and maintenance of normal shoot and leaf anatomy and ultrastructure.
