A comparative lowered temperature response in root apex cellular growth of Festuca pratensis and xFestulolium braunii

Root apex development was studied in two closely related perennial grasses differing in winter hardiness: highly resistant meadow fescue (Festuca pratensis Huds.) and less hardy xFestulolium braunii [(K. Richter) A. Camus]. Cytomorphometrie assessment was carried out to determine cellular growth modulations in the root apical meristem (RAM) comprised of cell proliferation and transition domains. At 20 degrees C in hydroponics, root apex growth in F. pratensis 'Dotritiva I' and xFl. braunii Punia DS' was rather similar, accounting for about 0.9 mm RAM length after 30 days. Further, upon hardening at temperature +8/+2 degrees C (14/14 days) the mean RAM length in xn. braunii exceeded that of F. pratensis by 42%, reaching 1.7 and 1.2 mm, respectively (xFlb>Fp at P <0.01). Such differences were mostly due to the apparent expansion of the transition domain of the RAM in the hybrid. Also, a specific acclimation feature in the RAM of xFl. braunii was revealed, manifesting itself as a sharp RAM cell width increment (xFlb>Fp at P < 0.01). We assume that different RAM growth modulation under lowered temperature results in setting up a different pattern of plant growth in autumn / early winter period, namely, xFl. braunii expands its RAM and keeps growing, while F. pratensis declines cellular growth in the RAM and halts its vegetation. For the first time, we describe the RAM growth in xFl. braunii and F. pratensis in detail which could serve as a layout for new methodologies in growth biology studies of perennial grasses.