GENERATION OF FORM AND ASSOCIATED MASS DEPOSITION DURING LEAF DEVELOPMENT IN GRASSES - A KINEMATIC APPROACH FOR NONSTEADY GROWTH

Growing leaves of tall fescue (Festuca arundinacea Schreb.) were studi ed from emergence to a short time before the leaf ceases growth. Leaf form (width, average thickness, number of vascular bundles and height of associated ridges) and growth patterns were determined. The tissue elements produced at the point of leaf insertion are wider and thicker with time, as the intercalary meristem develops. These elements under go further width and thickness changes as they traverse the elongation zone, and leaf width and average thickness can continue to increase a fter passing the elongation zone. In order to relate the generation of leaf form and dry matter (DM) deposition, three methods were used to describe DM fluxes: (1) we followed the path lines of material element s and determined that they accumulate DM as they are displaced away fr om leaf base, even when expansive growth and maturation are complete; (2) we calculated DM deposition on a unit length basis, which represen ts the total sink strength of the zone studied, and we deduced that th e sink strength of the elongation zone increases with time, in concert with the changes in width and thickness of the elements that are succ essively produced at leaf base; (3) we calculated DM deposition on a u nit volume basis, which represents the net metabolic activity of the z one considered, and we found that growth activity and associated DM de position were high 3 d after the leaf emerged, then decreased graduall y, whereas maturation and associated DM deposition were low at emergen ce, but increased as the leaf gradually became autotrophic. Our data i ndicate that different descriptors and measurements are needed during the totality of leaf growth. (C) 1997 Annals of Botany Company.