Leaf growth in the fast-growing Holcus lanatus and the slow-growing Deschampsia flexuosa: tissue maturation

Abstract

Inherent variation in the relative growth rate of grasses is negatively correlated with that in leaf mass per unit leaf area (LMA). To scrutinize this correlation, the LMA of two grass species was analysed. Changes in LMA and cell wall synthesis in leaf blades of the fast-growing grass Holcus lanatus and the slow-growing grass Deschampsia flexuosa were investigated above the elongation zone of the leaf blade. After the leaf had obtained its final length, in H. lanatus final LMA values of 40-44 g m - 2 were obtained at full leaf length, whereas in D. flexuosa LMA values continued to rise to 110 g m -2 . During this period of tissue maturation the LMA value doubled in H. lanatus, whereas in D. flexuosa an increase of 30% was measured. During this rise in LMA a substantial increase in cell wall polysaccharides was measured. Most of the cell walls could be hydrolysed with driselase, the residue was hydrolysed with sulphuric acid. Driselase hydrolysates were identical in sugar composition, whereas the sugars released by sulphuric acid treatment changed gradually in composition as the tissue matured. The major sites of cell wall deposition during cell maturation were the outer walls of epidermal cells, fibres adjacent to the epidermis and the mestome ring around the vascular bundles. Lignin deposition was restricted to the vascular bundles and lignin levels of the leaf blade did not exceed 0.9% of the total amount of cell wall polysaccharides. Lignin accumulation occurred mainly after the increase in LMA and is unlikely to affect measurably the growth of these leaves.