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

Inherent variation in the relative growth rate of grasses is negativelycorrelated with that in leaf mass per unit leaf area(LMA). To scrutinize this correlation, theLMA of two grass species was analysed. Changes inLMA and cell wall synthesis in leaf blades of thefast-growing grass Holcus lanatus and the slow-growinggrass Deschampsia flexuosa were investigated above theelongation zone of the leaf blade. After the leaf had obtained its finallength, in H. lantus final LMAvalues of 40-44 gm^-2 were obtained at full leaflength, whereas in D. flexuosa LMA values continued torise to 110 gm^-2. During this period of tissuematuration the LMA value doubled in H.lanatus, whereas in D. flexuosa an increaseof 30% was measured. Most of the cell walls could be hydrolysed withdriselase, the residue was hydrolysed with sulphuric acid. Driselasehydrolysates were identical in sugar composition, whereas the sugarsreleased by sulphuric acid treatment changed gradually in composition asthe tissue matured. The major sites of cell wall deposition during cellmaturation were the outer walls of epidermal cells, fibres adjacent to theepidermis and the mestome ring around the vascular bundles. Lignindeposition was restricted to the vascular bundles and lignin levels of theleaf blade did not exceed 0.9% of the total amount of cell wallpolysaccharides. Lignin accumulation occurred mainly after the increase inLMA and is unlikely to affect measurably the growth ofthese leaves.