MINERAL NUTRIENT SUPPLY, CELL-WALL ADJUSTMENT AND THE CONTROL OF LEAFGROWTH

The possibility that changes in the plasticity of expanding cell walls are involved in regulating early leaf growth responses to nutrient de ficiencies in monocot plants was investigated. Intact maize seedlings (Zea mays L.) which were hydroponically grown with their roots in low- nutrient solution (1 mol m(-3) CaCl2) showed early inhibition of first -leaf growth, as compared with seedlings on complete nutrient solution . This early inhibition of leaf growth was not associated with reduced cell production. However, segmental elongation along the cell expansi on zone at the base of the leaf and the lengths of mature epidermal ce lls were reduced by the low-nutrient treatment. Solute (osmotic) poten tials in the expanding leaf tissues were unchanged. In contrast, low-n utrient treatments significantly altered leaf plasticity, i.e. the irr eversible extension caused by applying a small force in the direction of leaf growth. For example, in vivo plasticity decreased, along with leaf growth, after transfer of seedlings from complete nutrient soluti on to low-nutrient solution for 15 h. Conversely, in vivo plasticity i ncreased, along with leaf growth, after transfer of plants previously grown on low-nutrient solution to complete nutrient solution for 15 h. The nutrient treatments also induced similar changes in the in vitro plasticity of the expanding leaf cell walls. There were no consistent changes in elasticity. Thus, reductions in the plasticity of expanding leaf cell walls appear to be involved in controlling the early inhibi tion of maize leaf growth by root imposition of nutrient stress.