Bean Leaf Expansion in Relation to Temperature

When dwarf Phaseolus vulgaris plants were grown in a controlledenvironment at 20, 25, 30, and 35° C, expansion of the primaryleaves occurred in two phases with an intermediate lag. Varyingrates and duration of expansion were involved, leading to greatestfinal areas at the two intermediate temperatures. Dry weightsof the leaves and leaf areas were similary influenced by temperature,except that the initial rates of increase continued for a longerperiod for weights than for areas. The rates of cell divisionand final numbers of cells were similar from 25 to 35° C,but both were decreased at 20° C. Final cell sizes were,on the other hand, decreased only at the highest temperature.The time trends of cell expansion varied greatly with temperature. Leaf expansion is discussed as a possible consequence of substratesupply, which may be determined by temperature in a number ofways. Cell division and cell expansion are not considered tobe joint direct determinants of leaf expansion. Temperatureinfluences division, with two consequences; the rate interactswith substrate supply to determine size of cells, and finalcell number affects potential leaf area. Cell size is regardedas being secondary to numbers of cells and total material available,although some factors can vary cell size independently of substrate,e.g. water status. An important control of leaf growth, until the attainment ofabout half the final area, may be exercised by way of the leaf.Subsequently, intra-plant competition is likely to dominate.