Growth and Development of the Lactuca sativa Shoot as Affected by NaCl Stress: Consideration of Leaf Developmental Stages

Abstract

The effect of salinization on development of the whole shoot and individual leaves of Lactuca sativa L. cv Black-seeded Simpson was studied nondestructively. Salinization by 80 mol m-3 NaCl (from the 10 mol m-3 control concentration) slowed shoot development. The lengthening of the plastochron because of salinization was evident in rates of leaf expansion, frequency of leaf emergence, and growth rate of the whole shoot. The plastochron effect on shoot development was sufficient to account for a 33% reduction in biomass of the shoot, equaling the entire growth inhibition measured during the first week following salinization. A second effect, reduction in maximum leaf size, could be measured after 2 more wk of plant growth. A 50% reduction in fresh weight of fully mature leaves of salinized plants was evident in leaves already beyond the most rapid phase of expansion at the time of salinization. Curtailment of the slow phase of leaf expansion seems, therefore, to reduce maximum leaf size. This cultivar lends itself to nondestructive growth study because of its rapid growth, high rate of leaf emergence, the open access to its leaves, and the absence of a significant contribution by the stem to shoot biomass. Mathematical reconstruction of the shoot allows comparison with results from destructive studies measuring growth of the bulked shoot.