An Exploration of the Carbon Economy of the Tobacco Plant. II. Patterns of Leaf Growth and Dry Matter Partitioning

As a sequel to calculations made in Part I about the carbon economy of the tobacco plant, a short-day variety of tobacco (Nicotiana tabacum L. cv. Mammoth 17L) was grown at controlled temperatures in two contrasting photoperiods (13 and 9 h) and the growth and gas exchange of the plants were determined as frequently as possible during the period 30–100 days from sowing. This paper describes aspects of the leaf emergence, leaf expansion, floral development, and dry matter partitioning in these plants. Part III will present the gas-exchange data. The most striking finding from the growth data concerned leaf expansion. The application of curve-fitting techniques showed that the expansion of each leaf studied could be accurately described by the Gompertz growth function, which implied that the maximum absolute rate of expansion had been achieved quite early in the leaf's development, at about 37% of full expansion. Furthermore, in all but the juvenile leaves, the time-spread of expansion was similar, despite up to 10-fold differences in the final area of the leaves due to photoperiod and position on the stem. Other relationships observed in the data seemed of fundamental interest. Attention is drawn (1) to the smooth progression in final leaf size with progress up the stem, and (2) to the changes with time in the ratio of the relative growth rates of the major plant parts, but whether these relationships, and those between leaf expansion and time, are typical of tobacco will remain uncertain until comparable studies are performed. * Part I, Aust. J. Biol. Sci., 1973, 26, 1057–71.