Growth rate, photosynthetic activity, and leaf development of Brazil pine seedlings (Araucaria angustifolia [Bert.] O. Ktze.)

Seedlings of Brazil pine, a large-seeded South American conifer, were grown in a climate chamber to investigate vertical growth pattern and the time c ourse of leaf development. We examined shoot growth, photosynthetic perform ance and markers of leaf maturation such as contents of soluble sugars and activities of sucrose-phosphate synthase (SPS), neutral invertase (nI) and sucrose synthase (Susy). The daily increment of shoot length showed an opti mum curve during the first 70 days after germination. The low growth rate d uring the first 20 days of development correlated with net CO2 emission of the seedling. Analyses of leaf maturation markers in older seedlings reveal ed low sucrose/hexose ratios and high activities of nI and Susy in the uppe rmost leaves. Although the SPS/Susy ratio was low in these leaves the extra ctable SPS activity did not change significantly among leaves of different age. The photosynthetic light compensation points of young leaves were abou t 2-fold higher than those of mature leaves and their photosynthetic capaci ty was only 50% as high. Our results indicate that a rapid maturation of le aves of Brazil pine seedlings may reduce the respiratory loss of carbohydra tes and that the mobilisation of seed storage compounds supports initial sh oot growth under light-limiting conditions which may occur in the forest-gr assland succession zone.