The modular character of growth in Nicotiana tabacum plants under steady-state nutrition

The impact of different plant growth rates on biomass allocation and growth distribution in tobacco was studied on the whole plant, total leaf area an d single leaf level. On the whole plant level, constant relationships were found between the total leaf area and the biomass allocation to leaves and the nonphotosynthetic organs (roots and stem) independent from the overall growth rate and the nutrient addition rate to the plants, On the level of t otal leaf area, plants grown at lower nutrient supply reached a distinct di stribution of leaf area later than those grown at higher nutrient supply, b ut the normalized distribution of leaf area along the stem at a certain pla nt size did not differ between plants growing at different nutrient supply and growth rates. On the leaf blade level, growth rates declined, initially linearly, from the leaf base to the leaf tip. Distinct gradients within th e side veins were not observed, but the growth rates of the side veins were closely correlated to the adjacent midvein segments. These gradients flatt ened with increasing size of the leaf. The modular character of growth in t obacco is discussed in the context of basic growth analysis and as a framew ork for physiological, cytological, biochemical, and molecular studies in g rowing plants.