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

Abstract

patterns evolve that determine the typical habitus for a certain species. Their basis is the organization of the plant The impact of different plant growth rates on biomass from modules like leaves, internodes and roots arranged allocation and growth distribution in tobacco was in a characteristic way (phytomers) (Scanlon, 1998). studied on the whole plant, total leaf area and single Underlying principles in these patterns represent the leaf level. On the whole plant level, constant relation- functional balance between diVerent parts of the plant ships were found between the total leaf area and and can only be understood from a multiscale approach: the biomass allocation to leaves and the non- whole plant processes need to be coupled mechanistically photosynthetic organs (roots and stem) independent to the underlying growth process in the individual modfrom the overall growth rate and the nutrient addition ules to understand growth regulation. On the other hand, rate to the plants. On the level of total leaf area, plants analysis of growth on the level of the organs and on grown at lower nutrient supply reached a distinct dis- smaller scales needs to be related to the framework of tribution of leaf area later than those grown at higher the whole plant. nutrient supply, but the normalized distribution of leaf Quantitative analysis of the patterns requires the use area along the stem at a certain plant size did not of adequate co-ordinate systems. The higher complexity differ between plants growing at different nutrient inherent to areal growth of dicot leaves has hampered supply and growth rates. On the leaf blade level, progress in this field significantly, in contrast to linearly growth rates declined, initially linearly, from the leaf arranged monocot leaves or roots (Schurr, 1997). Often base to the leaf tip. Distinct gradients within the side cartesian (rectangular) co-ordinate systems are used to veins were not observed, but the growth rates of the analyse spatial aspects of growth (Avery, 1933; Poethig side veins were closely correlated to the adjacent mid- and Sussex, 1985; Granier and Tardieu, 1998). They are vein segments. These gradients flattened with increas- useful for the description of Euclidean geometric objects ing size of the leaf. The modular character of growth (or models), or for spatio-temporal movements of points in tobacco is discussed in the context of basic growth like in classical mechanics, but hardly for natural objects. analysis and as a framework for physiological, cytolo- The physical description of movement or growth progical, biochemical, and molecular studies in growing cesses of natural objects subjected to natural conditions/ plants.