Plants: Unitary organisms emerging from integration and self-organization of modules

Abstract

The organs roots, stems and leaves of plants have evolved under the challenges of the terrestrial environment where they are firmly rooted. Emergence of plants as unitary integrated organisms occurs by integration of these parts, organs or modules. Below this scaling level of morphology and the organs, there are modules on finer scaling levels, tissues at the level of anatomy, organelles and compartments at the level of cell biology, macromolecules at themolecular level and so on. Modules are connected and integrated forming the knots in networks. Networks at a finer scale can integrate, condense and self-organize to form knots in networks at the next coarser scale. In this way, hierarchies of networks are built up leading to the emergence of whole plants. Requirements for the integration are (i) signals carrying information, (ii) receptors for the signals, (iii) transduction of signals within systems and networks, (iv) cross-talk between different types of signals by their translation into each other and (v) configuration of information as instruction for reactions. Integration is organized during development where tight structural and functional correlations are built up under the systemic control of development. Self-organization uses both correlative inhibition and correlative stimulation, with homoiogenetic induction of self-resemblance and heterogenetic induction of unlike-self, respectively. Examples of integration are source-sink relations of water, nutrients and photosynthetic products, induction of flowering, orientation in space under gravity and light, environmental relations under herbivory and salinity. Plants are unitary organisms without a neuronal system. The whole is more than the sum of its parts (Aristotle 384-322 BC).