Mechanical Integration of Plant Cells

Abstract

In order to function in changing environmental conditions, all living organisms need to be equipped with two sets of seemingly contradictory mechanisms; these enable them to (1) integrate themselves in separation from the environment, and (2) sense and communicate with their immediate surrounding. During the course of evolution, several factors—both physical and chemical—have emerged as organismal integrators. Among these, gravity provides a major directional stimulus, while chemical compounds are usually used as internal integratory molecules (Bhalerao and Bennett 2003).

Although the same cellular toolkit of their common ancestor gave rise to present-day eukaryotes through evolution, it should be remembered that plant and animal lineages diverged about 1 billion years before they became multicellular organisms. As a consequence, plants and animals differ in their lifestyles, responses to stimuli, and adaptations to the environment. This distinction results from the adoption of two different strategies of coping with the regulation of intracellular water content, and is reflected in the properties and behavior of "naked" animal cells vs. “walled” plant cells (Peters et al. 2000). Thus, while animals are able to move away when conditions are unfavorable, plants—since they are sessile organisms—must react and/or adapt to changes. As a result, much greater plasticity of plants and their cells is observed (Valladares et al. 2000).

All organisms have the ability to sense and respond to a variety of physical stimuli, such as radiation, temperature, and gravity (Volkmann and Baluška 2006). Although physical forces act in the same manner on different organisms, the effects of their actions depend on the organism's habitat. For example, the effect of gravitational force on an organism depends greatly on whether it lives in water or on land. On the other hand, the forces exerted on terrestrial plants by the movement of air are much lower than those exerted on aquatic ones by the movement of water (Niklas et el. 2000). Thus, although the overall construction of any particular plant or plant cell is generally similar to that of any other, the details of the biochemical and mechanical designs can vary considerably, as these are also shaped by the changing conditions in the cell's or organism's immediate surroundings.