Comparison of plant and animal development Developmental strategies of plants and animals have developed separately for millions of years. Both realms still have much in common, but some of their problems and solutions are unique. So what are the fundamental differences between the development of land plants and animals? Model organisms Animals Plants Mouse; Mus musculus Thale cress; Arabidopsis thaliana Zebrafish; Danio rerio Maize; Zea mays L. ssp. mays Fruit fly; Drosophila melanogaster Snapdragon; Antirrhinum C. elegans; Caenorhabditis elegans Petunia; Petunia hybrida African clawed frog; Xenopus laevis Physcomitrella patens; Chick; Gallus gallus domesticus Physcomitrella patens Multicellularity Mechanisms of multicellular development developed independently in plants and animals. The last ancestor of plants and animals was a unicellular eucaryote. Gene comparisons show there is not much homology between the genes that make up the body plan of plants and animals. Although homeobox- as well as MADS box genes existed in the last common ancestor, the MADS box gene family plays an important part in regulation of plant development, but not in animal development, where homeobox genes are important. Cell movement Animal cells are motile. Plant cells are positionally fixed. Animal tissues may be folded and moved Plant cells are trapped in rigid cell walls against each other easily. At metazoan made of cellulose, which prevents movement gastrulation this way a triple layered system is of cells and tissues. Plants form three basic built (entoderm, mesoderm and ectoderm). tissue systems as well (dermal, ground and Some animal cells may even move to other sites vascular), yet without gastrulation. autonomously. Rigidity of the body shape The animal body plan is in most parts clearly Plant development is highly regulated by determined. the environment. The basic body plan of an animal during its As in most cases it may not choose or different life stages is mostly clearly determined change its environment, it has to adapt to it. by its genes. If the environment changes they The body plan is variable and characterized may react e.g. by moving to another place or by multiple times occurring, often iterative changing their short and long term behavior. structures. Proportions and frequency of organs may vary. Multicellular stages During the animal life cycle there is just one The life cycle of land plants (and many
continuously multicellular stage It is what we refer to as "the animal". Yet many animals undergo one or more transformation, when their body plan changes dramatically.
other plants) has haploid and diploid stages. This kind of life cycle is called alternation of generations and leads to two different body plans during the life cycle of the plant (sporophyte and gametophyte).
Meiosis In animals gametes are formed directly Plants undergo no gametic meiosis, but a through meiosis. sporic meiosis. There is nothing that could be compared to the In plants the meiosis produces spores and not gametophyte in plants. gametes. First the gametophyte is formed by mitotic divisions, which then forms the gametes. Germline Many animal species set aside reproductory No reproductory stem cells are set aside stem cells early in development. early in development in plants. This decreases mutation accumulation. Still some plants leave certain meristems or meristem parts more inactive till the gametophyte is to be formed.
Morphogenesis Animals develop to a distinct, complete body Plants go through a longer period of shape. morphogenesis. During their life stages still some reorganization During their development plants do not head may take place, yet only in seldom cases new for a distinct body plan. Many plants just structures will develop. Some animals develop grow and develop on and on till they die. stepwise into different shapes. Areas of actively dividing, undifferentiated cells, called meristems, allow for iterative growth and the formation of more and more new organs and structures during a plants life. They resemble embryonal stem cells in animals, yet they continue existing during adult life stages. Plasticity Animal cells are determinated early in Plants show an enormous plasticity in development their development When animal cells develop into tissues they are If, for example, a shoot is nibbled by a clearly and in most cases irreversibly herbivore, axillary meristems often grow out determinate. While most tissues are regenerated to substitute for the lost part. This strategy from stem cells, the regeneration of whole resembles (limb) regeneration in some organs just occurs at some animal species like animals. Whole plants can even be
Ambystoma mexicanum.
regenerated from single cells. Furthermore, the form of a plant (including branching, height and relative portions of vegetative and reproductive structures) is strongly affected by environmental factors such as light and temperature, resulting in a great variety of morphologies from the same genotype. This amazing level of plasticity helps plants compensate for their lack of mobility.
Plants and animals grow and differentiate their tissues in different ways. The main differences are outlined in the table below. Feature
Plants
Animals
Pattern of growth
Often can grow continuously
Tend to grow to a maximum size
How growth happens
Mainly by cell enlargement (increase in cell size)
Increasing the number of cells
Where cell division happens
Mainly at meristems – found at the tips of shoots and roots
In most tissues
Cell differentiation
Many cells can differentiate
Most cells lose the ability to differentiate at an early stage
