When we look at a plant we often tend to consider it as a single living being, nowadays we know that this is not entirely true, in reality when we look at a plant we are looking at several hundred million living beings.
Plants, like any multicellular living beings, are colonised by micro-organisms that play a fundamental role in their metabolism; these micro-organisms occupy the interior of the plant or “endosphere”, and are therefore known as “endophytic” micro-organisms.
These endophytic micro-organisms live and/or are isolated inside plant tissues and do not cause any harm to the host (Hardoim et al. 2008).
Among them inseide the plants we find bacteria, protozoa, archaea, viruses, fungi (filamentous, oomycetes, mycorrhizal…).
Virtually all plants are colonised by a diversity of bacteria known as endophytes. These endophytic bacteria can be detected at a particular time within the tissues of apparently healthy plants (SCHULZ and BOYLE, 2006).
The presence of bacteria in other living organisms has been extensively studied. In animals for example, we find different micro-organisms in different organs, these micro-organisms fulfil different functions: some bacteria help to digest food, others help to destroy disease-causing cells or supply vitamins… their importance in animals is very well known, for example when a sheep (or any herbivore) feeds on grass, it is the bacteria in its digestive tract who digest the cellulose and lignin so that it can extract the nutrients from the plant tissue, without these bacteria herbivores would not be able to feed on plants, in consequence won´t even exist.
People themselves are colonised by micro-organisms: it is estimated that each person harbours 39 trillion bacteria, accounting for one to two kilos of our total body weight.
In plants, most endophytic bacteria colonise different plant compartments such as the apoplast, including intercellular spaces and xylem vessels. Some of them are able to colonise the reproductive organs of plants, e.g. flowers, fruits and seeds (STONE et al., 2000).
The main source of endophytic bacteria is the SOIL, from there the bacteria penetrate the vascular tissue of the plant, passing from the roots to the stems, and then to leaves, flowers and seeds. The plant select and filter the kind and quantity of micro-organisms, so that their quantity and diversity is greater in the roots and decreases as we move towards the stems and leaves until we reach the flowers and seeds.
PRESENCE of ENDOPHYTIC BACTERIA
There is a complex relationship between endophytic bacteria and the host plant, they are believed to stimulate plant growth through mobilisation of soil nutrients, producing numerous plant growth regulators, protection of plants from plant pathogens by controlling or inhibiting them, improving soil structure, bioremediation processes of contaminated soils by sequestering toxic heavy metals and xenobiotic compounds within plant tissues (AHEMAD, 2012).
The study of this plant-microorganism endophyte relationship is starting to be known in greater depth and with no doubt it is an important source of knowledge for the development of new Biofertiliser products as they can act as plant development promoters, as we will see in the next post..