Mechanism for the captation of nutrients in plants- unknown to date

Up to now it was thought that nutrients penetrated the interior of plant cells by means of substance-specific transporters. Nevertheless, researchers at the Agrobiotechnology Institute at the Public University of Navarra have shown that the nutrients (saccharose, amino-acids, etc.) penetrate the cells basically through an “endocitic”, mechanism similar to fagocitosis, and induced by saccharose. This finding, carried by the latest issue of the Japanese journal, Plant Cell Physiology, will enable the design of experiments aimed at enhancing vegetable species in the interest of humanity.

Researchers at the Institute have shown that, in the presence of saccharose (a substance produced in leaves to be subsequently distributed around the plant), the cells of the reserve organs – such as roots, tubers, seeds or fruits – “swallow up” nutrients in order to metabolise and store them. These “swallowed-up” substances are incorporated into micro-vesicles that end up pouring their contents into an internal compartment of a vegetable cell known as the vacuola. Once inside the vacuola, the substances or nutrients are broken up, stored and metabolised.

Two processes of captation

This discovery breaks with a fundamental dogma in basic plant science holding that all substances penetrate the interior of the cell through the participation of specific transporters present in the plasma membranes – a model implying that, if hundreds of substances enter vegetable cells and each substance has its specific transporter, or even if one transporter can recognise 3 or 4 different substances, an infinity of such transporters would be required.

The conclusion of this research is that, while not discarding the existence of specific transporters in plasma membranes, their number and relevance is considerably inferior to what has been believed to date. In the absence of saccharose, nutrients can penetrate the cell by means of transporters, but the amount entering through this mechanism is less than that incorporated via endocitosis.

Thus, the experiments carried out showed the existence of processes independent of nutrient captation: a saccharose penetration process independent of “endocitosis” and another dependent on “endocitosis” and which required approximately 90 minutes from the time the cell started to capture saccharose in order to start functioning. That is, for these first 90 minutes, the saccharose penetrates using the transporter mechanism while, parallely, the endocitosis phenomenon is activated to form microvesicles. Subsequently, the cell starts to capture huge quantities of saccharose through endocitosis.

The results of the research has shown, moreover, that only saccharose is capable of initiating endocitosis, given that, in the trials undertaken with substances similar to saccharose, such as glucose or fructose, the fact that none of these triggered the process could be confirmed.

Moreover, given that endocitosis is involved in the acquisition of substances for their subsequent conversion into “end products” (such as starch, oils, celluloses, etc.), basic knowledge of this mechanism provides great tips for the rational design of experiments aimed at enhancing vegetable species in the interest of humanity.

One of the great questions thrown up by the fact that saccharose pick-up is produced via endocitosis is, fundamentally, to find out if the saccharose captured through endocitosis is that involved in starch production. If this is the case, it will be necessary to discover what are the genetic and molecular mechanisms involved in the process, in order to improve the plant varieties. For example, in order to increase starch production in potato or maize, endocitosis would have to be encouraged through the stimulation of the genes involved in the formation of the vesicles – a hypothesis that is currently being verified.