The plastids or plastids they are cellular organelles eukaryotic characteristic of plants and algae whose function is the production and storage of chemical compounds within cells. In this way they participate in processes as important as the synthesis of lipids and amino acids, photosynthesis and the color of fruits and flowers.
There are two clearly differentiated types of plastids: the primary ones, simpler and located in most plants, and the secondary ones, much more complex and located in the plankton.
Plant plastids are ellipsoidal in shape and relatively large in size. A specific type are chromoplasts, which are called rhodoplasts when they are red, and chloroplasts when they synthesize chlorophyll, which gives the green color to leaves.
The language of tomato colors
Two types of pigments accumulate in chromoplasts: hydrogenated carotenoids (beta-carotene and lycopene stand out, responsible for the orange color of carrots and the red color of tomatoes, respectively) and oxygenated carotenoid pigments (xanthophyll stands out, which is responsible for the yellow color of corn kernels).
Tomatoes are the fruits of a plant of the nightshade family that are greenish in color when immature, a stage in which they contain high concentrations of solanine, a very harmful alkaloid even in small amounts. Its toxicity is due to the fact that it is an inhibitor of acetylcholinesterase, an enzyme that breaks down acetylcholine, so its intake can produce cholinergic effects. Solanine is a taste warning signal for animals.
When tomatoes ripen they acquire the characteristic reddish color, this is due to the accumulation of large amounts of hydrogenated carotenoids. The color change occurs at the moment in which the seeds can germinate and has a communicative purpose, an optical signal so that animals can recognize them more easily and consume the fruits, thus dispersing the seeds.
shadow escape syndrome
In the fifties of the last century, some proteins were discovered -phytochromes- present in plant cells whose function is to act as photoreceptors. In its chemical structure it has a chromophore that allows it to detect red light (600-700 nm) and far red light (700-800 nm).
If the light intensity captured by the phytochromes is insufficient, the plant can relocate the chloroplasts so that they are located in the area where a greater amount of light is intercepted. The reverse can also happen, if the amount of light is excessive, to the point that it can cause oxidative damage and deteriorate the photosynthetic machinery, the chloroplasts relocate.
Tomato phytochromes are decisive in the competitive battle for survival, since the existence of a distant red -semi-shade- indicates that they are under the shade of other plants and that their life cycle is in danger.
Scientists have discovered the existence of a protein – phytochrome 7 interacting factor – that acts as a messenger between light sensors and the production of hormones responsible for stem growth (auxin). Through this communication, it is possible to indicate to the stems that they must grow more to receive a greater amount of solar radiation and leave the “twilight”. This phenomenon is what is known as “shadow escape syndrome”.
This communication system is not trivial, since if the plant remains too long in the shade and does not receive the adequate amount of light, early flowering can occur, with a significantly lower number of seeds, putting genetic perpetuity at risk.