Gelation
In plant physiology, yellowing or etiolement is the term used to describe those characteristics that plants show when they grow in the absence of photosynthetically usable light .
It consists in a significantly accelerated growth in length, briefly several centimeters per day, because the plant tries to tap into a light source. The internodes are moved far apart; after this growth spurt , the leaves often appear small and, due to the lack of chlorophyll, pale yellow or slightly brownish due to the lack of chlorophyll . The roots, however, show only a reduced growth. As a rule, complete chlorophyll is not formed in the dark. Exceptions are: Tradescantia albiflora , some gymnosperms and many lower plants.
Etiolated seedlings usually only have very underdeveloped firming tissue, which makes them appear soft and pliable. This is sometimes used in a targeted manner in agriculture ; the stalks of actually woody plants such as asparagus or bamboo sprouts remain edible as long as they have cured. If they are exposed, the tissue quickly becomes tough, woody and very difficult to digest. Only then does chicory achieve the desired growth.
Horny spots can develop on piles of grazing cattle because the cattle avoid plants contaminated with manure and these areas are heavily overfertilized and the plants are shielded from light.
Water-based plants can grow horny if there is a lack of light or if the water is cloudy and in a short time they can grow enormously in length in order to reach the surface of the water; however, they do not maintain this growth spurt for long and consequently lose their leaves, especially in the lower parts of the stem. If they do not reach a usable light source during this time, they die or develop malformed shoots and adhesions. In the aquarium hobby this type of growth occurs especially when there is no light, but the supply of nutrients in the tank is consistently sufficient. Through targeted use of this growth behavior after lowering the lighting, cutting the plants and renewed sufficient lighting after the formation of young shoots, shapes can also be created that would not arise under constant lighting conditions.
Further development
A plant creates these fearful drives in order to move its leaf mass to an area with sufficient light. If this is successful and the leaves are then able to assimilate well, the previously poorly developed shoot will be strengthened by the storage and cultivation of materials and otherwise remains in its, now successful, form.
However, it can often happen that the drive is not stable enough for its task and is buckled by wind, gravity or animals passing by. Since the fear instincts are built up with little material expenditure at the beginning of the development, the resistance to such damage is quite low.