In 1956, Otto Ludwig Lange, a botanist, discovered plants in the Mauritania desert in West Africa whose leaves could heat up to 56 degree Celsius. It is astonishing that leaves could withstand such heat. At that time, the professor was unable to identify which mechanisms were responsible for preventing the leaves from drying out at these temperatures.
Fifty years down the line, the botanist Markus Riederer and Amauri Bueno from Julius-Maximilians-Universitat Wurzburg (JMU) in Bavaria, Germany, succeeded in revealing the secret.
One needs to know more about the somewhat complicated structure of a plant leaf to understand what the two scientists discovered. For instance, the leaves of the plant have a skin that is typically undetectable to the human eye.
Professor Riederer explained that it is easy to see the skin in the tomato. The skin of the plant is not a continuous layer that would extend over the whole leaf. It contains numerous pores called stomata which can open and close. The plant "feeds" through these stomata. It thereby uptakes the carbon dioxide the plant needs for photosynthesis.
One issue that happens is that whenever the pores open to acquiring carbon dioxide, water also evaporates. Therefore, desert plants especially are continually undergoing a balancing process. The question is if they uptake carbon dioxide to grow further, or if they close the pores to retain the precious water.
The plant colocynth, Citrullus colocynthis, also known as bitter cucumber, a wild relative of the watermelon, opens its pores when exposed to heat to cool down the leaves by transpiration cooling and this process makes colocynth a water-spender.
This process is possible for the plant since it has quite a deep root which enables the plant to tap water sources deep in the desert soil. As Otto Ludwig Lang discovered during his experiments in the desert, the colocynth manages to make its leaf up to 15 degrees more chill than the desert air.
The researchers published the result of this study in the Journal of Experimental Botany which revolved around the wax as embedded in the skin of plants and ensures their low permeability to water. After extensive laboratory tests, Bueno discovered that this wax differs between the colocynth and the date palm.
The date palm has a wax that can withstand high temperatures and therefore has a much more waterproof skin than the colocynth, even at extreme temperatures. The palm can survive in the desert only because of this special wax. If the wax had a slightly different chemical composition, the leaves would dry quite quickly particularly at high temperatures.
