Nutrition

 

As with the majority of plants, Atropa belladonna produces its own food through photosynthesis, a process that occurs within the chloroplasts that converts carbon dioxide, light energy, and water into oxygen and sugar. This sugar can be converted into starch for storage, or it can be converted to glucose, which is used in another process called cellular respiration. Respiration produces ATP (adenosine triphosophate), a compound that powers all the plant's functions, such as reproduction or protein synthesis.

 ©At09kg (Wikimedia Commons) 2011

However, like people, plants cannot exist solely on a sugar diet. Deadly Nightshade also needs nutrients to power cellular functions. Plants need 16 essential nutrients for basic functions.

The nutrients needed in the highest amounts, or macronutrients, are nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur. Of these, the primary nutrients needed are nitrogen, phosphorus, and potassium.

Nitrogen is found in proteins and enzymes vital to metabolic processes. It is also a component of chlorophyll. Phosphorus plays a role in photosynthesis, and also in the formation of oils and sugars. Potassium is mainly used to build proteins. Deadly Nightshade gets its nitrogen, phosphorus and potassium, along with the other 13 needed nutrients, by absorbing them through its roots.

Now that Deadly Nightshade has created its sugar and absorbed the necessary nutrients, how do all these materials get transported throughout the plant?

                                                                                                            © Michael Salaverry 2012

Deadly Nightshade, along with all other vascular plants, has the vascular tissues xylem and phloem to transport nutrients and water to all parts of the plant.

In the picture to the right, the different parts of the plant are denoted by a different number. The numbers 3 and 4 represent the cambium and pith, respectively. The cambium produces new xylem and phloem, and the pith aids in supporting the plant.

Xylem (1) is responsible for transporting water throughout the plant. It is made mostly of cells called vessel members and fibers. Both of these cells are dead at maturity. The driving force behind water movement in plants is water potential and the properties of water.

When water evaporates from the leaves, or transpires, it creates a higher solute concentration in the leaves. This creates a low water potential in that area.

The water from the xylem then moves into the cells of the leaves, because water always flows from areas of low solute concentration to areas of high solute concentration (or high water potential to low water potential).

This causes the pressure in the xylem to be reduced, which pulls the remaining water in the xylem upwards. This also results in more water being drawn into the xylem from the bottom, because water is cohesive - its molecules stick together. Water transport is continuously occurring in plants, as the leaves lose water and the roots take in more water.

 © Dr. Thomas Geier 1999

Phloem (2), on the other hand, is responsible for transporting the sugar throughout the plant. It is comprised mainly of cells called sieve-tube elements and companion cells (5).

The movement of sugar in plants can be described as going from source to sink. It is driven by osmotic pressure. The source is usually the leaves, where the photosynthesis that creates the sugars takes place. (In the winter, when most plants have lost their leaves, the roots take on the role of being the source). A sink can be any place in the plant that receives sugar from the leaves.

To start the process, water from the neighboring xylem enters the sieve-tube elements. This creates pressure, which pushes the sugar away from the source. The sugar then exits at various sinks along the path. This process is also ongoing, as the source continuously adds sugar (using energy from the companion cells), and water is continuously drawn into the area of high sugar concentration.

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