Simple facts about Betalain

Betalains are alkaloid pigments which are found in some families of plants belonging to the order Caryophyllales, but in no other plants.

They are named after the Beet family of plants (Beta).

Betalains are not found in plants containing anthocyanin pigments. Structurally they are unrelated. Unlike anthocyanins, they are not pH indicators as their colour is stable over a wide range of pH.  They are oxidised over time going brown in colour. This can be prevented by 0.1% ascorbic acid.

They have also been found in some fungi too e.g. Fly Agaric (mushroom)

Betalains can be divided into two types as betacyanins and betaxanthins; based upon their molecular structure.

Betacyanins

Usually appear red to red violet in colour (absorbance in 535-550nm)

Betaxanthins

Usually appear yellow in colour (absorbance in 475-480nm)

Betalains are found in the vacuole and they are water-soluble.

Also they cause colour in both flowers, fruits and sometimes vegetative organs

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Beetroot contains 2 Betacyanins. Thay are Betanin and a derivative.

Not much is known about the role of betalains. Commercially they are sometimes used as food colourants. As a food dye it’s cheap and no all allergic side effects are figured out yet.

Basic structure of betalain

Biosynthesis and function of aromatic amino acids in plants

Most aromatic amino acids in plants are formed by three main types of aromatic acids;

•    Phenylalanine
•     Tyrosine
•     Tryptophan

These three important aromatic amino acids are exclusively synthesized by Shikimic acid pathway that is unique to plants and microbes. This pathway got its name by an important intermediate forms,called Shikimic acid.

Shikimic acid pathway starts from the condensation of Erythrose-4-phosphate with Phosphoenolpyruvate (PEP). PEP is provided by the glycolysis while Erythrose-4-P comes from either oxidative pentose phosphate pathway or Calvin cycle. Therefore Shikimic acid pathway is combined with other important metabolic pathways of the cell. 

The condensation produces 3-deoxy-D-arabinoheptulosonic acid-7-phosphate (DAHP). DAHP undergoes another series of reactions including condensation with another molecule of PEP to give out Chorismic acid. Shikimic acid forms as an intermediate in this reaction and regarded as the key intermediate.

Chorismate is a central intermediate giving rise to two products; Prephenate and Anthranillic acid. Shikimic acid pathway is shown simply as below.

The synthesis of aromatic amino acids is important as these amino acids are the precursors for the synthesis of defense and repair compounds.

Phenylalanine

·         Flavonoids: in plant pigments (eg: Anthocyanine), act against pathogens. Antioxidants.

·         Coumarins: Has appetite-suppressing properties.

·         Liginin: In lignicolous fungi

Tyrosine

·         Tocopherol: Antioxidant in cornifers.

·         Plastoquinone: Important in photosynthesis.

·         Cyanogenic glucosides: Phytoanticipants. Important in plant defense against herbivores due to bitter taste and release of toxic hydrogen cyanide upon tissue disruption.

Tryptophan

·         Alkaloides: provides protection as it prevents insects and herbivores eating the plant.

·         Plant growth regulators

Plant senescence in brief

Senescence

Senescence is an important program in which the function of a cell/tissue/whole plant naturally leads to its death.

Senescence involves in plant aging.

When tissues senesce they produce enzymes which can recycle the “expensive” materials and reroute the sub-units to somewhere else that growth takes place.

Overall senescence

·         Occurs in the whole plant.

·         Death takes place right after flower and setting.

·         When the flower dies the whole plant dies too.

·         Ex: Asteraceae ( Sun flower)

image via Wikipedia

Top senescence

·         After the growth season the part above the ground dies remaining the underground part that can grow for several years.

·         Therefore a rhizome is present.

·         Ex: Weed, Grass

       

Deciduous senescence

·         In dry seasons like winter and summer, the leaves falls and trunk remains.

·         Leaves fall due to avoid the heavy transpiration occurs in the dry season.

·         Ex: Deciduous plants

image via ehow.co.uk

Progressive senescence

·         Older parts die due to the senescence and the new organs and tissues continue their development.

·         Ex: Green trees

image via clasohm.com

As above mentioned, senescence can occur in cells as well as tissues.

Cell senescence

·         Can be described according to the senescence in cell membrane and organelle level.

Senescence in cell membrane

Lipid phase change

·         Plasma membrane has the fluid mosaic structure.

·         This structure changes as the liquid crystalline state changes into the solid-gel state.

·         Therefore the membrane gets inflexible and hard.

Degradation and preoxidation of lipids

·         Lipid content gets decreased.

·         It occurs as the lipid synthesis decreases and lipase content increases.

·         Phospholipase, lipoxygenase, MDA and active O₂ content increase.

Increase in Phospholipase activity

·         Mainly the activity of Phospholipase D takes place in plants.

Biomembrane degradation and leakage

·         The equilibrium of ions breaks down.

·         Metabolisms get disordered.

Senescence in organelle level

·         Ribosomes and RER break down.

·         Chloroplasts collapse and mitochondrion cristae are swollen.

·           As the vacuoles break down, all the toxics inside them is released to the cell plasma.

·         Therefore the autophagy takes place and the senescence of organelles activates.