Tracing how humans and algae (Kung in Manipuri) see light and colour

Dr Irengbam Mohendra Singh *

'National characters' are certain habits and behaviours that are prototypes among the majority adult population of a nation-state. In post modern Manipur, many Meitei enthusiasts would know one of the great Meitei National Characters is the tendency not to accept anybody's word, phrased in Manipuri: mana kari khangdana: what does he know that I don't?(cf. author's book, The Meitei National Character, The Origin of the Meiteis. 2009:113-182).

This historical curiosity, apart from general syntactic playfulness, was the guiding passion of the erstwhile Meitei nation over the centuries. Call it vice or virtue. I'll call it vice, only when somebody's word is disregarded with a swipe of hand and without giving a thought.

The Royal Society of London, the oldest scientific society formed in 1660, has a motto, Nullius in verba, meaning "Take nobody's word for it," but it has a very important parenthesis - "without careful observations about it and original thinking."

With modern education, renaissance Meitei culture has at least begun to discolour this old pigment of imagination, as new scientific discoveries have begun to demystify many popular beliefs, such as the medicinal values of powdered Egyptian mummies. Back in Roman times, Pliny the Elder recommended powdered mummy as a toothpaste.

Shakespeare's son-in-law used it as a cure for epilepsy. Reddish purple colour robes became the potent symbol of Roman emperors. Nero is said to have a woman whipped and stripped of her property after he caught her wearing without permission, as it was the custom with khamenchatpa feijom'(a light-purple, printed silk dhoti) with Meitei kings.

The soothing familiarities with the colours of the moon and the colours of the rainbow are deep in human history. The moon also inspires awe and a wish-fulfilment benevolent for tiny tots. Various cultures see the moon differently. Meiteis see the moon with a fig tree while northern Indians see it as a man (chanda mama).

Some western countries see it as a rabbit. The seven colours ofthe rainbow have been thought since the middle ages, to be a mixture of light and darkness until Isaac Newton in 1672, proved it untrue. Newton placed a triangular glass prism near his window in the first floor of his house, against a beam of incoming light, when he saw a beautiful spectrum of light consisting of red, orange, yellow, green, blue and violet.

Further, to prove that the prism didn't colour the light, he constituted the coloured spectrum into white light by using another prism in reverse.

The most useful idea of Newton's discovery for artists was his conceptual arrangements of colours, such as red and green, blue and orange, yellow and purple, as a way of enhancing each other's effect through optical contrast. Other scientists have discovered how our eyes evolved to see light and colours during the long history of evolution.

Many genetic mutations have enabled humans to evolve from a primitive mammal that could only see a shadowy world, to apes and gorillas, and then humans, who could not only see things clearly but also all the colours of the rainbow.

After more than two decades of research, Shozo Yokoyama and others published an article in PLOS Genetics on December 18 2014. They traced the evolution of human colour vision. About 30 million years ago, our ancestors had evolved four classes of opsin genes (see below), giving them the ability to see the full colour spectrum of visible light except for UV.

The evolutionary history of algae (350,000 species) is remarkable, including their ability to 'see' light. Algae (kung in Manipuri) that evolved 1 billion years ago, have 'eyes to see light' ie they are able to swim towards light. During my boyhood days, the kung used to fill the surface of any pond in Manipur.

Here in the UK, until about 15 years ago, when UV pond-lamps were introduced in the market, the decorative pond in my garden, was always filled with algae during the hot summer. My pond water with algae is circulated around a 2.5x30 cm UV tube light, which gathers them into tiny clumps that are filtered out before the water is recirculated into the pond.

Algae are tiny green flattened sacs of plants,enclosed by an internal membrane and a thick cell wall. They live in colonies and move about, gliding along the surface of water. They make their own food (sugar) by photosynthesis. They also breathe across their thin membrane along with their photosynthetic electron transport (from water).

So did cyanobacteria that lived 3.5 billion years ago. These bacteria could sense light ie they had an "eye" with rhodopsin(see below), if we consider the most important function of an eye is to detect light. In 1996, a complete genome sequence of the cyanobacterium synechocystitis 6803, that has many light-sensors and signal transducers, has been identified.

It's considered that photosynthesis carried out by the present plants and algae might have its origin in cyanobacteria that plants acquired a very long time ago,by a process of endosymbiosis ie , cyanobacteria living symbiotically within plants and algae, like mitochondria in our cells. These cyanobacteria evolved into the present chloroplasts - the cells that contain chlorophyll, in which photosynthesis takes place. They are the powerhouses that keep plants alive.

The process of vision in our eyes starts with rhodopsin molecules. Human eyes have two types of light sensitive cells: rods and cones in the retina. Rods allow us to see things in black and white. Cones are of three types, each of which is tuned to different wavelengths of light, allowing us to have colour vision.

All these rods and cons use the same pigment called retinal, a form of Vitamin A, bound to proteins called opsins. Opsins vary a bit in order to tune to particular colours. Apart from rods and cones there is a third type of photosensitive cells in our eyes, called photosensitive retinal ganglion cells.

These ganglion cells are different in structure from rods and cones, but use the same pigment retinal. The whole family of these molecules is generically known as rhodopsin. In practice, rhodopsin refers to the particular molecule found in rods. That found in cones is called cone opsins, and that in retinal ganglion cells, contain melanopsin that also control our circadian rhythm.

When light photons enter our eyes through the lens, they are absorbed by rhodopsin molecules in retina, which create an action potential ie generate electrical impulses that pass down the optic nerve to the visual cortex, the centre of vision at the back of our brain.

The process is repeated as mitochondria in rhodopsin molecules, slowly release energy for rhodopsin to reform for detection of more photons. It can take up to 20 minutes for rhodopsin to reform to give our full night vision.

Scientists have begun to unravel the evolution of vision in men and other animals that use the same rhodopsin or closely related molecules,going back at least 540 million years to the early Cambrian period (540 to 490 MYA).

Prof Brian Cox suggests that rhodopsin may have been an evolutionary invention that predates all animals by a very long time. He writes about the most common type of single-celled algae volvox that is found all over the world in freshwater ponds and puddles. Simple it may seem, it has a quite unexpected level of complexity. They live in large spherical colonies that are made up about 50,000 individual cells each, connected by thin strands of cytoplasm.

Each individual cell of volvox has tail-like hairs called flagella. The whole colony can move around by synchronising their beating flagella, like a multi-cellular entity. As photosynthetic organisms they need sunlight to manufacture their food. For this, they need a sort of "eye" to see the strongest source of sunlight. Each single cell has a red "eye spot" - a photosensitive pigment that controls the beating of the flagella and allows the algal cell to swim towards the light.

In research, when a bright light stimulates the eye spots, they command the flagella to stop beating. When the light is dimmed, the stop sign is lowered and the search for light begins again. The cells in the colony are so well integrated that the eye spots are situated on one side of the colony than the other, and thus helping themselves to steer toward the light source.

The remarkable thing the scientists find is that the microscopic "visual" system of the volvox is based on a kind of rhodopsin known as Chennelrhodopsin - fairly similar to the rhodopsin of all animals, which imply a common origin.

The assertion is supported by the finding of similarities in the genes that control the emergence of the algal eye spots and the genes that control the development of our own eyes.

However, algal vision cannot be the origin of our eyes because they are not part of our branch of the tree of life, unless they find the common origin of algae and animals. Alternatively, once scientists find the origin of rhodopsin we may find the ancestral origin of the eye.

A casual observer will notice that we only see a rainbow when the sun is behind us and the drops of rain water in front break the white sunlight.