Skip to main content

A time for every purpose

All life moves. Or, more precisely, all life moves purposefully.  This is true even for trees and plants.  Movement is essential for maintaining life.  Animals migrate; plants disperse.  Some form of migration is an ingredient of all life.  For many organisms, it is a key function of reproduction.  We don't reproduce merely to create a new organism, but also to disperse the population - finding new fertile ground, or resources. Reproduction is a form of migration. Reproduction isn't merely to replicate. Reproduction produces change and diversity.  While we may have strong resemblences in families, we also have differences.  Creating a difference is how evolution works.  In this sense, nature is a continuous exploratory process, finding what works best.  Nature senses change and responds.  Some of this is immediate and physiological or behavioural; some of it is over generations. 

If we look at a forest over long periods of time, we would see that it shifts. There is a movement over generations.  But we see movement in plants on a daily basis.  Flowers open and stems bend toward the sun - they are phototropic.  As all gardeners know, light is vital to the plant. 

Charles Darwin and his son carried out an elegant experiment on grass stems.  They put a cap on the very tip of the young stems.  What they found was that the stems no longer bent towards the light.  The bending is produced by elongation of the plant cells on one side of the stem.  Clearly, some kind of signal was being sent to these cells from the light-sensitive tip.  The Danish physiologist, Peter Boysen-Jensen, later showed that this signal was a chemical that travelled down from the tip only on the shaded side of the stem. The tips contain light-sensitive proteins - phototropins - that cause a hormone - auxin - to be transported down the stem. 

Day length matters to a plant. Plants are good time-keepers. The Earth spins as it orbits the sun, and it is the measure of day length that really matters.  Some plants - short-day plants - such as rice, will only flower when the day length drops below a certain threshold.  Others, such as spinach and sugar beet are long-day plants - flowering only when the day length rises above a certain level.  In this way, the plants monitor the seasons. Some are day-length neutral. 

Hello, darkness my old friend.  We refer to short-day plants, but it is the night that matters - the period of darkness.  A short-day plant will only flower if it gets a continuous period of darkness for a given length of time.  So, how do plants do this? 

One idea is that it involves a synchrony - a lining up - of an internal physiological clock with the light/dark periodicity.  Plants flower when these are in synchrony. But how would this work?

The plant produces a bloom inducing protein in a rhythmic cycle - the protein production ebbs and flows, but it is usually broken down as soon as it is produced, and this prevents the concentration rising.  As the evenings get lighter, this breakdown of the protein is blocked, and the concentration increases and triggers flowering.  That is one idea, but plants may have found different ways to solve the problem. 

Production of seed is only half of the solution.  Dispersal is a major part of the trick, for which nature has produced a variety of means.  And this is where plants use animals - animals move at greater speeds and distance. They may collect and bury nuts; their fur may pick up seed.  For plants and trees, animals make ideal dispersal kits.  Evolution is an interactive process. 

Ray Noble is a chartered biologist and Fellow of the Royal Society of Biology


Popular posts from this blog

Ian Duncan-Smith says he wants to make those on benefits 'better people'!

By any account, the government's austerity strategy is utilitarian. It justifies its approach by the presumed potential ends. It's objective is to cut the deficit, but it has also adopted another objective which is specifically targeted. It seeks to drive people off benefits and 'back to work'.  The two together are toxic to the poorest in society. Those least able to cope are the most affected by the cuts in benefits and the loss of services. It is the coupling of these two strategic aims that make their policies ethically questionable. For, by combining the two, slashing the value of benefits to make budget savings while also changing the benefits system, the highest burden falls on a specific group, those dependent on benefits. For the greater good of the majority, a minority group, those on benefits, are being sacrificed; sacrificed on the altar of austerity. And they are being sacrificed in part so that others may be spared. Utilitarian ethics considers the ba

The secret life of Giant Pandas

Giant pandas, Ailuropoda melanoleuca , have usually been regarded as solitary creatures, coming together only to mate; but recent studies have begun to reveal a secret social life for these enigmatic bears.  GPS tracking shows they cross each others path more often than previously thought, and spend time together.  What we don't know is what they are doing when together.  Photo by  Sid Balachandran  on  Unsplash For such large mammals, pandas have relatively small home ranges. Perhaps this is no surprise. Pandas feed almost exclusively on bamboo. The only real threat to pandas has come from humans. No wonder then that the panda is the symbol of the WWF.  Pandas communicate with one another through vocalization and scent marking. They spray urine, claw tree trunks and rub against objects to mark their paths, yet they do not appear to be territorial as individuals.  Pandas are 99% vegetarian, but, oddly, their digestive system is more typical of a carnivore. For the 1% of their diet

Work Capability Assessments cause suffering for the mentally ill

People suffering from mental health problems are often the most vulnerable when seeking help. Mental health can have a major impact on work, housing, relationships and finances. The Work Capability Assessments (WCA) thus present a particular challenge to those suffering mental illness.  The mentally ill also are often the least able to present their case. Staff involved in assessments lack sufficient expertise or training to understand mental health issues and how they affect capability. Because of  concerns that Work Capability Assessments will have a particularly detrimental effect on the mentally ill,  an  e-petition  on the government web site calls on the Department of Work and Pensions to exclude people with complex mental health problems such as paranoid schizophrenia and personality disorders. Problems with the WCA  have been highlighted in general by the fact that up to 78% of 'fit to work' decisions are  being overturned on appeal. It is all to the good that they