Climbing plants like sweet peas can ‘feel’ their way around a support, a twig or fencing. Charles Darwin, who had an interest in climbing plants, described Clematis as a leaf climber.  Clematis has compound leaves with three to five leaflets,  It uses the stalks of the leaves or the leaflets to climb. Darwin noted that contact with another structure was enough for the leaf stalk / petiole to start bending around it.  This ability to respond to touch is termed thigmotropism.  It is a growth response.   The growth rate on the side of the stem that touches the 'support' is slower than on the side opposite the point of touch.  As a result the stem begins to curl around the support.  The same response is seen in plants that climb using tendrils, such as White Bryony.  Its tendrils are thin, wiry structures along the stem that ‘reach out’ into the space around a plant until they come into contact with something they can ‘grab’.  Once contact is made, the tendril curls, forming a coil. This sense of ‘touch’ has recently been investigated using Thale or Mouse Ear Cress.  It has been shown that the veins of the leaves respond to touch.  The investigators used small glass beads to apply a small but distinct pressure, and recorded a series of rapid electrical signals (not dissimilar to those seen in nerves).  Even when the veins were removed from the surrounding leaf tissue, they still showed electrical activity so the response was not reliant on surrounding cells.  The electrical activity was also associated with proton pumps (moving hydrogen ions).  The sensitivity of the veins to touch may be associated with the plant’s defence mechanism.  Animals like aphids use their mouthparts (stylets) to penetrate the vascular tissue in the veins.  The jasmonate system is involved in wound response. Another plant, the Venus fly trap (Dionaea muscipula), also responds to touch. It catches prey (insects and spiders) by means of touch.   Dionaea catches its prey with a trap, formed from the terminal portion of each of the plant's leaves.  The trap is activated by tiny hairs on the inner surfaces of the trap. When a hair is touched by an insect or spider crawling along the leaves, the trap prepares to close but it only snaps shut  if the hairs are touched again, within approximately twenty seconds of the first stimulus.  

Super fast poplar trees ? In theory, increasing the number of trees across the globe could help reduce the levels of atmospheric carbon dioxide that are so intimately associated with climate change.   As trees grow, they absorb carbon dioxide from the air turning into wood.  This effectively locks away the carbon for a period of time.  However, the growth of trees can be slow so if trees could be ‘persuaded’ to grow faster then more carbon could be ‘locked up’ A San Francisco based company called “Living Carbon” has genetically modified hybrid poplar trees to speed up photosynthesis so that they grow faster.  They picked on the poplar trees as their genome had already been sequenced. The work of Living Carbon is at early stage and further work is needed to see if the enhanced photosynthetic rates and growth are maintained over the life time of the modified trees.  Another possible benefit of these modified trees is that they might help restore damaged land as their roots also grow faster, helping to address soil erosion.  Further details are available on their website : https://www.livingcarbon.com/ A discussion about the value / usefulness of such trees in affecting climate change / carbon sequestration was featured in the BBC program Positive Thinking this week. Effects of climate change. Climate change is associated with extreme weather events, such as flooding, heat waves and prolonged periods of drought.  American scientists at Ohio State University have been looking at the effects of higher temperatures and lower water availability on fungal infection in Austrian pines. They found that within three days of infection (by certain fungi - Diplodia species),  the warmer and drier conditions resulted in  Reduced photosynthesis by the tree Enhanced removal of carbon resources of the tree to the fungus. This means that there are fewer sugars and other metabolites available to the tree for growth (and defence against infection).   It would seem that a warming climate will render many trees more susceptible to invasion by various pathogens.   Full details of this research here.    Stressed out plants. Thale cress or Arabidopsis thaliana is a small flowering plant, that is native to many parts of Europe and Asia.  It is generally viewed as a weed, found by roadsides and on disturbed land. It is an annual that has a short life cycle. Its genome was one of the first to be sequenced. It has become a popular plant in the researching of the biology of flowering, light sensing and understanding the molecular biology of many plant traits, including flower development and light sensing.   Recently it has been used to investigate the stress response to heat, intense sun and drought.  Such stresses result in the production of reactive oxygen species (ROS).  High levels of ROS are lethal but low level of ROS are a signal to the plant to protect itself.  This is done through the photosynetic machinery which generates an ‘alarm molecule’ (MEcPP).  As this molecules accumulates in the plant, it in turn triggers the production of salicylic acid (essentially a form of aspirin).  This helps protect the chloroplast from damage.  Salicyclic acid is involved in many plant systems, notably defence against infection but also germination and stomatal physiology.