Researchers uncover how small plants compete with bigger neighbours for light
Have you ever wondered how small plants get light when they're surrounded by bigger plants? Researchers in the Netherlands and Germany say the plants work against this problem by adapting via rapid shoot elongation and stretching their leaves towards the Sun. Their study, presented in the journal Proceedings of the National Academy of Sciences (PNAS), demonstrates the adaptation process, and in turn the growth process of these plants. Researchers from Utrecht University in the Netherlands and Ruhr-Universitaet-Bochum (RUB) in Germany said information on the molecular basis of the 'shade avoidance syndrome' was lacking until now. Their work effectively led them to unravelling a regulation pathway, where a specific transport protein (PIN3) allows the plant hormone auxin to build up. Auxin is a critical element of the adaptation process in the outer cell layers of plants, giving the growth process a boost. Because smaller plants are at greater risk of being overshadowed by their larger neighbours they have various mechanisms that help them adjust and allow them to register competing neighbours and improve their competitive edge. Doing this gives the smaller plants more flexible reaction, the team said, adding that permanent perception of light intensity and quality is a must for this process to run. RUB's Professor Stephan Pollmann pointed out that chlorophyll, the photosynthetic pigment in leaves, absorbs nearly all shades of blue and far red, only permitting dark red light to pass through the leaves. According to him, there is a considerable change in the red to far-red ratio if foliage shades the plant. When a plant's light receptors register this change they kick-start several adjustment mechanisms in their development and growth process. This is called the 'shadow avoidance syndrome'. The result is that plants get improved shoots growth and upward movement of the leaves (i.e. hyponastic response). The researchers said vascular plants generate an entire series of various small signalling molecules, known as phytohormones, which regulate growth and differentiation processes. Professor Pollmann pointed out that it had been known that the effect of auxin is based on an interaction of auxin formation, transportation and signal transduction. A low red to far-red ratio affects these processes. The big question was how does it work? Dr Ronald Pierik at Utrecht University and his colleagues found that the shoot growth during a low red to far-red ratio is subject to an intact auxin perception mechanism and is dependent on the accumulation of auxin in the shoot. The auxin transport protein PIN-FORMED 3 (PIN3) is largely responsible for this accumulation, according to the researchers. When the ratio between red to far-red is low, PIN3 if formed much better. The researchers noted that it primarily accumulates in the lateral endodermal cell walls. This distribution of PIN3 triggers a flow of auxins towards the epidermal cell layers, effectively leading to the shoot's elongation growth. Professor Pollman and his team used advanced mass spectrometry to quantify and compare the auxin content in wild-type and genetically created PIN3 mutants, which cannot generate the transport protein. They found that the shade avoidance syndrome was absent in the genetically altered plants without PIN3. 'It is possible to deduce the important role of PIN3 controlled auxin accumulation during the shade avoidance reaction,' Professor Pollman said.For more information, please visit:Utrecht University:http://www.uu.nl/en/pages/default.aspxRuhr-Universitaet-Bochum (RUB):http://www.ruhr-uni-bochum.de/index_en.htmPNAS:http://www.pnas.org/
Countries
Germany, Netherlands