Why do plants with too little light get leggy?
In short: Plants measure the amount of red and blue light reaching their leaves. When that light falls to too low of a level the plant releases hormones which allow it to shoot up past the plants around it so it may get more light.
Plants grow in dense vegetations at the risk of being out-competed by neighbors. To increase their competitive power, plants display adaptive responses, such as rapid shoot elongation (shade avoidance) to consolidate light capture.
These responses are induced upon detection of proximate neighbors through perception of the reduced ratio between red (R) and far-red (FR) light that is typical for dense vegetations. The plant hormone auxin is a central regulator of plant development and plasticity, but until now it has been unknown how auxin transport is controlled to regulate shade-avoidance responses.
Here, we show that low R:FR detection changes the cellular location of the PIN-FORMED 3 (PIN3) protein, a regulator of auxin efflux, in Arabidopsis seedlings. As a result, auxin levels in the elongating hypocotyls are increased under low R:FR. Seedlings of the pin3-3 mutant lack this low R:FR-induced increase of endogenous auxin in the hypocotyl and, accordingly, have no elongation response to low R:FR.
We hypothesize that low R:FR-induced stimulation of auxin biosynthesis drives the regulation of PIN3, thus allowing shade avoidance to occur. The adaptive significance of PIN3-mediated control of shade-avoidance is shown in plant competition studies. It was found that pin3 mutants are outcompeted by wild-type neighbors who suppress fitness of pin3-3 by 40%. We conclude that low R:FR modulates the auxin distribution by a change in the cellular location of PIN3, and that this control can be of great importance for plants growing in dense vegetations. paper
New Species of Carnivorous Plant found
A new species of carnivorous pitcher plant has been found by Fauna & Flora International (FFI) in Cambodia’s remote Cardamom Mountains.
The discovery of Nepenthes holdenii is an indicator of both the stunning diversity and lack of research in the forests of the Cardamom Mountains.
The large red and green pitchers that characterize Nepenthes holdenii are actually modified leaves designed to capture and digest insects. The pitchers can reach up to 30 cm long. The carnivorous strategy allows the plants to gain additional nutrients and flourish in otherwise impoverished soils.
A further unusual adaptation seen in this new species is its ability to cope with fire and extended periods of drought. Cambodia’s dry season causes forests to desiccate and forest fires are common.
Nepenthes holdenii exploits the clearings caused by these regular blazes by producing a large underground tuber which sends up a new pitcher-bearing vine after the fires have passed.
British photographer Jeremy Holden, who first found the plant on the FFI survey and after whom it is named, said: ‘The Cardamom Mountains are a treasure chest of new species, but it was a surprise to find something as exciting and charismatic as an unknown pitcher plant’.
This discovery is the latest in a series of new species described from the Cardamom Mountains, including a green-blooded frog and a number of new reptiles.
Jenny Daltry, FFI Senior Conservation Biologist said: ‘The flora of Cambodia is still poorly known and potentially holds many new species for researchers to discover’.
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