IRGA-Live Clamp: An integrated infrared gas-analysis platform to investigate systemic signalling within the plant canopy

Continued global warming is drastically changing weather patterns, with both daily and seasonal extremes that limit crop productivity. Approaches to address this problem include mitigation through human intervention (e.g. irrigation, polytunnels, controlled environment agriculture), or by introducing genetic editing to optimise crops' responses. However, in each of these cases we lack an understanding of how plants respond to the interventions at an organismal level. For example, in the presence of drought (more prevalent during the summer when temperatures are higher) how do plants balance water retention against the need for evaporative cooling and photosynthesis? Stomatal pores within the leaf surface are crucial in this response, with plants integrating multiple environmental signals to control gas exchange between the leaf interior and the environment. While the behaviour of single leaves is well understood, we have not assessed how the entire canopy responds to environmental stress. Do they divide up tasks between different leaves? How would this be co-ordinated - can plant leaves talk to each other?

New results from our laboratories have shown that a soybean leaf opens the stomata under heat stress but closes them when heat stress is accompanied by low humidity. Thus, in this leaf water retention is prioritised. Neighbouring leaves, even if not stressed themselves, also react with changes in stomatal behaviour. This reflects a process called systemic signaling in which the non-stressed leaves 'receive' mobile signals from the stressed 'sender' leaf. Surprisingly, our findings indicate that 'receiver' leaves react differently depending on whether they are positioned above or below the 'sender' leaf, showing either stomatal opening or closure. These data demonstrate that plant leaves can communicate with each other, and they divide up tasks between different parts of the canopy. It is likely that this strategy improves the overall plant performance. However, the findings also pose many new questions; what are the signals, why does position matter, do natural gradients of light across the canopy alter responses and performance, how do disease or pests interfere with the systemic signaling of heat and drought? And how can we quantify the potential gains?

Plant photosynthetic performance and gas exchange are routinely monitored using infrared gas analysis (IRGA) to measures the exchange of carbon dioxide and water across the leaf. Until now, scientists have used one IRGA machine at a time to measure gas exchange in one leaf in one plant (or in several plants with multiplexed headsets controlled from one console). We will advance the state of the art by integrating several IRGA machines to enable the individual control of environmental conditions in multiple leaves whilst simultaneously recording their gas exchange and photosynthetic performance. Crucially, we will apply networking technologies to integrate the functions of individual IRGA machines. This will allow data obtained from one leaf to drive protocols applied to other leaves. We call this 'IRGA-Live Clamp' in analogy to similar approaches used in neurophysiology. Due to the novelty of the IRGA-Live Clamp platform and the opportunities to answer important research questions many researchers from across the UK will be interested to use the IRGA-Live Clamp platform installed at the University of Glasgow to investigate different questions, fostering new collaborations. For example, we will be able to leverage optogenetic expertise to understand how artificial lighting can be used to optimise gas exchange. The IRGA-Live Clamp platform will therefore enable major progress in scientific knowledge and help solving fundamental questions that are important for plant stress tolerance and agriculture.

The funds will therefore contribute to food security under climate change and provide a step-change in photosynthetic research capability within the UK.

The aim of this project is to provide a flexible infrared gas analysis (IRGA) platform enabling research on the molecular pathways underpinning local and temporal plasticity of environment responses within a plant.
The setup will allow us to individually control the global and local environment (temperature, CO2, humidity, light) of several individual leaves in a plant canopy, and to simultaneously measure dynamic responses both locally and systemically (in other leaves). The platform is an ensemble of five infrared gas analysis (IRGA) systems equipped with fluorometers which we will connect through an integrated data management system enabling feedback control (Live Clamp). The units ('nodes') can be linked to several individual leaves of one or several crop plants. We will build an integrated data acquisition and analysis setup that will allow synchronized measurement of gas exchange (CO2/H2O) kinetics from all nodes upon environmental stimuli imposed both locally at each node and through the ambient environment of the plant.
While IRGA has been widely applied to plants both in the field and in the laboratory, measurements have been limited to single leaves or entire canopies. The novelty of the planned platform resides in the manner we multiply, integrate and apply the technology through the platform. In each application, the information gain from the experiments will be maximised by obtaining data on carbon assimilation, maximal assimilation changes, photosynthetic capacities, stomatal conductance, and compensatory CO2/H2O fluxes. Most importantly, through the network of nodes with the Live Clamp, the user will be able to probe the kinetics of communication between different leaves, the relative gains and their spatio-temporal relationships, and dependencies on global as well as local environmental variables. The IRGA Live Clamp platform will generate novel research capability (Glasgow, UK and worldwide) for answering a wide range of fundamental questions.