Abstract
Coffee (Coffea arabica L.) has been traditionally considered as shade-demanding, although it performs well without shade and even out-yields shaded coffee. Here we investigated how coffee plants adjust their metabolic machinery to varying light supply and whether these adjustments are supported by a reprogramming of the primary and secondary metabolism. We demonstrate that coffee plants are able to adjust its metabolic machinery to high light conditions through marked increases in its antioxidant capacity associated with enhanced consumption of reducing equivalents. Photorespiration and alternative pathways are suggested to be key players in reductant-consumption under high light conditions. We also demonstrate that both primary and secondary metabolism undergo extensive reprogramming under high light supply, including depression of the levels of intermediates of the tricarboxylic acid cycle that were accompanied by an up-regulation of a range of amino acids, sugars and sugar alcohols, polyamines and flavonoids such as kaempferol and quercetin derivatives. When taken together, the entire dataset is consistent with these metabolic alterations being primarily associated with oxidative stress avoidance rather than representing adjustments in order to facilitate the plants from utilizing the additional light to improve their photosynthetic performance.
Highlights
Light is the fundamental energy resource for plants since it fuels photosynthesis, driving plant growth, low and high sunlight can limit plant performance
Given that high light (HL) plants received levels of photosynthetic photon flux density (PPFD) well above their light saturation point (607 mmol photons m22 s21; Table 1), adjustments in light use and dissipation are required to avoid an excess energy that would otherwise lead to photoinhibition
We found that the non-photochemical quenching coefficient (NPQ) was higher (283%) in HL than in low light (LL) plants (Table 3), suggesting an enhanced energy dissipation as heat
Summary
Light is the fundamental energy resource for plants since it fuels photosynthesis, driving plant growth, low and high sunlight can limit plant performance. Whilst the shortages of key resources, such as light, can compromise growth and survival, plants face heat, desiccation and excessive irradiance at high sunlight [1] To cope with these stresses, plants have evolved a number of well-known biochemical, physiological and structural changes at the leaf and whole-plant levels that enable them to adjust to a particular set of light conditions [2,3]. Given that plants perform photosynthesis and assimilatory processes in a continuously changing environment, energy production in the various cell compartments and energy consumption in endergonic processes have to be well adjusted to the prevailing conditions [4] In this regard, homeostasis is crucial in maintenance of all cellular functions, one means by which this is achieved is by ensuring that the pools of ATP/ADP, NAD(P)H/ NAD(P) and other redox carriers remain at balanced ratios [4,5,6]. Most metabolomics-based studies dealing with carbon economy have focused on model woody temperate species such as poplar (e.g., [17]) and on herbaceous plants such as Arabidopsis (e.g., [10,11]), tobacco (e.g., [12]) and tomato (e.g., [9,18]), whereas almost no studies focus on tropical woody species
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