Ultraviolet radiation underlies metabolic energy reprograming in Coffea arabica and Coffea canephora genotypes

Depletion of the stratospheric ozone layer enhances UV exposure to living organisms. We hypothesized that the adaptative physiological and bioenergetic responses of modern genotypes of Coffea arabica cv. Catuaí Amarelo IAC 62, and C. canephora (Conilon LB1) to actual UV levels would generate additional costs to the detriment of biomass formation and partitioning. Coffee plants were cultivated for six months in a mini greenhouse under either near ambient (UVam) or reduced (UVre) UV conditions, after which leaf gas exchanges, chlorophyll a fluorescence parameters and proton pump phosphohydrolase activities were analyzed. Growth under UVam did not affect the photochemical efficiency and net CO2 assimilation in both Coffea species, but reduced stomatal conductance (gs) and increased intrinsic water use efficiency (iWUE), maximum photosynthetic O2 evolution, and apparent quantum yield. Coffee plants under UVam showed decreased P-type H+-ATPase activity, whilst H+-PPase activity increased, preserving metabolic energy. Coffee biomass accumulation decreases under UVam were more pronounced in C. canephora, which generally invested more in the root system than in shoot biomass as compared to C. arabica. Reduced biomass in C. canephora under UVam susuggested restrained C-sequestration in plant biomass, which might be partly associated with gs reduction, along with a equilibrium between the ATP- and PPi-driven electrochemical H+ gradients, providing a mechanism for energy buffering and cellular robustness. The stability of fluorescence parameters and net CO2 assimilation rate under UVam, reduced gs and increased iWUE, oxygen-evolving complex activity, and elevated SPAD values, supported photomorphogenetic responses acclimation to actual UV in two modern coffee genotypes, with detrimental impact on shoot biomass, especially in C. canephora.