Three Coffea species (C. arabica cv. Icatu, C. canephora cv. Apoat and C. dewevrei) were tested in order to identify and study the mechanisms of tolerance to low, non-freezing temperatures. Several photosynthesis-related parameters were monitored during a 20-day period of gradual temperature decrease, from 25/20 8C (day/night) down to 15/10 8C, during chilling treatments (15/4 8C), and upon rewarming (25/20 8C). Differences were found among species, both during low temperature exposure and during rewarming. In general, Coffea species showed cold-induced photoinhibition of photosynthesis, which was attributable to biochemical (in vivo ribulose-1,5-bisphosphate carboxylase/oxygenase activity and carbohydrate synthesis) and biophysical (antennae functioning, photosystem II efficiency and linear electron transport) inactivation, rather than to stomatal constraints. The moderately low temperature of 15/10 8C was enough to cause a negative impact on net photosynthesis (A), mostly due to low (initial) rubisco activity in all species. However, C. arabica cv. Icatu showed a higher tolerance to chilling and recovered quickly and completely upon rewarming, as assessed from the impacts on the photosynthetic machinery (e.g. A max , F o , F v /F m , F v ¢/F m ¢, q P , f e , rubisco activity) and on carbohydrate metabolism. Such lesser effects are likely to be related to the strong increases and higher contents of zeaxanthin, lutein and b-carotene that presumably increased the ability to dissipate excitation energy and contributed to protect the photosynthetic apparatus. During cold exposure, a significant reduction of the a/b carotene ratio, which is considered an acclimation feature, was observed solely in C. arabica cv. Icatu. However, C. canephora cv. Apoat and, especially, C. dewevrei showed to be highly cold-sensitive. In these latter species, the photoinhibitory impairments to photosynthesis were stronger, probably due to the lower contents of protecting pigments during chilling conditions that lead to a higher vulnerability to excess excitation energy. Moreover, the mesophyll impairments (e.g. A max , F v /F m , f e ) became significant even at moderately low temperatures of 15/10 8C, and a lower ability to recover after chilling exposure was observed. The limitation of in vivo rubisco activity and A max may have been due to substrate limitation, but disturbances in sugar metabolism could also play an important role in the expression of chilling sensitivity in C. canephora cv. Apoat and C. dewevrei.

No abstract

No abstract

A suitable light quantity and quality is essential for optimal photosynthetic metabolism. Using combinations of three lamp types, the impact of the quality of artificial light conditions on the photosynthetic apparatus of leaves developed in growth chambers was analysed. The VIALOX‐Planta lamps are quite poor outside the green to orange (520 ‐ 620 nm) wavelength range, while the HQI‐BT lamps present a more uniform spectral intensity between 425 and 650 nm (blue to red). The halogen lamps are particularly rich in the red and far red range of the electromagnetic spectra. The lamps also differ in the red: far red ratio, which were 3.07 (VIALOX), 2.06 (HQI‐BT) and 1.12 (halogen). Clear positive effects were detected in most of the photosynthetic parameters in relation to light quality, both at stomatal and mesophyll levels. Despite some species‐dependent sensitivity to blue and red/far red wavelengths, observed among the studied parameters, the best photosynthetic performances of the test plants (Packyrhizus ahipa and Piatã, a hybrid of Coffea dewevrei×Coffea arabica) were obtained almost always with the reinforcement of blue (HQI‐BT lamps), red and far red (halogen lamps) wavelengths and with a red: far red ratio closer to that observed in nature. This suggests the involvement of more than one photoreceptor family in photosynthetic performance. Under such light conditions, increases in net photosynthesis and stomatal conductance were observed and, despite the moderate effects on photosynthetic capacity, strong effects were observed in the capture and transfer of light energy in the antennae pigments, photochemical efficiency of photosystem II and electron transport. This was related to the striking quantitative and qualitative impacts observed on total chlorophylls and carotenoids, which reached, in some cases, increases of 100 and 200 %, respectively. Among carotenoids, increases as high as 9‐fold for α‐carotene were observed (P. ahipa), with chlorophyll (a/b), total (chlorophyll/carotenoid) and carotene (α/β) ratios also strongly affected. This would have affected the structure and stability of photosynthetic membranes which, in turn, affected photosynthetic‐related processes (e.g., antennae pigments, photosystem II and electron transport efficiencies). This was particularly clear in the HQI + halogen treatment. The results unequivocally show that light quality could remain a clear limiting factor for leaf/plant development under artificial light conditions, which could be overcome using more than one lamp type, with complementary emission spectra.