High irradiance impairments on photosynthetic electron transport, ribulose-1,5-bisphosphate carboxylase/oxygenase and N assimilation as a function of N availability in Coffea arabica L. plants.

摘要

Young coffee cv. Catuai plants grown under low irradiance (PPFD up to～150μmol m-2 s-1) and high (2 N), medium (1 N) and low (0 N) nitrogen availability conditions were exposed to natural sunlight (midday PPFD up to～1700μmol m-2 s-1) for 14-15 days, during which parameters related to photosynthesis and N assimilation were monitored. In the plants with lower N availability, donor and acceptor side photoinhibition may have affected PSII functioning. During high irradiance stress plants with higherN availability maintained the highest contents of cytochromes (cyt) b559HP, b559LP, b563 and f and plastoquinone-9 (PQ-9). Those plants also presented significant increases in rubisco content and activity, and a preferential investment in rubisco ratherthan in light harvesting components by the end of the high irradiance stress. Despite the effects observed on PSII and rubisco, PSI activity and cyt b6/f complex were much more severely affected by high irradiance stress in all N treatments. Leaf nitrate reductase activity decreased whereas nitrate and amino acid contents increased during high irradiance in 2 N and 1 N plants. The data shows that high irradiance affected both the photochemical and enzymatic reactions of photosynthesis (especially in 0N and 1 N plants), that PSI was a preferential photoinhibitory target and that higher N availability promoted the recovery of important physiological parameters, such as electron transport rates, PQ-9 and rubisco activity and content.