Photosynthesis in coffee (Coffea arabica and C-canephora) as affected by winter and summer conditions

Photosynthetic and biochemical responses of potted plants of Coffea arabica cv Red Catuai and C. canephora cv Kouillou were examined during winter and summer. There were large decreases in the photosynthetic rates of both cultivars from summer to winter, with more pronounced declines shown by Catuai. The photochemical efficiency of photosystem II, as evaluated by the ratio of variable to maximum chlorophyll fluorescence, decreased to a greater extent in Catuai than in Kouillou during winter. This probably was a secondary effect due to the loss of the photosynthetic capacity, which was mostly determined by non-stomatal factors. In response to winter conditions, Kouillou accumulated three times more proline and ascorbate with no changes in the content of malonedialdehyde (MDA). Catuai accumulated 160% more proline and 206% more MDA in winter in comparison to summer values, but there was no significant change in ascorbate levels. The content of chlorophylls and carotenoids did not change in response to natural seasonal acclimation. The leaf starch content in winter was higher by 53% in Catuai than in Kouillou. Photosynthetic rates, as measured by oxygen evolution, were well correlated with starch content in Catuai, but not in Kouillou. When winter-grown leaves were darkened for 96 h, their normal starch levels were halved: this was accompanied by the restoration of the photosynthetic rates to levels similar to those found in summer in both cultivars, with a concurrent resumption of the photosystem II efficiency. (C) 1997 Elsevier Science Ireland Ltd.