tissues stopped fixing CO . When the plants were repeatedly kept during nights at 4 and 6°C, photosynthesis was progressively reduced in the following days, and after 10 days it was 10% lower than the initial rates. Keeping the plants for 15 days at 12°C did not trigger tolerance to cold, implying that the plant avoided a reduction in photosynthetic activity. It was further observed that 25% of the photosynthetic reduction was due to stomatal closure and 75%
to a decrease of carboxylation reactions of the photosynthesis (Bauer et al. 1985).