An overnight chill induces a delayed inhibition of photosynthesis at midday in mango (Mangifera indica L.)

The effect of a cold night on photosynthesis in herbaceous chilling-sensitive crops, like tomato, has been extensively studied and is well characterized. This investigation examined the behaviour of the subtropical fruit tree, mango, to enable comparison with these well-studied systems. Unlike tomato, chilling between 5 °C and 7 °C overnight produced no significant inhibition of light-saturated CO₂ assimilation (A) during the first hours following rewarming, measured either under controlled environment conditions or in the field. By midday, however, there was a substantial decline in A, which could not be attributed to photoinhibition of PSII, but rather was associated with an increase in stomatal limitation of A and lower Rubisco activity. Overnight chilling of tomato can cause severe disruption in the circadian regulation of key photosynthetic enzymes and is considered to be a major factor underlying the dysfunction of photosynthesis in chilling-sensitive herbaceous plants. Examination of the gas exchange of mango leaves maintained under constant conditions for 2 d, demonstrated that large depressions in A during the subjective night were primarily the result of stomatal closure. Chilling did not disrupt the ability of mango leaves to produce a circadian rhythm in stomatal conductance. Rather, the midday increase in stomatal limitation of A appeared to be the result of altered guard cell sensitivity to CO₂ following the dark chill.