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-sensiti ve crops, like tomato, has been extensively studied and is well characteriz ed. This investigation examined the behaviour of the subtropical fruit tree , mango, to enable comparison with these well-studied systems. Unlike tomat o, chilling between 5 degreesC and 7 degreesC overnight produced no signifi cant inhibition of light-saturated CO2 assimilation (A) during the first ho urs following rewarming, measured either under controlled environment condi tions 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 Rubis co activity. Overnight chilling of tomato can cause severe disruption in th e circadian regulation of key photosynthetic enzymes and is considered to b e a major factor underlying the dysfunction of photosynthesis in chilling-s ensitive herbaceous plants. Examination of the gas exchange of mango leaves maintained under constant conditions for 2 d, demonstrated that large depr essions in A during the subjective night were primarily the result of stoma tal closure. Chilling did not disrupt the ability of mango leaves to produc e a circadian rhythm in stomatal conductance. Rather, the midday increase i n stomatal limitation of A appeared to be the result of altered guard cell sensitivity to CO2 following the dark chill.