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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 sub-tropical fruit tree, mango, to enable comparison with these well-studied systems. Unlike tomato, chilling between 5 degrees C and 7 degrees C overnight produced no significant inhibition of light-saturated CO(2) 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 CO(2) following the dark chill.
D. J. Allen (Wed,) studied this question.