| Photoperiodic injury of vegetative tissues in tomato ( Lycopersicon esculentum Mill.) can occur under extended photoperiods and non-24 h light/dark cycles, and this phenomenon may reduce the response of greenhouse tomatoes to supplemental lighting. Although documented nearly 80 years ago, the physiological basis for this injury is not known. Excess starch accumulation and interactions with growth rhythms have been implicated. Four tomato cultivars that demonstrate variation in their response to photoperiod were used and tested under various environments. Cultivars with greater predisposition for photoperiodic injury displayed reduced growth under extended photoperiods. No correlations were found between starch levels and photoperiodic injury. A correlation was found between circadian rhythm patterns, nitrite accumulation in response to continuous light, and photoperiodic injury. We propose that the physiological basis for photoperiodic injury in plants is nitrite toxicity resulting from an altered coordination between nitrate and nitrite reduction activities under photoperiodic cycles favouring the injury. |
