Chlorophyll regulation relationship with superoxide during Photoperiodic Injury and an exploration of natural solar spectral changes to entrain the circadian rhythm in Solanum lycopersicum L.

Abstract

Photoperiodic injury (PI) in tomato is characterized by leaf chlorosis & necrosis when exposed to continuous (CL) or non-24-h artificial lighting photoperiods, suggesting a role for the circadian clock. PI is less obvious under high-latitude natural CL, thus it was hypothesized and discovered to have shifting solar spectra with geo-temporal information to clock inputs like phytochrome. In addition, circadian outputs including N-assimilatory enzymes become arrhythmic in PI-intolerant ‘Basket Vee’ (BV) under CL, whereas they do not in PI-tolerant ‘Micro-Tom’ (MT). Recently reported PI-tolerance from a light harvesting complex (LHC) gene was hypothesized to alter chlorophyll regulation’s effect on reactive oxygen species (ROS) rhythms such as superoxide. MT and BV shared similar short-term (<24hrs) CL acclimation through increased chlorophyll (Chl) contents, Chl a/b, PSII operating efficiency (YII), and dampening of superoxide rhythms. Unexpectedly, long-term (>5days) CL further damped rhythms regardless of cultivar while only BV’s Chl content dropped, and YII destabilized.