The Compensatory Response of Photosystem II Photochemistry to Short-Term Insect Herbivory Is Suppressed Under Water Deficit

Photosystem II (PSII) is very sensitive to both biotic and abiotic stress conditions, mirroring global climate changes. Crop production worldwide faces rising hazards from the increased duration, frequency, and intensity of drought stress episodes as a result of climate change, and its effects, when combined with biotic stress, are becoming more noticeable. In the present work, we examined PSII responses of well-watered (WW) tomato plants or mildly drought-stressed (MDS) plants to 20 min of <i>Tuta absoluta</i> larvae feeding. The effective quantum yield of PSII photochemistry (Φ<i>_PSII</i>) of the whole leaf in WW plants, after 20 min of larvae feeding, compensated for the reduction in Φ<i>_PSII</i> observed at the feeding area. In contrast, the reduced Φ<i>_PSII</i> at the feeding areas of MDS plants, after 20 min of larvae feeding, was not compensated at the whole-leaf level because of the drought stress. The increased Φ<i>_PSII</i> and electron transport rate (ETR) at the whole-leaf level in WW plants was attributed to the increased fraction of open PSII reaction centers (q<i>p</i>), since there was no difference in the efficiency of the open PSII reaction centers (F<i>v</i>'/F<i>m</i>') before and after feeding. Therefore, the response of PSII photochemistry in WW plants to short-term biotic stress resulted in an overcompensation reaction, which developed a whole-leaf photosynthetic enhancement. However, short-term biotic stress in combination with mild abiotic stress resulted in decreased PSII photochemistry. It is concluded that increased crop damage is likely to occur due to the global climate-change-induced drought episodes, influencing insect herbivory.