Assessment of Photosynthetic Dysfunction in a Whole Tomato Plant with Chlorophyll Fluorescence Induction Imaging

Chlorophyll fluorescence is red light emitted from chlorophyll a pigment and hence accurate measurement of this emission allows us to assess photosynthetic functions of the plant. The chlorophyll fluorescence induction imaging measures a chlorophyll fluorescence induction phenomenon. This phenomenon is a dynamic change in chlorophyll fluorescence intensity induced by illuminating plant body with an excitation light at a stable intensity under dark condition. The time course of the chlorophyll fluorescence intensity during this phenomenon is called induction curve. In this study, we developed a chlorophyll fluorescence induction imagining system for whole tomato plants as a first prototype for plant diagnosis in greenhouse. By using this system, we assessed the effects of sunlight exposure treatment, i.e. PPFD 1500 μmol m−2s−1 for 2.5 h, on the photosynthetic functions of a whole tomato plant of 1.1 m high. A substantial transformation of induction curve was observed between before and just after the treatment, but it was recovered in 6 h under dark condition. During the recovery process, the inflection points of P and M, which are the characteristic inflections of an induction curve, showed different behaviour. The M kept lower values for 1.5 h after the sunlight exposure treatment even though the P had been almost recovered. This result suggests that the chlorophyll fluorescence induction imaging, especially concurrent monitoring of the images of P and M inflection points, is useful to detect invisible photosynthetic dysfunctions at whole plant level.