Impact of local light on number and growth of cells in tomato fruit

In most studies on fruit growth in response to light, treatments are imposed at plant level. Such treatments lead to only limited insight into generative growth response since the interaction with vegetative response cannot be ignored. In order to study the effect of light on tomato fruit growth, a cuvette system with 100 µmolm-2s-1 light was constructed. The light was from white Light Emitting Diodes (LEDs). The system was used to illuminate individual tomato trusses. Three local light treatments were applied (no light, light for 12 hours and light for 24 hours) to one truss per plant of tomato cultivar Komeett. The hypothesis tested was whether fruits grown in the presence of light exhibit higher sink strength compared to those grown in the dark. Fruit diameter and fresh weight, pericarp cell number and cell size were measured half way and at the end of fruit development. Preliminary results indicate no significant difference in fruit fresh weight and diameter at both harvest stages. Half way during fruit development, pericarp cell number was 23% higher in light-grown fruits while cell size was 11% lower compared to fruits grown in the dark. These results contradict findings reported from an earlier in vitro experiment where light was found to increase fruit sink strength through activation of enzymes within the starch synthesis pathway. Our results suggest a compensatory mechanism for final fruit diameter and weight at the cell level since cell size increase appeared to make up for deficiencies in cell division activity.