Far-red illumination of the lower adult plant parts affects morphology and growth of the upper young plant parts in tomato

Most of the studies on light spectrum do not consider effects of spectrum perceived by different plant parts. Local and long-distance plant responses to localized light spectrum have hardly been studied in large plants. This paper aims to investigate whether local supplementation of FR results in local or long-distance architectural and growth responses in full-grown tomato plants. Tomato plants grown in a climate chamber were separated horizontally with white plastic at 85 days after sowing (lower half was 50 cm and upper half 15 cm long). The lower half was already full-grown and did not elongate anymore. The following 17 days both halves received 123 µmol m-2 s-1 red/blue light. The lower, upper, or none of the plant halves received 94 µmol m-2 s-1 additional far-red radiation (FR). FR supplied to the upper half increased petiole and internode elongation as well as specific leaf area (SLA) in the upper half of the plant, while petiole angle decreased. Moreover, dry weights of leaf stem (petiole+rachis+petiolules) and stem increased while leaf (lamina) dry weight decreased. Leaf area was unaffected. When FR was supplied to the lower half of the plant SLA, stem length, and stem dry weight of the upper half also increased, but to a lesser extent than when FR was supplied to the upper half. However, FR supplied to the lower half of the plant did not significantly affect other parameters such as petiole length, petiole angle and leaf dry weight of the upper plant half. We conclude that locally supplied FR has long-distance effects on length and dry weight of the stem and on SLA, while some other parameters (petiole elongation, petiole angle, leaf weight) are only locally affected. Hence, morphology and growth of upper young developing plant tissue can be influenced by light spectrum perceived by lower adult plant parts.