Abstract
Tomato (Solanum lycopersicum L.) belongs to the crops that are the most sensitive to continuous lighting (CL). We studied age-dependent changes in the sensitivity of tomato leaves to CL. The leaves exposed to CL from a lag-phase of their growth exhibited pronounced chlorosis with the loss of 30% chlorophyll after 2 weeks. The values of the maximum (Fv/Fm) and actual (φII) quantum yields of the PSII photochemical activity were decreased, the photosynthesis rate was suppressed, and the relative electrolyte leakage was enhanced. In contrast, the leaves were less sensitive to CL if they had passed their early growth (lag-phase) under normal light conditions (16-h photoperiod) and encountered the CL as late as in the log-phase. In this case, the chlorophyll content, the photosynthesis rate, and the electrolyte leakage were close to the levels of the control leaves grown at the 16-h photoperiod except for the antioxidant enzymes—catalase, ascorbate peroxidase, and guaiacol peroxidase—which were more active. The conclusion was drawn that the age-related changes in the CL-sensitivity are due to the difference in activities of the antioxidant enzymes. In general, the elder plants were less sensitive to CL than the younger ones.
Highlights
In recent years the interest grows to the use of continuous lighting (CL) for crop growing in greenhouses and especially in closed systems of plant factories with artificial lighting (PFAL), which are being widely exploited in some countries (United States, Japan, China, Korea, etc.)
In the plants initially grown under the 16-h photoperiod, the content of chlorophyll and the maximum (Fv/Fm) and actual quantum yields of the PSII photochemical activity decreased in comparison with the control plants one week after switching to the 24-h photoperiod (Figs. 3, 4)
The plants exposed to CL from the 14th days after sowing (DAS) (Fig. 1b: A) manifested these traits (and the subsequent chlorosis (Fig. 2a)) (Figs. 2b: A; 3) on the 3rd and younger leaves, which were at the lag-phase at the onset of CL
Summary
In recent years the interest grows to the use of continuous lighting (CL) for crop growing in greenhouses and especially in closed systems of plant factories with artificial lighting (PFAL), which are being widely exploited in some countries (United States, Japan, China, Korea, etc.) [1]. If other growing conditions are optimal, the plant biomass is determined to a large extent by an amount of the absorbed light energy, which depends on light intensity and duration. Long photoperiods cause interveinal chlorosis or necrosis in many plant species. Using long (including 24-h) photoperiods with relatively low photon flux density is economically profitable because of a reduction in initial and operational energy costs [5, 6].
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