Regulation of Chloroplast Ultrastructure, Cross-section Anatomy of Leaves, and Morphology of Stomata of Cherry Tomato by Different Light Irradiations of Light-emitting Diodes

The chloroplast structural alteration and the photosynthetic apparatus activity of cherry tomato seedlings were investigated under dysprosium lamp [white light control (C)] and six light-emitting diode (LED) light treatments designated as red (R), blue (B), orange (O), green (G), red and blue (RB), and red, blue, and green (RBG) with the same photosynthetic photon flux density (PPFD) (’320 mmol m s) for 30 days. Compared with C treatment, net photosynthesis of cherry tomato leaves was increased significantly under the light treatments of B, RB, and RBG and reduced under R, O, and G. Chloroplasts of the leaves under the RB treatment were rich in grana and starch granules. Moreover, chloroplasts in leaves under RB seemed to be a distinct boundary between granathylakoid and stromathylakoid. Granathylakoid under treatment B developed normally, but the chloroplasts had few starch granules. Chloroplasts under RBG were similar to those under C. Chloroplasts under R and G were relatively rich in starch granules. However, the distinction between granathylakoid and stromathylakoid under R and G was obscure. Chloroplasts under O were dysplastic. Palisade tissue cells in leaves under RB were especially well-developed and spongy tissue cells under the same treatment were localized in an orderly fashion. However, palisade and spongy tissue cells in leaves under R, O, and G were dysplastic. Stomatal numbers per mm were significantly increased under B, RB, and RBG. The current results suggested blue light seemed to be an essential factor for the growth of cherry tomato plants. Cherry tomato (Solanum lycopersicum Mill.) plants are one of the cultivars of tomato species and annual plants that prefer a high light fluence rate. The fruits of cherry tomato plants have pleasing appearances and a delicious taste and are well accepted by consumers. The photosynthesis and growth of the tomato plants are greatly influenced by the quality and quantity of light (Hiroshi et al., 2000; Kinet, 1977). Nowadays, many kinds of garden crops are cultivated under electric lights such as fluorescent lamps and LEDs. LEDs are becoming especially popular for the cultivation of vegetable crops (Amaki and Hirai, 2008; Goins et al., 1997; Hoenecke et al., 1992; Kim et al., 2004a, 2004b; Schuerger et al., 1997; Tennessen et al., 1994). The quality and quantity of light have been shown to alter the structure and function of chloroplasts in leaves (Albertsson, 2001; Anderson, 1999; Danielsson et al., 2004). The alteration of photosynthesis activity and the structure of granathylakoids and stromathylakoids by the different light treatments is of particular interest (Danielsson et al., 2004; Mustardy and Garab, 2003). Light quality influences the growth of cells and tissue, photosynthetic characteristics (Liu, 1993) and yield of crops, physiological and morphological qualities, and the regulation of stress and aging of leaves (Voskresenskaya et al., 1968). At present, photobiological studies have been mainly focused on the effects of ultraviolet radiation on physiological and morphological characteristics of plants (Holzinger et al., 2006; Holzinger and Lütz, 2006; Michael et al., 2009; Poppe et al., 2002; Zancana et al., 2008). Different treatments of blue, red, and far-red light have been used to analyze the ultrastructure of organelles in leaf cells (McMahon and Kelly, 1996; Schuerger et al., 1997). However, few studies on the ultrastructure and response of cell organelles in leaves exposed to light of different spectral qualities have been carried out. In the present experiment, we investigated the effects of dysprosium lamps (white light, control) and the respective light treatments of LEDs designated as red, blue, orange, green, red and blue, and red, blue and green on the photosynthesis of leaves, ultrastructure of chloroplasts, palisade/spongy tissue, and stomata of cherry tomato leaves. Materials and Methods Plant materials and culture conditions. Seedlings of cherry tomato (Solanum lycopersicum Mill.) (provided by Taiwan Farmers Co.), which developed two leaves after germination, were transplanted and grown in plastic pots containing a mixture of peat and vermiculite (3:1, v/v) under light treatments. The treatments were provided by a dysprosium lamp (It is a high-intensity gas discharge lamp, a new type of metal halide lamp. Its spectrum is similar to the solar spectrum.) (white light, C) (LZ400D/H, 400W; YaHuaNing Co., Nanjing, China) and LEDs designated as R, B, O, G, RB, and RBG. The RB combination of spectral energy distribution was shown to be R:B = 1:1. The RBG combination of spectral energy distribution was shown to be R:B:G = 3:3:1. Except for the power of green lamp in the RBG treatment, which was 3 W, the power of every LED lamp treatment was 9 W. The number of LED lamps in treatments of R, B, and RB was 10 each, whereas the numbers used in treatments O, G, and RBG were 12. Respective LEDs were operated with the same PPFD ( 320 mmol m s) for 30 d. Spectral distribution and total power for each treatment are shown in Figure 1 and Table 1. Seedlings were incubated at 28 C in the daytime and at 18 C at night; relative humidity (RH) was 60% 80%, and daylength of 12 h was used. The light system was designed and made by Nanjing Agricultural University. Measurements of photosynthesis. All measurements were carried out using the young and fully expanded third leaf of cherry tomato plants. PPFD was measured using a quantum sensor (LI-250; LI-COR) and photosynthesis was measured using a photosynthesis instrument (LI-6400; LI-COR). PPFD was set to measure at 800 mmol m s, and the experimental conditions such as leaf temperature, CO2 concentration, and RH were 23 ± 1 C, 380 ± 5 mL L, and 16% to 20%, respectively. Spectral distribution of light treatments was measured by spectroradiometer (OPT-2000; ABDPE Co., Beijing, China). Leaves of three plants per treatment were measured and repeated twice. Chloroplast ultrastructure. Leaf samples were collected after illumination for 3 h at 30 d and placed into 0.2 M phosphate buffer (pH 7.2) containing 2.5% glutaraldehyde and then subjected to suction by a vacuum pump. After that, the samples were placed in a refrigerator at 4 C for 8 h; they were washed Received for publication 30 Aug. 2010. Accepted for publication 25 Nov. 2010. Supported by National Natural Science Foundation (2006AA03A165) and (30972035). Presently Professor Emeritus of Nagoya University. To whom reprint requests should be addressed; e-mail srguo@njau.edu.cn; xuzhigang@njau.edu.cn. HORTSCIENCE VOL. 46(2) FEBRUARY 2011 217 CROP PRODUCTION