Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis

Photosynthetica, Oct 2015

Lowering irradiance can delay the flower stalk, i.e., spike development, in order to schedule flowering time of Phalaenopsis; however, the effect on photosynthetic performance and spiking inhibition remains poorly understood. We compared light and shade treatments of Phalaenopsis aphrodite subsp. formosana in order to determine how limiting light affects day-night changes in the photosynthetic capacity of leaves and the carbon pool of leaves and stems resulting in delayed spiking. The low irradiance treatment [20 μmol(photon) m−2 s−1] for six weeks did not affect potential functions of photosynthetic apparatus estimated by chlorophyll a fluorescence analysis, but it significantly reduced the net CO2 uptake and O2 evolution rates, carbohydrate and organic acid concentrations, and amplitudes of CAM activity in new and fully expanded leaves of Phalaenopsis and delayed the spiking compared with the control kept at 150 μmol(photon) m−2 s−1. The shortened stem contained a remarkably high sucrose concentration, accounting for more than 80% of total soluble sugars for both treatments throughout the day. Moreover, the sucrose concentration was unaffected by the lowering of irradiance. The relationship between the sucrose content and spiking seemed to be loose; the major factor(s) for spiking in Phalaenopsis remained to be ascertained as the flower stalk bud is attached to the shortened stem.

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Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis

Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis Y.-C. LIU 0 1 C.-H. LIU 0 1 Y.-C. LIN 0 1 C.-H. LU 0 1 W.-H. CHEN 0 1 H.-L. WANG 0 1 0 Department of Life Sciences 1 , Institute of Biotechnology Lowering irradiance can delay the flower stalk, i.e., spike development, in order to schedule flowering time of Phalaenopsis; however, the effect on photosynthetic performance and spiking inhibition remains poorly understood. We compared light and shade treatments of Phalaenopsis aphrodite subsp. formosana in order to determine how limiting light affects day-night changes in the photosynthetic capacity of leaves and the carbon pool of leaves and stems resulting in delayed spiking. The low irradiance treatment [20 μmol(photon) m2 s1] for six weeks did not affect potential functions of photosynthetic apparatus estimated by chlorophyll a fluorescence analysis, but it significantly reduced the net CO2 uptake and O2 evolution rates, carbohydrate and organic acid concentrations, and amplitudes of CAM activity in new and fully expanded leaves of Phalaenopsis and delayed the spiking compared with the control kept at 150 μmol(photon) m2 s1. The shortened stem contained a remarkably high sucrose concentration, accounting for more than 80% of total soluble sugars for both treatments throughout the day. Moreover, the sucrose concentration was unaffected by the lowering of irradiance. The relationship between the sucrose content and spiking seemed to be loose; the major factor(s) for spiking in Phalaenopsis remained to be ascertained as the flower stalk bud is attached to the shortened stem. Additional key words: CAM; carbohydrate; chlorophyll fluorescence; flower stalk; gas exchange; oxygen evolution. - Phalaenopsis orchids are popular and valued potted ornamental plants worldwide for their beautiful longlasting flowers with a variety of shapes, sizes, and colors (Endo and Ikusima 1992, Chugh et al. 2009). In order to meet market demands, flowering time must be precisely scheduled. One of key steps in regulating Phalaenopsis flowering is to control the emergence of the flower stalk or spiking. Lowering of irradiance is a known strategy to delay spiking in Phalaenopsis (Kubota and Yoneda 1993, Wang 1995, Wang 1997, Hisamatsu et al. 2001, Liu et al. 2010, Wu et al. 2013). For example, Wang (1995) demonstrated that the spiking of Phalaenopsis cultured in a growth chamber was inhibited under irradiance of 8 μmol(photon) m2 s1 during a 12-h photoperiod or complete darkness for 6 weeks. Many studies have mentioned that the decrease in the sucrose concentration under lower irradiance may be an inhibitory signal for spiking, but their deduction was only based on the results from studies where new and fully expanded leaves were used (Konow and Wang 2001, Kataoka et al. 2004, Guo and Lee 2006, Tsai et al. 2008, Wu et al. 2013). Phalaenopsis is a monopodial orchid with thick leaves alternating on each side of the plant and the bases of leaves are connected to a shortened stem. One or two dormant spike buds emerge from the stem at the base of the third to fourth leaves that are numbered basipetally from the aerial portion of the plant (Sakanishi et al. 1980). Although the leaf is the site of light perception, it is reasonable to speculate that the signal in the stem of Phalaenopsis is involved more directly with spike development than with the leaf, because the spike bud is connected with the stem. To our knowledge, little is known about the relationships between carbohydrates, particularly, sucrose concentrations in the stem, and spiking inhibition of Phalaenopsis subjected to low irradiance. A reduction in photosynthesis by lowering of irradiance is axiomatic. Photosynthetic capacity can be investigated by noninvasive methods, such as net CO2 assimilation rate and chlorophyll (Chl) a fluorescence, and the invasive method, e.g., O2 evolution rate. Phalaenopsis is an obligate CAM plant with a day-night fluctuation of Materials and methods Plant material and growth conditions: Mature P. aphrodite subsp. formosana plants were purchased from the Wusulin Farm of the Taiwan Sugar Corp., Tainan County, southern Taiwan (23°34'N, 120°38'E) and transplanted in transparent plastic pots (10.5 cm) filled with sphagnum moss in an environment-controlled greenhouse at 28.0  1.2°C for four months in order to inhibit spiking. The plants with six leaves were then kept for six weeks in a growth chamber under a photoperiod with 14 h of light (06:0020:00) and 10 h of dark (20:0006:00) with 150 and 20 μmol(photon) m2 s1 of PAR supplied with cool-white fluorescence tubes (F20T12, GE Inc., Schenectady, NY, USA) at the tops of the plants for control (CK) or shade (SH) treatment, respectively. The day and night temperature for both treatments were 28.5  0.4 and 20.5  0.4°C, respectively. The plants were irrigated once a week, alternating between water and Peters fertilizer (1.0 g L1) (Hyponex Corp., Marys (...truncated)


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Y.-C. Liu, C.-H. Liu, Y.-C. Lin, C.-H. Lu, W.-H. Chen, H.-L. Wang. Effect of low irradiance on the photosynthetic performance and spiking of Phalaenopsis, Photosynthetica, 2016, pp. 259-266, Volume 54, Issue 2, DOI: 10.1007/s11099-016-0079-z