Photosynthesis in Pineapple (Ananas comosus comosus [L.] Merr) Measured Using PAM (Pulse Amplitude Modulation) Fluorometry

Tropical Plant Biology 3(4):193-203. DOI: 10.1007/s12042-010-9057-y

ABSTRACT PAM (Pulse Amplitude Modulation) fluorometer techniques directly measure the light reactions of photosynthesis that are otherwise difficult to estimate
in CAM (Crassulacean Acid metabolism) plants such as pineapple (Ananas comosus comosus cv. Phuket). PAM machines calculate photosynthesis as the Electron Transport Rate (ETR) through PSII (4 electrons per O2 produced) as molm−2s−1. P vs. E curves fitted the waiting-in-line function (an equation of the form ETR = ( ETR max E/Eopt ).e1 - E/Eopt {\hbox{ETR}} = \left( {{\hbox{ET}}{{\hbox{R}}_{{ \max }}} \times {\hbox{E}}/{{\hbox{E}}_{\rm{opt}}}} \right).{{\hbox{e}}^{{1} - {\rm{E}}/{\rm{Eopt}}}} ) allowing half-saturating and optimal irradiances (Eopt) to be estimated. Effective Quantum Yield (Ymax), Electron Transport Rate (ETRmax) and the Non-Photochemical Quenching parameter, NPQmax all vary on a diurnal cycle but the parameter qNmax does not show a systematic variation over a diurnal period. Phuket pineapple is a “sun plant” with Optimum Irradiance (Eopt) from 755 to 1,130μmolm−2s−1 (400–700nm) PAR but photosynthetic capacity is very low in the late afternoon even though light conditions are favourable
for rapid photosynthesis. Total CO2 fixed nocturnally as C4-dicarboxylic acids by leaves of the Phuket pineapple was only ≈0.14gC m−2 d−1 (0.012mol C m−2 d−1). Titratable acid of leaves was depleted about 3pm (15:00) and shows a classical CAM diurnal cycle. The Phuket pineapple
variety only stored enough CO2 as C4 acids to account for only about 2.5% of photosynthesis (Pg) estimated using the PAM machine (≈5.6gC m−2 d−1). Phuket pineapples are classifiable as CAM-Cycling plants but nocturnal fixation of CO2 is so low compared to the more familiar Smooth Cayenne variety that it probably recycles only a small proportion of the respiratory
CO2 produced in leaves at night and so even CAM-cycling is only of minor importance to the carbon economy of the plant. Unlike
the Smooth Cayenne pineapple variety, which fixes large amounts of CO2 nocturnally, the Phuket pineapple is for practical purposes a C3 plant.

KeywordsPineapple-Cultivar Phuket-CAM photosynthesis-Carbon fixation-Diurnal cycle-Gross photosynthesis-PAM fluorometry-PAR-Primary productivity

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    ABSTRACT: Photosynthetic bacteria are attractive for biotechnology because they produce no oxygen and so H2-production is not inhibited by oxygen as occurs in oxygenic photoorganisms. Rhodopseudomonas palustris and Afifella marina containing BChl a can use irradiances from near-UV-violet (VNUV) to orange (350-650 nm) light and near-infrared (NIR) light (762-870 nm). Blue-diode-based PAM (Pulse Amplitude Modulation) technology was used to measure their photosynthetic electron transport rate (ETR). ETR vs. Irradiance curves fitted the waiting-in-line model (ETR = (ETRmax×E/Eopt) × exp (1-E/Eopt)). The equation was integrated over pond depth to calculate ETR of Afifella and Rhodopseudomonas in a pond up to 30 cm deep (A376, 1 cm = 0.1). Afifella saturates at low irradiances and so photoinhibition results in very low photosynthesis in a pond. Rhodopseudomonas saturates at ≈ 15% sunlight and shows photoinhibition in the surface layers of the pond. Total ETR is ≈ 335 mol (e-) m-2 s-1 in NUV+PAR light (350-700 nm). Daily ETR curves saturate at low irradiances and have a square-wave shape: ≈ 11-13 mol (e-) m-2 d-1 (350-700 nm). Up to 20-24% of daily 350-700 nm irradiance can be converted into ETR. NIR is absorbed by water and so competes with the bacterial RC-2 photosystem for photons. This article is protected by copyright. All rights reserved.
    Photochemistry and Photobiology 06/2013; · 2.29 Impact Factor
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