Article

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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