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Pitcher plants (Nepenthes sp.) are insectivorous angiosperm plants with modified leaves known as pitchers best known as acting as traps for insects. Pitcher plants are typically found under boggy conditions under both forest cover and open areas with very poor nutrient status, particularly N-status. The pitchers have low photosynthetic activity. The Chl a content of the pitcher tissue of both Nepenthes mirabilis (green and red) varieties was very low. Chl b/a ratios of the green variety phyllodes (lamina) and pitchers were ≈ 0.24 to 0.29. In the red variety, the mature phyllodes had a Chl b/a ratio ≈ 0.28 but both the pitchers and the young phyllodes had Chl b/a ratios of nearly 0.5. Photosynthetic electron transport (ETR) was measured using PAM technology. Phyllodes of both varieties showed photoinhibition at supra-optimal irradiances [Nepenthes mirabilis (green variety), Eopt ≈ 200-250 µmol photon m-2 s-1; red variety, Eopt ≈ 100-150 µmol photon m-2 s-1]. Pitchers had low optimum irradiances (Eopt ≈ 40-90 µmol photon m-2 s-1). Maximum ETR (ETRmax) of phyllodes of both varieties was low (ETRmax ≈ 50 µmol e- g-1 Chl a s-1); ETRmax was higher for pitchers on a Chl a basis (ETRmax ≈ 80-100 µmol e- g-1 Chl a s-1); a consequence of their low Chl a content on a surface area basis. ETRmax of cut disks of phyllodes did not respond strongly to incubation in NH4+, glutamate or aspartate as N-sources but did respond positively to added urea.

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RESUMEN

Although pulse amplitude modulation (PAM) fluorometry has revolutionized photosynthetic studies, Photosynthetic Electron Transport Rate (ETR) cannot be measured using PAM technology in some organisms. We compare in vivo absorbance information on a selection of photosynthetic organisms using an integrating sphere spectrophotometry on a variety of oxygenic and nonoxygenic photo-organisms and provide fluorescence data to help in understanding why PAM technology is unsuccessful on some organisms, particularly cyanobacteria. The study includes anoxygenic photosynthetic bacteria: Afifella marina, Rhodopseudomonas palustris and Thermochromatium which are all RC-2 type photosynthetic bacteria (Bacteriochlorophyll a or BChl a) which are known to have measureable delayed fluorescence, Yield and hence measureable ETR. The common unicellular green alga, Chlorella sp (Chl a + b) uses the same primary photosynthetic pigments as vascular plants. Comparisons are made to some other representative oxygenic unicellular organisms: Trebouxia (Chlorophyta, Chl a + b), Chaetoceros (a diatom, Chl a + c1 c2 ) and the unusual cyanobacterium Acaryochloris marina which has Chl d + a but uses Chl d as its primary photosynthetic pigment. Synechococcus R-2 (Cyanobacteria) has only Chl a. Its fluorescence is outside the range normally used for measuring photosynthesis using PAM technology: delayed fluorescence is not readily detectable.

RESUMEN

Launaea sarmentosa (Willd.) Sch. Bip ex Kunze (Asteracaeae) is a littoral sand dune herb found in the Indian Ocean region, used as a folk medicine and as a savory vegetable in Thailand. It is in the transition stage from a kitchen & cottage industry to a commercial proposition. Rapid light curves to measure the photosynthetic electron transport rate (ETR) were conducted on the plants over the course of daylight from 6:00 to 18:00 using a PAM fluorometer on plants grown under 50% (nominal) green horticultural and 20% black (nominal) shade cloth and in the open. Plants grown in the open were sun plants. Eopt (µmol photon m-2 s-1) decreased slightly under shade cloth (open air: 890 > green shade cloth, 778 > green shade cloth, 713). Launaea shows limited shade adaptation. ETR decreased under shade cloth on both a surface area and Chl a basis (µmol e- g Chl a-1 s-1) [open air: 388 > (green shade cloth, 209 = black shade cloth, 263)]. Maximum non-photochemical quenching (NPQmax) was significantly decreased under black shade cloth [(open air: 1.02 = green shade cloth, 0.969) > black shade cloth, 0.694]. ETR showed midday inhibition (9:00-15:00) when irradiance exceeded the Eopt of Launaea. Daily total photosynthetic electron transport was (mmol e- m-2 d-1): open air, 1890 ± 157; green shade cloth, 1620 ± 203, black shade cloth, 1217 ± 143. Green shade cloth has no effect on total daily photosynthetic electron transport of Launaea but offers some protection from desiccation and excessive evapotranspiration. Waterlogging decreases ETR by about 40%. Launaea can be grown watered with brackish (½ seawater) water unlike many other vegetables. Launeae is a physiologically undemanding cottage industry/market garden crop suitable for sandy coastline fishing communities.

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PAM fluorometry showed that the orchid Vanda sp (Gaud ex Pfitzers, Vandeae) had photosynthetic electron transport yields in leaves reaching ≈ 0.617 ± 0.262 at midday. Yield decayed exponentially as irradiance increased (Y½ = 128 ± 12.4 µmol photon m-2 s-1). Optimum irradiance (Eopt) for ETR (Photosynthetic Electron Transport Rate) was ≈ 369 ± 23.3 µmol photon m-2 s-1; the maximum photosynthetic ETR (ETRmax) (on a Chl a basis) ≈ 97.6 ± 3.76 µmol e-g-1 Chl a s-1. Rapid light curves exhibited classic photoinhibition at high irradiances: Vanda sp is a shade plant. Photosynthetic kinetics was strongly diurnal with minimal Eopt and ETRmax in the early morning, reaching a maximum at midday and decreasing in the afternoon. The aerial roots were normally photosynthetically dormant but rapidly activated when wet (homiochlorophyllous) then becoming dormant again after drying. Wet roots deliberately incubated under moist conditions had photosynthetic light curves comparable to leaves (Ymax ≈0.332, Y½ = ≈ 78.3 ± 27.8 µmol photons m-2 s-1, Eopt ≈ 278 µmol photons m-2 s-1 and ETRmax ≈ 317 ± 86.9 µmol e-g-1 Chl a s-1): wetting for only 15 min activated photosynthesis. Leaves showed a small degree of diurnal cycling of titratable acid but acid was accumulated in the early morning, not at night, this is a type of CAM-cycling. Titratable acid was low at sunrise (≈ 54.1 µmol H+g-1 FW), but increased until about 9 a.m. (≈ 137 µmol H+g-1 FW) and then gradually decreased over the course of the day.

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