Low growth temperature inhibition of photosynthesis in cotyledons of jack pine seedlings (Pinus banksiana) is due to impaired chloroplast development

Abstract

Cotyledons of jack pine seedlings (Pinus banksiana Lamb.) grown from seeds were expanded at low temperature (5°C), and total Chl content per unit area of cotyledons in these seedlings was only 57% of that observed for cotyledons on 20°C-grown controls. Chl a/b ratio of 5°C-grown jack pine was about 20% lower (2.3 ± 0.1) than 20°C controls (2.8 ± 0.3). Separation of Chl-protein complexes and SDS-PAGE indicated a significant reduction in the major Chl a containing complex of PSI (CP1) and PSII (CPa) relative to LHCII1 in 5°C compared to 20°C-grown seedlings. In addition, LHCII1/LHCII3 ratio increased from 3.8 in control (20°C) to 5.5 in 5°C-grown cotyledons. Ultrastructurally, 5°C-grown cotyledons had chloroplasts with swollen thylakoids as well as etiochloroplasts with distinct prolamellar bodies. Based on CO2-saturated O2 evolution and in vivo Chl a fluorescence, cotyledons of 5°C jack pine exhibited an apparent photosynthetic efficiency that was 40% lower than 20°C controls. Seedlings grown at 5°C were photoinhibited more rapidly at 5°C and 1200 µmol·m–2·s–1 than controls grown at 20°C, although the final extent of photoinhibition was similar. Exposure to high light at 5°C stimulated the xanthophyll cycle in cotyledons of both controls and 5°C-grown seedlings. In contrast to winter cereals, we conclude that growth of jack pine at 5°C impairs normal chloroplast biogenesis, which leads to an inhibition of photosynthetic efficiency.Key words: chloroplast, growth, temperature, photosynthesis, photoinhibition, Pinus banksiana Lamb., ultrastructure.

Increased Air Temperature during Simulated Autumn Conditions Does Not Increase Photosynthetic Carbon Gain But Affects the Dissipation of Excess Energy in Seedlings of the Evergreen Conifer Jack Pine

“…2C). Previous work also showed that a higher amount of aggregated LHCs is associated with improved photoprotection in overwintering evergreens and other plants (Horton et al, 1991;Ruban et al, 1993;Ottander et al, 1995;Gilmore and Ball, 2000;Krol et al, 2002). Reorganization of pigment-protein complexes, which is indicated by an increased aggregation state of LHCII, was observed in all but the LD/HT control treatment (Fig.…”

“…Thylakoids of fresh needles were isolated at 4°C according to Krol et al (2002) by grinding needles in 50 mM Tricine, pH 7.8, containing 0.4 M sorbitol, 10 mM NaCl, 5 mM MgCl 2 , and 20% (w/v) polyethylene glycol 4000. The ground samples were filtered through Miracloth, followed by three washing steps in double-distilled water, 1 mM EDTA, and washing buffer, containing 50 mM Tricine, pH 7.8, 10 mM NaCl, and 5 mM MgCl 2 by centrifugation at 4°C at 5,000g for 10 min.…”

“…Extracts were separated by HPLC with a Spherisorb ODS-1 analytical column (S.P.E. ), modified from Gilmore and Yamamoto (1991) as described in detail by Krol et al (2002). Total Chl and total carotenoids were estimated spectrophotometrically according to Lichtenthaler (1987).…”

Buildup of Screening Pigments and Resistance of Plants to Photodamage

“…The second function has at least two environmentally important consequences -when the water potential of the epidermis is lowered, two environmental stresses can be avoided: ice nucleation via freezing events on the leaf surface and drought. As speculated by Krol et al (2002), the phenomenon of anthocyanin buildup in young Pinus seedlings "may somehow help them establish under a suite of suboptimal environmental conditions including photooxidation, low temperature, water and nutrient stress." Steyn et al (2009) argued that anthocyanins afford photoprotection to peel during low-temperature-induced light stress in apple (MalusÂdomestica L.) and pear (Pyrus communis L.) and that the protection is not a fortuitous side effect of light absorption by anthocyanin.…”

“…Additional evidence for the participation of anthocyanins in the development of cross-resistance to high light under chilling stress was obtained from studies on jack pine (Pinus banksiana Lamb.) seedlings subjected to variable excitation pressures (Krol et al 2002). Seedlings acclimated at 5 C accumulated anthocyanins in needles exposed to 250 mmol m À2 s À1 PAR and UV radiation.…”