Chlorophylls and Carotenoids during Leaf Ontogeny

We examined photosynthetic activities and thermostability of photosystem 2 (PS2) in leaves of elm (Ulmus pumila) seedlings from initiation to full expansion. During leaf development, net photosynthetic rate (P N ) increased gradually and reached the maximum when leaves were fully developed. In parallel with the increase of P N , chlorophyll (Chl) content was significantly elevated. Chl a fluorescence measurements showed that the maximum quantum yield of PS2 (φ PS2 ), the efficiency a trapped exciton, moved an electron into the electron transport chain further than Q A -(Ψ o ), and the quantum yield of electron transport beyond Q A (φ Eo ) increased gradually. These results were independently confirmed by our low irradiance experiments. When subjected to progressive heat stress, the young leaves exhibited considerably lower φ PS2 and higher minimal fluorescence (F 0 ) than the mature leaves, revealing the highly sensitive nature of PS2 under heat in the newly initiating leaves. Further analysis showed that PS2 structure in the newly initiating leaves was strongly altered under heat, as evidenced by the increased fluorescence signals at the position of the K step. We therefore demonstrated an inhibition in the oxygen-evolving complex (OEC) in the young leaves. This resulted in decrease in amount of the functional PS2 reaction centres and relative increase in the PS2 reaction centres with inhibited electron transport at the acceptor side under heat. We suggest that the enhanced thermostability of PS2 during leaf development is associated with improved OEC stability.Additional key words: chlorophyll a fluorescence; JIP-test; leaf growth; thermostability of photosystem 2.

Section: Development Of Ps2 Complexsupporting

confidence: 92%

Enhanced photosystem 2 thermostability during leaf growth of Elm (Ulmus pumila) seedlings

Jiang¹,

Wang²,

Li³

et al. 2006

“…Photosynthetic activity during leaf ontogeny surprisingly did not correlate with the decrease in total Chl content and photochemical efficiency, as it is frequently seen in ex vitro plants (Šesták 1985, Gratani and Ghia 2002, Lu et al 2003, Yoo et al 2003. In contrast, in our experiments P N in all the treatments exhibited the typical ontogenetic course (cf.…”

Section: --contrasting

confidence: 40%

Excess irradiance causes early symptoms of senescence during leaf expansion in photoautotrophically in vitro grown tobacco plants

Radochová¹,

Tichá²

2008

Photosynthetic parameters, growth, and pigment contents were determined during expansion of the fourth leaf of in vitro photoautotrophically cultured Nicotiana tabacum L. plants at three irradiances [photosynthetically active radiation (400-700 nm): low, LI 60 μmol m -2 s -1 ; middle, MI 180 μmol m -2 s -1 ; and high, HI 270 μmol m -2 s -1 ]. During leaf expansion, several symptoms usually accompanying leaf senescence appeared very early in HI and then in MI plants. Symptoms of senescence in developing leaves were: decreasing chlorophyll (Chl) a+b content and Chl a/b ratio, decreasing both maximum (F V /F M ) and actual (Φ PS2 ) photochemical efficiency of photosystem 2, and increasing non-photochemical quenching. Nevertheless, net photosynthetic oxygen evolution rate (P N ) did not decrease consistently with decrease in Chl content, but exhibited a typical ontogenetic course with gradual increase. P N reached its maximum before full leaf expansion and then tended to decline. Thus excess irradiance during in vitro cultivation did not cause early start of leaf senescence, but impaired photosynthetic performance and Chl content in leaves and changed their typical ontogenetic course.Additional key words: chlorophyll a fluorescence; leaf area; leaf dry mass; leaf ontogeny; net oxygen evolution rate; Nicotiana; photosynthesis. --In vitro plants are usually grown under high relative humidity, low irradiance (usually 50-60 μmol m -2 s -1 ), and low CO 2 concentration. These conditions may result in low photosynthetic activity of the plants, therefore the cultivation media are often supplemented by saccharides as carbon and energy sources (e.g. Pospíšilová et al. 1992, Hazarika 2006. This may cause bacterial and fungal contamination of the saccharose containing media and changes during transfer of plants from in vitro culture to soil (Preece and Sutter 1991). Current research concentrates on the development of photoautotrophic systems in which the sugar content in the medium is reduced or eliminated and CO 2 concentration and irradiance are increased (Kozai 1991, Düring and Harst 1996, Nguyen et al. 1999, Sha Valli Khan et al. 2003, Teixeira Da Silva et al. 2006. However, application of high irradiance during cultivation is limited by susceptibility to photoinhibition of both photoautotrophically (Tichá et al. 1998, Kadleček et al. 2003 and photomixotrophically (Serret et al. 1996(Serret et al. , 2001 in vitro grown plants.Chronic photoinhibition was found in in vitro photoautotrophically cultured plants already at irradiance of 200 μmol m -2 s -1 (Tichá et al. 1998) and was demonstrated as decreased efficiency and/or decreased maximum rate of photosynthesis, decreased Chl a+b content and Chl a/b ratio, increased content and de-epoxidation state of xanthophyll cycle pigments, decreased both maximum and actual photochemical efficiency of photosystem 2 (PS2), and increased non-photochemical quenching (NPQ) (Tichá et al. 1998, Kadleček et al. 2003.The symptoms of photoinhibition mentioned above are similar to the symptoms o...

“…Thus, higher Chl a/b (>3) in adult leaves would be related to a larger photochemical capacity of PS2 as compared to expanding leaves. Values of Chl a/b above three are considered typical for adult, healthy, sunny leaves (Šesták 1985(Šesták , Hagg et al 1992. The content of Car followed the trend of the Chl (a+b) content, showing an increase with leaf age (Fig.…”

Section: Resultsmentioning

confidence: 99%

Leaf characteristics and diurnal variation of chlorophyll fluorescence in leaves of the 'bana' vegetation of the amazon region

Sobrado¹

2008

In six dominant species of the Amazonian 'Bana' vegetation, leaf blade characteristics, pigment composition, and chlorophyll (Chl) fluorescence parameters were measured in young and mature leaves under field conditions. Leaf δ 13 C was comparable in the six species, which suggested that both expanding and expanded leaves contained organic matter fixed under similar intercellular and ambient CO 2 concentration (C i /C a ). High leaf C/N and negative δ 15 N values found in this habitat were consistent with the extreme soil N-deficiency. Analysis of Chl and carotenoids showed that expanding leaves had an incomplete development of photosynthetic antenna when compared to adult leaves. Dynamic inactivation of photosystem 2 (PS2) at midday was observed at both leaf ages as F v /F m decreased compared to predawn values. Adult leaves reached overnight F v /F m ratios typical of healthy leaves. Overnight recovery of F v /F m in expanding leaves was incomplete. F 0 remained unchanged from midday to predawn and F v tended to increase from midday to predawn. The recovery from midday depression observed in adult leaves suggested an acclimatory down-regulation associated with photo-protection and non-damage of PS2.