Forty-four genotypes from the rice germplasm were identified under photoinhibition/photooxidation and shade conditions and divided into four basic types: (1) cultivars tolerant to both photooxidation and shading, (2) cultivars tolerant to photooxidation but sensitive to shading, (3) cultivars tolerant to shading but sensitive to photooxidation, and (4) cultivars sensitive to both photooxidation and shading. Photosynthetic characteristics of a cultivar tolerant (cv. Wuyugeng 3) and a cultivar sensitive (cv. Xiangxian) to photooxidation and shading were compared. The photochemical efficiency (Fv/Fm) of photosystem 2 (PS2) and the content of PS2-D1 protein in the tolerant cultivar Wuyugeng 3 decreased less under photooxidative conditions as compared with Xiangxian. Under similar conditions, superoxide dismutase was induced rapidly to a higher activity and the active oxygen (O-) built up to a lower level in Wuyugeng 3 than in Xiangxian. Net photosynthetic rate (PN) decreased by 23 % in Wuyugeng 3 vs. 64 % in Xiangxian. Shading (80 %) during the booting stage caused only small decreases (7-13 %) in ribulose-1,5-bisphosphate carboxylase activity and PN in Wuyugeng 3 but severe decreases (57-64 %) were observed in Xiangxian which corresponded to the decreases in grain yield of the two cultivars (38 and 73 %, respectively). We described a simple and effective screening method and physiological basis for breeding crops for enhanced tolerance to both high and low irradiance. and Demao Jiao, Xia Li.
The fundamental cause of down-regulation of photosynthesis at elevated carbon dioxide concentration (EC) is thought to be a slower rate of utilization of saccharides than their stimulated rate of production, but there are few studies directly supporting this idea under field conditions. We hypothesized that within Brassica oleracea, down-regulation would not occur in kohlrabi because it has a large sink for saccharides in an enlarged stem, but would occur in collards, which lack this sink. Field tests were consistent with this hypothesis. In collards, the degree of down-regulation of photosynthesis in plants grown at EC varied depending on the daily integral of photosynthetically active radiation (PAR) of the day prior to the measurement of photosynthetic capacity, as did leaf saccharide content. However, EC did not result in lower leaf contents of chlorophyll, soluble protein, ribulose-1,5-bisphosphate carboxylase, or nitrate in collards, nor was there any evidence of a triose phosphate utilization rate limiting photosynthesis. Experiments in controlled environment chambers confirmed that there was a threshold response for the down-regulation of photosynthesis in collards at EC to the PAR of the previous day, with down-regulation only occurring above a minimum daily integral of PAR. Down-regulation of photosynthesis could be induced in plants grown at ambient carbon dioxide by a single night at low temperature or by a single day with high PAR and EC. In the controlled environment study, the degree of down-regulation of photosynthesis was highly correlated with leaf glucose, fructose, and sucrose contents, and less well correlated with starch content. Hence down-regulation of photosynthesis at EC in collards in the field represented feedback inhibition from the accumulation of soluble saccharides and day-to-day variation in its occurrence was predictable from the weather. and J. A. Bunce, R. C. Sicher.
Chlorophyll (Chl) a fluorescence transient and 820-nm transmission kinetic were investigated to explore the development of photosynthetic apparatus in grapevine leaves from emergence to full expansion. In this study, all leaves at various developing stages exhibited typical Chl a fluorescence transient. In newly initiating leaves, the maximum quantum yield of primary photochemistry (ϕP0) was slightly lower (<10 %) than that in fully expanded leaves. Nevertheless, the fluorescence rise from O to J step was clearly speeded up in young leaves compared with that in fully expanded leaves. Additionally, a distinct K step appeared in young leaves at high irradiances. With leaf development, the efficiency that a trapped exciton can move an electron into the electron transport chain further than QA - (Ψ0), the quantum yield of electron transport beyond QA (ϕE0), electron transport flux per excited cross section (ET0/CS0), the amount of active photosystem (PS) 2 reaction centres per excited cross section (RC/CS0), and the performance index on cross section basis (PICS) increased gradually and rapidly. Young leaves had strikingly lower amplitude of transmission at 820 nm. A linear relationship between Ψ0 and the transmission at 820 nm (I30/I0) was evident. Based on these data, we suggest that (1) the primary photochemistry of PS2 may be not the limiting step of the photosynthetic capacity during leaf growth under natural irradiance; (2) oxygen evolving complex (OEC) might be not fully connected to PS2 at the beginning of leaf growth; (3) though there are a few functional PS1 and PS2 at the early stages of leaf development, they match perfectly. and C.-D. Jiang ... [et al.].
Field studies of gas exchange and chlorophyll fluorescence of three desert shrub species, Hedysarum fruticosum var. mongolicum, Artemisia ordosia, and Salix pasmmophylla, showed different patterns under different leaf temperature (T1) and incident photosynthetic photon flux density (PPFD). H. fruticosum var. mongolicum and A. ordosia exhibited higher PN and gs than S. pasmmophylla, especially under very high T1 (>46 °C) and high PPFD (>2 100 µmol m-2 s-1) in hot summer. The decreases of PN with the diurnal course were due mainly to stomata closure. However, PN of S. pasmmophylla was seriously depressed by very high temperature from midday to evening as shown by the negative PN in hot summer, whereas none of such depression was found in spring. Maximal spring photochemical efficiency of photosystem 2 (PS2), i.e, Fv/Fm, was the lowest at 16:00, indicating the injury of PS2 by heat at this stage. In hot summer again, all the three shrubs underwent pronounced midday depression of PN and gs, while in spring they showed a one-peak response. And the first peak appeared 2 h earlier in hot summer than in spring for all the three shrubs. It was the high temperature that led to the different patterns of gas exchange and the serious depression of PN in S. pasmmophylla. H. fruticosum var. mongolicum and A. ordosia were much more tolerant to heat and high irradiance than S. pasmmophylla, which fixed most of CO2 at the fast growing stage in spring. Nevertheless, in hot summer it had to survive the severe hot environment through strong respiration and storage of CO2 only in the early morning. and G. M. Jiang, G. J. Zhu.
In addition to other factors, high altitude (HA) environment is characterized by high photosynthetic photon flux density (PPFD). Photosynthetic characteristics of wild and cultivated plants were studied at different irradiances at Losar, India (altitude 4 200 m). Wild plants were tolerant to high PPFDs. Slopes of curve between net photosynthetic rate (PN) and intercellular CO2 concentration
(Ci) or stomatal conductance (gs) increased with increase in irradiance suggesting insensitivity or tolerance of these plants to higher PPFD. Cultivated plants, however, were sensitive to higher PPFD, their slopes of curves between PN and Ci or gs decreased with increased PPFD. Tolerance or insensitivity to higher PPFD was an important parameter affecting plant performance at HA. and N. Kumar, S. Kumar, P. S. Ahuja.
The acclimation depression of capacity of photon utilisation in photochemical reactions of photosystem 2 (PS2) can develop already after three months of cultivation of the Norway spruces (Picea abies [L.] Karst.) under elevated concentrations of CO2 (i.e., ambient, AC, + 350 µmol(CO2) mol-1 = EC) in glass domes with adjustable windows. To examine the role that duration of EC plays in acclimation response, we determined pigment contents, rate of photosynthesis, and parameters of chlorophyll a fluorescence for sun and shade needles after three seasons of EC exposure. We found responses of shaded and exposed needles to EC. Whereas the shaded needles still profited from the EC and revealed stimulated electron transport, for the exposed needles the stimulation of both electron transport activity and irradiance saturated rate of CO2 assimilation (PNmax) under EC already disappeared. No signs of the PS2 impairment were observed as judged from high values of potential quantum yield of PS2 photochemistry (FV/FM) and uniform kinetics of QA reoxidation for all variants. Therefore, the long-term acclimation of the sun-exposed needles to EC is not necessarily accompanied with the damage to the PS2 reaction centres. The eco-physiological significance of the reported differentiation between the responses of shaded and sun exposed needles to prolonged EC may be in changed contribution of the upper and lower crown layers to the production activity of the tree. Whereas for the AC spruces, PNmax of shaded needles was only less than 25 % compared to exposed ones, for the EC spruces the PNmax of shaded needles reached nearly 40 % of that estimated for the exposed ones. Thus, the lower shaded part of the crown may become an effective consumer of CO2. and J. Kalina ... [et al.].
The plants of Prosopis juliflora growing in northern India are exposed to large variations of temperature, vapour pressure deficits (VPD), and photosynthetic photon flux density (PPFD) throughout the year. Under these conditions P. juliflora had two short periods of leaf production, one after the winter season and second after summer, which resulted in two distinct even aged cohorts of leaves. In winter with cold nights (2-8 °C) and moderate temperatures during the day, the plants showed high rates of photosynthesis. In summer the midday temperatures often reached <45 °C and plants showed severe inhibition of photosynthesis. The leaves of second cohort appeared in July and showed typical midday depression of photosynthesis. An analysis of diurnal partitioning of the absorbed excitation energy into photochemistry showed that a smaller fraction of the energy was utilised for photochemistry and a greater fraction was dissipated thermally, further the photon utilisation for photochemistry and thermal dissipation is largely affected by the interaction of irradiance and temperature. The plants showed high photochemical efficiency of photosystem 2 (PS2) at predawn and very little photoinhibition in all seasons except in summer. The photoinhibition in summer was pronounced with very poor recovery during night. Since P. juliflora exhibited distinct pattern of senescence and production of new leaves after winter and summer stress period, it appeared that the ontogenic characteristic together with its ability for safe dissipation of excess radiant energy in P. juliflora contributes to its growth and survival. and P. A. Shirke, U. V. Pathre.
Diurnal courses in net photosynthetic rate (PN), stomatal conductance (gs), leaf water potential (ψ), internal CO2 concentration (ci), and water use efficiency (WUE) were studied as season progressed, in relation to environmental factors in field grown Prunus amygdalus. In sun leaves PN reached maximum between 09:00 to 11:00 h and subsequently declined when high temperature and low humidity occurred. An increase was observed late in the afternoon. A decrease in gs and ψ was found as season progressed in both years of measurements. In periods of high evaporative demand, ψ was very low, however, it did not explain the reductions of PN in all the three periods (spring, early and late summer). Midday depression of PN and gs seemed to be related with leaf temperature (Tl) and high irradiance. Increase in ci and F0 and decrease in Fv/Fm found between 12:00 and 14:00 h corresponded to the decrease in PN. Therefore, a transient modification of photosynthetic machinery might be considered. WUE was negatively correlated with vapour pressure difference of leaf to air, that decreased during the day. The September values, higher than in the previous months, were due to the lower seasonal decreases in PN than in gs. and M. C. Matos ... [et al.].
Diurnal changes in net photosynthetic rate (PN), chlorophyll (Chl) fluorescence, and stomatal aperture of several hybrid poplar clones subjected to midday light stress were measured in July and August of 1996. Midday depression of PN, photosystem 2 (PS2) efficiency, stomatal conductance (gs), and stomatal aperture was observed in all clones, though at differing rates among them. Non-uniform stomatal closure occurred at noon and at other times, requiring a modification of intercellular CO2 concentration (C1). A linear relationship was found between gs and stomatal aperture. More than half of the photons absorbed by PS2 centre dissipated thermally when subjected to light stress at noon. There was a linear relationship between the rate of PS2 photochemical electron transport (PxPFD) and PN. There was a consensus for two fluorescence indicators (1 - qP/qN and (Fm' - F)/Fm') in assessment of susceptibility of photoinhibition in the clones. According to PN, Chl fluorescence, and stomatal aperture, we conclude that midday depression of photosynthesis can be attributed to both stomatal and non-stomatal limitations. and Shouren Zhang, Rongfu Gao.
Chlorophyll (Chl) fluorescence of warm day/cool night temperature exposed Phalaenopsis plants was measured hourly during 48 h to study the simultaneous temperature and irradiance response of the photosynthetic physiology. The daily pattern of fluorescence kinetics showed abrupt changes of photochemical quenching (qP), non-photochemical quenching (NPQ) and quantum yield of photosystem II electron transport (ΦPSII) upon transition from day to night and vice versa. During the day, the course of ΦPSII and NPQ was related to the air temperature pattern, while maximum quantum efficiency of PSII photochemistry (Fv/Fm) revealed a rather light dependent response. Information on these daily dynamics in fluorescence kinetics is important with respect to meaningful data collection and interpretation. and B. Pollet ... [et al.].