The effects of shade on the growth, leaf photosynthetic characteristics, and chlorophyll (Chl) fluorescence parameters of Lycoris radiata var. radiata were determined under differing irradiances (15, 65, and 100% of full irradiance) within pots. The HI plants exhibited a typical decline in net photosynthetic rate (PN) during midday, which was not observed in MI- and LI plants. This indicated a possible photoinhibition in HI plants as the ratio of variable to maximum fluorescence (Fv/Fm) value was higher and the minimal fluorescence (F0) was lower in the, and LI plants. Diurnal patterns of stomatal conductance (gs) and transpiration rate (E) were remarkably similar to those of PN at each shade treatments, and the intercellular CO2 concentration (Ci) had the opposite change trend. Under both shading conditions, the light saturation point, light compensation point and photon-saturated photosynthetic rate (Pmax) became lower than those under full sunlight, and it was the opposite for the apparent quantum yield (AQY). The higher the level of shade, the lower the integrated daytime carbon gain, stomatal and epidermis cell densities, specific leaf mass (SLM), bulb mass ratio (BMR), leaf thickness, and Chl a/b ratio. In contrast, contents of Chls per dry mass (DM), leaf area ratio (LAR), leaf mass ratio (LMR), leaf length, leaf area and total leaf area per plant increased under the same shade levels to promote photon absorption and to compensate for the lower radiant energy. Therefore, when the integrated daytime carbon gain, leaf area and total leaf area per plant, which are the main factors determining the productivity of L. radiata var. radiata plant, were taken into account together, this species may be cultivated at about 60-70% of ambient irradiance to promote its growth. and S. B. Zhou ... [[et al.].
The photosynthetic performances of regenerated protoplasts of Bryopsis hypnoides, which were incubated in seawater for 1, 6, 12, and 24 h, were studied using chlorophyll (Chl) fluorescence and oxygen measurements. Results showed that for the regenerated protoplasts, the pigment content, the ratios of photosynthetic rate to respiration rate, the maximal photosystem II (PSII) quantum yield (Fv/Fm), and the effective PSII quantum yield (ΦPSII) decreased gradually along with the regeneration progress, indicated that during 24 h of regeneration there was a remarkable reduction in PSII activity of those newly formed protoplasts. We assumed that during the cultivation progress the regenerated protoplasts had different photosynthetic vigor, with only some of them able to germinate and develop into mature thalli. The above results only reflected the photosynthetic features of the regenerated protoplasts at each time point as a whole, rather than the actual photosynthetic activity of individual aggregations. Further investigation suggested a relationship between the size of regenerated protoplasts and their viability. The results showed that the middle-sized group (diameter 20-60 μm) retained the largest number of protoplasts for 24 h of growth. The changes in Fv/Fm and ΦPSII of the four groups of differently sized protoplasts (i.e. < 20, 20-60, 60-100, and > 100 μm) revealed that the protoplasts 20-60 μm in diameter had the highest potential activity of the photosynthetic light energy absorption and conversion for several hours. and F. Lü, G. C. Wang, J. F. Niu.
Photosynthetic irradiance response of vegetative and reproductive structures of the green-flowered deciduous perennial green hellebore was studied by the comparative use of chlorophyll (Chl) fluorescence techniques and gas exchange measurements. All the Chl-containing organs (leaves, sepals, stalks, and fruits) examined were photosynthetically active showing high intrinsic efficiencies of photosystem 2 (Fv/Fm: 0.75-0.79) after dark adaptation. Even in the smaller fertile and sterile parts of the flower (nectaries and anthers) a remarkable photosynthetic competence was detected. With increasing photon flux densities (PFD) electron transport rates, actual quantum yields, and photochemical quenching coefficients of the main photosynthetic organs decreased in the order: leaf>sepal>fruit>stalk. At moderate to high PFDs the sepals achieved maximum electron transport rates corresponding to about 80 % of concomitant mature leaves. In contrast, maximum net photosynthetic rate of the sepals [2.3 μmol(CO2) m-2 s-1] were less than one fourth of the leaves [10.6 μmol(CO2) m-2 s-1]. This difference is explained by a 70-80 % lower stomatal density of sepals in comparison to leaves. As the basal leaves emerge late during fruit development, the photosynthetically active sepals are a major source of assimilates, contributing more than 60 % of whole-plant CO2 gain in early spring. The ripening dehiscent fruits are characterized by an effective internal re-fixation of the respirational carbon loss and thus additionally improve the overall carbon budget. and G. Aschan ... [et al.].
Photosynthesis and leaf traits of five species in genus Cypripedium were compared in natural habitats and transplant nursery to develop effective strategy for cultivation and conservation. Among five species, C. guttatum had the highest photosynthetic capacity
(PNmax) in the natural habitat and nursery, while C. lichiangense the lowest. The differences in PNmax among species were correlated with leaf N content (LNC) and leaf dry mass per unit area (LMA). After transplanting from natural habitats to nursery, the
PNmax of C. lichiangense and C. yunnanense decreased, that of C. guttatum increased, while those of C. flavum and C. tibeticum remained relatively constant. The variations in LNC and biochemical efficiency would be responsible for the differences in
PNmax between plants in natural habitats and in the nursery, but not the relative stomatal limitation. After transplanting, the Fv/Fm of C. lichiangense and C. yunnanense were declined. Meanwhile, the temperature ranges maintaining 90 % PNmax of C. lichiangense and C. yunnanense were narrower than those of the other three species. Thus the biochemical process in five species played a major role in the differences of PNmax after transplanting, and the widespread species had higher photosynthetic adaptability than the narrow-spread species. and S.-B. Zhang ... [et al.].
The thermo-sensitivity of two new pea (Pisum sativum L.) cultivars-Afila (mutant in the gene transforming leaves into mustaches) and Ranen (mutant for early ripening)-as compared to the control cultivar Pleven-4 to either low (4 °C, T4) or high temperature (38 °C, T38) was investigated by means of chlorophyll (Chl) fluorescence kinetics. The low temperature treatment decreased the photosynthetic activity, measured via a decline of the Chl fluorescence decrease ratios RFd690 and RFd735, and this was mainly due to a decline of the Chl fluorescence decrease parameter Fd and maximum Chl fluorescence Fm. In the new cv. Ranen the RFd ratios at first decreased and increased again after 24-h exposure to 4 °C, indicating its good acclimation ability to low temperature. The cold-induced changes in the photosynthetic performance of all cultivars were reversed after transferring plants back to 23 °C for 48 h. In the Chl and carotenoid (Car) contents no or little changes occurred during the T4 treatment, except for a slight but clear increase of the ratio Chl a/b and a decrease in the ratio Chl/Car. In contrast to this, the T38 treatment for 72 h decreased the RFd ratios more strongly than the T4 exposure did. In fact, an irreversible injury of the photosynthetic apparatus was caused in the control pea cv. Pleven-4 by a 48-h T38 exposure and for the new cv. Afila after a 72-h T38 exposure. In contrast, the cv. Ranen was less and little sensitive to the T38 exposure. In the heat-sensitive cvs. Pleven-4 and Afila, the decrease in RFd values at T38 was associated with a strong decline of the Chl a+b and total Car contents. The Chl a+b decline could also be followed via an increase of the Chl fluorescence ratio F690/F735. Parallel to this, a strong decline of Chl a/b from ca. 3.0 (range 2.85-3.15) to ca. 1.9 (range 1.85-1.95) occurred indicating a preferential decline of the Chl a-pigment proteins but not of the Chl a/b-pigment protein LHC2. In the relatively heat-tolerant cv. Ranen, however, the ratio Chl a/b declined only partially. After the T4 treatment the stress adaptation index Ap was higher in cv. Ranen than in controls and reached in heat-treated Ranen plants almost the starting value indicating a cold and heat stress hardening of the treated plants. The Chl fluorescence parameters and pigment contents were influenced by T38 and T4 treatments in various ways indicating that the mechanisms of low and high temperature injury of the photosynthetic apparatus are different. The new cv. Ranen exhibited a cross tolerance showing a fairly good acclimation ability to both T4 and T38, hence it is a very suitable plant for outdoor growth and for clarification of the accl, imation mechanisms to unfavourable temperatures., and K. Georgieva, H. K. Lichtenthaler.
The poikilochorophyllous, desiccation-tolerant (PDT) angiosperm, Pleurostima purpurea, normally occurs in less exposed rock faces and slightly shady sites. Our aim was to evaluate the light susceptibility of the photosynthetic apparatus during dehydration-rehydration cycle in P. purpurea. In a controlled environment, the potted plants were subjected to water deficit under two different photosynthetic photon flux densities [PPFD, 100 and 400 μmol(photon) m-2 s-1]. In the higher PPFD, net photosynthetic rate (PN) become undetectable after stomata closure but photochemical efficiency of photosystem II, electron transport rate, and photochemical quenching coefficient were maintained relatively high, despite a partial decrease. The photochemical activity was inhibited only after the complete loss of chlorophylls, when leaf relative water content dropped below 72% and total carotenoids reached maximal accumulation. Nonphotochemical energy dissipation increased earlier in response to dehydration under higher PPFD. PN and photochemical activity were fully recovered after rehydration under both light treatments. Our results suggested that the natural occurrence of P. purpurea should not be restricted by the light intensity during the complete desiccation-rehydration cycles., S. T. Aidar, S.T. Meirelles, R. F. Oliveira, A. R. M. Chaves, P. I. Fernandes-Júnior., and Obsahuje bibliografii
The physiological response of two soybean varieties to salt stress was examined. The results showed that salt stress induced a significantly (p<0.01) lower decrease of the net photosynthetic rate (PN) in salt-tolerant S111-9 than in salt-sensitive Glycine max. PN decrease was positively related to the decrease of stomatal conductance (gs) and intercellular CO2 concentration (Ci) in S111-9, while with g s in G. max. a threshold of relative water content (RWC) was found, above which a slight decrease in RWC lead to a sharp reduction in gs. The photochemical quenching (qP), the efficiency of open PSII centers (ΦPSII) and the Rubisco activity (RA) significantly decreased with increasing salinity level in G. max. The maximum PSII quantum yield (Fv/Fm) decreased significantly under the highest NaCl in both varieties. The higher reduction of RA in G. max was attributed to Rubisco content, which was mainly regulated at LSU expression level rather than at rbcL transcript level. These findings led us to conclude that the salt-induced reduction in PN was mainly due gs and RA for S111-9 and G. max, respective. and K. X. Lu ... [et al.].
We investigated the characteristics of gaseous exchanges and chlorophyll a fluorescence under different irradiances in two liana species Canavalia parviflora Benth. (Fabaceae) and Gouania virgata Reissk (Rhamnaceae), both of a semi-deciduous tropical forest of Southeast Brazil. We used cultivated plants growing under irradiances of 100, 40, 10, and 1.5 % of the photosynthetic photon flux density (PPFD). Higher net photosynthetic rates (PN) were observed during early morning under full sunlight. After this, reduced PN values were recorded due to pronounced stomatal closure. In Canavalia, the gas exchange responses diminished concomitant with reduced irradiance. Gouania exhibited a narrower range of response, with high PN values even at 10 % PPFD. Marked reduction of the effective photochemical yield (ΔF/Fm') near midday was observed, followed by increases in the non-photochemical quenching for both species under full sunlight. Despite the common occurrence of these species in open areas of the forest, both were able to maintain relatively high PN in shaded environments. We suggest that lianas present an intermediate physiological behaviour between shade and non-shade tolerant species. and M. C. Sanches, I. F. M. Válio.
Gas exchange, chlorophyll (Chl) fluorescence, and contents of some metabolites in two genotypes of jasmine (Jasminum sambac), single petal (SP) and double petal (DP) one, were analyzed during dehydration and re-hydration. Water stress significantly decreased net photosynthetic rate, stomatal conductance, and maximum photochemical efficiency (Fv/Fm) in both jasmine genotypes, but increased minimum fluorescence (F0) only in DP-jasmine. Water stress also decreased starch content, while increased contents of total soluble sugars and proline in leaves of both genotypes. SP-jasmine demonstrated higher drought tolerance as evidenced by maintaining higher gas exchange and photochemical efficiency and lower alteration of metabolites than DP-jasmine. Recovery analysis revealed that drought-induced injury in photosynthetic machinery in jasmine plants was reversible. DP-jasmine exhibited a slow recovery of drought-induced impairment in photosynthetic activity and associated metabolites, suggesting that this genotype had lower capacity to adapt to water limited condition. Higher yield stability of SP-than that of DP-jasmine under rain-fed condition finally confirmed higher drought tolerance of SP-jasmine. and H. Cai ... [et al.].
Cuttings of P. przewalski were exposed to two different watering regimes which were watered to 100 and 25 % of field capacity (WW and WS, respectively). Drought stress not only significantly decreased net photosynthetic rate (PN), transpiration rate (E), stomatal conductance (gs), efficiency of photosystem 2 (PS2) (Fv/Fm and yield), and increased intrinsic water use efficiency (WUEi) under controlled optimal conditions, but also altered the diurnal changes of gas exchange, chlorophyll fluorescence, and WUEi. On the other hand, WS also affected the
PN-photosynthetically active radiation (PAR) response curve. Under drought stress, PN peak appeared earlier (at about 10:30 of local time) than under WW condition (at about 12:30). At midday, there was a depression in PN for WS plants, but not for WW plants, and it could be caused by the whole microclimate, especially high temperature, low relative humidity, and high PAR. There were stomatal and non-stomatal limitations to photosynthesis. Stomatal limitation dominated in the morning, and low PN at midday was caused by both stomatal and non-stomatal limitations, whereas non-stomatal limitation dominated in the afternoon. In addition, drought stress also increased compensation irradiance and dark respiration rate, and decreased saturation irradiance and maximum net photosynthetic rate. Thus drought stress decreased plant assimilation and increased dissimilation through affected gas exchange, the diurnal pattern of gas exchange, and photosynthesis-PAR response curve, thereby reducing plant growth and productivity. and C. Y. Yin, F. Berninger, C. Y. Li.