The influence of different leaf-to-fruit (l-t-f) ratios on leaf net photosynthetic rate (PN) and fruit characteristics in Olea europaea L. cv. Frantoio was evaluated in 2001 and 2002. In both years, at the end of June, at the end of July, and in mid-September (first, second, and third time of treatment, respectively), defoliation or fruit thinning were performed to give l-t-f ratios of 1/1, 3/1, 5/1, and 7/1 (about 5.1, 15.3, 25.6, and 35.8 cm2 of leaf area per fruit, respectively) on girdled and ungirdled peripheral shoots. PN showed substantial seasonal and diurnal variations. In ungirdled shoots, no differences due to the different l-t-f ratios were observed, whereas in girdled shoots PN tended to be lower in shoots with a high l-t-f ratio. In general, the values of leaf transpiration rate (E), stomatal conductance (gs), sub-stomatal CO2 concentration (Ci), and dark respiration rate (RD) were associated with those of PN. The starch and reducing sugar contents and area leaf dry mass (ADM) tended to be higher in leaves on girdled shoots with high l-t-f ratio, whereas in ungirdled shoots no differences related to the different l-t-f ratios were observed. The higher saccharide content in the leaves and the lower PN, in the presence of a high Ci, observed in girdled shoots with a high l-t-f ratio suggests that the depression in PN in these shoots may be the result of a feedback inhibition of the photosynthetic mechanism that regulates such a process. The l-t-f ratio did not have a substantial effect on fruit drop. In ungirdled shoots, the different l-t-f ratios did not produce significant differences in terms of fruit growth and leaf dry matter and saccharide contents, whereas in girdled shoots fruit growth increased as the l-t-f ratio increased, particularly when treatments were applied at the initial stage of fruit development. The percentage of oil in the pulp, on a dry matter basis, was not substantially influenced by girdling and l-t-f ratio. The abundant availability of assimilates seemed to cause earlier fruit ripening and, at the same time, retard fruit senescence (fruit detachment force). Shoot growth was slightly reduced by girdling. The abundant availability of assimilates, induced by girdling associated with high l-t-f ratio, stimulated flower induction. and P. Proietti, L. Nasini, F. Famiani.
The effects of different light-emitting diode (LED) lights on saffron growth and photosynthetic characteristic were explored. Physiological mechanisms were explained by chlorophyll a fluorescence transient curves (OJIP) and JIP-test parameters. A decrease in the red to blue light ratio resulted in negative effects, particularly for monochromatic blue (B) LED light; saffron seedlings showed reduced chlorophyll accumulation, inhibited leaf elongation, and decreased photosynthetic performance. In the OJIP curve, the higher positive K-band observed for B LED light indicated that oxygen-evolving complex activation significantly decreased. B LED light inhibited the electron transport between primary quinone acceptor and secondary quinone acceptor as well as the existence of reducing plastoquinone centers, and increased energy dissipation of reaction centers. Otherwise, the red to blue light ratio of 2:1 had a positive effect on saffron cultivation, resulting in the longest leaf lengths, highest chlorophyll content, and photosynthetic characteristics. This study provides theoretical guidance for saffron agricultural practices.
The influence of surplus normál oř deficient nitrogen nutrition on the organization of maize chloroplast pigment apparatus was investigated. The amoímt of light- harvesting pigment-protein complexes (LHC) was the highest in chloroplasts fi^om high-nitrogen plants. Nitrogen deficiency resulted in a strong reduction of LHC, especially of its oligomer form. The fine structure of low temperature chloroplast absorption spectra revealed a relative decrease in the intensity of the 663, 666 and 678 nm components, while that of the components at 672 and 674 nm was increased. The changes in fine structure of the red fluorescence excitation spectra (F720 and F736) reflected similar changes in absorbance spectra. The changes do not allow to draw conclusions about the disturbance in energy transfer efficiency between some chlorophyll forms.
The effects of metabolisable sugars sucrose and glucose along with non-metabolisable isomers of sucrose palatinose and turanose were tested. Rate of oxygen evolution (P), electron transport rate (ETR), and photochemical quenching (qp) showed substantial decrease after 24 and 48 h by glucose and sucrose treatments, whereas there was no effect on all these parameters by the treatment with palatinose and turanose. Also the Fv/Fm ratio remained constant through the time of studies revealing that the maximal photochemical capacity of the cells was unchanged. Non-photochemical quenching (qN) showed a decrease compared to the control values by all the treatments. Hence P and Chl fluorescence parameter were affected only by those sugars which are used in the metabolic pathways and not by sugar analogues. and A. K. Sinha, T. Roitsch.
The rubber tree (Hevea brasiliensis) is an important tropical crop with a high economic value that has been successfully cultivated in Xishuangbanna, China. Xishuangbanna has a long dry season (November-February) with cold nights and frequent fog events. Thus, it is important to select chilling-tolerant cultivars in order to understand better the role of fog in protecting rubber tree from chilling-induced photodamage. In this study, we examined the photosynthetic responses of six rubber tree cultivars (Lan 873, Yunyan 77-2, Yunyan 77-4, GT1, Reken 523, and Reyan 733-97) to night-chilling stress (0, 5, and 10°C) and two different irradiances (100 and 50% of full sunlight). Our results showed that all six cultivars could withstand nights at 10°C for three days, while night chilling at 0 and 5°C impaired photosynthesis, which was indicated by photoinhibition, decrease of soluble protein content, and accumulation of malondialdehyde. Reken 523 and Reyan 733-97 were more sensitive to night chilling than other cultivars. Low irradiance (50% of full sunlight) after the chilling treatment apparently mitigated the effect of night-chilling stress. It indicates that frequent fog events after cold nights might greatly contribute to the success of rubber tree cultivation in Xishuangbanna., Y.-H. Tian, H.-F. Yuan, J. Xie, J.-W. Deng, X.-S. Dao, Y.-L. Zheng., and Seznam literatury
We investigated net photosynthetic rate (PN) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The PN of ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (gs) was similar for the two cultivars, but intercellular CO2 concentration (Ci) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (ψ1) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ψ1 between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained PN of flag leaf during grain filling under drought stress. The higher PN of ear in Hongmangmai under drought could also be related to its drought resistance. and T. Inoue ... [et al.].
Development of water stress in Trifolium subterraneum L. plants, growing in growth room or in the field during autumn-winter and latě springtime, was studied under ťhe conditions of irrigation replenishing every day the evaporated water (1), withholding watering (WW), and slowly induced drought, replenishing daily with a fraction of water evaporated (SID). The method ušed to induce drought substantially affected the leaf water relations. In WW plants drought developed rapidly and in consequence the leaf water relations dramatically changed afler 10 d of treatment. The treatment maintained a stable moderate water stress (SID) that enabled the development of new acclimated leaves even under high tempertures and low humidity.
The CO2 assimilation rate the transpiration rate (E), the stomatal conductance (gg), C index and the instantaneous water use efficiency of attached leaves háve been estimated in sixteen cultivars of subterranean clover (Trifolium subterraneum L.) fíeld growing plants, both irrigated and subjected to water stress, during latě spring in Mallorca, Spain. Variability among the genotypes with regard to the and other related parameters was highly significant for tiie irrigated plants. Drou^t promoted a marked decrease in both gg and ®ven when the relative water content of leaves was only slightly decreased. For water-stressed plants, genotypic variability in E and C index was also statistically significant. However, variability among the genotypes with regard to gg and was no longer evident under drought. The C index might represent a valuable parameter for evaluation of the genotypic responses of plants to drought.
The effect of a short (7 d), prolonged (14 d) soil drought (D) and (7 d) recovery (DR) on the leaf optical properties - reflectance (R), transmittance (T) and absorptance (A) in photosynthetically active radiation (PAR) and near infrared radiation (NIR) range of irradiation (750-1100 nm) was studied for maize and triticale genotypes differing in drought tolerance. The drought stress caused the changes in leaf optical properties parameters in comparison with non-drought plants. The observed harmful influence of drought was more visible for maize than triticale. and M. T. Grzesiak ... [et al].
Water stress usually impairs photosynthesis and plant growth. Acacia tortilis subsp. raddiana is well adapted to dry environments. The aim of the present study was to determine the impact of a progressive decrease in soil water content on photosynthetic-related parameters at the young seedling stage. Drought-induced plant responses occurred according to two types of kinetics. Water potential, stomatal conductance, and transpiration rates were rapidly affected by a decrease in soil water content, while chlorophyll fluorescence-related parameters and chlorophyll concentrations decreased only when soil water content was lower than 40%. The maximal efficiency of PSII photochemistry in the dark-adapted state remained unaffected by the treatment, whatever the stress duration. A. raddiana accumulated high concentrations of soluble sugars in relation to a stress-induced early stimulation of sucrose-phosphate synthase activity, while stimulation of invertase and sucrose synthase led to fructose accumulation only at the end of the stress period. We suggested that sugar accumulation may be involved in osmotic adjustment and protection of stressed tissues. A. raddiana was thus able to protect its photosynthetic machinery under drought conditions and may be considered as a promising species for revegetation of dry areas., S. Kebbas, S. Lutts, F. Aid., and Obsahuje bibliografii