Changes in Sulfur Metabolism During Needle Development of Norway Spruce*

In a field-study with approx. 150-year-old spruce trees, seasonal changes in thiol composition and content, sulfate content, and oxtractable activities of enzymes of sulfate reduction and assimilation were analyzed in needles and buds and were related to developmental processes during flushing. GSH was the predominant thiol in spruce needles throughout the year, with maximum contents of more than 400nmol g FW^?1 during winter and minimum contents of less than 200 nmol g FW^?1 during summer. Negative correlation of changes in GSI1 contents during winter and spring with air temperature showed a low correlation coefficient (r =– 0.55), suggesting minor significance of GSH in frost protection. Drastic changes in thiol contents during flushing suggested that GSH accumulated in the previous year's needles during winter supports the growing needles with reduced sulfur. Sulfate and other substrates for sulfate assimilation appeared to be available in buds and the new needles. An external supply with reduced sulfur may still be required because of insufficient activities of enzymes of sulfate reduction and assimilation, esp. ATP-sulfurylase and APS-sulfotransferase.     

Responses of Photosynthesis,Carbohydrates and Antioxidants in Needles of Norway Spruce to Slow and Rapid Changes in Ozone

The goal of the present study was to examine the effects of slow and rapid changes of ozone (O₃) concentrations on the physiological behaviour of current-year needles of Norway spruce (Picea abies (L.) Karst.). For this purpose five-year-old spruce seedlings were exposed in growth chambers for 49 days to either charcoal-filtered air, slowly increasing O₃ concentrations from zero up to 100 nl I^?1 in weekly steps of 25 nl I^?1, or immediately to 100 nl I^?1 of O₃. During the investigation period gas exchange, carbohydrate and antioxidant contents of the current flush were measured. In needles which experienced slowly increasing O₃ concentrations, cumulative O₃ uptake was approximately 30 % lower than in needles continuously fumigated with 100 nl I^?1 of O₃. The higher 0₃ uptake in the permanent 100 nl I^?1 O₃ treatment caused a pronounced decline in net photosynthesis, in the efficiency of CO₂ uptake and in the starch content of the seedlings. Initially the ascorbate pool increased, but after 5 weeks of exposure ascorbate concentrations declined and were comparable to values obtained in charcoal-filtered controls, while the thiol contents were enhanced during fumigation with permanent 100 nl I-^?1 O₃. On the contrary, slowly increasing O₃ caused a significant increase in total needle ascorbate throughout the fumigation period, which probably prevented an O₃-induced decline in the photosynthetic machinery as photosynthesis was not affected although the thiol contents were not enhanced. Furthermore, starch content was slightly higher than in O₃-free controls. These results suggest that seedlings of Norway spruce have the possibility to acclimate to O₃ stress, as slowly increasing O₃ concentrations seemed to increase resistance and the seedlings were able to compensate.     

Changes in Unsaturated Levels of Fatty Acids in Thylakoid PSII Membrane Lipids During Chilling-induced Resistance in Rice

Temperature is one of the abiotic factors limiting growth and productivity of plants. In the present work, the effect of low non‐freezing temperature, as an inducer of “chilling resistance”, was studied in three cultivars of rice (Oryza sativa L.), japonica cv. 9516 (j‐9516), the two parental lines of superhigh‐yield hybrid rice between subspecies, Peiai/E32 (ji‐PE), and the traditional indica hybrid rice Shanyou 63 (i‐SY63). Leaves of chill‐treated rice showed chilling‐induced resistance, as an increase of their low‐temperature tolerance was measured using chlorophyll fluorescence measurements, revealing a change in photosystem II (PSII) efficiency. After 5 d of exposure to 11°C under low light (100 μmol m^‐2 s^‐1), levels of unsaturated fatty acids in PSII thylakoid membrane lipids decreased during the initial 1‐2 d, then increased slowly and reached 99.2%, 95.3% and 90.1% of the initial value (0 d) in j‐9516, ji‐PE and i‐SY63, respectively, on the fifth day. However, under medium light (600 μmol m^‐2 s^‐1), all cultivars experienced similar substantial photoinhibition, which approached steady state levels after a decline in levels of unsaturated fatty acids in PSII thylakoid membrane lipids to about 57.1%, 53.8% and 44.5% of the initial values (0 d) in j‐9516, ji‐PE and I‐SY63 on the fifth day. Under either chilling‐induced resistance (the former) or low temperature photoinhibition (the latter) conditions, the changes of other physiological parameters such as D1 protein contents, electron transport activities of PSII (ETA), F_v/F_m, xanthophyl cycle activities expressed by DES (deepoxide state) were consistent with that of levels of unsaturated fatty acids in PSII thylakoid membrane lipids. So there were negative correlations between saturated levels of fatty acids (16:1(3t), 16:0, 18:0), especially the 16:1(3t) fatty acid on thylakoid membrane and other physiological parameters, such as D1 protein contents, ETA and (A+Z)/(A+V+Z). A specific role of desaturation of fatty acids and the photoprotective pigments of the xanthophyl cycle, leading to an acclimation response in thylakoid membrane lipids may be involved. We conclude that chilling‐induced resistance is accelerated by the unsaturation of thylakoid membranes, and the ability of rice plants to cold‐harden can be enhanced by genetic engineering.     

Changes of Freeze-Fracture Ultrastructure and Light Harvesting Chlorophyll Protein Complex in Thylakoid Membranes During Ontogeny of Maize

Freeze-fracture electron microscopy enables us to observe and count the freeze-fracture particles which correspond to the different functional components of thylakoid membranes. The present paper reports the observation on freeze-fracture ultrastructure of thylakoid membranes and the analysis of proteins by the SDS-polyacrylamide gel electrophoresis within the membranes from differenly located leaves of maize. In the past, we found that the leaies subtending the ear of maize had a much higher chlorophyll content, a lower chlorophyll a/b ratio and more staking thylakoid membranes and provided the photosynthetic energy used to fill the maize seeds more than that of other leaves. Recently, we have further found that the particle densities of all four faces of thylakoid membranes from the ear leaf were the highest, than those, successively, from the terminal leaf, and the fifth leaf (from the base of the plant). The particle densities on all four fracture faces of thylakoid membranes isolated from the ear leaves of maize were significantly higher than those from the terminal leaves with the increases of 19% in EFs, 28% in PFs and 20% in PFu. Increases in particle densities on the PFs, EFs and PFu faces result in increased densities of LHCP II, PSⅡ and PSI reactions centres, respectively. It is significant that this supramolecular architecture of the ear leaves is consistent with our analytical results of the SDS-polyacrylamide gel electrophoresis within the membranes (a detailed report in another paper). The contents of major polypeptides of 21 kD (LHCP Ⅰ) and 25 kD (LHCP Ⅱ) in thylakoid membranes from the ear leaves were more than those from the terminal leaves. The characteristics of both supramolecular architecture and polypeptide components are in favour of absorbing, transferring, distributing and conversing light energy in the course of photosynthesis of the ear leaves in maize.     

Absorption of Atmospheric NO2 by Spruce (Picea abies) Trees. III. Interaction with Nitrate Reductase Activity in the Needles and Phloem Transport

In order to compare the effects of excess pedospheric and atmospheric nitrogen supply on nitrate reductase activity (NR. EC 1.6.6.1) excised spruce branches were exposed to nitrate solutions or were fumigated with NO₂. Immersion of spruce branches in 6 mM nitrate caused an increase in NR activity by a factor of 14 or 19 in current-year and in one-year-old needles, respectively, as compared to controls incubated in tap water. Exposure to 65 nl I^?1 NO₂ increased NR activity by a factor of 1.5 in current-year needles and by a factor of 2.5 in one-year-old needles as compared to non-fumigated controls. Addition of cycloheximide (0.17 μM) or puromycin (200 μM) to the incubation solution prevented the induction of NR activity from both nitrate and NO₂ exposure. This finding indicates that induction of NR activity by both atmospheric NO₂ or increased nitrate supply of the needles is both caused by de-novo synthesis of NR protein. The increase in NR activity in needles of branches still attached to the tree as a consequence of exposure to 65 nl I^?1 NO₂ was found to be a transient phenomenon. The increase persisted for several days only and was no longer observed after one week of sustained NO₂ exposure. An interruption of phloem transport by girdling, applied subsequent to the induction of NR activity by atmospheric NO₂, prevented the decrease in NR activity. Apparently, export out of the exposed needles and phloem transport within the stem are involved in the regulation of NR activity upon NO₂ exposure.     

Changes in the Non-Photochemical Quenching of Chlorophyll Fluorescence During Aging of Wheat Flag Leaves

Ultrastructural changes in chloroplasts of primary leaves of 15-d-old bean plants (Phaseolus vulgaris L. cv. Cheren Starozagorski) in response to a single stress (increasing water deficit, WD) as well as to combined stress (WD plus high temperature, WD+HT) were investigated under the possible protective or reparatory effects of the carbamide cytokinin 4-PU-30 [N-(2-chloro-4-pyridyl)-N-phenylurea] applied before or after the stress. Essential structural changes in chloroplast ultrastructure occurred mainly in plants that had experienced WD+HT: the thylakoids were swollen, the envelope was destroyed, and the spatial orientation of inner membrane system was not typical. Changed starch accumulation was also observed. 4-PU-30 protected chloroplast ultrastructure under WD+HT.