bluuebunny/crossref_metadata_2025 huggingface dataset:
Water relations of Picea abies. II. Determination of the apoplastic water content and other water relations parameters of needles by means of capillary microcryoscopy and the pressure‐volume
Authors: Gross K. , Koch W.
Published: May 2006

Using the pressure volume analysis (PV analysis) on the shoots of Norway spruce (Picea abies [L.] Karst.) and the here presented capillary microcryoscopy of the needle press sap of the same shoots, it was possible to determine the amount of apoplastic water in the needles (Wan) as well as in the defoliated shoots (Was). Additionally, the bulk osmotic pressure at full water saturation in the symplast of the needles and defoliated shoots (πon and πos) was determined. The dependence of the bulk‐averaged turgor pressure (Pt) on the water content and the relationship between the bulk modulus of elasticity of the needles (ɛn) and the bulk‐averaged needle turgor pressure (Ptn) was shown with help of the PV analysis on the whole shoots and defoliated shoots. The study was conducted at the end of the vegetation period in 1987 and during winter 1988.

The proportion of Wan in the total needle water content (Wtn) was 14% in September 1987 and 12.5% in March 1988. The respective percentage of Was in Wts were 27% and 25%. The amount of apoplastic water depended on the ratio of the dry weight of defoliated shoots to the dry weight of the whole shoots. A standard mean value for the amount of Wan in the total water content of the shoots (Wt) was therefore not possible. The bulk osmotic pressure at full water saturation in the needle symplasts was –1.9 MPa in September 1987 and –2.2 MPa in winter 1988. The respective values of the bulk osmotic pressures in the symplast of the defoliated shoots (πos) were –1.5 MPa and –1.7 MPa. Thus πon was 0.1 MPa lower and πos 0.3–0.4 MPa higher than the average osmotic pressure during full water saturation in the symplast of the whole shoots (πo).

The relation between bulk‐averaged turgor pressure and water content showed that during water loss Ptn dropped more rapidly than the turgor pressure of defoliated shoots (Pts). Consequently the needles were less elastic than the defoliated shoots. The turgor values of whole shoots followed an intemediate course between Ptn and Pts. The flat course of Pts seems to be the main reason for the often observed “plateau” of ψ‐isotherms of whole shoots near full turgor.
Re‐evaluation of the role of ureides in the xylem transport of nitrogen in Arachis species
Authors: Peoples M.B. , Atkins C.A. , Pate J.S. , Chong K. , Faizah A. W. , Suratmini P. , Nurhayati D.P. , Bagnall D.J. , Bergersen F.J.
Published: May 2006

There are conflicting reports in the literature of the possible role of the ureides, allantoin and allantoic acid, in the nitrogen economy of Arachis species. Therefore, xylem sap composition in food peanut (Arachis hypogaea L.), and two forage peanuts (A. pintoi L. and A. glabrata Benth.) has been studied in detail. Xylem saps were collected from peanuts grown under different nutritional regimes and environmental conditions in the glasshouse and field in Australia, Malaysia and Indonesia, and the N‐containing solutes analysed. The relative amounts and concentrations of ureides in these peanut exudates were compared with those of soybean (Glycine max [L.] Merr.) – a species known to export ureides in its xylem stream as the major product of N2 fixation.

Xylem concentrations of ureides in soybean were high in N2‐fixing plants (2.9 to 3.7 μmol ml−1), representing 60 to 88% of xylem solute nitrogen, but it contributed only 9% (0.7 μmol ml−1) if plants were unnodulated and supplied nitrate. In all species of peanut, concentrations of ureides measured in xylem sap were generally much smaller (0.02 to 0.37 μmol ml−1; 1–7% of xylem nitrogen) and were unaffected by peanut species or cultivar, rhizobial strain, plant size, growth rate, or stage of development, and were not related to N2 fixation (less than 0.1% of currently fixed nitrogen exported as ureides) or the assimilation of nitrate. Apparently high levels of ureides in sap from some field‐grown plants were shown to be due to interference with the ureide colorimetric assay by some contaminating compound rather than represent increased ureides per se.
Accumulation of label from radioactive precursors into dry matter by wheat endosperm cultured in vitro
Authors: Millet Eitan , Jenner Colin F.
Published: May 2006

The capacity of in vitro cultured common wheat (Triticum aestivum L.) endosperms to incorporate starch and protein precursors was investigated. Isolated 2–3 week‐old endosperms were cultured up to 2 weeks in a liquid medium containing labelled (14C)‐sucrose and (3H)‐glutamine. Cultured endosperms were separated into ethanolsoluble, starch and protein fractions and the incorporation of the label into each of these fractions was assessed at different times after commencement of culture. The same medium was introduced through the peduncle into normally‐developing grains, which were then similarly analyzed. Accumulation of both 14C and 3H in the ethanol‐soluble fraction occurred, at a decreasing rate, only during the first 3 days, and then ceased. The accumulated label in the starch fraction, which originated mainly as 14C sucrose, proceeded at a relatively constant rate for one week and reached only about 1/5 of the expected in vivo starch production. Incorporation of both isotopes into the protein fraction reflected similar utilization of sucrose and glutamine from the medium (molar base), decreasing in rate with time. Culturing beyond one week produced deteriorated endosperms. Compared to cultured endosperms, normally‐developing grains incorporated proportionally less precursors into the ethanol‐soluble and more into the insoluble fraction. It is suggested that the reduced starch and protein synthesis in cultured grains stems from impaired capacity of the biosynthetic machinery rather than from low availability of precursors.
Appearance of alternative respiration in cucumber cotyledon mitochondria after treatment with cycloheximide
Authors: Morohashi Yukio , Seto Tadahito , Matsushima Hisashi
Published: May 2006

Treatment of cotyledons of 4‐day‐old cucumber (Cucumis sativus L. cv. Tokiwa‐jibae) seedlings with cycloheximide (0.3 mM) inhibited protein synthesis in the cotyledons by 80%. In spite of this inhibition, the cycloheximide treatment induced a marked increase in the capacity of the alternative respiration in mitochondria, accompanied by an increase in the contribution of the pathway to the total respiration. In contrast, the activity of the cytochrome pathway was reduced by cycloheximide treatment. As a result, the total respiration was almost the same in mitochondria from cycloheximide‐treated cotyledons and untreated cotyledons. Activities of some mitochondrial enzymes examined were also similar. Mitochondrial proteins synthesized during the treatment were separated by two‐dimensional gel‐electrophoresis and examined by fluorography. No new spots appeared and no spots disappeared on the fluorograms, but the labeling intensity of some polypeptides showed a relative increase or decrease as the result of cycloheximide treatment.
Changes in endogenous levels of three cytokinins during development of excised watermelon cotyledons
Authors: Rossi Gianfranca , Marziani Giovanna P. , Uneddu Paola , Longo Claudio P.
Published: May 2006

We have determined by an immunological method the endogenous levels of three cytokinins: dihydrozeatin riboside (DHZR), transzeatin riboside (tZR) and isope‐ntenyladenosine (IPA) in watermelon (Citrullus vulgaris Schrad., cv. Fairfax) cotyledons that were either attached to the seedling or excised from the seed after imbibition and then grown on water. Both seedlings and cotyledons were grown either for 5 days in continuous light or for 3 days in the dark and 2 days in light. Our aim was to verify whether endogenous cytokinin levels are lower in excised than in attached cotyledons as could be expected since excised cotyledons are much more sensitive to exogenous cytokinin application. The levels of the three cytokinins were very low immediately after imbibition, but gradually increased during the following days. They were higher in excised cotyledons after 5 days of culture in the dark than in cotyledons of the same age that had developed on the seedling. Dihydrozeatin riboside was by far the most abundant of the three cytokinins in cotyledons as well as in the hypocotyl and the root.

Irradiation reduced the level of DHZR, negating the concept that light promotes cotyledon development by increasing endogenous cytokinins. Transzeatin riboside when supplied exogenously, stimulated cotyledon development at a lower concentration than the other two cytokinins. Exogenous supply of ben‐zyladenine (BA) induced a strong increase in endogenous tZR already after 24 h.
Effect of modification of storage atmosphere on phospholipids and ultrastructure of cauliflower mitochondria
Authors: Romo‐Parada L. , Vézina L.‐P. , Charest P. M. , Castaigne F. , Willemot C.
Published: May 2006

Differences in mitochondrial membrane composition and ultrastructure were studied after storage of cauliflower (Brassica oleracea, L., Botrytis group) for 5 days at 25°C in air or under controlled atmospheres: 3% O2, 21% O2+ 15% CO2 or 3% O2+ 15% CO2. In air, postharvest senescence involved a 20% decrease in mitochondrial phospholipid content. A large reduction in the relative abundance of phosphati‐dylcholine (PC) and in the degree of unsaturation of PC and phosphatidyl ethanolamine (PE) was observed. However, the degree of unsaturation increased in cardiolipin (CL). Storage under 3% O2 did not prevent phospholipid breakdown. Low O2 prevented the relative decrease in PC observed during storage in air and the loss of linoleic acid from PC, but not from PE. This relative protection offered by the low O2 atmosphere was lost under 3% O2+ 15% CO2. The high CO2 atmospheres caused twice as much loss in phospholipids as that observed during storage in air. Extensive loss of mitochondrial protein, a marked decrease in phospholipid to protein ratio, and electron micrograph observations suggest structural alterations in the presence of high CO2.
Flowering response of Ipomoea batatas scions grafted onto Pharbitis nil stocks
Authors: Takeno Kiyotoshi
Published: May 2006

Young seedlings of Ipomoea batatas (L.) Lam. cv. Big One did not form floral buds, but were induced to flower when grafted onto Pharbitis nil Chois. cv. Violet with its cotyledons exposed to a 16 h dark period (SD). Four SD were required to induce flowering in I. batatas scions when the grafted plants were first grown under an 8 h dark period (LD) for 18 days and then exposed to SD. Transmission of the flowering stimulus across the graft union required 4 days. It was also slow in the graft combination of P. nil and P. nil, but increased greatly when the graft union was established more completely. These results suggest that the flowering stimulus of P. nil may move symplastically and its life may be between 4 and 6 days. Although the leaves of I. batatas inhibited flowering, the flowering response of P. nil grafted onto I. batatas suggested that the involvement of a transmissible flowering‐inhibitor was unlikely.
Assimilate relations in source and sink leaves during acclimation to a CO2‐enriched atmosphere
Authors: Cure Jennifer D. , Rufty Thomas W. , Israel Daniel W.
Published: May 2006

Evidence from previous studies suggested that adjustments in assimilate formation and partitioning in leaves might occur over time when plants are exposed to enriched atmospheric CO2. We examined assimilate relations of source (primary unifoliolate) and developing sink (second mainstem trifoliolate) leaves of soybean [Glycine max (L.) Merr. cv. Lee] plants for 12 days after transfer from a control (350 μl l−1) to a high (700 μ l−1) CO2 environment. Similar responses were evident in the two leaf types. Net CO2 exchange rate (CER) immediately increased and remained elevated in high CO2. Initially, the additional assimilate at high CO2 levels in the light and was utilized in the subsequent dark period. After approximately 7 days, assimilate export in the light began to increase and by 12 days reached rates 3 to 5 times that of the control. In the developing sink leaf, high rates of export in the light occurred as the leaf approached full expansion. The results indicate that a specific acclimation process occurs in source leaves which increases the capacity for assimilate export in the light phase of the diurnal cycle as plants adjust to enriched CO2 and a more rapid growth rate.
Photoinhibition of photosynthesis and growth responses at different light levels in psbA gene mutants of the cyanobacterium Synechococcus
Authors: Krupa Zbigniew , öquist Gunnar , Gustafsson Petter
Published: May 2006

Photoinhibition of photosynthesis and growth responses at diffrent light levels (10, 120 and 250 μmol m−2 s−1) were studied in psbA gene mutants R2S2C3 (psbAI gene present) and R2K1 (psbAIIIpsbAIII genes present) of the cyanobacterium Synechococcus sp. PCC 7942 (Anacystis nidulans R2). Mutant R2K1 (possessing form II of the D1 protein of photosystem II) was much more resistant to photoinhibition than the mutant R2S2C3 (possessing form I of the D1 protein). At moderate inhibitory light levels (100 to 300 μmol m−2 s−1) this was largely ascribed to an increased rsistance of the photosystem II reaction cetres possessing form II of the D1 protein. However, at higher light levels the higher resistance mutant R2K1 was assigned to a higher rate of photosystem II repair, i.e. turnover of the D1 protein. Moreover, our results support the hypothesis that photoinhibition of photosystem II and photoinhibitory induced quenching are due to separate processes. Results from growth experiments show that the R2K1 mutant has a slower growth rate than the R2S2C3 mutant but shows an increased survival under high light stress conditions. It is hypothesized that high resistance to photoinhibition, though allowing a better survival under high light, is not advantageous for optimal growth.
Root hydrotropism of an agravitropic pea mutant, ageotropum
Authors: Takahashi Hideyuki , Suge Hiroshi
Published: May 2006

We have partially characterized root hydrotropism of an agravitropic pea mutant, ageotropum (from Pisum sativum L. cv. Weibull's Weitor), without interference of gravitropism. Lowering the atmospheric air humidity inhibited root elongation and caused root curvature toward the moisture‐saturated substrate in ageotropum pea. Removal of root tips approximately 1.5 mm in length blocked the hydrotropic response. A computer‐assisted image analysis showed that the hydrotropic curvature in the roots of ageotropum pea was chiefly due to a greater inhibition of elongation on the humid side than the dry side of the roots. Similarly, gravitropic curvature of Alaska pea roots resulted from inhibition of elongation on the lower side of the horizontally placed roots, while the upper side of the roots maintained a normal growth rate. Gravitropic bending of Alaska pea roots was apparent 30 min after stimulation, whereas differential growth as well as curvature in positive root hydrotropism of ageotropum pea became visible 4–5 h after the continuous hydrostimulation. Application of 2,3,5‐triiodobenzoic acid or ethyleneglycol‐bis‐(β‐aminoethylether)‐N,N,N',N'‐tetraacetic acid was inhibitory to both root hydrotropism of ageotropum pea and root gravitropism of Alaska pea. Some mutual response mechanism for both hydrotropism and gravitropism may exist in roots, although the stimulusperception mechanisms differ from one another.
Physiological effects of long term exposure to low concentrations of SO2 and NH3 on poplar leaves
Authors: van Hove L. W. A. , van Kooten O. , van Wijk K. J. , Vredenberg W. J. , Adema E. H. , Pieters G. A.
Published: May 2006

Shoots of poplar (Populus euramericana L. cv. Flevo) were exposed to filtered air, SO2, NH3 or a mixture of SO2 and NH3 for 7 weeks in fumigation chambers. After this exposure gas exchange measurements were carried out using a leaf chamber. As compared to leaves exposed to filtered air, leaves pretreated with 112 μg m−3 SO2 showed a small reduction in maximum CO2 assimilation rate (Pmax) and stomatal conductance (gs). They also showed a slightly higher quantum yield and dark respiration. In addition, the fluorescence measurements indicated that the Calvin cycle of the leaves pretreated with 112 μg m−3 SO2 was more rapidly activated after transition from dark to light. An exposure to 64 μg m−3 NH3 had a positive effect on Pmax, stomatal conductance and NH3 uptake of the leaves. This positive effect was counteracted by an SO2 concentration of 45 μg m−3. The exposure treatments appeared to have no effect on the relationship between net CO2‐assimilation and gs. Also, no injury of the leaf cuticle or of epidermal cells was observed.

Resistance analysis showed that NH3 transfer into the leaf can be estimated from data on the boundary layer and stomatal resistance for H2O transfer and NH3 concentration at the leaf surface, irrespective of whether the leaves are exposed for a short or long time to NH3 or to a mixture of NH3 and SO2. In contrast SO2 uptake into the leaves was only partly correlated to the stomatal resistance. The results suggest a large additional uptake of this gas by the leaves. The possibility of a difference in path length between SO2 and H2O molecules is proposed.
Metabolism of C19‐ and C20‐gibberellins by cell‐free preparations from immature Phaseolus coccineus seed
Authors: Malcolm Joan M. , Crozier Alan , Turnbull Colin G. N. , Jensen Einar
Published: May 2006

Gibberellin biosynthesis pathways were investigated using isotopically‐labelled C19‐ and C20‐gibberellins and cell‐free preparations from immature seed of Phaseous coccineus cv. Prizewinner. The initial steps in an early 13‐hydroxylation pathway involved the conversion gibberellin A12‐aldehyde (GA12‐aldehyde) to GA12 which was 13‐hydroxylated to yield GA53, Metabolism of GA53 yielded GA44. In contrast to other cell‐free systems, GA44 was not further converted, either as a δ‐lactone or an open‐lactone structure, to the C‐20 aldehyde GA19. GA19 was, however, metabolised to GA20, GA5 and GA1. GA20 represented a branch point in the pathway as it was converted both to GA1, which was an end product, and GA5 which was further converted to GA6. Like GA1, GA6 was also an end‐product of the early 13‐hydroxylation pathway.

A non‐13‐hydroxylation pathway involving GA4, GA15, GA24 GA37 and GA36 also originated from GA12. The terminal product of this pathway was the 3β‐hydroxy C19‐gibberellin, GA4.
Effects of agar concentration on water status and growth of rose plants cultured in vitro
Authors: Ghashghaie J. , Brenckmann F. , Saugier B.
Published: May 2006

Rose (Rose hybrida cv. Madame G. Delbard) was micropropagated in vitro on agar at varying concentrations: 0, 4, 5.5, 6, 7.5, 8, 9 and 15 g l−1. Water status of the culture medium, leaf water potential, plant growth and propagation rate were investigated.

Water potential of the medium was lincar function of agar concentration, and gel strength increased linearly from zero as agar concentration increased from 5 to 15 g l−1.

Except for liquid medium, where shoot proliferation (total shoot number) was imparied by vitrification, fresh and dry weights and unmber of tatal shoots decreased linearly with increasing agar concentration. At low agar concentration, where water potential of the gelled medium was high, only few among numerous shoots that had attained a length of >0.3 cm were usable. Number of usable (elongated) shoots was significanly higher at a moderate level of agar, namely 7.5 g l−1. This can be explained in terms of the antagonistic actions of cytokinin and water on shoot elongation.

At low agar concentration, leaf water potential and absolute water content were high. At high agar concentration, under gel water deficit, leaf water potential and absolute water content were low but an osmotic adjustment maintained turgor pressure. At moderate agar concentration, when the number of usable shoots was high, lower leaf turgor was found.
Short‐chain fatty‐acid‐induced effects on the cell cycle in root meristems of Pisum sativum
Authors: Tramontano W. A. , DeLillo A. R. , Yung S. Y. , Natarajan C. , Kearns C. M.
Published: May 2006

Propionic acid and valeric acid at 1 mM reduced the mitotic index of root meristem cells of Pisum sativum to <1% after 12 h in aerated White's medium. After 12 h exposure to either acid, seedlings transferred to fresh medium resumed their normal mitotic index 12 h after transfer, with a burst of mitosis at 8 h. Exposure times of 8 h to either acid inhibited DNA synthesis, and nuclei released from either propionic or valeric acid inhibition were still unable to resume normal DNA synthesis after 12 h. Neither acid significantly altered the distribution of meristematic cells in G1 and G2 after 12 h. Propionic acid at 1 mM reduced the uptake of [14C]‐leucin but conversion rates to protein were constant regardless of whether any acid was present. Another longer fatty acid, caprylic acid, at 1 mM did not significantly reduce the mitotic index nor did 1 mM benzoic acid, another organic acid. This information suggests that only the short‐chain fatty acids, propionic acid and valeric acid, limit progression through the cell cycle by inhibiting DNA synthesis and arresting cells in G1 and G2 in a manner similar to butyric acid, a known cell arresting agent.
The hexose transporters at the plasma membrane and the tonoplast of higher plants
Authors: Rausch Thomas
Published: May 2006

The uptake of hexoses in higher plant cells is thought to be catalyzed by an H+/hexose contrasporter in the plasma membrane. Transport studies with isolated plant vacuoles indicate that, at the tonoplast, a second hexose transporter is located with properties different from the plasma membrane transporter. Recently membrane vesicles of high purity and defined orientation have been used for a more rigorous individual characterization of these two carriers. Concomitantly, a cDNA for the inducible H+/hexose cotransporter of the green alga Chlorella has been sequenced and shown to exhibit homology to a group of hexose transporters (for facilitated diffusion) of other eukaryotic and prokaryotic organisms. With a probe derived from the Chlorella sequence, the first plant gene for an H+/hexose contransporter (Arabidopsis thaliana) has been isolated, opening the route to molecular studies of structure, function and evolution of the hexose transporters of higher plants. The present review discusses recent work on the kinetic characterization and identification of the higher plant plasma membrane and tonoplast hexose transporters as well as their respective cellular functions. Furthermore, perspectives for future research on the plant hexose transporters are outlined.
Photosynthetic acclimation of Tradescantia albiflora to growth irradiance: morphological, ultrastructural and growth responses
Authors: Adamson Heather Y. , Chow W. S. , Anderson Jan M. , Vesk Maret , Sutherland M. W.
Published: May 2006

Tradescantia albiflora (Kunth), a trailing ground species naturally occurring in deep shade in rainforests, has an unusual photosynthetic acclimation profile for growth irradiance. Although capable of increasing its capacity for electron transport, photophosphorylation and carbon fixation when grown in full sunlight, Tradescantia has constant chlorophyll alb ratios, photosystem reaction centre stoichiometry and pigment‐protein composition at all growth irradiances (Chow et al. 1991. Physiol. Plant. 81: 175–182). To gain an insight into the compensatory strategies which allow Tradescantia to grow in both high and low lights, plants were grown under shade cloth (100 to 1.4% relative growth irradiance) and leaf and chloroplast attributes were compared. While shade Tradescantia chloroplasts had three times more chlorophyll per chloroplast and twice the length of thylakoid membranes compared to plants grown in full sunlight, the ratios of appressed to nonappressed thylakoid membranes were constant. The average net surface charge density of destacked thylakoids was the same for plants grown at moderate and low‐irradiance, consistent with their similar stacking profiles. Tradescantia plants grown in direct sunlight had 10‐times more fresh and dry weight per plant compared to plants grown in shade, despite a lower photosynthetic capacity on a leaf area basis with partial photoinhibition. We conclude that having a light‐harvesting apparatus permanently locked into the “shade‐plant mode” does not necessarily prevent a plant from thriving in high light. Analyses of leaf growth at different irradiances provide a partial explanation of the manner in which Tradescantia compensates for very low photosynthetic capacity per unit leaf in sunlight.
Hormone levels in the cambial region of intact Picea abies during the onset of cambial activity
Authors: Eklund Leif
Published: May 2006

Microdialysis probes were used to sample the cambial region of Picea abies stems during the cambial reactivation period. The concentrations of ethylene and zeatinriboside in each sample were measured by gas chromatography and enzyme‐linked immuno‐sorbent assay, respectively. The ethylene level increased throughout the experimental period, except for a temporary decrease that occurred about the time of budburst on the lower branches. The zeatin‐riboside level changed relatively little during the same period. The results indicate that increased activity in the cambial region was associated with an increase in the level of ethylene but not of zeatinriboside.
Expression of β‐galactosidase multiple forms during barley (Hordeum vulgare) seed germination. Separation and characterization of enzyme isoforms
Authors: Giannakouros Thomas , Karagiorgos Athanasios , Simos George
Published: May 2006

β‐Galactosidase (EC 3.2.1.23) activity in barley (Hordeum vulgare) seedlings increases moderately during the first stages of germination. The level of activity in the whole seedling is the result of increasing activity of β‐galactosidase in the roots and shoots and of declining enzyme activity in the grain. β‐Galactosidase was purified during different developmental stages and from various parts of the barley seedling using affinity chromatography and was resolved into multiple forms by isoelectric focusing on polyacrylamide gels. The expression of the isoforms was shown to be under temporal and tissue‐specific control. Four sets of isozymes were separated by DEAE‐cellulose chromatography and were shown to be functionally similar. β‐Galactosidase isoforms also exhibit size microheterogeneity, the more acidic entities having higher molecular masses. The differences in molecular weight are mainly restricted to the size of the small subunit. Multiplicity can not be attributed to glycosylation, since treatment of the enzyme preparation with N‐ or O‐glycanase did not alter the isoelectric points or the molecular weights of the isoforms.
Light acclimation potential and xanthophyll cycle pigments in photoautotrophic suspension cells of Chenopodium rubrum
Authors: Schäfer Christian , Schmidt Elke
Published: May 2006

The present study investigates the light acclimation potential of photoautotrophic suspension culture cells of Chenopodium rubrum L. grown in 16 h light/8 h dark cycles. Typical features of sun/shade acclimation could be demonstrated in cultures grown at photon flux densities of 30 and 150 μmol m−2 s−1. Low light grown cells had lower chlorophyll a/b ratios, lower respiration rates and lower light compensation points than high light grown cells. Maximum photosynthetic rate per cell dry weight was highest in low light conditions, indicating that the cells did not enlarge their photosynthetic machinery upon exposure to high light. Transfer of cultures to 800 μmol m−2 s−1 caused photoinhibition as indicated by a decrease in photosynthetic efficiency and by the occurrence of a slowly reversible quenching of variable chlorophyll fluorescence. Extension of the photoinhibitory treatment over six light dark cycles did not result in further dramatic changes of these parameters, whereas the chlorophyll content per dry weight and the chlorophyll a/b ratio decreased. Measurements of photochemical quenching showed that the capability of the cells to dissipate excessive energy had increased during the acclimation process. The presence of the xanthophyll cycle pigments and the operation of the cycle could be demonstrated. In agreement with the putative photoprotective function of antheraxanthin and zeaxanthin these pigments could only be detected under photoinhibitory conditions. Prolonged photoinhibitory treatment resulted in increases in the xanthophyll pigment concentration but not of the potential to deepoxidate violaxanthin. The limited potential of the cells to accumulate zeaxanthin and antheraxanthin might indicate that the xanthophyll cycle is not the main factor determining their resistance to high light stress.
The occurrence of haemoglobin and hydrogenase in nodules of twelve Casuarina‐Frankia symbiotic associations
Authors: Sellstedt A. , Reddell P. , Rosbrook P.
Published: May 2006

Seedlings of Casuarina cunninghamiana Miq., C. equisetifolia L. and C. glauca Sieber growing in N‐deficient potting mix were inoculated with Frankia sp. from each of 4 different sources. After ca 4 months, plants were harvested and nodules from the 12 Casuarina‐Frankia combinations evaluated for (1) concentrations of haemoglobin (measured as CO‐reactive haem) and (2) occurrence of hydrogenase. The aim was to determine if these factors were related to nitrogen accumulation and biomass production.

There were marked host‐Frankia source interactions with up to 10‐fold differences in plant dry weight and 50‐fold differences in the efficiency of nitrogen fixation (as estimated by N2 accumulated mg−1 nodule dry weight). Differences in plant growth and nitrogen accumulation were apparently related to nodule specific activity, because the 12 associations had similar nodulation characteristics, e.g. time for nodulation to occur.

The concentration of haemoglobin in Casuarina nodules ranged from 0 to 27 nmol haem (g FW)−1. There was a strong linear correlation between concentrations of haemoglobin and dry weights of the whole plants (r=0.77, 0.92 and 0.97, P≤0.05) for C. cunninghamiana, C. equisetifolia and C. glauca symbiotic associations, respectively. However, the linear correlation between concentration of haemoglobin and nitrogen content of whole plant was lower (r=0.60, 0.64 and 0.71, P≤0.05) for the three Casuarina symbioses, respectively, and there was only a poor correlation between haemoglobin concentration in nodules and the rate of nitrogen accumulation on nodule weight basis. This indicates that haemoglobin concentration is not the sole physiological determinant of nitrogen fixation in Casuarina.

All the Casuarina‐Frankia symbiotic associations studied also showed the presence of a hydrogen uptake enzyme. The activity of the enzyme ranged from 5.1 to 34.1 μmol H2 (g FW)−1 h−1, and hydrogen uptake was not correlated with plant dry weight, nitrogen content or the rate of nitrogen fixation. Hydrogen evolution could not be detected in any of the associations.
Shoot‐tip abscission and adventitious abscission of internodes in mulberry (Morus alba)
Authors: Suzuki Takeo
Published: May 2006

In mulberry (Morus alba L. cv. Shin‐ichinose), shoot‐tip abscission following the cessation of apical growth could be induced in different internodes, depending on the vigour of the shoot and its apex and other internal and external factors. In the lateral, short shoots of 1‐year‐old stems of low‐pruned trees, the apical growth cessation and shoot‐tip abscission (May–June) resulted primarily from the dominance of the upper, long shoots and intense competition among laterals along the stem. Decapitation of the laterals, before abortion of their apices took place (early May), readily caused adventitious abscission of the distal internode. Similar decapitation‐induced, adventitious abscission of the distal internode of the upper, long shoots of 1‐year‐old stems of pruned trees also occurred (May–September), demonstrating that the abscission itself is not directly associated with photoperiod. In May and June, decapitation induced abscission primarily in parallel with or after sprouting of lateral buds and shoot elongation, while in July, August and September, the abscission was induced by decapitation and independently of sprouting. Shoot (stem) orientation positively affected the abscission, which is related to gravimorphic effects on buds and shoots on the lower and lateral sides of the horizontally trained stem. These results suggest that the vigour of shoots and apices is an important determinant of growth and apex abscission in mulberry.
Cold‐acclimation induced changes in freezing tolerance and translatable RNA content in Citrus grandis and Poncirus trifoliata
Authors: Durham Richard E. , Moore Gloria A. , Haskell Dale , Guy Charles L.
Published: May 2006

Cold‐acclimation‐induced changes in freezing tolerance and translatable RNA content were compared in seedlings of a relatively cold sensitive citrus species, Citrus grandis L. Osb. cv. Thong Dee (pummelo), and the cold‐hardy citrus relative, Poncirus trifoliata L. Raf. cv. Pomeroy (trifoliate orange). Cold acclimation of pummelo (10 days at 15°C followed by 4 weeks at 10°/5°C, day/night) resulted in a decrease in LT50 from −6 to −8°C, while in trifoliate orange (acclimated for 7 weeks at 5°C), the LT50 decreased from −9 to −18°C. Qualitative changes in the in vitro translation profile, revealed by two‐dimensional gel electrophoresis, were observed following cold acclimation in both species. An mRNA for a large polypeptide (ca 160 kDa) was detected following cold acclimation of trifoliate orange. A similar change was not observed in pummelo following cold acclimation.
Prior temperature exposure affects subsequent chilling sensitivity
Authors: Saltveit Mikal E.
Published: May 2006

The chilling sensitivity of small discs or segments of tissue excised from chillingsensitive species was significantly altered by prior temperature exposure subsequent to holding the tissue at chilling temperatures as measured by a number of physiological processes sensitive to chilling. This temperature conditioning was reversible by an additional temperature exposure before chilling, and mature‐green and red‐ripe tomato tissue exhibit similar chilling sensitivities.

Exposing pericarp discs excised from tomato fruit (Lycopersicon esculentum Mill. cv. Castelmart), a chilling‐sensitive species, to temperatures from 0 to 37°C for 6 h before chilling the discs at 2.5°C for 4 days significantly altered the rate of ion leakage from the discs, but had no effect on the rate of ion leakage before chilling and only a minimal effect on discs held at a non‐chilling temperature of 12°C. Exposing chillingsensitive tissue to temperatures below that required to induce heat‐shock proteins but above 20°C significantly increased chilling sensitivity as compared to tissue exposed to temperatures between 10 and 20°C. Rates of ion leakage after 4 days of chilling at 2.5°C were higher from fruit and vegetative tissue of chilling‐sensitive species (Cucumis sativus L. cv. Poinsett 76, and Cucurbita pepo L. cv. Young Beauty) that were previously exposed for 6 h to 32°C than from similar tissue exposed to 12°C. Exposure to 32 and 12°C had no effect on the rate of ion leakage from fruit tissue of chilling tolerant species (Malus domestica Borkh. cv. Golden Delicious, Pyrus communis L. cv. Bartlett). Ethylene and CO2 production were higher and lycopene synthesis was lower in chilled tomato pericarp discs that were previously exposed for 6 h to 32°C than the values from tissue exposed to 12°C for 6 h before chilling. Increased chilling sensitivity induced by a 6 h exposure to 32°C could be reversed by subsequent exposure to 12°C for 6 h.
Nitrate reductase activity, nitrogenase activity and photosynthesis of black alder exposed to chilling temperatures
Authors: Vogel Christoph S. , Dawson Jeffrey O.
Published: May 2006

Actinorhizal (Frankia‐nodulated) black alder [Alnus glutinosa(L.) Gaertn.] seedlings fertilized with 0.36 mMnitrate (low nitrate fertilizer treatment) or 7.14 mMnitrate (high nitrate fertilizer treatment) and acclimated in a growth chamber for 2 weeks were exposed to 2.5 h of night‐time chilling temperatures of −1 to 4°C. Cold treatment decreased nitrogenase activity (acetylene reduction activity) 33% for low nitrate fertilized plants and 41% for high nitrate fertilized plants. Recovery of nitrogenase activity occurred within 7 days after chilling treatment. In contrast, in vivo nitrate reductase (NR) activities of leaves and fine roots increased immediately after chilling then decreased as nitrogenase activities recovered. Fine roots of alder seedlings exhibited NR activities proportional to the amounts of nitrate in the rooting medium. In contrast, the NR activities of leaves were independent of substrate and tissue nitrate levels and corresponded to nitrogenase activity in the root nodules. In a separate experiment, net photosynthesis (PS) of similarly treated black alder seedlings was measured before and after chilling treatments. Net PS declined in response to chilling by 17% for plants receiving low nitrate fertilizer and 19% for plants receiving high nitrate fertilizer. After chilling, stomatal conductance (gs) decreased by 39% and internal CO2concentration (ci) decreased by 5% in plants receiving the high nitrate fertilizer, whereas plants receiving the low nitrate fertilizer showed no change in gsand a 13% increase in ci. Results indicate that chilling stimulates stomatal closure only at the high nitrate level and that interference with biochemical functions is probably the major impact of chilling on PS.
Polyamines in various rice (Oryza sativa) genotypes with respect to sodium chloride salinity
Authors: Basu Rina , Ghosh Bharati
Published: May 2006

Physiological responses of various rice genotypes were studied in relation to salt (NaCl) stress. Cultivars CSR‐1 and Dular germinated well in different NaCl regimes compared to cvs Rupsail, Assam Getu and M‐1–48. At 100 mM NaCl, the lowest germination was observed in cv. M‐1–48. Cvs CSR‐1 and Dular were relatively effective in maintaining high concentrations of polyamines as well as arginine decarboxylase (EC 4.1.1.19) activity in coleoptiles and roots in a non‐stressed condition. The activities of two biodegradative enzymes, diamine oxidase (EC 1.4.3.6) and polyamine oxidase (EC 1.4.3.4), were lowest in cv. CSR‐1. The polyamine content was not significantly altered when seedlings of cv. CSR‐1 were exposed to 100 mM NaCl. However, in cv. M‐1–48 enhancement of arginine decarboxylase activity with concomitant accumulation of polyamines was observed. Leakage of metabolites and changes in the levels of Na+ and Cl− were prominent in cv. M‐1–48 under saline conditions. The results suggest a correlation between polyamine and salt stress‐induced responses in rice genotypes.
The distribution of hydroxyproline‐rich glycoprotein mRNAs in shoots of cucumber and pea
Authors: Fennoy Sheila L. , Jones Russell L.
Published: May 2006

The distribution of hydroxyproline‐rich glycoprotein (HRGP) mRNAs in the shoots of dark‐grown and irradiated cucumber (Cucumis sativus L. cv. Burpee pickler) and pea (Pisum sativum L. cv. Alaska) was studied. A cloned genomic DNA fragment encoding carrot (Daucus carota) root extensin (pDC5A1) was used to measure HRGP mRNAs from cucumber and pea along the length of dark‐grown and irradiated shoots. There was a marked difference in the levels of HRGP mRNAs isolated from apical and basal regions of cucumber. Whereas apical, elongating regions had low levels of HRGP mRNAs, basal regions of the shoot had high levels. Levels of HRGP mRNAs were also compared in shoots of dark‐grown and irradiated cucumber. Although light inhibits hypocotyl growth, it had no effect on levels of HRGP mRNAs. There was no gradient in the distribution of HRGP mRNAs along the epicotyl of dark‐grown pea. As was the case with cucumber, light did not affect the accumulation of HRGP mRNAs in pea shoots. We conclude that light does not affect elongation by regulating the accumulation of HRGP mRNAs. The gradient of accumulation of HRGP mRNAs along the hypocotyl of cucumber probably reflects differences in cellular differentiation along the shoot.
Developmental heterogeneity of the lipid distribution in the thylakoid membranes of Euglena gracilis
Authors: Brandt Peter , Eichenberger Waldemar
Published: May 2006

The thylakoid membranes of isolated Euglena chloroplasts were separated into two fractions (appressed and non‐appressed membranes) by aqueous two‐phase partitioning (mixture of dextran 500 and polyethylene glycol 4000) following press disruption. The lipid composition of these two fractions differ in many respects during most of the cell cycle of this alga in comparison with the thylakoid characteristics of higher plants or green algae. The monogalactosyldiglyceride to digalactosyldiglyceride ratio changes during the cell cycle and the vesicles originating from appressed and nonappressed thylakoid membranes, respectively, differ in this property at the beginning, but tend to be equal at the end of the cell cycle. The levels of sulfoquinovosyldiglyceride and phosphatidylglycerol are highest in appressed membrane regions at about the 6th hour of the cell cycle but are highest in non‐appressed membranes near the end of the cell cycle. The insertion and/or assembly of synthesized LHCII is correlated with a high monogalactosyldiglyceride to digalactosyldiglyceride ratio in appressed membrane regions. The heterogeneity of the lipid composition is discussed in relation to the stage‐specific development of structure and function of Euglena chloroplasts.
Fatty acid changes during development of zygotic and microspore‐derived embryos of Brassica napus
Authors: Pomeroy M. K. , Kramer J. K. G. , Hunt D. J. , Keller W. A.
Published: May 2006

Cultured microspores of Brassica napus L. cvs Topas and Reston initiated cell divisions within 3 to 4 days, and globular, heart and torpedo shaped embryos were prevalent after approximately 6, 8, and 10 days, respectively. Embryos with rudimentary cotyledons were evident within 2 weeks, but those that reached this stage of development represented only 1–5% of the original microspore population. The fresh weight of microspore‐derived embryos at all stages of development was significantly greater than that for zygotic embryos, but the pattern of change in fresh weight and fatty acid accumulation was similar in developing zygotic and microspore embryos. In freshly isolated microspores of both Topas (low erucic acid) and Reston (high erucic acid), the predominant fatty acid was 18:3, while 18:1 comprised less than 15% of total fatty acids. During development in both zygotic and microspore embryos, the level of 18:3 declined markedly while 18:1 rapidly increased. Erucic acid (22:1) was not detected in the early stages of embryogenesis in Reston. However, small amounts of 22:1 appeared by early cotyledonary stage and the level gradually increased in both zygotic and microspore embryos through the later stages of development. The fatty acid compositions of mature embryos was nearly identical to that of dry seed, except the level of 22:1 in Reston embryos was consistently less than in the seed. Triacylglycerols comprised only 15% of total lipids in freshly isolated microspores, but increased to more than 90% by 4 weeks. The fatty acid composition of the triacylglycerol fraction was generally similar to that of total lipids at all stages of development of microspore‐derived embryos.
Tissue distribution and developmental patterns of NADH‐dependent and ferredoxin‐dependent glutamate synthase activities in maize (Zea mays) kernels
Authors: Muhitch Michael J.
Published: May 2006

Both NADH‐dependent glutamate synthase (NADH‐GOGAT, EC 1.4.1.14) and ferredoxin‐dependent glutamate synthase (Fd‐GOGAT, EC 1.4.7.1) activities were present in the endosperm, embryo, pedicel and pericarp of maize (Zea mays L. var. W64A × A619) kernels. The endosperm contained the highest proportions of each activity on a per tissue basis. In the endosperm, NADH‐GOGAT and Fd‐GOGAT activities increased 12‐ and 2.5‐fold, respectively, during early zein accumulation. NADH‐GOGAT and Fd‐GOGAT activities were expressed in the upper, middle and lower portions of the endosperm in a manner that paralleled but preceded zein accumulation. Maize endosperm NADH‐GOGAT was purified 159‐fold using ammonium sulfate fractionation, anion exchange chromatography and dye‐ligand chromatography. Apparent Km values for glutamine, α‐ketoglutarate and NADH were 850, 19 and 1 μM, respectively. The results are consistent with endosperm GOGAT functioning to redistribute nitrogen from glutamine, the predominant nitrogenous compound delivered to the endosperm, into other amino acids needed for storage protein synthesis.
Cell cycle kinetic analysis with flow cytometry in pea root meristem synchronized with aphidicolin
Authors: Sgorbati Sergio , Sparvoli Elio , Levi Marisa , Galli Maria Grazia , Citterio Sandra , Chiatante Donato
Published: May 2006

Meristematic cells in pea root were synchronized after treatment with aphidicolin. Flow cytometric analysis of DNA content variations revealed a variety of information: ca 50% of the cells were synchronized in the first part of the S phase; kinetic studies of the S‐phase traverse revealed an increase of the DNA synthesis rate from early to late S; some of the cells in the meristem were non‐cycling, arrested in Gl (19%) and G2 (12%). The possibility of using such a synchronized system in cytogenetic and biomolecular studies is discussed.
Sucrose‐phosphate synthase from wheat. Characterization of peptides by immunoblotting analysis
Authors: Salerno G. L. , Crespi M. D. , Zabaleta E. J. , Pontis H. G.
Published: May 2006

The structure of sucrose‐phosphate synthase (SPS: EC 2.4.1.14) from wheat (Triticum aestivum L. cv. San Agustin was studied using antibodies prepared against the enzyme purified from wheat germ. The antibodies revealed the presence of 55 and 35 kDa polypeptides in wheat germ, endosperm, embryos and whole seed, while in whole wheat leaf, a 90 kDa was detected. It is not clear whether the 35 and 55 kDa polypeptide are truly subunits of SPS or they are the product of protease action, more active in non‐photosynthetic tissues than in leaves. The antibodies from wheat germ clearly recognized polypeptides in leaf protein preparations from other plants (barley, soybean, maize) and, weakly in others (peanut, tobacco). It did not recognize any polypeptide in spinach and mustard leaf extracts. In the case of maize leaf, a peptide of higher molecular mass (116 kDa) than the wheat ones was revealed. The results may indicate the presence of different polypeptide compositions for sucrose‐phosphate synthase, and suggest the existence of at least two types of this enzyme.
Evidence for the ultraviolet‐B (280–320 nm) radiation induced structural reorganization and damage of photosystem II polypeptides in isolated chloroplasts
Authors: Nedunchezhian N. , Kulandaivelu G.
Published: May 2006

Direct evidence for the possible loss of photosystem II (PS II) activity in chloroplasts ofVigna sinensisL. cv. Walp after ultraviolet‐B (UV‐B, 280–320 nm) radiation treatment was provided by polyacrylamide gel electrophoretic analysis of PS II polypeptides. A 30 min UV‐B treatment of chloroplasts caused a 50% loss of PS II activity. The artificial electron donor. Mn2+failed to restore UV‐B radiation induced loss of PS II activity, while diphenyl carbazide (DPC) and NH2OH only partially restored activity. Such a loss in PS II activity was found to be primarily due to a loss of 23 and 33 kDa extrinsic polypeptides. UV‐B treatment induced the synthesis of a few polypeptides and a 29 kDa light‐harvesting chlorophyll protein.