摘要:

ABSTRACTLow temperatures are known to restrict chloroplast development and prevent the attainment of photosynthetic competence in maize leaves. The responses of the photosynthetic apparatus of mature maize leaves grown at 14°C on transfer of the plants to 25°C are examined. The synthesis of thylakoid proteins increased immediately on transfer of leaves from 14 to 25°C, with a dramatic accumulation of thylakoid proteins and chlorophylls occurring after 3 d at 25°C. Thylakoid structure and organization also became similar to those observed in leaves grown at 25°C over this period. However, no comparable development of photosynthetic competence in photosystems I and II or in the rate of CO2assimilation was observed on transfer of leaves from 14 to 25°C. Immunocytological analyses demonstrated heterogeneity in the distribution of a range of thylakoid proteins (cy tochromef, the α and β subunits of the coupling factor, Dl of the photosytem II reaction centre, the 33kDa protein of the extrinsic oxygen‐evolving complex of photosystem II, and subunit II of photosystem I between mesophyll cells in leaves grown at 14°C, and in the responses of individual proteins to transfer of the leaves to 25°C. Such heterogeneity between mcsophyll cells would account for the inability of the leaves to develop the expected degree of photosynthetic competence on transfer to 25°C. The effects of low growth temperatures on chloroplast biogenesis are complex, as are the changes induced by the transfer ofleaves grown at low temperatures to optimal growth temperature, and both these factors may limit the canopy development and photosynthetic productivity of crops in tempe

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00538.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWe present the first study of abscisic acid (ABA) concentrations and fluxes in the xylem sap of conifers during a drought cycle. In bothPinus sylvestrisandPicea sitchensisthe concentration of ABA in the sap rose 11‐fold as the drought progressed. There were clear diurnal trends in this concentration, which reached its maximum (6–8.ininol ABA m−3) near the middle of the day. The fluxes of ABA were calculated by multiplying the xylem ABA concentration by the sap flow rate. The ABA fluxes in the droughted plants in the middle of the day were usually no higher than those of the controls, as a result of the very low sap flow in the droughted plants at that time. However, the ABA flux in the droughted plants was higher than in the controls in the morning, and we postulate that the stomata are responding to these ‘morning doses’Stomatal conductance,gs, could not be related statistically to leaf turgor or to the ABA flux. However, £s did display a negative exponential relationship with ABA concentration in the xylem.Pinus displayed more acclimation to drought thanPicea, Its ABA concentration rose and its stomatal conductance fell at day 6 of the drought, as opposed to day 17 forPicea, and its osmotic potential fell during the drought

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00539.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTMutations at thechsllocus inArabidopsis thaliana(L.) confer a chilling‐sensitive phenotype in which plants become chlorotic and die after more than 3 d of exposure to temperatures in the range of 18 to 10°C. Within 8h after transfer of mutant plants from growth at 23 to 13°C, accumulation of the newly synthesized chloroplast‐localized polypeptides stearoyl‐ACP desaturase, glutamine synthetase and OEC 23 was severely impaired. By contrast, there was no apparent deleterious effect on the accumulation of two extrachloroplastic proteins examined: the elongation factor lα, and the phloem‐specific, extrachloroplastic isoform of glutamine synthetase. In one instance examined in detail, chilling did not decrease the accumulation of mRNA for stearoyl‐ACP desaturase, indicating that the effect was post‐transcriptional. Chloroplasts isolated from chilled wild‐type andchslplants were equally able to process and protect from protease digestionin vitrosynthesized pre‐plastocyanin. The results suggest that thechslmutant may be defective in some aspect of chloroplast protein accumulation

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00540.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTExcision of a growing stem causes local wound responses, such as membrane depolarization and growth inhibition, as well as effects at larger distances from the cut. In this study, cucumber hypocotyls were excised 100mm below the hook, so that the growing region was beyond the reach of the wound‐induced depolarization (up to 40mm). Even at such a distance, the cut still caused a considerable and rapid drop in the hypocotyl growth rate. This growth response is not a direct wound response because it does not result from the cut‐induced depolarization and because it can be simulated by root pressure manipulation (using a pressure chamber). The results indicate that the growth response resulted from the rapid release of the xylem pressure upon excision. To test this conclusion we measured the xylem pressure by connecting a pressure probe to the cut surface of the stem. Xylem pressure (Px) was found to be +10 to +40kPa in cucumber hypocotyls and ‐5 to ‐10 kPa or lower in pea epicotyls. Excision of the cucumber hypocotyl base led to a rapid drop in Pxto negative values, whereas excision in pea led to a rapid rise in Pxto ambient (zero) pressure. These fast and opposite pxchanges parallel the excision‐induced changes in growth rate (GR): a decrease in cucumber and a rise in pea.The sign of the endogenous xylem pressure also determined whether excision induced a propagating depolarization in the form of a slow wave potential (SWP). Under normal circumstances pea seedlings generated an SWP upon excision whereas cucumber seedlings failed to do so. When the Pxin cucumber hypocotyls was experimentally inverted to negative values by incubating the cumber roots in solutions of NaCN or n‐ethylmaleimide, excision caused a propagating depolarization (SWP). The experiment shows that only hydraulic signals in the form of positive Pxsteps are converted into propagating electric SWP signals. These propagating depolarizations might be causally linked to systemic ‘wound’ responses, which occur independently of the short‐distance or direc

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00541.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTUsing a combination of gas‐exchange and chlorophyll fluorescence measurements, low apparent CO2/O2specificity factors (1300 mol mol−1) were estimated for the leaves of two deciduous tree species (Fagus sylvatica and Castanea sativa). These low values contrasted with those estimated for two herbaceous species and were ascribed to a drop in the CO2mole fraction between the intercellular airspace (Ci) and the catalytic site of Rubisco (Cc) due to internal resistances to CO2transfer. Cc. was calculated assuming a specificity of Rubisco value of 2560 mol mol−1. The drop between Ciand Ccwas used to calculate the internal conductance for CO2(gi). A good correlation between mean values of net CO2assimilation rate (A) and giwas observed within a set of data obtained using 13 woody plant species, including our own data. We report that the relative limitation of A, which can be ascribed to internal resistances to CO2transfer, was 24–30%. High internal resistances to CO2transfer may explain the low apparent maximal rates of carboxylation and electron transport of some woody plant species calculated from A/C

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00542.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTWheat (Triticum aestivum L. cv Broom) coleoptiles were stimulated by unilateral blue light pulses, the duration of which varied between 3 s and 30 min, under microgravity conditions on the IML‐1 Spacelab mission and in ground controls. The stimuli covered first positive, indifferent and second positive response regions. When phototropic responses were observed under low‐gravity conditions, slightly fewer seedlings responded compared with 1 g conditions. The latent period was similar in flight and 1g treatments (10–20 min), except for the response to 300,μmol m−2in the indifferent response region, where a positive response in flight plants followed a 130 min latent period, while no response was observed in 1 g plants. First positive responses at Og were slightly enhanced, both in magnitude and in duration, compared to the 1 g controls, but not to the extent predicted by clinostat studies. The response kinetics in the second positive region at 1g showed a plateau at 120 min, in contrast to the single maximum at Og. The fluence‐response relationship was similar in both flight and ground controls. Only the responses to 4 and 6μmolm‐2 showed significantly greater curvatures at 9g. This contrasts with previous clinostat studies, which reported substantial response enhancement at all f

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00543.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTSalinity reduces fertility in rice (Oryza sativa L.), but little is known of the underlying cause(s). In order to determine the relative importance of pollen viability and stigmatic receptivity for seed setting, plants of the rice cultivar IR36 were treated with ‘artificial’ sea water (0,10, 25 or 5Omol−3with respect to NaCl) from 1 month after germination until the main tiller flowered.An increase in the salinity in the medium resulted in a decrease in the number of fertile florets and in the viability of pollen as determined both by pollen germination and by pollen staining with the tetrazolium salt 3‐(4,5‐dimethyl‐ithyazolyl)‐2,5‐diphenyl monotetrazolium bromide.In order to assess the effects of salt on stigmas, seed production was measured for salt‐grown and non‐salt‐grown female plants pollinated with viable pollen (from plants grown in the absence of salt). The percentage of seed set was reduced by 38% when the female plants were grown in 1Omol m−3Na and by 72% at 25mol m−3Na: no seed setting was recorded for plants grown in 50mol m−3Na. Comparisons between crosses involving male and female parents grown at different salinities indicated that effects on the female plants dominated those on pollinator plants. Mineral analysis of leaves of different ages showed that there was a gradient of K concentration from leaf to leaf which was opposite to that of Na and Cl at all levels of applied salinity: K was maximal in the flag leaf, where Na and Cl were minimal. Analysis also revealed that there was an increase in the concentrations of Na and Cl and a decrease in the concentration of K in the pollen grains and stigmas of plants subjected to saline conditions. Correlations between the concentration of Na and Cl in pollen and pollen staining and pollen germinationin vitrosuggest that Na and Cl perse were responsible for the poor viability. The change in ionic concentrations in pollen and stigmas was much larger than that in the younger leaves, and in particular very much larger than th

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00544.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTCold‐hardening of winter rye (Secale cerealeL. cv. Musketeer) increased dark respiration from −2.2 to −3.9 μmol O2m−2s−1and doubled light‐and CO2‐saturated photosynthesis at 20°C from 18.1 to 37.0μmol O2m−2s−1We added oligomycin at a concentration that specifically inhibits oxidative phosphorylation to see whether the observed increase in dark respiration reflected an increase in respiration in the light, and whether this contributed to the enhanced photosynthesis of cold‐hardened leaves. Oligomycin inhibited light‐ and CO2‐saturated rates of photosynthesis in non‐hardened and cold‐hardened leaves by 14 and 25%, respectively, and decreased photochemical quenching of chlorophyll a fluorescence to a greater degree in cold‐hardened than in non‐hardened leaves. These data indicate an increase both in the rate of respiration in the light, and in the importance of respiration to photosynthesis following cold‐hardening. Analysis of metabolite pools indicated that oligomycin inhibited photosynthesis by limiting regeneration of ribulose‐1,5‐bisphosphate. This limitation was particularly severe in cold‐hardened leaves, and the resulting low 3‐phospho‐glycerate pools led to a feed‐forward inhibition of sucrose‐phosphate synthase activity. Thus, it does not appear that oxidative phosphorylation supports the increase in photo‐synthetic O2evolution following cold‐hardening by increasing the availability of cytosolic ATP. The data instead support the hypothesis that the mitochondria function in the light by using the reducing equivalents gen

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00545.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTGenetic variants for abscisic acid (ABA) sensitivity are important for investigating the role of ABA sensitivity in conditioning plant response to environmental stress, and especially to those soil conditions that may elicit a root‐mediated hormonal signal. This study was performed in order to isolate variation in ABA sensitivity among wheat (Triticum aestivumandT. durum) cultivars, as characterized by two plant responses: (i) shoot growth reduction in response to 5×10−2mol m−3ABA (racemic) in the root medium of hydroponically grown plants, and (ii) changes in transpiration and gas exchange in a bioassay of detached leaves (leaflaminac) infused with 10−4mol m−3ABA.Very significant (P≤0.01) and repeatable differences were found among 36 wheat cultivars and 19 landraces in the growth rate in ABA‐containing nutrient solutions, expressed as a percentage of the growth rate in control nutrient solutions (ABA/control ratio). In duplicate experiments, the ABA/control ratio ranged between 60 and 83% for the least sensitive cultivars (V2151‐3, Bethlehem, K1056 and Sunstar) and between 9 and 19% for the most sensitive cultivars (Sundor, Comet, Barkaec and V5). In the transpiration bioassay, performed with seven selected cultivars, it was found that the reductions in transpiration of ABA‐infused leaves corresponded very well with the reductions in growth in response to ABA in the root media. Measurement of gas exchange in the detached leaves of two cultivars differing in ABA sensitivity (Bethlehem and Sundor) showed that variable ABA sensitivity was expressed very well in the stomatal conductance, carbon exchange rate (CER) and photosynthetic capacity (CER/Ciratio) of the leaf. These results therefore allowed us to isolate wheat variants for ABA sensitivity and to conclude that, while ABA sensitivity is expressed in the growth of plants challenged by ABA in the root medium, the control of sensitivity resides, at least p

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00546.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY

摘要:

ABSTRACTThe foliar natural abundance of15N was analysed to compare the potential nitrogen sources of vascular rainforest epiphytes and associated soil‐rooted trees. Leaves of epiphytes collected from six rainforest communities in Brazil, Australia and the Solomon Islands were depleted in15N relative to the trees at each site. Epiphyte δ15N was as low as ‐6.4%o, while trees were generally enriched in15N (0.7 to 3.5%o). These results indicate either that epiphytes use nitrogen sources depleted in15N or that discrimination against15N is an intrinsic function of epiphyte physiology. At three sites, epiphytes could be grouped into those having both low δ15N and low leaf‐nitrogen content and those possessing both high δ15N and high leaf‐nitrogen content. The second group had δ15N values in the range sometimes attributable to N2fixation (‐2 to 0%o). There was no correlation between growth form and δ15N. It is concluded that epiphytes may utilize15N‐depleted nitrogen from atmospheric depositio

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1995.tb00547.x

出版商:Blackwell Publishing Ltd    

年代:1995

数据来源: WILEY