摘要:

The dynamics of root growth was studied in weightlessness. In the absence of the gravitropic reference direction during weightlessness, root movements could be controlled by spontaneous growth processes, without any corrective growth induced by the gravitropic system. If truly random of nature, the bending behavior should follow socalled ‘random walk’ mathematics during weightlessness. Predictions from this hypothesis were critically tested.In a Spacelab ESA‐experiment, denoted RANDOM and carried out during the IML‐2 Shuttle flight in July 1994, the growth of garden cress (Lepidium sativum) roots was followed by time lapse photography at 1‐h intervals.The growth pattern was recorded for about 20 h. Root growth was significantly smaller in weightlessness as compared to gravity (control) conditions.It was found that the roots performed spontaneous movements in weightlessness. The average direction of deviation of the plants consistently stayed equal to zero, despite these spontaneous movements. The average squared deviation increased linearly with time as predicted theoretically (but only for 8–10 h).Autocorrelation calculations showed that bendings of the roots, as determined from the 1‐h photographs, were uncorrelated after about a 2‐h interval.It is concluded that random processes play an important role in root growth. Predictions from a random walk hypothesis as to the growth dynamics could explain parts of the growth patterns recorded. This test of the hypothesis required microgravity conditions as provided for in a s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00198.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The growth rate of maize (Zea maysL. cv. Cross Bantam T51) coleoptiles in the dark was highest at the basal zone and decreased towards the tip. Growth was strongly inhibited by white fluorescent light (5 W m−2), especially in the basal zone of coleoptiles. Light irradiation caused an increase in the values of stress‐relaxation parameters, theminimumstress‐relaxation time and the relaxation rate and a decrease in the extensibility (strain/stress) of the cell walls at all zones. In addition, during growth, the accumulation of osmotic solutes was strongly inhibited by white light irradiation, resulting in an increased osmotic potential. The influences of white light on the mechanical properties of the cell wall and the osmotic potential of the tissue sap were most prominent in the basal zone. Significant correlations were observed between the increment of coleoptile length and the mechanical properties of the cell walls or the osmotic potential of the tissue sap and osmotic solutes content. Furthermore, light inhibited the outward bending of split coleoptile segments. These facts suggest that white light inhibits elongation of maize coleoptiles by modifying both the mechanical properties of the cell walls and cellular osmotic potential, which control the rate of water u

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00199.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The role of tubulin and actin in the development of Scots pine (Pinus sylvestris) roots and in the formation of the ectomycorrhiza with the basidiomyceteSuillus bovinuswas studied by immunoblotting of 2D‐gels with anti‐tubulin and anti‐actin antibodies. In the short roots the α‐tubulin pattern was different from that in the other root types due to the more acidic pI of the two α‐tubulins. During the formation of the ectomycorrhiza, two new α‐tubulins were detected in the acidic α‐tubulin cluster. No such variation occurred in the plant β‐tubulin patterns. The fungal tubulins dominated in the ectomycorrhiza, but no changes in tubulin polypeptide patterns from those in theS. bovinusmycelium were observed. Contrary to the tubulins, plant actin dominated in the mycorrhiza. The specific α‐tubulin patterns of uninfected and infected short roots indicate that α‐tubulin is involved in the morphogenesis ofPinus sylvestrisshort roots. The high level of plant actin at early stage of the mycorrhiza formation suggests a significant role of this protein in the interaction between pla

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00200.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

We investigated the relation between the toxic effect of aluminum (Al) on root growth and the lignin deposition in wheat (Triticum aestivumL. cvs Atlas 66 and Scout 66). In the Al‐tolerant cultivar Atlas 66, control treatment without AlCl3at pH 4.75, cell length increased dramatically in the portion of the root that was 0.6 to 3.2 mm from the root cap junction (approximately 1.0 to 3.6 mm from the root tip). However, treatment with 20 μMAlCl3for 24 and 48 h completely inhibited root elongation and markedly decreased the length and increased the diameter of the cells in the same portion of the root. Moreover, marked deposition of lignin was observed in the cells that corresponded to the portion 1.5 to 4.5 mm from the root tip in Atlas 66 roots treated with 20 μMAlCl3, while no deposition of lignin was detected in control roots. Treatment with 5 μMAlCl3slightly inhibited root growth and there was no deposition of lignin in the root. On the other hand, in roots of the Al‐sensitive cultivar Scout 66, treatment with 5 μMAlCl3completely inhibited root growth and markedly induced deposition of lignin. These results suggest that lignification in the elongating region coincided with the extent of inhibition of root growth by Al in two wheat cultivars that differed in their sensitivit

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00201.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Screening for mutants deficient in the high affinity system of nitrate uptake was performed using mutagenized M2population of rice (Oryza sativa, cv. Nipponbare or Kinmaze). For selecting mutants, M2seedlings were transferred individually to 10 ml solution containing 250 μMpotassium nitrate and 500 μMcalcium sulphate at 20 or 28°C. After 6 or 24 h, nitrate concentration of the solution was determined with a nitrate selective electrode and the seedlings showing impaired nitrate uptake were selected as nitrate uptake deficient variants. Of 74 variants, three were confirmed to be mutants with low nitrate uptake ability in the M3generation. Potassium uptake ability also decreased in the mutants. Three mutants were divided into two groups based on the analysis of nitrate reductase (NR, EC 1.6.6.1) activity and chlorate resistance. Two,NUE13andNUE36, had a lower level of NR activity than the original cultivar and were not resistant to chlorate, while the seedlings ofNUE50had the same level of NR activity as the original cultivar and were more resistant to chlorate than the original cultivar. All mutants were resistant to cesium, a toxic ion analogue for potassium, suggesting that the decreased levels of both nitrate and potassium uptake were coupled to the change of plasma membrane H+‐ATPase acti

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00202.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Basipetal auxin transport along the zucchini hypocotyl requires the cell‐to‐cell translocation of this hormone. Several authors have demonstrated that naphthylphthalamic acid (NPA) blocks auxin efflux. It is believed that NPA binds to a regulatory protein that modulates the activity of the carrier rather than to the carrier itself. A few regulatory mechanisms have been suggested but all lack strong supporting experimental evidence. Four classes of protein tyrosine kinase inhibitors (PTKIs) have been used to investigate the NPA perception pathway. First, six synthetic tyrphostins, inhibitors of the epidermal growth factor receptor (EGF‐R), were shown to displace NPA on plasmalemma fractions. The most potent compound was (3,4‐dihydroxybenzylidene)‐thiocyanoacetamide (tyrphostin A47). The inactive counterpart of tyrphostin A47, (4‐methoxybenzylidene)‐malononitrile (tyrphostin A1), was unable to displace NPA. Tyrphostins did not inhibit auxin efflux but were antagonists of the inhibition of auxin efflux by NPA. Again, tyrphostin A47 was the most effective and tyrphostin A1 was inactive. Second, the flavonoid genistein, also an EGF‐R inhibitor, showed an effect on NPA binding and NPA antagonism similar to the one for the tyrphostins. Daidzein, the inactive counterpart of genistein, was ineffective in displacing NPA and in antagonizing its inhibition of auxin efflux. Two other PTKIs, curcumin and lavendustin A, displayed similar characteristics. Calmodulin antagonists, protein serine/threonine kinase inhibitors, and phosphatase inhibitors were inactive. These results suggest that the NPA binding protein may be related to mammalian tyrosine kinases and may regulate the auxin efflux carrier by

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00203.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Some processes of excess radiation dissipation have been associated with changes in leaf reflectance near 531 nm. We aimed to study the relations between the photochemical reflectance index (PRI) derived from this signal, and photosynthetic radiation‐use efficiency (defined as net CO2assimilation rate/incident photon flux density) in a cereal canopy. Measurements of reflectance, fluorescence, gas exchange and xanthophyll cycle pigments were made in the morning, midday and afternoon in barley canopies with two levels of nitrogen fertilization. The photosynthetic radiation‐use efficiency decreased at midday, mainly in the third leaf, in both treatments, with lower values for the nitrogen deficient leaves. The zeaxanthin content showed the inverse pattern, increasing at midday and in the nitrogen deficient treatment. The photosynthetic radiation‐use efficiency was well correlated with the epoxidation state, EPS (violaxanthin + 0.5 antheraxanthin)/(violaxanthin + antheraxanthin + zeaxanthin). The PRI [here defined as (R539‐ R570)/(R539+ R570)] was significantly correlated with epoxidation state and zeaxanthin and with photosynthetic radiation‐use efficiency. These results validate the utility of PRI in the assessment of radiation‐use efficiency at c

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00204.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitative changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower (Helianthus annuusL.) canopies. Mean leaf duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly (P<0.05) reduced from 51 to 19 days as crop population density was increased from 0.47 to 4.76 plants m−2. High compared to low plant population density was associated with earlier reduction in the photosynthetically active radiation (PAR) and red/far‐red ratio (R/FR) reaching the target leaf. However the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR‐reflecting mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR‐ (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly (P<0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR‐controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both leaf surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR‐ control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decre

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00205.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Uptake of14C‐sugars and activities of sucrose metabolizing enzymes were determined in order to study the mechanism(s) of sucrose accumulation in developing peach fruit. Mesocarp of young peach fruit contained glucose and fructose but little sucrose. Starting 88 days after anthesis (DAA) the sucrose concentration increased greatly. The mechanism of sucrose accumulation was studied by measuring14C‐sucrose and14C‐glucose uptake rates at three different stages of fruit development, and by assaying weekly the activity of enzymes involved in the hydrolysis and/or synthesis of the soluble sugars. Uptake of 0.5–100 mM14C‐sucrose and14C‐glucose by mesocarp tissue slices showed a complex pattern at the first stage of fruit development (62 DAA). During the subsequent growth stages the pattern of sugar uptake changed and was approximately monophasic at the third stage of fruit development.At 10 mM, glucose was taken up more rapidly than sucrose at the first and second stage of fruit development. Uptake was partially inhibited by the uncoupler carbonylcyanidem‐chlorophenylhydrazone (CCCP) at 25 μM.These results, together with the presence of a putative extracellular invertase, suggest an apoplastic route for sucrose uptake which is dependent, at least in part, on energy supply.Activities of sucrose hydrolyzing enzymes (insoluble acid invertase, soluble acid invertase, neutral invertase, sucrose synthase) were high in young fruits and declined sharply with fruit development concomitantly with accumulation of sucrose. The storage of the sugar was not accompanied by a rise in synthetic activities (sucrose synthase, sucrose phosphate synthase), suggesting that sucrose could, at least in part enter the carbohydrate

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00206.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

The effects of seed priming with 6MNaCl solution have been investigated with respect to growth and physiological responses of tomato plants (Lycopersicon esculentumMill. cv. Pera) exposed to 70 and 140 mMNaCl nutrient solutions from 11 to 60 days after sowing. Tomato seedlings from primed seeds emerged earlier than from non‐primed seeds. At 70 mM, a lower shoot and root dry weight reduction was found in plants from primed seeds at the different harvests (30, 45 and 60 days after sowing), while at 140 mMthe positive effect of seed priming was only shown in roots. Significant changes in Na+and CI−accumulation with seed priming were only found in roots at 60 days after sowing, with ion accumulation in roots being higher in plants grown at 70 and 140 mMfrom primed seeds. In leaves of salt‐treated plants, significant increases in sugars and organic acids with seed priming were found from 30 days after sowing, and these increases were higher at longer treatment times. In roots, however, only the organic acids tended to increase in plants from primed seeds, although they increased less than in leaves, especially at 60 days after sowing. These results support the hypothesis that priming of seeds with NaCl induces physiological changes in the plants, changes which are shown more clearly at advanced growth s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1996.tb00207.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY