ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00383.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThis study was conducted lo determine whether naturally occurring xylem cytokinins, when supplied to leaves via the xylem at approximately endogenous concentrations, increase transpiration and delay senescence in selected monocot species (oat and wheat). The concentrations of some of the major cytokinins (zeatin, dihydrozeatin, ciszeatin and their ribosides, the O‐glucosides and nucleotides) were determined in the xylem exudate of oat and wheat seedlings by radioimmunoassay. Evidence is presented that the small volume of exudate (4–5 mm3) collected per plant was xylem sap in transit at the time of shoot excision. Using the data on cytokinin levels, the individual bases and ribosides (and a base/riboside mixture), at multiples of concentrations determined in xylem sap, were tested in transpiration and senescence bioassays. The individual O‐glucosides (and mixtures of the O‐glucosides) were similarly tested at (i) multiples of the molar concentrations of the corresponding bases and ribosides, and/or at (ii) multiples of the endogenous concentrations. Similarly, zeatin and dihydrozeatin nucleotides were tested at multiples of the molar concentration of zeatin riboside and, in some instances, at multiples of endogenous concentrations.Our results suggest that, at least in oat and possibly in wheat, zeatin‐type bases, ribosides and O‐glucosides supplied to the leaf in xylem sap are likely to play a role in regulating transpirationin vivo. O‐glucosides in oat xylem sap may be important regulators of leaf senescence in the intact plant. The nucleotides were present in xylem sap at lower concentrations than most of the bases, ribosides and O‐glucosides. The nucleotides appear likely to play a lesser role than the bases, riboside and O‐glucosidcs in controlling transpiration and senescence in

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00384.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTInfestation ofAcacia acuminataby the xylem‐tapping mistletoeAmyema preissiiinvariably results in inhibition of growth, defoliation and eventual death of host branch parts distal to the mistletoe. Branch sectional areas proximal (P) and distal (D) to mistletoes are used to classify stages of parasitism, with P:D area ratios of 5–6 invariably associated with distal branch senescence. As monopolization of the branch proceeds, mistletoe leaf area increases in parallel with declining host foliage area, and the specific hydraulic conductivity of distal host wood declines sharply relative to that of proximal wood, mineral composition and concentrations of nitrogenous solutes in xylem sap are at no stage appreciably different from those of proximal wood. After the demise of the distal branch parts, the transectional area of the host branch stump increases linearly with increasing mistletoe leaf area, the branch area supporting a unit of mistletoe leaf area always being about 3 times greater than that supporting a unit of host foliage area on unparasitized branches. This differential, compounded with high transpiration rates and selective uptake of host xylem solutes by the haustorium, fosters substantial mineral enrichment of the mistletoe relative to its host. The study provides a background for future investigation of possible cellular mechanisms continuously driving structural and functional changes in favour of the mistle

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00385.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTLow phosphorus availability stimulates root hair elongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation ofArabidopsis thalianaroot hairs.Arabidopsis thalianaplants were grown in plant culture containing high (1000 mmol m−3) or low (1 mmol m−3) phosphorus concentrations, and root hair elongation was analysed by image analysis. After 15d of growth, low‐phosphorus plants developed root hairs averaging 0.9 mm in length while high‐phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low‐phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairlessaxr2 mutant, exogenously applied IAA stimulated root hair elongation in wild‐type high‐phosphorus plants and the auxin antagonist CM PA inhibited root hair elongation in low‐phosphorus plants. These results indicate that auxin may be involved in the low‐phosphorus respo

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00386.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTTo obtain information on plant microtubule stability to low temperature and Ca2+, the regulatory domain of polymerized tubulin from maize (Zea maysev. Black Mexican Sweet) was dissected by limited proteolysis with subtilisin. Tubulin in taxol‐stabilized microtubules was cleaved in a subtilisin concentration‐ and time‐dependent manner. Immunoblotting of microtubules with antibodies having mapped epitopes on α‐ and β‐tubulins revealed that cleavage initially removed ≤15 residues from the β‐tubulin carboxyl terminus to produce αβs‐microtubules. Subsequent cleavage occurred at an extreme site and an internal site within the α‐tubulin carboxyl terminus. Electron microscopy revealed that αβs‐microtubules were ultra structurally indistinguishable from uncleaved control αβ‐micro‐tubules. Quantitative polymer sedimentation showed that low temperature treatment (0°C) caused significant depolymerization of αβ‐microtubules, but little depolymerization of αβs‐microtubules. Ca2+enhanced the cold‐induced depolymerization of both αβ‐ and αβs‐microtubules. However, αβs‐microtubules were significantly more stable to depolymerization by cold and Ca2+than were αβ‐micro‐tubules. The results showed that maize microtubules containing shortened β‐tubulin carboxyl termini are relatively resistant to the combined depolymerizing effects of cold and Ca2+. Thus, the extreme carboxyl terminus of β‐tubulin is a crucial element of the plant tubulin regulatory domain and may be involved in the modula

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00387.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIsoprene is the primary biogenic hydrocarbon emitted from temperate deciduous forest ecosystems. The effects of varying photon flux density (PFD) and nitrogen growth regimes on rates of isoprene emission and net photosynthesis in potted aspen and white oak trees are reported. In both aspen and oak trees, whether rates were expressed on a leaf area or dry mass basis, (1) growth at higher PFD resulted in significantly higher rates of isoprene emission, than growth at lower PFD, (2) there is a significant positive relationship between isoprene emission rate and leaf nitrogen concentration in both sun and shade trees, and (3) there is a significant positive correlation between isoprene emission rate and photosynthetic rate in both sun and shade trees. The greater capacity for isoprene emission in sun leaves was due to both higher leaf mass per unit area and differences in the biochemical and/or physiological properties that influence isoprene emission. Positive correlations between isoprene emission rate and leaf nitrogen concentration support the existence of mechanisms that link leaf nitrogen status to isoprene synthase activity. Positive correlations between isoprene emission rate and photosynthesis rate support previous hypotheses that isoprene emission plays a role in protecting photosynthetic mechanisms during stress.

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00388.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTFollowing UV mutagenesis of protonemal tissue of the mossCeratodon purpureuswe have isolated different aphototropic mutant lines that can be divided into two distinct classes. One class, represented by the lineptr1, shows characteristic features of phytochrome chromophore deficiency.ptrlshows negligible photoreversibility (<5% of wild type), whereas immunoblots show normal apoprotein levels. The aphototropic phenotype could be partially restored with biliverdin, a precursor of the phytochrome chromophore. It was found that, whereas in wild type formation of Pfr leads to suppression of gravitropism, there is no such suppressionptrl. In addition,ptr1shows lower chlorophyll levels than the wild type. These findings indicate that, as expected for a chromophore‐deficient mutant, multiple phytochrome effects are lost. The other class of mutants, represented by the lineptr103, shows more specific effects. In this mutant, only phototropism is affected. Suppression of gravitropism, the content of chlorophyll and photoreversibility of phytochrome were similar to those of the wild typ

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00389.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIsolated characean internodal cells ofNitellopsis obtusacan be stored in artificial pond water for many days, but they cannot survive in 100mol m−3NaCl solution unless more than several mol m−3Ca2+is added. Short‐term effects of NaCl stress on the cytosolic concentration of Ca2+([Ca2+]c), cytosolic pH (pHc) and vacuolar pH (pHv) were studied in relation to the external concentration of Ca2+([Ca2+]e). Changes in [Ca2+]cwere measured with light emission from a Ca2+‐sensitive photoprotein, semisyntheticfch‐aequorin which had been injected into the cytosol. Both pHcand pHvwere measured with double‐barrelled pH‐sensitive microelectrodes. When internodal cells were treated with 100 mol m−3NaCl (0–1 mol m−3NaCl (0.1 mol m−3[Ca2+]e), [Ca2+]cincreased and then recovered to the original level within 60 min. The time course of the transient change in [Ca2+]cwas not influenced by the level of [Ca2+]c(0.1 and 10 mol m−3). In some cases, the transient increase in [Ca2+]cwas induced only by increasing external osmotic pressure with sorbitol. In response to treatment with 100 mol m−3NaCl (0.1 mol m−3[Ca2+]c), pHcdecreased by 0.1–0.2 units after 10min but recovered after 30–60 min, while pHvincreased by 0.4–0.5 units after 2–50 min and tended to recover after 60 min. The initial changes in both pHcand pHvwere suppressed when [Ca2+]ewas raised from 0.1 to 10mol m−3. These results show that the charophyte algaNitellopsiscan regulate [Ca2+]c, pHcand pHvunder NaCl stress in the short term and that the protective effect of Ca2+on salinity stress is apparently unrelated to p

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00390.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTA two‐component model of growth and maintenance respiration is used to study the response of northern red oak (Quercus rubraL.) seedlings and 32‐year‐old trees to sub‐ambient (10 μmol h; cumulative dose based on 7 h daily mean), ambient (43 μmol h), and twice‐ambient (85 μmolh) ozone. The relative growth rates (RGR) of leaves sampled from seedlings and trees were similar across treatments, as were specific leaf respiration rates (SRR). Growth coefficients estimated from the SRR versus RGR relationship averaged 25‐3 mol CO2 kg−1leaf dry mass produced for seedlings and 21‐5 mol kg−1for trees. Maintenance coefficients ranged from 0‐89 to 1‐07 mol CO2kg−1leaf dry mass d−1for seedlings and from 0‐64 to 0‐84 mol kg‐1 d−1for trees. Neither coefficient was affected by ozone. Leaves sampled throughout the growing season also showed little response of respiration to ozone. This occurred despite a 30% reduction in net photosynthesis for trees grown at twice‐ambient ozone. These results suggest that growth and maintenance respiration in young northern red oak leaves are not affected by ozone and that in older leaves injury can occur without a parallel increase

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00391.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTInAgave salmianaOtto ex Salm. var.salmianagrown for 4½ months in open‐top chambers, 55% more leaves unfolded and 52% more fresh mass was produced at 730 than at 370μmol CO2mol−1. A doubling of the CO2concentration also stimulated growth in another highly productive CAM species,Opuntia ficus‐indica(L.) Miller, leading to earlier initial ion and 37% more daughter cladodes. Substantial net CO2uptake occurred earlier in the afternoon and lasted longer through the night forA. salmianaat 730 than at 370μmol CO2mol−1, resulting in 59% more total daily net CO2uptake. The Michaelis constant (HCO3−) for PEPCasc was 15% lower forA. salmianaand 44% lower forO. ficus‐indicawhen the CO2concentration was doubled; the percentage of Rubisco in the activated statein vivowas on average 64% higher at the doubled CO2concentration. Thus the substantial increases in net CO2uptake and biomass production that occurred in these two CAM species when the ambient CO2concentration was doubled resulted mainly from higher inorganic carbon levels for their carboxylating enzymes, a greater substrate affinity for PEPCase, and a greater percentage of Rubisco in the a

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00392.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY