摘要:

We examined the roles of turgor potential and osmotic adjustment in plant growth by comparing the growth of spring wheat (Triticum aestivumcv. Siete cerrors) and sudangrass (Sorghum vulgarevar. Piper) seedlings in response to soil water and temperature stresses. The rates of leaf area expansion, leaf water potential and osmotic potential were measured at combinations of 5 soil water potentials ranging from −0.03 to −0.25 MPa and 6 soil temperatures ranging from 14 to 36°C. Spring wheat exhibited little osmotic adjustment while sudangrass exhibited a high degree of osmotic adjustment. However, the rate of leaf area growth for sudangrass was more sensitive to water stress than that of spring wheat. These results were used to evaluate the relationship between growth and turgor potential. The modified Arrhenius equation based on thermodynamic considerations of the growth process was evaluated. This equation obtains growth rate as a function of activation energy, enthalpy difference between active and inactive states of enzymes, base growth rate and optimum temperature. Analyses indicate that the modified Arrhenius equation is consistent with the Lockhart equation with a metabolically controlled cell wall extensibi

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02184.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Changes in the concentrations of free amino acids and specific organic acids were analysed during the induction of drought stress inBrassica napus. Most of the amino acids showed a characteristic linear increase with the induction of drought stress inBrassicaleaves, increasing an average of 5.9‐fold over control levels, followed by a reduction in concentration upon rehydration of the plants. Pyruvate concentrations doubled after 4 days of drought stress whereas 2‐oxoglutarate concentrations remained relatively constant. The activities of two of the enzymes involved in amino acid biosynthesis, alanine aminotransferase (EC 2.6.1.2) and aspartate aminotransferase (EC 2.6.1.1), were also measured. Neither enzyme showed any increase in activity, except when the plants were rehydrated. This suggests that the increase in both alanine and aspartate levels results from the increase in their precursors pyruvate and glutamate and may not require increased enzyme activity. The effect of drought stress upon changes in protein synthesis was analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. We found that there was an overall decrease in protein synthesis with the induction of drought stress, followed by a resumption of synthesis upon rehydration. In addition, the synthesis of a number of specific polypeptides was found to decrease upon water loss in the lea

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02185.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Free and conjugated abscisic acid (ABA) levels in stem‐cultured plantlets of potato (Solanum commersoniiDun, PI 458317) during cold acclimation were measured. The levels of free and conjugated ABA were measured by an enzyme immunoassay (EIA) with rabbit anti‐ABA‐serum. The use of immunoglobulin G fraction purified from rabbit antiserum and the methylated form of ABA resulted in an improved measuring range (0.01 to 10 pmol ABA) and precision (slope of logit‐log plot, −1.35) of EIA, compared to the use of antiserum and free ABA. Estimates of the EIA were consistent with those resulting from a commercial EIA. Under a 4/2°C (day/night) temperature regime, the potato plantlets increased cold hardiness from −5°C (warm‐grown control) to −10°C by the 7th day. During the same period, there were two transitory increases in free ABA, the first one three‐fold from 1.5 to 5.3 nmol (g dry weight)−1on the 2nd day and the second one five‐fold from 1.5 to 7.6 nmol (g dry weight)−1on the 6th day. Each increase in ABA concentration was followed by an increase in cold hardiness. There was no significant change in conjugated ABA content (4.2±0.6 nmol [g dry weight]−1) throughout the cold acclimation period. The lack of an interrelationship between levels of free and conjugated ABA suggested that the transitory increase in free ABA during cold acclimation was not a result of the conversion of conjugated ABA. The increase in free ABA due to biosynthesis of ABA during potato

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02186.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

During cold acclimation of potato plantlets (Solanum commersoniiDun, PI 458317), there are two transitory increases in free ABA content corresponding to a three‐fold increase on the 2nd day and a five‐fold increase on the 6th day (Ryu and Li 1993). During this period, plantlets increased in cold hardiness from −5°C (killing temperature, control grown at 22/18°C, day/night) to −10°C by the 7th day of exposure to 4/2°C (day/night). This increase in free ABA was not found when cycloheximide (CHI), an inhibitor of cytoplasmic protein synthesis, was added to the culture medium 6 h before exposure to low temperatures. Plantlets treated with CHI did not acclimate to cold, maintaining a hardiness level (−5°C) similar to that of the 22/18°C‐grown plantlets. When the CHI‐treated plantlets were exposed to low temperatures for 3 days, transferred to CHI‐free culture medium and grown at low temperatures, the plantlets showed a transitory increase in free ABA 2 days later. This increase was followed by the development of cold hardiness (−8°C). Application of CHI to the culture medium after 3 days of cold acclimation, when the first ABA peak and a partial development of cold hardiness (−8°C) had occurred, blocked the second transitory increase in free ABA and resulted in no further development of cold hardiness. These results suggest that de novo synthesis of proteins is required for these transitory increases in free ABA during cold accl

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02187.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Carbohydrate and mineral nutrition was studied in relation to abscission in fruitlets from leafy inflorescences of the Washington navel orange (Citrus sinensis[L.] Osbeck). Differences in the growth rate of the fruitlets permitted to predict abscission several weeks in advance. This allowed characterization of early differences in composition and behaviour of persisting and abscising fruitlets.Inflorescences with persisting fruitlets accumulated more mineral elements than inflorescences with abscising fruitlets, and for the phloem‐mobile elements the excess accumulation was allocated to the fruitlets. Starch accumulated in the inflorescence leaves during early fruitlet growth, and this accumulation was enhanced by the persisting fruitlets despite their higher growth rate and mobilizing ability. The relations between the fruitlets and the inflorescence leaves cannot be explained totally in terms of source sink relationships; a hormonal regulation of the leaves by the fruitlets is postulated.Acid invertase activities and hexose concentration in the pericarp were higher in the abscising fruitlets. The lower early growth rate of these fruitlets is thus not caused by a limitation in carbohydrate supply. It seems more related to carbohydrate utilization, probably hormonally mediated, as demonstrated by the higher dependence on hormone supply for the growth in vitro of the endocarp explant

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02188.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Glycosidases were extracted from grapefruit (Citrus paradisiMacf. cv. Ruby Red) flavedo, albedo, and juice vesicles harvested at five periods throughout the season. Flavedo β‐galactosidase activity was high at the September harvest and then significantly declined by November. Thereafter, no further changes occurred in β‐galactosidase activity. Flavedo α‐galactosidase activity was low and unchanged throughout the study. α‐Mannosidase, initially low in flavedo, steadily increased with advanced maturity. Trends in glycosidase activities of albedo were similar but attenuated. Juice vesicle β‐galactosidase did not change through the study period, whereas α‐galactosidase activity decreased 70% after the initial harvest period. α‐Mannosidase was initially high and then decreased to 50% of the original activity. A second peak of activity was measured in March, followed by a second decline. Extractability differences of the glycosidases suggest differences in compartmentation and function. Two isozymes of α‐mannosidase were separated in flavedo and one in juice vesicles, and characteristics were determined at an early and late harvest period. The results suggest that changes in the three glycosidases could be used to further define maturity and s

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02189.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Upon exposure to air at 20°C and 60% relative humidity (RH), an occlusion to water uptake developed in the basal stem segment of cut, flowering Sonia roses. The development of the occlusion was delayed by removing the leaves before storage, indicating an effect of transpiration. Placing the stem ends at 100% RH during exposure to air had no effect, which shows that water loss through the cut end is not the cause. Scanning electron microscopy did not show plant gums or tyloses in the water conducting elements.The hypothesis by Scholander et al. (1955) that water uptake into stems held in air and then placed in water occurs through conduit walls rather than the lumen was tested by using stems of which the cut surface was covered with laboratory grease and a ring of bark was removed (girdling). Girdled stems placed in water remained fully turgid when the girdled area was about 60 mm2or more. Water uptake was strongly inhibited when the girdled stems were exposed to air for 24–36 h, as in non‐girdled controls exposed to air for the same period. Inclusion of a surfactant (nonylphenoxypolyethoxy ethanol) in the vase water, however, facilitated water uptake after dry storage of normal cut flowering stems but did not improve water uptake into the girdled stem system, which is inconsistent with the hypothesis.It is concluded that the vascular occlusion developing upon exposure to air cannot be explained by decreased flow in the wall pathway for w

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02190.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The effects of aluminium ions on respiration of excised root apices from wheat (Triticum aestivum L. cv. Vulcan) and on isolated mitochondria have been investigated. Addition of 75μ M aluminium to the growth medium of 4‐day‐old seedlings inhibited O2uptake by excised root apices by 23 and 35% after 12 and 24 h, respectively. This decreased rate of respiration was initially caused by inhibition of the cytochrome pathway of mitochondrial electron transport. The cyanide‐insensitive, alternative pathway was inhibited only after more prolonged exposure to aluminium. Mitochondria isolated from roots of aluminium‐treated seedlings had reduced oxidative capacity with substrates that supply electrons to Complexes I and II, compared with mitochondria from roots of untreated control seedlings. The state 3 and state 4 rates of O2uptake and the uncoupled rates with these substrates were also inhibited when aluminium was added directly to reaction mixtures containing mitochondria isolated from untreated plants. In contrast, when aluminium was added to reaction mixtures oxidizing exogenous NADH, state 4 O2uptake was stimulated, whereas no effect was observed on the state 3 rate or the rate in the presence of uncoupler. The results suggest that aluminium initially affects electron flow through Complexes I and II, and that after more prolonged exposure, aluminium may also interact with other sites in mito

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02191.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA‐synthesis, applied during culture in vitro, inhibited the swelling of the petioles and promoted leaf formation. At high fluridone concentrations (10 or 33μM), swelling was completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and resulted in plantlets with scales only. When applied simultaneously with fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlets regenerated in vitro on scale explants at 20 or 25°C were harvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve rapid emergence after planting in soil. Fluridone added during the culture in vitro prevented the development of dormancy, and the bulblets did not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of culture at 20°C had not yet developed dormancy. Bulblets regenerated at 15°C were only slightly dormant. In both types of bulblets, it is unlikely that the lack of dormancy was due to low ABA‐levels since addition of ABA did not affect the dormancy status. These data indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of d

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02192.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Regulation of the cyclic activity of asparaginase (obtained as a purified protein complex) by a reversible auto‐phosphorylation process has been previously reported in the fungusLeptosphaeria michotii(West) Sacc.In the present study, the protein complex was purified in the presence of either a mixture of 3 protein phosphatase inhibitors (fluoride, vanadate and molybdate) or EGTA, during the cycle of asparaginase activity, and the protein kinase and protein phosphatase activities characterized. (I) At the phase of increasing asparaginase activity, a Ca2+/calmodulin‐dependent kinase activity was identified by (a) its inhibition by calmidazolium, reversed by calmodulin, and its inhibition by EGTA, but not by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole or polylysine (b) an increasing level of calmodulin bound to the complex, as estimated by enzyme‐linked immunosorbent assay (ELISA). (2) At the phase of decreasing asparaginase activity, the Ca2+‐calmodulin‐dependent kinase activity disappeared and a little calmodulin remained associated with the complex: phosphorylation of the complex was increased several‐fold by 1 nMokadaic acid and 25 nMinhibitor‐2, and was not affected by EGTA, indicating a protein phosphatase‐2A‐like activity. (3) When asparaginase activity was low, a little calmodulin was bound to the complex. The kinase could phosphorylate casein and phosvitin. was inhibited by poly(Glu/Tyr 4:1)n. dichloro‐(ribofuranosyl)‐benzimidazole and heparin, stimulated by polylysine and not affected by calmidazolium or EGTA, just as a casein kinase 2. A Ca2+‐dependent but calmodulin‐independent protein phosphatase activity, not affected by okadaic acid and inhibitor‐2. was then identified.We postulate the presence in the complex, of (a) only one protein kinase and one protein phosphatase, whose properties could change during thecycleof asparaginase activity: (b) two Ca2+/‐binding proteins: first calmodulin, which could bind to Ca2+and the casein kinase‐2 form to give a Ca2+/calmodulin‐dependent kinase, which could become Ca2+/calmodulin‐independent following an auto‐phosphorylation process: second a protein homologous to calmodulin, able to bind to the protein phosphatase‐2A catalytic subunit to give

ISSN:0031-9317    

DOI:10.1111/j.1399-3054.1994.tb02193.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY