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1.
I. G. Burns 《Plant and Soil》1992,142(2):221-233
A method is described for determining the way in which growth rate varies with plant nutrient concentration using a simple
nutrient interruption technique incorporating only 2 treatments. The method involves measuring the changes in growth and nutrient
composition of otherwise well-nourished plants after the supply of one particular nutrient has been withheld. Critical concentrations
are estimated from the relationship between the growth rate (expressed as a fraction of that for control plants of the same
size which remained well-nourished throughout) and the concentration of the growth-limiting nutrient in the plants as deficiency
developed. Trials of the method using young lettuce plants showed that shoot growth rate was directly proportional to total
N (nitrate plus organic N) concentration, and linearly or near-linearly related to K and P concentration over a wide range;
the corresponding relationship for nitrate was strongly curvi-linear. Critical concentrations (corresponding to a 10% reduction
in growth rate) determined from these results were similar to critical values calculated from models derived from field data,
but were generally higher than published estimates of critical concentration (based on reductions in shoot weight) for plants
of a similar size. Reasons for these discrepancies are discussed. Nitrate, phosphate or potassium concentrations in sap from
individual leaf petioles were highly sensitive to changes in shoot growth rate as deficiency developed, with the slope of
the relationships varying with leaf position, due to differences both in their initial concentration and in the rates at which
they were utilized in individual leaves. Each nutrient was always depleted more quickly in younger leaves than in older ones,
providing earlier evidence of deficiency for diagnostic purposes. Although the plants were capable of accumulating nitrate,
phosphate and potassium well in excess of that needed for optimum dry matter production during periods of adequate supply,
the rate of mobilization of these reserves was insufficient to prevent reductions in growth rate as the plants became deficient.
This brings into question the validity of the conventional concept that luxury consumption provides a store of nutrients which
are freely available for use in times of shortage. The implications of these results for the use of plant analysis for assessing
plant nutrient status are discussed. 相似文献
2.
The effects of P fertilizer rate on shoot growth and the total P concentration of the whole shoot, new and mature leaves,
symptom leaves and stems of Banksia ericifolia L. f., a P-sensitive species, were investigated in a six month greenhouse pot experiment. Shoot dry weight of plants growing
in an Australian sedge peat, coarse sand and perlite potting mix (1:1:1) increased with up to 100 mg P L−1 supplied as a six month controlled release P (0:18:0) fertilizer, but was reduced by toxicity at the highest application
rate (200 mg P L−1). Plants receiving this treatment developed chlorotic new and mature leaves. Leaf symptoms observed at rates of 60–100 mg
P L−1 were confined to old leaves and were related to the P concentration of the shoot. Growth was not affected at these rates.
The P concentration of stems was strongly influenced by P supply. This tissue acted as a sink for excess P, helping to regulate
the P concentration of leaves. The approximate range of P concentrations in stem tissue, associated with greater than 90%
of maximum shoot dry weight, was 0.5–1.5 g P kg−1 tissue dry weight. This was greater than that calculated for mature leaves (0.5–0.8 g kg−1) or for whole shoots (0.5–1.2 g kg−1). This wider range, and the capacity to store P in excess to requirement, makes the stem a better index tissue for plant
P status than either leaves or whole shoots.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
3.
Isoosmotic regulation of cotton and peanut at saline concentrations of k and na 总被引:2,自引:0,他引:2
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Peanut (Arachis hypogaea L.) and cotton (Gossypium hirsutum) plants were grown for 4 weeks in saline, isoosmotic rooting substrates with different proportions of K and Na. Isoosmotic media did not affect growth (except at the highest external K concentrations) or estimates of intracellular osmotic pressure in expanding leaves (i.e. osmotic pressure of leaf sap and intracellular osmotic pressure as calculated from pressure-volume curves). In expanded leaves, an increase in the proportion of external K increased sap osmotic pressure. The sum of [K+Na+Cl] in the sap of expanding and expanded leaves accounted for the effect of isoosmotic media on the concentration of osmolytes with high electrical conductance, so the difference between sap osmotic pressure and [K+Na+Cl] accounted for the concetration of osmolytes with low conductance. In expanding leaves, an increase in the proportion of external K increased [K+Na+Cl] and decreased the concentration of osmolytes with low conductance. In expanded leaves, an increase in the proportion of external K increased [K+Na+Cl] to approximately the same extent as sap osmotic pressure. Isoosmotic regulation was apparent in expanding leaves but not evident in expanded leaves. This suggests a turgor homeostat which can influence the concentration of organic solutes in expanding leaves but cannot control the import of inorganic solutes from a rooting medium nor the total production of organic solutes in plants with a low sink:source ratio. 相似文献
4.
Danuta Chołuj Romualda Karwowska Agnieszka Ciszewska Marta Jasińska 《Acta Physiologiae Plantarum》2008,30(5):679-687
Accumulation of various osmolytes was examined in plants of sugar beet cv. Janus grown under two soil water treatments: control
(60% of the field water capacity; FWC) and drought (30–35% FWC). The water shortage started on the 61st day after emergence
(DAE), at the stage of the beginning of tap-roots development and was imposed for 35 days. Osmotic potential of sugar beet
plant organs, particularly tap-roots, was decreased significantly as a consequence of a long-term drought. Water shortage
reduced univalent (K+, Na+) cations concentrations in the petioles and divalent (Ca2+, Mg2+) ions level in the mature and old leaves. Cation concentrations in the tap-roots were not affected by water shortage. The
ratio of univalent to divalent cations was significantly increased in young leaves and petioles as a consequence of drought.
Long-term water deficit caused a significant reduction of inorganic phosphorus (Pi) concentration in young and old leaves. Under the water stress condition, the concentration of proline was increased in all
individual plant organs, except proline concentration in the youngest leaves. Drought treatment caused a significant increase
of glycine betaine content in shoot without any change in tap-roots. Glucose concentrations were significantly increased only
in tap-roots as the effect of drought. In response to water shortage the accumulation of sucrose was observed in all the examined
leaves and tap-roots. Overall, a long-term drought activated an effective mechanism for osmotic adjustment both in the shoot
and in the root tissues which may be critical to survival rather than to maintain plant growth but sugar beet organs accumulate
different solutes as a response to water cessation. 相似文献
5.
The effect of low root temperature on the growth and K requirements of young tomato (Lycopersicon esculentum Mill. cv Sonatine) plants was investigated. When K was supplied in solution at high concentration (5 mM), lowering the temperature of the root system from 25° to 15°C reduced the relative growth rate so that after ten days plant dry weight was 60% and leaf area 44% of that of controls maintained at 25°C. Shoot: root dry weight ratio was initially increased by cooling, but declined to 84% of controls after ten days. In spite of these changes in shoot: root ratio the concentration of K in whole plants, expressed on the basis of tissue water, was stable throughout the experiment and was significantly higher than that of controls. Further, the critical concentration of K for shoots (the concentration in the shoot associated with 90% maximum growth) was also increased at root temperatures of 15° and 30°C compared with 24°C. It is suggested that the higher concentration of K at low root temperature may reflect a real increase in requirement for the element at the physiological level. Preliminary measurements of the solute potential demonstrated a less osmotically active sap in leaves of root-cooled plants, thus there may be a greater reliance on K as an osmoticum in these individuals. When supplies of K limited growth, root-cooling had no effect on any of the parameters determining the efficiency of its use; the minimum concentration to which roots could deplete the solution of K was identical for cooled and control plants and at the same stage of visible deficiency there was no significant difference in the efficiency ratio (mg DW, mg-1 K) or utilization efficiency (mg DW mM
-1 K), in spite of large differences in the partitioning of dry matter. 相似文献
6.
Root-shoot interactions in mineral nutrition 总被引:9,自引:0,他引:9
In this paper four classes of co-operative root-shoot interations are addressed. (I) Nitrogen concentrations in the xylem sap originating from the root and in the phloem sap as exported from source leaves are much lower than those required for growth by apices and developing organs. Enrichment of xylem sap N is achieved by xylem to xylem (X-X) transfer, by which reduced N, but not nitrate, is abstracted from the xylem of leaf traces and loaded into xylem vessels serving the shoot apex. Nitrogen enrichment of phloem sap from source leaves is enacted by transfer of reduced N from xylem to phloem (X-P transfer). Quantitative data for the extent of the contribution of X-X and X-P transfer to the nutrition of young organs of Ricinus communis L. and for their change with time are presented. (II) Shoot and root cooperate in nitrate reduction and assimilation. The partitioning of this process between shoot and root is shifted towards the root under conditions of nitrate- and K-deficiency and under salt stress, while P deficiency shifts nitrate reduction almost totally to the shoot. All four changes in partitioning can be attributed to the need for cation-anion balance during xylem transport and the change in electrical charge occurring with nitrate reduction. (III) Even maintenance of the specificity of ion uptake by the root may – in addition to its need for energy – require a shoot-root interaction. This is shown to be needed in the case of the maintenance of K/Na selectivity under the highly adverse condition of salt stress and absence of K supply from the soil. (IV) Hormonal root to shoot interactions are required in the whole plant for sensing mineral imbalances in the soil. This is shown and addressed for conditions of salt stress and of P deficiency, both of which lead to a strong ABA signalling from root to shoot but result in different patterns of response in the shoot. 相似文献
7.
Plantlet regeneration via organogenesis was achieved in callus cultures derived form mature leaves, stems and leaves, petioles and roots of young seedling of Psoralea corylifolia on Murashige and Skoog medium supplemented with 2.5–3.0 mg L-1 BA, 1.0 mg L-1 NAA and 3% (w/v) sucrose. The rate of shoot bud regeneration was positively correlated with the concentration of hormones in the nutrient media. Shoot buds regenerated more readily from juvenile explants (seedling source) as compared to the mature explants. Addition of adenine sulphate (5 mg L-1) to the culture medium increased the growth of shoot buds. Optimum responses were obtained in hypocotyl and leaf explants using NAA in combination with BA, the highest rate of shoot bud regeneration being in hypocotyl explants. Rooting was readily achieved on the differentiated shoots on MS basal media without growth regulators. Regenerated plantlets were successfully established in the greenhouse. 相似文献
8.
Janneke A. Dieleman Francel W. A. Verstappen René R. J. Perik Daan Kuiper 《Physiologia plantarum》1997,101(2):347-352
Cytokinins from the roots may be involved in regulating rose ( Rosa hybrida ) shoot growth and development. The objective of this study was to estimate the export of cytokinins from the roots and their degradation rate in the shoot, which were expected to be correlated with plant development. Hence, the total cytokinin content of the shoot, the concentration of zeatin riboside (ZR) in bleeding sap, and the transpiration rates in three stages of development were determined. The estimations performed are based on the assumption that the cytokinin concentration in bleeding sap is representative for the cytokinin concentration in xylem sap in situ. This was verified by comparing the ZR concentration in bleeding sap and in sap obtaíned after pressurizing the root system to a level equivalent to the leaf water potential; no significant differences could be found. The import of cytokinins could not be correlated with plant development, as it increased linearly with time. The estimated relative degradation rate of cytokinins in the shoot decreased as the plants matured. The half-life of cytokinins in the shoot was found to be approximately 1 day, indicating that cytokinins are rapidly metabolized in the shoot. 相似文献
9.
A high frequency plant regeneration system was developed for the production of high yielding elite clones of Garcinia indica via direct organogenesis. A maximum number of 86.2 shoot buds per explant were induced from the mature seed segments cultured
on Woody plant medium (WPM) supplemented with 2.0 mg dm−3 N6-benzyladenine and 1 mg dm−3 indole-3-acetic acid. Rooting was achieved on half-strength WPM medium supplemented with 3 mg dm−3 indole-3-butyric acid. Rooted plantlets were acclimatized and transferred to greenhouse for further growth. The highest survival
rate of 95 % was recorded using a mixture of garden soil and sand. Histological studies clearly revealed multiple shoot formation
from mature seed segments. 相似文献
10.
Melastoma (Melastoma malabathricum L.) is an aluminum-accumulating woody plant that accumulates more than 10 000 mg kg–1 of aluminum (Al) in mature leaves. The influence of Al and phosphorus (P) applications on plant growth and xylem sap was examined in the present study in order to elucidate the interaction between Al-induced growth enhancement and P nutrition, and to determine the form of Al for translocation from roots to shoots. Although the Al application significantly increased the growth of Melastomaseedlings with the high P pre-treatment, and P concentrations in the leaves and Pi concentrations in the xylem sap regardless of the P pre-treatment, we could not come to the conclusion that a primary cause of the Al-induced growth enhancement in Melastoma is the stimulation of P uptake. The degree of Al-induced growth enhancement corresponded not with the P concentrations but with the Al concentrations in the plant tissue, suggesting that the Al-induced growth enhancement in Melastoma is primarily caused by Al itself in the plant tissue rather than by the stimulation of P uptake. Through the analysis of organic acids and Al in the xylem sap and plant tissue, the form of Al for translocation from roots to shoots was shown to be an Al-citrate complex that was transformed into Al-oxalate complex for Al storage in the leaves. In addition, the xylem sap of Melastoma seedlings grown in the absence of Al contained higher concentrations of malate. In the presence of Al, however, higher concentrations of citrate were found, indicating that Melastoma changes its organic acid metabolism in the presence or absence of Al; more specifically, it increases the synthesis of citrate. 相似文献
11.
The role of mineral nutrients in the increased growth response of tomato plants in solarized soil 总被引:3,自引:1,他引:2
Soil solarization is a non-chemical disinfestation technique that frequently promotes plant growth in the absence of known
major pathogens, a phenomenon termed increased growth response (IGR). The effect of solarization on plant nutrients and their
role in the IGR was studied with tomato plants grown in solarized or non-solarized (control) sandy soil, under controlled
conditions. Solarization considerably increased the soil concentrations of water extractable N, K, Ca, Mg and Na at most sites,
whereas Cl and DTPA extractable Mn, Zn, Fe and Cu were decreased by the treatment. Plant growth and specific leaf area were
enhanced in solarized as well as in N-supplemented control soil. In tomato plants grown in solarized soil, concentrations
of most nutrients in the xylem sap, including N, were increased compared to the control, whereas Cl and SO4 levels decreased.
The most significant increase in leaf nutrient concentration caused by soil solarization was recorded for N. Furthermore,
leaf N concentration was highly and positively correlated with shoot growth. The concentration of Cu increased in leaves from
the solarization vs. the control treatment, whereas that of SO4 and Cl decreased, the latter presumably below the critical
toxicity level. The correlation between shoot growth and leaf concentration was positive for Cu and inverse for Cl and SO4.
In conclusion, we found that soil solarization significantly affects nutrient composition in tomato plants, and provided strong
evidence that N, and eventually also Cl, play a major role in IGR. 相似文献
12.
The natural cytokinin import from the root into the shoot of Urtica dioica plants was enhanced by supplying zeatin riboside (ZR) solutions of various concentrations to a portion less than 10 % of the root system after removal of their tips. After 6 h ZR pretreatment of the plants, 14CO2 was supplied for 3 h to a mature (source) leaf or to an expanding leaf and the 14C-distribution in the whole plant was determined after a subsequent dark period of 14 h. ZR substantially increased 14C fixation by the expanding leaves and also enhanced export of carbon and transport to the shoot apex. The effect of the hormone treatment was, however, more pronounced when the 14CO2 was supplied to a mature leaf. In the control plants these leaves exported carbon only to the roots: When the amount of the natural daily ZR input from the roots to the shoot was enhanced by 20%, the bulk of the 14C exported from a mature leaf moved to the shoot apex and only a minor portion of 14C was still detected in the root fraction. A several-fold increase of the natural daily ZR input into the shoot resulted in a flow of 14C only to the growing parts of the shoot. The results suggest control of the sink strength of the shoot apex by ZR in Urtica diocia. 相似文献
13.
Qualitative changes of cytokinins in leaves of different ages from Populus x robusta (Schneid.) have been determined, together with seasonal changes in cytokinin activity in mature leaves and xylem sap. Chromatography on Sephadex LH-20 has shown that total cytokinin activity and diversity are at a maximum in expanding leaves. As leaves age, the amount and number of cytokinins decrease, with yellow senescent leaves having only one detectable cytokinin, thought to be a glucoside. Seasonal changes were followed by chromatography of the extracts on paper in butan-2-ol: 25 % NH4OH (4:1). Maximum cytokinin levels, due to Fraction Z (Rf 0.5–0.8), in leaves and xylem sap were found in mid-summer. Prior and subsequent to cessation of shoot elongation growth, fraction Z decreased and fraction N (Rf 0–0.2) increased to predominate in senescent leaves. Removal of the apex resulted in an increase of fraction N in leaves from decapitated plants when compared to similar leaves from intact plants. It is suggested that, once apical sink activity has ceased, cytokinins in the xylem sap are diverted into leaves and converted to a cytokinin glucoside, possibly a storage form of the hormone. 相似文献
14.
Plant analysis can diagnose boron (B) deficiency when the standards used have been properly developed by establishing that a close relationship exists between B concentration in a plant part and its physiological function. The purpose of the present study was to demonstrate the importance of choosing the growing immature leaves for B deficiency diagnosis and for establishing critical B concentrations for the diagnosis of B deficiency in oilseed rape (Brassica napus). In Experiment 1, the plants were subject to seven levels of B supply using programmed nutrient addition, for the estimation of critical B concentrations in plant parts for shoot growth. In Experiment 2, the plants were treated with two levels of B supply in solution: 10 (+B) and 0 (-B) M B, for the estimation of functional B requirements for leaf elongation. The results showed that critical B concentrations varied amongst the plant parts sampled and decreased with leaf age. As B taken up by roots is largely phloem-immobile, B concentrations in mature leaves are physiologically irrelevant to plant B status at the time of sampling, giving rise to a significant over- or underestimation of the B requirement for plant growth. By contrast, a growing, immature leaf, in this case the youngest open leaf (YOL), was the most reliable plant part for B deficiency diagnosis. Critical B concentrations developed from both methods were comparable-i.e. 10–14 mg B kg–1 dry matter in the YOL at vegetative growth stages up to stem elongation. 相似文献
15.
A pot experiment was conducted to examine the effect of arbuscular mycorrhizal fungus, Glomus fasciculatum, and salinity on the growth of Acacia nilotica. Plants were grown in soil under different salinity levels (1.2, 4.0, 6.5, and 9.5 dS m−1). In saline soil, mycorrhizal colonization was higher at 1.2, 4.0, and 6.5 dS m−1 salinity levels in AM-inoculated plants, which decreased as salinity levels further increased (9.5 dS m−1). Mycorrhizal plants maintained greater root and shoot biomass at all salinity levels compared to nonmycorrhizal plants.
AM-inoculated plants had higher P, Zn, and Cu concentrations than uninoculated plants. In mycorrhizal plants, nutrient concentrations
decreased with the increasing levels of salinity, but were higher than those of the nonmycorrhizal plants. Mycorrhizal plants
had greater Na concentration at low salinity levels (1.2, 4.0 dS m−1), which lowered as salinity levels increased (6.5, 9.5 dS m−1), whereas Na concentration increased in control plants. Mycorrhizal plants accumulated a higher concentration of K at all
salinity levels. Unlike Na, the uptake of K increased in shoot tissues of mycorrhizal plants with the increasing levels of
salinity. Our results indicate that mycorrhizal fungus alleviates deleterious effects of saline soils on plant growth that
could be primarily related to improved P nutrition. The improved K/Na ratios in root and shoot tissues of mycorrhizal plants
may help in protecting disruption of K-mediated enzymatic processes under salt stress conditions. 相似文献
16.
Mayrhofer S Heizmann U Magel E Eiblmeier M Müller A Rennenberg H Hampp R Schnitzler JP Kreuzwieser J 《Plant biology (Stuttgart, Germany)》2004,6(6):730-739
In the present study, important components of carbon metabolism of mature leaves of young poplar trees (Populus x canescens) were determined. Carbohydrate concentrations in leaves and xylem sap were quantified at five different times during the day and compared with photosynthetic gas exchange measurements (net assimilation, transpiration and rates of isoprene emission). Continuously measured xylem sap flow rates, with a time resolution of 15 min, were used to calculate diurnal balances of carbon metabolism of whole mature poplar leaves on different days. Loss of photosynthetically fixed carbon by isoprene emission and dark respiration amounted to 1% and 20%. The most abundant soluble carbohydrates in leaves and xylem sap were glucose, fructose and sucrose, with amounts of approx. 2 to 12 mmol m(-2) leaf area in leaves and about 0.2 to 15 mM in xylem sap. Clear diurnal patterns of carbohydrate concentration in xylem sap and leaves, however, were not observed. Calculations of the carbon transport rates in the xylem to the leaves were based on carbohydrate concentrations in xylem sap and xylem sap flow rates. This carbon delivery amounted to about 3 micromol C m(-2) s(-1) during the day and approx. 1 micromol C m(-2) s(-1) at night. The data demonstrated that between 9 and 28 % of total carbon delivered to poplar leaves during 24 h resulted from xylem transport and, hence, provide a strong indication for a significant rate of carbon cycling within young trees. 相似文献
17.
Tree carbohydrate reserves are usually compromised following insect outbreak, which results in a delay in leaf emergence and a reduction in growth, especially in cold environments. However, in recent times, severe defoliation of subarctic mountain birches (Betula pubescens ssp. czerepanovii) by the winter moth (Operophtera brumata) has not induced such responses. This may be the result of a warming climate stimulating plant primary metabolism. We examined if increasing thermal sum (sum of daily mean temperatures above +5 °C, d.d.) and complete foliage loss affected the concentrations of carbohydrates in sap, juvenile leaves, and fine roots of mountain birches in northern Finland and Norway. The sampling was conducted at the beginning of the growing season, two years after the insect outbreak. We also investigated the morphologic properties of mature leaves and the shoot growth of the trees. Our results showed that the carbohydrate concentrations in leaves and roots (averages 67.8 and 12.5 mg g?1 DW, respectively) decreased in defoliated trees with increasing thermal sum (>400 d.d.), whereas the response in intact trees was the opposite. The carbohydrates in the sap were unaffected by defoliation or thermal sum accumulation. The leaf area of mature leaves and the height growth of long shoots were greater in trees at warmer sites, irrespective of defoliation. However, defoliation increased the leaf weight per area (SLW: specific leaf weight). We conclude that under warmer growing conditions, low early-season leaf and fine root carbohydrate concentrations of previously defoliated trees cannot be used as indicators of aboveground growth. 相似文献
18.
19.
Distribution and partitioning of newly acquired boron (B) in a mature sunflower (Helianthus annuus L., cv. 3101) plant was investigated. In leaf blades of sunflower plants grown under 0.93, 2.8, and 9.3 mmol B m−3, the level of cell-wall-bound B was rather uniform, irrespective of leaf position and B concentration. Boron concentration
gradients among leaf positions were produced mainly by different levels of water-soluble B. To determine the distribution
of newly taken-up B in plant parts, 10B-labeled boric acid at a concentration of 2.8 mmol B m−3 was applied. The majority of newly acquired B was delivered to the younger leaves, however, approximately one-fourth of the
B in the top and second leaves was the older B which was taken up before the 6 d treatment period. In the root tissues, two-fifth
of the water-soluble B was new B taken up in the last 6 d, however, within 6 h of the application new B contributed to approximately
80% of the xylem sap B, suggesting that newly taken-up B is preferentially transported to the shoots. When B was withdrawn
from the culture solution, the B concentration per leaf area of the lower leaves decreased slightly over 9 d. However, there
was an abrupt decrease in the younger leaves, even when taking into account the rapid expansion of the leaf blade, suggesting
that B moves more rapidly from the younger leaves than from the older leaves 相似文献
20.
Hartmann T Mult S Suter M Rennenberg H Herschbach C 《Journal of experimental botany》2000,51(347):1077-1088
35S-sulphate was flap-fed to poplar leaves of different leaf development stages - young developing, expanding, mature, and old mature poplar leaves. (35)S-sulphate was taken up independent of the leaf development stage. Whereas young development leaves did not export the (35)S taken up, export increased with increasing leaf development stage. Expanding leaves allocated the exported (35)S mainly into apical tree parts (73-87%) and only to a minor extent (13-27%) in basipetal direction. Neither lower trunk sections nor the roots were sinks for the exported (35)S. Expanding and developing leaves, but not the shoot apex, were the main sinks for the (35)S allocated in apical direction. In contrast, mature and old mature leaves exported the (35)S taken up mainly in basipetal direction (65-82%) with the roots constituting the main sinks. The (35)S allocated into apical tree parts was found in expanding and developing leaves, but only to a minor extent in the shoot apex. Apical allocated (35)S was identified as sulphate. Apparently the demand of young developing leaves for reduced sulphur was not fulfilled by mature leaves. Therefore, reduced sulphur for growth and development of young developing leaves must be supplied from other sources. In vitro activity of enzymes involved in assimilatory sulphate reduction was measured to investigate whether demand for reduced sulphur by young leaves is met by their own sulphate reduction. ATP sulphurylase and APS reductase activities were not significantly lower in developing than in mature leaves. Sulphite reductase and serine acetyltransferase activities were highest in developing leaves; O:-acetylserine (thiol) lyase activity was similar in all leaf developing stages. Apparently, young developing poplar leaves are able to produce their own reduced sulphur for growth and development. Whether other sources such as storage tissues and/or roots are involved in reduced sulphur supply to developing leaves remains to be elucidated. 相似文献