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1.
Net CO(2) Assimilation Rate of Grapevine Leaves in Response to Trunk Girdling and Gibberellic Acid Application
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Net CO2 assimilation rate (A), stomatal conductance (gs), and weight per unit leaf area (W) were determined on Thompson Seedless grapevines grown in the field. Treatments included fruit set applications of gibberellic acid (40 milligrams gibberellic acid (GA3) per liter) to vines, shoots and clusters, alone and in combination with trunk girdling. Leaf A and gs were measured prior to and 3, 6, and 13 days after fruit set. Weight per unit leaf area was determined on leaves collected subsequent to gas exchange measurements. Leaf A of girdled vines was reduced approximately 30% when compared to the control 13 days after treatment. The reduction in A due to girdling was not as great when vines were sprayed with GA3. GA3 sprays alone had no significant effect on A. Stomatal conductance was reduced by girdling 13 days after treatment. Weight per unit leaf area was 17% greater for trunk girdled vines when compared to the controls. Results indicate GA3 affected net CO2 assimilation rate only on girdled vines, a treatment which increased weight per unit leaf area. 相似文献
2.
Carbohydrate metabolism in a heat-girdled maize source leaf 总被引:6,自引:0,他引:6
E. Jeannette A. Reyss N. Grégory P. Gantet† and J.-L. Prioul 《Plant, cell & environment》2000,23(1):61-69
3.
Application of a heat girdle near the base of the lamina ofthe fifth, fully expanded leaf of young pearl millet (Pennisetumamericanum [L.] Leeke) plants resulted in a decrease in solutepotential, an increase in leaf dry matter content, and a declinein stomatal conductance and in the rate of CO2 assimilation.Total water potential was largely unaffected by girdling whileturgor potential increased as a consequence of the decreasein solute potential. Abscisic acid (ABA) content of the leaf increased 5 to 6-foldwithin 1 h of girdling, then declined equally rapidly beforeincreasing again at a slower rate. The decline in conductance was correlated with both the decreasein solute potential and the increase in ABA. To determine whichof these factors could be controlling conductance, girdled leaveswere exposed either to 14 h of continuous light or to a similarperiod of darkness followed by a brief light treatment to allowstomata to open. Girdling reduced conductance equally followingdarkness or light but solute accumulation occurred only in thelight. ABA accumulated in girdled leaves in both darkness andlight. Simultaneous measurements of conductance and CO2 assimilationshowed that intercellular CO2 concentration did not increasefollowing girdling. It was concluded that the decrease in conductancein millet leaves after girdling was most probably mediated bythe increase in ABA content. Key words: Leaf girdling, Solute accumulation, Stomatal conductance, Abscisic acid; Pennisetum americanum 相似文献
4.
We assessed the potential of using 14C contents of soil respired CO2 to calculate the contributions of heterotrophic and autotrophic respiration to total soil respiration. The partitioning of these fluxes is of utmost importance to evaluate implications of environmental change on soil carbon cycling and sequestration. At three girdled forest stands in Sweden and Germany, where the tree root (autotrophic) respiration had been eliminated, we measured both flux rates and 14C contents of soil respired CO2 in girdled and control plots in the summers of 2001 or 2002. At all stands, CO2 flux rates were slightly higher in the control plots, whereas the 14C contents of respired CO2 tended to be higher in the girdled plots. This was expected and confirmed that heterotrophically respired CO2 cycles more slowly through the forest ecosystem than autotrophically respired CO2. On the basis of these data, the contributions of hetero‐ and autotrophic respiration to total soil respiration were calculated using two separate approaches (i.e. based on flux rates or 14C). Fractions of heterotrophic respiration ranged from 53% to 87%. Values calculated by both approaches did not differ significantly from each other. Finally, we compared the 14C contents of soil respired CO2 in the girdled plots with the 14C contents of heterotrophically respired CO2 calculated by three different 14C models. None of the models matched the measured data sufficiently. In addition, we suspect that inherent effects of girdling may cause the 14C content of CO2 respired in the girdled plots to be lower than ‘true’ heterotrophically respired CO2 in an undisturbed plot. Nevertheless, we argue that measurements and modeling of 14C can be developed into a valuable tool for separating heterotrophic and autotrophic soil respiration (e.g. when girdling cannot be performed). 相似文献
5.
MAYORAL MARIA LUISA; MEDINA ERNESTO; GARCIA VICTOR 《Journal of experimental botany》1991,42(9):1123-1129
The effect of manipulations of the sink-source at the above-groundlevel and girdling of source leaves was measured in 4-month-oldplants of the CAM species Kalancho pinnata (Lam.) Pers. At thisage plants developed five pairs of leaves. The upper fourthand fifth leaf pairs were not fully expanded and behaved ascarbohydrate sinks. Removal of the developing leaves induceda progressive accumulation of glucans and sugars in the matureleaves. The titratable acidity increased during the second weekbut accumulation was less than in the control plants three tofour weeks after sink removal. Similar, but more rapid, resultswere observed in mature leaves with girdled petioles. Up tothe second night after girdling dark CO2 fixation increased,but decreased steadily afterwards. CAM Phase 4 (afternoon CO2fixation) however, was more sensitive to girdling, being reducedby 38% on the first day, and disappearing completely 3 d aftergirdling. The glucan and sugar contents of girdled leaves increasedcontinuously after treatment, but day-night changes ceased completelyon the fifth day. Girdling also caused a considerable increasein chloroplast area, with up to 80% of their internal spaceoccupied by starch grains, leading to grana distortion. In girdledleaves, or in source leaves in plants lacking aerial carbohydratesinks, dawn-dusk changes in titratable acidity started to decreasewhen the leaf glucan content exceeded 1·0 mol equivalenthexoses kg1 dry weight. Increased sink strength throughshading of all leaves except one source leaf did not affectits CAM activity. The titratable acidity and non-structuralcarbohydrate content of the shaded mature leaves was reducedby around 55%. Removal of all the mature source leaves acceleratedthe maturation process of sink leaves, increasing titratableacidity at dawn and synthesis of glucans during the light period.The results support the hypothesis that CO2 fixation in a CAMplant is controlled by accumulation of glucans in chloroplasts. Key words: CAM, glucan accumulation, sink-source ratio, CO2 fixation 相似文献
6.
Karine?D.?Batista Wagner?L.?Araújo Werner?C.?Antunes Paulo?C.?Cavatte Gustavo?A.?B.?K.?Moraes Samuel?C.?V.?Martins Fábio?M.?DaMatta
It has long been held that the regulation of photosynthesis in source leaves may be controlled by carbohydrates. The mechanisms
that govern the diurnal fluctuation of photosynthesis and the potential role of feedback regulation by carbohydrates during
photosynthesis in coffee (Coffea arabica) leaves were investigated in three independent and complementary experiments. An integrative approach using gas exchange
measurements in addition to carbon isotope labelling and steady-state carbohydrate and amino acid analysis was performed.
Canonical correlation analysis was also performed. In field-grown plants under naturally fluctuating environmental conditions
(Experiment I), the overall pattern of gas exchange was characterised by both low stomatal conductance (g
s) and net carbon assimilation rate (A) in the afternoon; no apparent signs of photoinhibition were observed. Under conditions of low air evaporative demand (Experiment
II), only slight decreases (~20%) in A were observed at the end of the day, which were associated with a reduction (~35%) in g
s. For both conditions, any increase in carbohydrate and amino acid pools over the course of the day was small. In leaves from
girdled branches (Experiment III), a remarkable decrease in A and particularly in g
s was observed, as were increases in starch but not in hexoses and sucrose pools. Furthermore, the rate of 14CO2 uptake (assessed under saturating CO2 conditions) and the partitioning of recently fixed 14C were not affected by girdling. It is proposed that the diurnal oscillations in A and the differences in A in leaves from girdled and non-girdled branches were merely a consequence of diffusive limitations rather than from photochemical
constraints or direct metabolite-mediated down-regulation of photosynthesis. 相似文献
7.
High-light effects on CO2 fixation gradients across leaves 总被引:2,自引:1,他引:1
Chlorophyll fluorescence and internal patterns of 14CO2 fixation were measured in sun and shade leaves of spinach after treatment with various light intensities. When sun leaves were irradiated with 2000μmol m?2 s?1 for 2h, FV/FM decreased by about 15%, but 14CO2 fixation was unaffected, whereas shade leaves exhibited a 21% decrease in Fv/FM and a 25% decrease in 14CO2 fixation. Irradiation of sun and shade leaves with 4000μmol m?1 for 4 h decreased FV/FM by 30% in sun leaves and 40% in shade leaves, while total 14CO2 fixation decreased by 41% in sun leaves and 55% in shade leaves. After light treatment, gradients of CO2 fixation across leaves were determined by measuring 14CO2 fixed in paradermal leaf sections after a 10s pulse of 14CO2. Gradients of 14CO2 fixation in control sun and shade leaves were identified when expressed on a relative basis and normalized for leaf depth. Treatment of leaves with 2000 μmol PAR m?2 s?1 for 2h did not after patterns of carbon fixation across sun leaves, but slightly altered the pattern in shade leaves. In contrast, treatment of sun and shade leaves with 4000μmol m?2 s?1 for 4h decreased carbon fixation more in the palisade mesophyll cells than in the spongy mesophyll cells of sun and shade leaves, and fixation in medial tissue of shade leaves was dramatically decreased compared to the adaxial and abaxial tissue. The interaction between leaf anatomy and biochemical parameters involved in tolerance to photoinhibition in spinach is discussed. 相似文献
8.
Regulation of photosynthesis by end-product accumulation in leaves of plants storing starch, sucrose, and hexose sugars 总被引:40,自引:11,他引:29
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In the present study, leaves of different plant species were girdled by the hot wax collar method to prevent export of assimilates. Photosynthetic activity of girdled and control leaves was evaluated 3 to 7 days later by two methods: (a) carbon exchange rate (CER) of attached leaves was determined under ambient CO2 concentrations using a closed gas system, and (b) maximum photosynthetic capacity (Amax) was determined under 3% CO2 with a leaf disc O2 electrode. Starch, hexoses, and sucrose were determined enzymically. Typical starch storers like soybean (Glycine max L.) (up to 87.5 milligrams of starch per square decimeter in girdled leaves), cotton (Gossypium hirsutum L.), and cucumber (Cucumis sativus L.) responded to 7 days of girdling by increased (80-100%) stomatal resistance (rs) and decreased Amax (>50%). On the other hand, spinach (Spinacia oleracea L.), a typical sucrose storer (up to 160 milligrams of sucrose per square decimeter in girdled leaves), showed only a slight reduction in CER and almost no change in Amax. Intermediate plants like tomato (Lycopersicon esculentum Mill.), sunflower (Helianthus annuus L.), broad bean (Vicia faba L.), bean (Phaseolus vulgaris L.), and pea (Pisum sativum L.), which upon girdling store both starch and sucrose, responded to the girdle by a considerable reduction in CER but only moderate inhibition of Amax, indicating that the observed reduction in CER was primarily a stomatal response. Both the wild-type tobacco (Nicotiana sylvestris) (which upon girdling stored starch and hexoses) and the starchless mutant (which stored only hexoses, up to 90 milligrams per square decimeter) showed 90 to 100% inhibition of CER and approximately 50% inhibition of Amax. In general, excised leaves (6 days) behaved like girdled leaves of the respective species, showing 50% reduction of Amax in wild-type and starchless N. sylvestris but only slight decline of Amax in spinach. The results of the present study demonstrate the possibility of the occurrence of end-product inhibition of photosynthesis in a large number of crop plants. The long-term inhibition of photosynthesis in girdled leaves is not confined to stomatal responses since the Amax declined up to 50%. The inhibition of Amax by girdling was strongest in starch storers, but starch itself cannot be directly responsible, because the starchless mutant of N. sylvestris was also strongly inhibited. Similarly, the inhibition cannot be attributed to hexose sugars either, because soybean, cotton, and cucumber are among the plants most strongly inhibited although they do not maintain a large hexose pool. Spinach, a sucrose storer, showed the least inhibition in both girdled and excised leaf systems, which indicates that sucrose is probably not directly responsible for the end-product inhibition of photosynthesis. The occurrence of strong end-product inhibition appears to be correlated with high acid-invertase activity in fully expanded leaves. The inhibition may be related to the nature of soluble sugar metabolism in the extrachloroplastic compartment and may be caused by a metabolite that has different rates of accumulation and turnover in sucrose storers and other plants. 相似文献
9.
Alteration of C-assimilate partitioning in leaves of soybeans having increased reproductive loads at one node
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The objectives of this study were to determine if the partitioning of recently fixed carbon between starch and water-soluble compounds could be altered by increasing the pod load in the leaf axil, and if the presence of source leaves acropetal to such a node would influence the partitioning of carbon within the subtending leaf. Soybeans (Glycine max L. Merr. cv Hodgson 78) were grown to full-bloom in a controlled environment chamber, and then deflowered at all nodes except the eighth. This treatment resulted in an 83% increase in the number of pods at the eighth node. At 24 days after flowering, one-half of the treated plants were girdled above the untreated node. Forty-two hours later, the eighth trifoliolate was pulsed with 14CO2 and sampled for radiolabeled starch and water-soluble compounds (WSC) at 0.5, 2, 4, 8, 12, and 24th after labeling.
When no girdling was applied above the increased pod load at the eighth node more label was accumulated by the pod walls (+6.9%) and seeds (+6.3%) when compared to the controls. Starch accumulation was not altered in the labeled leaf of the nongirdled plants. When the stem was girdled above the eighth node, significantly less starch was retained in the labeled leaf. Girdling also resulted in an increase in label accumulation by the pod walls (+5.4%) and seeds (+6.6%). These data suggest that the plant will change the distribution patterns of assimilate to supply added sink demand before altering the partitioning of recently fixed carbon in the subtending leaf.
相似文献10.
Detached Nicotiana rustica leaves were exposed for 2 minutes to temperatures in the range 36° to 51°C. Above 45°C, 14CO2 fixation was reduced by half as compared with controls. The fall in 14CO2 fixation continued for 2 1/2 h. Recovery was completed 45 h after the treatment. Above 45°C there was an increase in the labeled cationic and anionic fractions and a decrease in the neutral fractions, both increase and decrease being associated with the impaired CO2 fixation. However, these changes in products were also demonstrated when leaves were exposed to the high temperature after labeling. 相似文献
11.
Tree-girdling to separate root and heterotrophic respiration in two Eucalyptus stands in Brazil 总被引:4,自引:0,他引:4
The release of carbon as CO2 from belowground processes accounts for about 70% of total ecosystem respiration. Insights about factors controlling soil CO2 efflux are constrained by the challenge of apportioning sources of CO2 between autotrophic tree roots (and mycorrhizal fungi) and heterotrophic microorganisms. In some temperate conifer forests, the reduction in soil CO2 efflux after girdling (phloem removal) has been used to separate these sources. Girdling stops the flow of carbohydrates to the belowground portion of the ecosystem, which should slow respiration by roots and mycorrhizae while heterotrophic respiration should remain constant or be enhanced by the decomposition of newly dead roots. Therefore, the reduction in CO2 efflux after girdling should be a conservative estimate of the belowground flux of C from trees. We tested this approach in two tropical Eucalyptus plantations. Tree canopies remained intact for more than 3 months after girdling, showing no reduction in light interception. The reduction in soil CO2 efflux averaged 16–24% for the 3-month period after girdling. The reduction in CO2 efflux was similar for plots with one half of the trees girdled and those with all of the trees girdled. Girdling did not reduce live fine root biomass for at least 5 months after treatment, indicating that large reserves of carbohydrates in the root systems of Eucalyptus trees maintained the roots and root respiration. Our results suggest that the girdling approach is unlikely to provide useful insights into the contribution of tree roots and heterotrophs to soil CO2 efflux in this type of forest ecosystem. 相似文献
12.
We investigated phloem-xylem interactions in relation to leaf hydraulic capacity in hybrid aspen (Populus tremula L. × P. tremuloides Michx.) by using phloem girdling method. Removal of bark tissues (phloem girdling) at the branch base resulted in a substantial decline in stomatal conductance (gS), net photosynthetic rate (PN), and leaf hydraulic efficiency, and in increase of leaf water potential (ΨL). Although gS declined more than PN (83 versus 78 %), the ratio of intercellular to ambient CO2 concentrations (ci/ca) increased from 0.67 to 0.87 in three days after girdling. Girdling induced a decrease in leaf hydraulic conductance (KL) on average by 43 % (P = 0.006). The changes in gS and leaf conductance to water vapour were co-ordinated with KL only in girdled branches whereas intrinsic water-use efficiency was invariant to KL. The declines in KL with girdling were not accompanied by changes in potassium ion concentration ([K+]), electrical conductivity, or pH of xylem sap. The results suggest that phloem girdling at the branch base does not influence the recirculation of ions between the phloem and xylem in hybrid aspen and the decrease of KL in response to the manipulation is not related to changes in [K+] and total ionic content of xylem sap. 相似文献
13.
《Environmental and Experimental Botany》2009,65(3):256-263
The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (Fo) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms. 相似文献
14.
Fernando Rivas Fernando Fornes Manuel Agustí 《Environmental and Experimental Botany》2008,64(3):256-263
The effects of girdling on oxidative damage, antioxidant enzyme activity, antioxidant metabolites and proline (Pro) were studied in leaves arising from different shoot types of potted 2-year-old ‘Loretina’ mandarin (Citrus reticulata Blanco) trees during the spring flush period. Girdling increased malonyldialdehyde (MDA) and basal chlorophyll (Chl) a fluorescence (Fo) in young leaves 30 days after girdling but not in the mature leaves (ML) suggesting a disruption of photosynthetic apparatus and oxidative damage in young leaves. This phenomenon was accompanied by increasing levels of Pro. Paralleling these changes, an increase of all antioxidant enzyme activities occurred in leaves from vegetative (VG) and multiflowered leafy shoots (MLY) of girdled trees. Similarly, in ML of girdled trees, ascorbate peroxidase (APX), catalase (CAT) and glutathione reductase (GR) activity also increased. However, dehydroascorbate reductase (DHAR) activity decreased and superoxide dismutase (SOD) activity remained unchanged. Total leaf carbohydrate content and starch also increased as a result of girdling in all shoot types. Whilst soluble sugars increased markedly in young leaves, they increased only slightly in ML. In conclusion, this study provides evidence that girdling gives rise to oxidative damage in Citrus during carbohydrate accumulation, triggering enzymatic and non-enzymatic defence mechanisms. 相似文献
15.
The rates of dark14CO2 fixation by natural phytoplankton communities growing in eutrophic and oligotrophic waters were studied with short-term in situ experiments. Three aspects were investigated: (1) the time course incorporation of14CO2 in darkness, (2) the depth variability in dark14CO2 fixation, and (3) the variability in14CO2 fixation within a year. The highest dark14CO2 incorporation rates were observed during the first interval of incubation (20 min) after which they approached a constant rate with time. The observed differences in dark14CO2 fixation rates between populations from different depths were associated with differences in species composition as well as with physiological differences caused by exposure to different illumination conditions prior to their exposure to darkness. Autocorrelation coefficients were computed for the analysis of variability of dark14CO2 fixation rates within a year. It was suggested that dark14CO2 incorporation might be a periodic phenomenon depending mainly on the productive capacity of the phytoplankton community. 相似文献
16.
Two transgenic potato lines, T1 and T2, expressing the trehalose-6-phosphate synthase (TPS1) gene of yeast were isolated. In our experimental approach, we applied two novelties, namely the fusion of the drought-inducible
promoter StDS2 to TPS1 and a marker-free transformation method. In contrast to the expected drought-induced expression, only a very low constitutive
TPS1 expression was detected in the transgenic lines, probably due to chromosomal position effects. The observed expression pattern,
however, was sufficient to alter the drought response of plants. Detached leaves of T1 and T2 showed an 8 h delay in wilting
compared to the non-transformed control. Potted plants of T1 and T2 kept water 6 days longer than control plants and maintained
high stomatal conductance and a satisfactory rate of net photosynthesis. During drought treatment, CO2 assimilation rate measured at saturating CO2 level was maintained at maximum level for 6–9 days in transgenic plants while it decreased rapidly after 3 days in the wild
type plants. Under optimal growth conditions, lower CO2 fixation was detected in the transgenic than in the control plants. Stomatal densities of T1 and T2 leaves were reduced by
30–40%. This may have contributed to the lower CO2 fixation rate and altered drought response.
Ibolya Stiller, and Sándor Dulai contributed equally to this work. 相似文献
17.
Net CO(2) Assimilation and Carbohydrate Partitioning of Grapevine Leaves in Response to Trunk Girdling and Gibberellic Acid Application 总被引:4,自引:1,他引:3
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Leaf net CO2 assimilation rate (A), stomatal conductance (gs), carboxylation efficiency, and foliar nonstructural carbohydrates were measured on mature, field-grown Vitis vinifera L. (cv Thompson Seedless) vines that had been trunk girdled, sprayed with gibberellic acid, or both, shortly after anthesis. Girdling reduced A, gs, and carboxylation efficiency when measured 2 weeks after imposition of the treatments. Diurnal measurements indicated that A of girdled vines was less than that of control vines between 1000 and 1800 hours. Gibberellic acid mitigated the depressing effect of girdling on gs during the same diurnal measurements. The concentrations of foliar carbohydrates were greatest for the girdled vines, followed by the combination treatment and were lowest for the control vines. Foliar carbohydrates were greater for girdled vines 4 weeks after the treatments were imposed, however, by this time there was no significant difference in A between the control and girdled vines. Two and 4 weeks after the experiment was initiated root carbohydrate concentrations were less for the girdled vines when compared to the control vines. The data indicate that the reduction in A of girdled grapevines is not associated with the accumulation of leaf nonstructural carbohydrates following the girdling treatment. 相似文献
18.
Stem girdling influences concentrations of endogenous cytokinins and abscisic acid in relation to leaf senescence in cotton 总被引:3,自引:0,他引:3
Many studies have shown that root–shoot imbalance influences vegetative growth and development of cotton (Gossypium hirsutum L.), but few have examined changes in leaf senescence and endogenous hormones due to stem girdling. The objective of this
study was to determine the correlation between some endogenous phytohormones, particularly cytokinins and abscisic acid (ABA),
and leaf senescence following stem girdling. Field-grown cotton plants were girdled on the main stem 5 days after squaring
(DAS), while the non-girdled plants served as control. Plant biomass, seed cotton yield, main-stem leaf photosynthetic (Pn)
rate, chlorophyll (Chl) and malondialdehyde (MDA) concentrations, as well as levels of cytokinins and ABA in main-stem leaves
and xylem sap were determined after girdling or at harvest. Main-stem girdling decreased the dry root weight and root/shoot
ratio from 5 to 70 days after girdling (DAG) and reduced seed cotton yield at harvest. Main-stem leaf Pn and Chl concentration
in girdled plants were significantly lower than in control plants. Much higher levels of MDA were observed in main-stem leaves
from 5 to 70 DAG, suggesting that stem girdling accelerated leaf senescence. Girdled plants contained less trans-zeatin and its riboside (t-Z + t-ZR), dihydrozeatin and its riboside (DHZ + DHZR), and isopentenyladenine and its riboside
(iP + iPA), but more ABA than control plants in both main-stem leaves and xylem sap. These results suggested that main-stem
girdling accelerated leaf senescence due to reduced levels of cytokinin and/or increased ABA. Cytokinin and ABA are involved
in leaf senescence following main-stem girdling. 相似文献
19.
The influence of different leaf-to-fruit (l-t-f) ratios on leaf net photosynthetic rate (P
N) and fruit characteristics in Olea europaea L. cv. Frantoio was evaluated in 2001 and 2002. In both years, at the end of June, at the end of July, and in mid-September
(first, second, and third time of treatment, respectively), defoliation or fruit thinning were performed to give l-t-f ratios
of 1/1, 3/1, 5/1, and 7/1 (about 5.1, 15.3, 25.6, and 35.8 cm2 of leaf area per fruit, respectively) on girdled and ungirdled peripheral shoots. P
N showed substantial seasonal and diurnal variations. In ungirdled shoots, no differences due to the different l-t-f ratios
were observed, whereas in girdled shoots P
N tended to be lower in shoots with a high l-t-f ratio. In general, the values of leaf transpiration rate (E), stomatal conductance (g
s), sub-stomatal CO2 concentration (C
i), and dark respiration rate (R
D) were associated with those of P
N. The starch and reducing sugar contents and area leaf dry mass (ADM) tended to be higher in leaves on girdled shoots with
high l-t-f ratio, whereas in ungirdled shoots no differences related to the different l-t-f ratios were observed. The higher
saccharide content in the leaves and the lower P
N, in the presence of a high C
i, observed in girdled shoots with a high l-t-f ratio suggests that the depression in P
N in these shoots may be the result of a feedback inhibition of the photosynthetic mechanism that regulates such a process.
The l-t-f ratio did not have a substantial effect on fruit drop. In ungirdled shoots, the different l-t-f ratios did not produce
significant differences in terms of fruit growth and leaf dry matter and saccharide contents, whereas in girdled shoots fruit
growth increased as the l-t-f ratio increased, particularly when treatments were applied at the initial stage of fruit development.
The percentage of oil in the pulp, on a dry matter basis, was not substantially influenced by girdling and l-t-f ratio. The
abundant availability of assimilates seemed to cause earlier fruit ripening and, at the same time, retard fruit senescence
(fruit detachment force). Shoot growth was slightly reduced by girdling. The abundant availability of assimilates, induced
by girdling associated with high l-t-f ratio, stimulated flower induction. 相似文献
20.
Effect of altered sink: source ratio on photosynthetic metabolism of source leaves 总被引:13,自引:1,他引:12
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When seven crop species were grown under identical environmental conditions, decreased sink:source ratio led to a decreased photosynthetic rate within 1 to 3 days in Cucumis sativus L., Gossypium hirsutum L., and Raphanus sativus L., but not in Capsicum annuum L., Solanum melongena L., Phaseolus vulgaris L., or Ricinus communis L. The decrease was not associated with stomatal closure. In cotton and cucumber, sink removal led to an increase in starch and sugar content, in glucose 6-phosphate and fructose 6-phosphate pools, and in the proportion of 14C detected in sugar phosphates and UDPglucose following 14CO2 supply. When mannose was supplied to leaf discs to sequester cytoplasmic inorganic phosphate, promotion of starch synthesis, and inhibition of CO2 fixation, were observed in control discs, but not in discs from treated plants. Phosphate buffer reduced starch synthesis in the latter, but not the former discs. The findings suggest that sink removal led to a decreased ratio inorganic phosphate:phosphorylated compounds. In beans 14C in sugar phosphates increased following sink removal, but without sucrose accumulation, suggesting tighter feedback control of sugar level. Starch accumulated to higher levels than in the other plants, but CO2 fixation rate was constant for several days. 相似文献