Carbon and Nitrogen Transport during Grain Filling in Rice Under High-temperature Conditions

Rice ( Oryza sativa cv. Koshihikari) seedlings were grown in a sandy dune soil in pots with a basal dressing of N (0.5 g N), P and K. Two N treatments were applied, a +N treatment in which a top dressing of ¹⁵N-labeled 0.5 g N was supplied on July 20 and a −N treatment in which no additional fertilizer was supplied. During the grain-filling stage from August 6 to 13, plants were subjected to one of three temperature treatments; controlled low temperature, LT (day/night 28/23 °C), controlled high temperature, HT (35/30 °C) and uncontrolled glasshouse temperature, UT (day/night averages, 38/26 °C). All plants were then exposed to ¹³CO₂ for 1 h on August 11 in a growth chamber at 25 °C. On August 13, all plants were harvested and the ¹³C and ¹⁵N abundances and starch and sugar concentrations in the ears, shoots and roots were determined. The ¹³C content of the ear was lower in UT than in LT irrespective of the +N or −N treatment. The translocation of ¹⁵N to the ears was also slightly depressed in UT compared with LT. Under high-temperature conditions (HT and UT), the starch content per plant was reduced for −N, but for +N, it was not significantly different among the temperature treatments. A high accumulation of sucrose was observed in all plant parts under UT conditions. It is suggested that extreme high day temperatures during the grain-filling period may reduce starch synthesis in the grains and, especially so under N-deficient conditions. High temperatures also induce an accumulation of sucrose and a decrease in carbon and nitrogen transport from the shoots to the ears via the phloem.     

Influence of Soil Drought on Plant Growth, Assimilation and Dissimilation of CO2 and Accumulation of Photosynthates in Field Bean (Vicia faba L. minor) During Pod Formation and Rapid Pod Growth

Field bean planes cultivar Nadwiślański were submitted to soil drought (30 % of field soil water capacity) for 5 days at the stage of pod formation (A) and of rapid pod growth (B) and then exposed for 20 minutes to ¹⁴CO₂. Radioactivity of leaves, stems, roots, and pods or pod shells and seeds was measured 1, 5, 24 and 48 hours after exposition.
In both stages soil drought reduced by about five times total CO₂ assimilation, mainly owing to lower activity of the photosynthetic apparatus and also, though less so, to reduced leaf growth. Photosynthetic activity referred to the dry weight of the leaves dropped to 22-35% of controls. Accumulation of photosynthetates in generative organs was much less depressed than ¹⁴CO₂ assimilation. 48 hours after exposition to ¹⁴CO₂ of drought treated plants, the contents of ¹⁴C of pods in phase A, and seeds in phase B, amounted to respectively 24% and 36% of assimilated ¹⁴C and equalled 91.5% and 74% of the corresponding values for controls.
The progressive decline of radioactivity in leaves and stems after ¹⁴CO₂ exposition was distinctly correlated to the rise of radioactivity of generative organs both in soil drought treated plants and in controls. Slightly lower values of correlation coefficients in drought treated plants may indicate impairment under drought conditions of synchronization in processes of unloading and accumulation of assimilates.
In plants drought treated in phase A the ability to dissimilate ¹⁴C was reduced to about 59% of that in controls, but when drought was applied in phase B, dissimilation rate was about three times as high.     

Assimilation, Dissimilation and Accumulation of 14C in Two Maize (Zea mays L.) Hybrids of Different Drought Tolerance

The effects of exposure in the vegetative phase of growth to 5- or 10-day spells of soil drought (30% field water capacity) on assimilation, dissimilation and accumulation of ¹⁴C and on dry matter growth were studied in two maize hybrids, nos. 8344 and 8388 (Garst Seed Co.) of high and low drought tolerance. Under control water regime in soil there was no difference in ¹⁴CO₂ uptake and dry matter growth between hybrids. After five days of drought ¹⁴CO₂ assimilation dropped by about 75% referred to unit weight of dry matter in hybrid 8344 and by 56% in hybrid 8388. After 10 days of drought ¹⁴CO₂ assimilation rate was reduced by 75% in both hybrids. Soil drought increased the ¹⁴C dissimilation. There were no significant differences between hybrids in all treatments, with the exception of 5 days drought; after this treatment the dissimilation rate of hybrid 8344 was higher than that of 8388. Changes of translocation of ¹⁴C and its accumulation in particular organs occurred in drought treated plants; the amount of ¹⁴C accumulated in roots of plants of hybrid 8344 increased, while that of hybrid 8388 decreased. Changes of ¹⁴C accumulation in roots were positively correlated to changes of dry matter of those organs. One day after 10 days of drought assimilation and dissimilation rates in both hybrids were about 60% of controls.     

Untersuchungen zur Assimilatverteilung in Ackerbohnen (Vicia faba L.) während der Blühphase

Investigations about the distribution of assimilates during flowering in broad beans ( Vicia faba L.)
The distribution of assimilates during flowering was studied on single plants exposed to ¹⁴CO₂ in the field. The plants were harvested 1, 3, 15 days after exposition and at ripening. Results:
1. At the begin of flowering the nodes with flowers assimilated much ¹⁴C with a tendency of higher contents in the more above situated nodes. The concentration of ¹⁴C was similar in blades, stalks and flowers.
2. The assimilates incorporated after 24 hours were only to a small amount translocated afterwards. Only 3 % went to the apical region. An intensive restorement out of the blades took place at the time of ripening.
3. In the midst of flowering the concentration of ¹⁴C was lower in the nodes with open flowers than in those with shut or with pods. At that time pods are already strong sinks that withdraw assimilates from blades and stalks.
4. At the time when large and small pods are growing on the lower and middle nodes, the nodes in the apical region will be deprived of assimilates (effects of dominance).
5. Roots and nodules had low but stable contents and concentrations of ¹⁴C during flowering. These descended distinctly at ripening.     

Plant Growth Regulators Influence 14CO2 Assimilation and Translocation of Assimilates in Indian Mustard

Effect of plant growth regulators Naphthalene acetic acid (NAA), Gibberellic acid (GA₃) and Kinetin on ¹⁴CO₂ assimilation, partitioning of ¹⁴C into major biochemical fractions and translocation of assimilates was studied in different parts of Indian Mustard ( Brassica juncea ) at late ripening stage. Leaves, stem and pod walls are photosynthetically active and are important sources for seed filling. NAA and kinetin increased the ¹⁴CO₂ assimilation rate in all the three photosynthetically active parts. All the three growth regulators increased the export of ¹⁴assimilates out of source organs and increased the movement of assimilates into the reproductive parts (pods). The increased movement of photoassimilates into the developing pods may be due to the stimulation of sink activity by the growth regulators which resulted in the higher demand for photoassimilates. It was suggested that growth regulators may increase yield by altering distribution of assimilates in the mustard plants.     

Genotypische Unterschiede in der Translokation von zwischengelagertem 14C aus dem Halm in die Körner bei Sommerweizen (Triticum aestivum L.)

Genotypic differences in the translocation of temporarily stored ¹⁴C from the stem to the grains in spring wheat (Triticum aestivum L.)
In three field experiments with two spring wheat genotypes (Kolibri and breeding line 93117 ), changes in the total nonstructural carbohydrates (TNC) of the stem were observed after anthesis. Maximum values were measured in the third or fourth week following anthesis when stems contained 300 to 400 mg TNC. Thereafter TNC content declined up to maturity.
Flag leaves of individual shoots or all plants in micro-plots were labelled with ¹⁴C 5 days prior to anthesis, at anthesis or 5 days after anthesis to observe long term movements of assimilates during grain filling. After a chase period of two to three days, 60 to 80 % of total ¹⁴C recovered in the shoot was in the stem. From total ^l4C recovered two to three days after labelling, Kolibri had translocated 12.5 to 27.0 % into the grains by maturity whereas this portion was significantly higher for the breeding line 93117 (22.5 to 43.9 %). It was concluded that genotypes differ in the translocation of soluble carbohydrates from the stem to the grains. These differences were not related to parameters describing the 'source-sink' relationship, such as leaf area, grain number or grain size. However, the lower translocation rates of Kolibri coincided with a lower TNC concentration in the stem dry matter. This was due to a higher stem weight at anthesis, a longer period of stem elongation and a higher incorporation of assimilates into structural carbohydrates in non elongating stem parts after anthesis. It was therefore suggested that the accumulation of TNC in the stem and the remobilisation of these reserves for grain filling are determined partly by factors related to the carbohydrate metabolism in the stem.     

Translocation of 14C-sucrose within the Ear in Durum and Aestivum Wheat Varieties

Excised ears of Triticum durum (HD 4502 and B 449) and T. aestivum (Kalyansona and Kundan) varieties were cultured in ¹⁴C-sucrose, and the uptake and distribution of ¹⁴C within the ear was examined. Species-level differences in the distribution of ¹⁴C to spikelets at basal, middle and apical positions in the wheat ear (vertical distribution) were observed. T. aestivum var. Kalyansona and Kundan showed no limitation in vertical translocation of ¹⁴C-sucrose, whereas in T. durum there was a decrease in the distribution of ¹⁴C to apical spikelets. Within a spikelet, the distribution of ¹⁴C-sucrose to distal grains was significantly less than that to proximal grains in all the genotypes.     

Untersuchungen zur Assimilatakkumulation im Weizenblatt nach Schwarzrostinfektion

Accumulation of assimilates in stem-rust-infected wheat leaves
Using wheat plants (cv. 'Prelude'), the effects of stem-rust infection on photosynthesis and assimilate partitioning were studied with the aid of the short-lived carbon isotope ¹¹C. Photosynthesis of strongly infected leaf parts declined by about 30 % within 1 day. This rapid inhibition was caused by the formation of appressoria and the growth of infection tubes into the stomata, leading to a reduction in gas exchange. Further decline of photosynthesis to 5–10 % was accompanied by the degradation of chlorophyll. Nevertheless, during sporulation, the dry weight of the infected leaf area increased by about 50 %. With the use of ¹¹C, the reduced export of photosynthate from the infected leaf part and the capture of labelled compounds from the apical leaf section were quantified. The enhanced storage of assimilates in stem-rust-infected leaves can be attributed to the increase in invertase activity.     

Electrolyte Leakage, ATP Content in Leaves and Intensity of Net Photosynthesis in Maize Seedlings at Permanent or Different Daily Exposure to Low Temperatures

Changes were determined in electrolyte leakage (EL), ATP content in leaves and intensity of net photosynthesis (FJ in maize seedlings as a result of continued exposure to low temperatures for several days or, after a cold night (5 °C, 9 h), alternating application of 5 °C and 20 °C temperatures during the lit phase of the day (h of chilling during day/night: 0/9, 5/9, 10/9, 15/9).
At continuous exposure to low temperatures, permanent reduction of ATP content occurred between days 7 and 10, while EL increased significantly between days 4 to 7 (depending on experimental conditions). Of three leaves differing in age, most injuries were found in the oldest leaf. An increased intensity of irradiation from 150 to 500 μE. m⁻².s⁻¹ caused an earlier decrease in the ATP content and a further increase in electrolyte leakage. ATP content showed a 24 h rhythm, it increased at the end of the night and decreased at the end of the day. The rhythm was particularly noticeable in the control plants (20 °C), as well as, however to a lesser extent, in plants exposed to daily fluctuating chilling temperatures. It has also been observed that higher temperatures occurring in day time may diminish electrolyte leakage induced by previous low temperatures
The intensity of F_n determined at 20 °C, 4 h after withdrawal of chilling, decreased with the prolongation of the chilling period during the day.
Thus, it may be assumed that the EL and F_n values as indicators of the plants' sensitivity are in better agreement with the induced chill doses than the ATP content in leaves, which to a greater extent depends on the interaction between chilling and other experimental factors, such as irradiation intensity or the sequence of light and darkness.     

Effect of Low Night Temperatures on Photosynthetic Activity of the Maize Seedlings (Zea mays L.)

Night chilling (5 °C) subsequently lowered photosynthetic intensity in the leaves of maize seedlings at 20 °C through an increase in leaf diffusive resistance brought on by lower tissue water content in morning hours. A more significant increase in leaf diffusion resistance was observed when soil temperature was lowered than in the case of lower air temperature.
The unfavorable effect of soil and air cooling temperature on photosynthesis was limited by air saturated with water vapour. However, as a result of lowering the night temperature from 5 °C to 1 °C, the efficiency of the protective influence of higher atmospheric humidity was decreased. This demonstrates that the participation of factors unrelated to plant water status in inhibiting photosynthesis increases with lower night temperatures.
An additional reason for inhibited photosynthesis following cool nights was a decrease in chlorophyll accumulation, below 50 μg per 1 cm² of leaf area.     

Effect of Soil Temperature on the Carbohydrate Status in the Potato Plant (S. tuberosum L.)

Seed tubers of the variety Ostara were raised in growth chambers of 16°C air temperature continuously. The vessels were placed in a water bath of automatic temperature regulation so that soil temperatures of 16°C and 28°C could be maintained. Four weeks after emergence the plants were treated with ¹⁴CO₂ and 24 hours later the plants were harvested. Three more treatments and time harvests followed in two weeks intervals. C-14 activity was determined in soluble carbohydrates, in insoluble carbohydrates, and in non extractable residues respectively of the various plant parts in order to obtain information about the translocation of assimilates in the plant.
While the plants at 28°C soil temperature reduced the soluble sugar levels to 50% up to 70 days after emergence, the plants at 16° brought it down to 33% much faster. — The C-14 activity in insoluble carbohydrates amounted to only 50 % in the plants at 28°C while at 16°C it was more than 2/3 (Tables 1 and 2). — The C-14 activity in non extractable residues is much less at 28°C than at 16°C (Tables 3 and 4). — The starch weight reaches only 30% of the value obtained at lower temperature 70 days after emergence (Table 5). — At the higher temperature starch is also increasingly transferred to the tubers but to a much lesser extent and not from the stems and stolons (Table 6).
Possible causes, particularly the role of phytohormones, and consequences are discussed.     

14C-labelled Assimilate Distribution in Flowering Maize Plants

Maize ( Zea mays L.) plants were grown in the field and labelled with ¹⁴CO₂ at four leaf positions from silking up to maturity. The ear leaf was the most important source of labelled photosynthates to the ear, followed by the first leaf blade above and below the ear. The movement of labelled assimilates from the second leaf blade below the ear was predominantly downwards. The ear became an important sink soon after silking and continued in importance till harvest.
Initially assimilates were partitioned within the ear as husk < cob < grains but at harvest as grains < cob < husk. There was considerable remobilization of assimilates from the husk and stem. Removal of leaves drastically altered the pattern of distribution of labelled photosynthates and the direction of movement was determined by the position of the source leaf blade and the defoliation treatment. Darkening the leaf blades did not much alter the translocation of the labelled photosynthate and increased slightly its proportion to the grains. The removal of the ear severely altered the pattern of distribution of ¹⁴C, which was mostly deposited in the stem.     

High Temperature Influence 14CO2 Assimilation and Allocation of 14C into Different Biochemical Fractions in the Leaves of Indian Mustard

Influence of high temperature stress on photosynthesis and allocation of carbon into different biochemical fractions in mature leaves of Indian mustard [ Brassica juncea (L) Czern] was investigated. Heat stress reduced ¹⁴CO₂ fixation and inhibited the translocation of carbon from the leaves. Allocation of ¹⁴C into starch and residue fractions was significantly lower in heat stressed plant leaves. Starch content was significantly reduced in heat stressed plants.     

Conversion of SO2−4-S and Changes in Glucosinolate Content in Leaves of Rape Seedlings Transplanted

The conversion of SO^2-₄ -S and changes in content of S in various constituents in leaves of rape seedlings transplanted were investigated by using (NH₄)₂³⁵SO₄ as a tracer to exploit formation and accumulation of glucosinolates in oilseed rape. Seedlings grown under sandy culture absorbed ³⁵SO^2-₄ which was added to the cultural solution and incorporated into amino acids, glucosinolates and proteins rapidly. Distribution of extractable ³⁵S with 70 % methanol in glucosinolates in leaves declined with time from labelling, while those in amino acids rised correspondingly. Per cents of ³⁵S incorporated into bound form in total ³⁵S increased linearly and those of ³⁵S into glucosinolates and amino acids decreased with time within five days from labelling. After that the relative amounts of ^3SS in three constituents was basically constant. Content on dry weight basis of labelled glucosinolates and amino acids expressed as μmol S/g.d.w. increased linearly with time from labelling with absorption of ³⁵SO^2-₄from soil by the seedlings under soil culture. Compared with seedlings grown under sandy culture, more ³⁵S was incorporated into glucosinolates in leaves of seedlings grown under soil culture.     

Pflanzenwachstum durch CO2/HCO3-Eintrag über die Wurzel

Plant Growth after Application of CO₂/HCO₃ to the Roots
After applying H¹⁴CO₃ to the root system of summer wheat in hermetically sealed pots, absorption and incorporation of HCO₃ in the sugar-, starch-, and fibre-fraction (approximately 50 % of the absorped ¹⁴C) could be shown. This fraction reached 0.44–1.21 % of total C-assimilation of the shoot during growing stage F9/F10 on the Feeke-scala. 1/3 of the HCO₃-fraction resting in the soil was bound organically indicating that microorganisms may be able to utilize exogenous anorganic CO₂/HCO₃ for their photosynthesis.     

The Effect of Short Warm Breaks during Chilling on Water Status, Intensity of Photosynthesis of Maize Seedlings and Final Grain Yield

The effects of short-term exposure of seedlings to suboptimal temperature (14 °C for 1 or 4 h in 24 h cycles) during chilling (5 °C for 12 days) on the water status and intensity of photosynthesis of tolerant (TG) and chilling-sensitive (SG) maize genotypes were studied. Daily warming for 1 or 4 h resulted in a decrease in the hydration of the seedlings to 31.1 % and 61.5 % (SG) and 14.8 % (TG) and 39.1 % (SG), respectively, in comparison with the continuously chilled control. During warming for 4 h, both genotypes absorbed water from soil in amounts that partly compensated for its loss through transpiration, after the plants had been moved to the lower temperature. A protective effect of shorter warming (1 h) on the hydration of the seedlings was a result of a strong, stomatal limitation of transpiration during the initial days of chilling. Warming for 1 or 4 h also increased the ability of TG stomata to close in reaction to water deficit in chilling conditions. The effect of increased temperature delayed the decrease of P_N in leaves and limited RGR inhibition of the seedling mass caused by chilling. Daily warming of plants at the seedling phase (14 and 20 °C for 1 or 4 h) reduced the unfavourable effect of chilling (5 °C for a period of 8 days) on the final yield, the filling of caryopses and their number in a cob after growth in natural conditions.     

The Effect of Chilling Temperature on the Permeability of Membranes to K+, Mg2+, Ca2+ ions and on the Electric Potential of Leaves in the Seedlings of Maize (Zea mays L.)

The relations between the extent of injuries in seedlings caused by a few day-long exposures to chill (5°C) and the leakage of K⁺, Mg²⁺ and Ca²⁺ ions from the leaves as well as the electric potential in seven maize hybrids, were investigated. The permeability of cells to ions was defined based on their absolute concentration in a water diffusate (C_t) and concentration expressed in relation to the total ion content in the leaves (IL index).
At lowered temperature the hybrids of higher resistance to chilling temperature were characterized by a lower value of the IL index for K⁺ and Mg²⁺ ions than the chill-sensitive hybrids. On the other hand, absolute concentration of the ions (C_t) Mg²⁺ and Ca²⁺ leaking from the leaves before chill exposure of the seedlings was positively and highly correlated with the extent of injuries in hybrids caused by 4 day-long exposures to chill. This observation is evidence that the chill injuries were predetermined through increased cell permeability to the mentioned ions at room temperature.
Changes in the electric potential of leaves in conditions of lowered temperature preceded the injuries of leaves, which became apparent after a longer period of exposure to chill. Thus, as the leakage of Mg²⁺ and Ca²⁺ ions occurs, changes in the electric potential may supply early information about the predisposition of the particular maize hybrids to chilling injuries. Leakage measurements of Mg²⁺ and Ca²⁺ ions from the leaves at room temperature may find application in the selection of chill-tolerant maize genotypes.     

Effect of Soil Moisture and Potassium Fertilizer on Shoot Water Potential, Photosynthesis and Partitioning of Carbon in Mungbean and Cowpea

The effect of different rates of potassium (K⁺) on shoot water potential, photosynthesis and carbon movement (using ¹⁴C) at the V3/4 growth stages was studied in mungbean ( Vigna radiata L. Wilczek), a drought-susceptible legume, and cowpea ( Vigna unguiculata L. Walp), a drought-tolerant legume, grown under low- and high-irrigation regimes under controlled conditions. Soil moisture and K⁺ affected all measured parameters in the two species. The rate of photosynthesis was higher at reduced water stress when K⁺ was applied. The impact was greater in cowpea, which had an inherently high rate of carbon assimilation. Mungbean and to a lesser extent cowpea allocated greater quantities of carbon to roots under dry conditions, especially with added K⁺. The distribution of ¹⁴C into other plant parts was also increased at higher rates of K⁺ application under both soil moisture regimes. Thus, application of K⁺ seems to have a beneficial effect in overcoming soil moisture stress and increasing physiological parameters and carbon partitioning in these two important tropical food legumes.     

Transport of 14C-Sucrose and 14C-Benzyl Adenine in Winter Wheat (Triticum aestivum L.) in the Pre-Anthesis Period

A lysimeter trial is described in which the fate of ¹⁵N was monitored in a sand, loam and clay soil by using it over a period of 6 years. The following results were obtained.
1. The uptake of fertilizer nitrogen by plants, determined by using ¹⁵N, is lower than by using the conventional method ("difference method"). Nitrate ¹⁵N is better utilized by the plants than is ammonium ¹⁵N. The total nitrogen uptake only gives hints of these differences.
2. The extent to which plants utilize fertilizer ¹⁵N is between 38 and 58%; in the case of the method of differences this figure is between 48 and 68%.
3. Plants remove more nitrogen from the soil when fertilizer N is applied than when without fertilization. The influence of these two nutrient forms is of subordinate significance.
4. After a trial period of six years between 26 and 54 % of the fertilizer ¹⁵N remains in the soil. The resulting sequences are clay > loam > sand > and ammonium > nitrate.
5. The immobilization of the fertilizer ¹⁵N is most pronounced in the first four years but then decreased considerably; in the case of the sandy soil it is then even slightly regressive.
6. The biggest part of the ¹⁵N is deposited in the uppermost layer of the soil. The amount of ¹⁵N in the deeper layers is diminished appreciably. The type of soil has a greater influence than the form of nitrogen.
7. If the amount of fertilizer N left in the soil is compared with the N losses from the soil's reservoir (plants' uptake, leaching) there is a negative balance for the soil nitrogen which mainly is determined by the type of soil.     

Pre-anthesis Interaction of Cytokinins and ABA in the Transport of 14C-sucrose to the Ear of Winter Wheat (Triticum aestivum L.)

The effect of the application of abscisic acid (ABA, 10⁻⁴ mol 1⁻¹), benzyl adenine (BA, 10⁻⁶ mol - 1⁻¹), N⁶-m-hydroxybenzyl-adenosine (HBA, 10⁻⁶ mol - 1⁻¹) and combinations of these cytokinins with ABA on the transport of ¹⁴C-sucrose into the developing kernels of winter wheat, their number and mass, was studied. Growth substances were applied in the period 10 to 5 days before anthesis and their effects were examined 4 and 18 days after anthesis on ears that were detached 10 days before anthesis and then cultivated on a complete nutrient solution. The stimulating effect of HBA on the transport of ¹⁴C-sucrose, number of kernels and their mass was higher than that of BA. ABA partly decreased the stimulating effect of cytokinins and reduced up to several days after anthesis the transport of ¹⁴C-sucrose to the developing kernels, their number and mass. The results revealed that a higher level of cytokinins in the period before anthesis could effectively interact with the inhibiting effect of ABA in that period and influence the accumulation of assimilates in the kernels.