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.     

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.     

14CO2 Assimilation and Translocation of 14C-Photosynthates by Different Parts of Indian Mustard (Brassica juncea L.)

The role of leaves, stem and reproductive parts in ¹⁴CO₂ fixation and subsequent photosynthate translocation was studied in Indian mustard ( Brassica juncea L.) at three growth stages. The data indicated that leaves, stem and pods are important sources of photosynthates for seed filling. At bud emergence stage leaves are the principle site of ¹⁴CO₂, fixation. The contribution of leaves declines at subsequent stages, where as the contribution of pod walls increased from bud emergence stage to ripening stage. The contribution of the stem remains more or less constant at all three growth stages studied. Although stem can fix ¹⁴CO², at bud emergence and flowering stages it imported ¹⁴C-photosynthates from leaves. However, stem exported photosynthates during subsequent growth stages.     

Effect of High Temperature Stress on 14CO2 Assimilation and Partitioning in Indian Mustard

Effect of heat stress on ¹⁴CO₂ assimilation and translocation by different parts was investigated in Indian mustard ( Brassica juncea (L.) Czern.]. Heat stress reduced ¹⁴CO₂ assimilation by leaves, stem and pods. Export of radioactive carbon from upper and lower leaves, upper and lower stem and stem of terminal raceme was inhibited in response to heat stress. Import of ¹⁴C-photosynthates into pods was also inhibited by heat stress indicating reduction in sink strength of the developing pods.     

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.     

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.     

Effect of Low Soil Temperature on Weight Increase, Gas Exchange and Distribution of 14C-Assimilates in Seedlings of a Maize Hybrid

Seedlings of a maize hybrid sensitive to chilling initially grew in the growth chamber of the phytotron at 20/ 17°C (day/night) and after the formation of the fourth leaf, the soil temperature was lowered to 5°C. Under such growth conditions the dynamics of dry weight change, gas exchange and the distribution of ¹⁴C-assimilates in seedlings were examined. The low soil temperature inhibited daily growth of dry weight of whole seedlings more than their photosynthesis. Simultaneously, it was also responsible for a greater increase in dissimilative losses.
During 37 hours (day-night-day), following exposure to ¹⁴CO₂, dissimilation in seedlings in cool soil (5°C) and in non-chilling conditions amounted to 35.1 % and 23.4 % of assimilated ¹⁴C (AC), respectively. At lower soil temperature relatively high dissimilative losses were observed on the first day after exposure (23.5 %), lower at night (9.9 %) and the lowest on the following day - merely 1.7 % AC. Higher losses of ¹⁴C under chilling conditions occurring on the first day were a result of limited photosynthetic refixation of ¹⁴CO₂ At night, however, they were associated with a prolonged period of intensive translocation of assimilates to the stem. It was assumed that an excessive accumulation of assimilates in leaf blades might be an additional factor responsible for increased dissimilative losses at low temperature during the first twenty-four hours. In the third period of measurements, as a result of a limited transport of ¹⁴C, dissimilative losses were lower than in previous ones and were not dependent upon soil temperature.     

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.     

Pod photosynthesis and drought adaptation of field grown rape (Brassica napus L.)

In rape (Brassica napus L., cv. Global) seed growth mainly depends on husk CO₂ assimilation. In irrigated plants, the net photosynthetic rate (A_max) was 10–13 μmol CO₂ m⁻² s⁻¹ in non-maturing pods and correlated with nitrogen content. The stomatal conductance of water vapour (g_H2O) was 0.3 mol m⁻² s⁻¹ in non-maturing pods. The photosynthetic nitrogen use efficiency (NUE) was 8.3 μmol CO₂g⁻¹ N s⁻¹, about one-third of that in leaves. The photosynthetic water use efficiency (WUE; A_maxg_H2O⁻¹) was similar in pods and leaves. In severely droughted plants, the photosynthetic rate was reduced to 38%. The seed growth rate, however, was not influenced by intermittent periods of water stress, indicating translocation of assimilates to the seeds. The drought resistant character of the pods was due to low specific area, succulence, low stomatal conductance causing a small decrease of ΔΨ day⁻¹ during soil drying and maintenance of high relative water content during severe drought. A mathematical formulation of the pod water release curve was undertaken. © (1997) Elsevier Science B.V.     

Changes in Content of Glucosinolates and its Accumulation in Siliquae and Seeds of Oilrape (Brassica napus L.)

Rape plants were labelled by applying (NH⁴)₂³⁵SO₄ to soil. Changes in content of ³⁵S in various constituents in pods and grains were determined during siliquae development to exploit formation and accumulation of glucosinolates in oilseed rape. Content of ³⁵S in glucosinolates expressed as μmol S/g.d.w. and its relative amounts in extractable forms in young siliquae were in constant level within one week after flowering, but either absolute content or relative content of ³⁵S in glucosinolates increased largely by two weeks after flowering, thereafter the distribution of extractable ³⁵S in glucosinolates of siliquae and grains increased linearly as proceeding of its development, ³⁵S in extracts of grains almost was in form of glucosinolates after 8 weeks from flowering. Amounts of both ³⁵S in glucosinolates and dry matter per pod increased linearly with time after flowering. According to the changes of amounts of ³⁵S in other constituents per pod, it could be supposed that glucosinolates accumulated in seeds might be transported from other organs together with nutrients.     

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.     

Effects during Period of Siliqua Developing of KH2PO4 and MgSO4 Application on Nitrogen Transportation in Pods of Oilseed Rape(Brassica napus L.)

An experiment was conducted in field experiment plot to investigate nitrogen transportation from hulls of pods in different periods at early stage of siliqua developing and effect of KH₂PO₄ and MgSO₄ application on it using ¹⁵N-urea.
More than 80 % of ¹⁵N applied on the surface of pods at lower terminal during flowering was recovered from all pods one month after flowering, most of them were still in the hulls of labelled pods, 17-27 % of ^l5N applied was transported into seeds, a small amount was transported to pods at upper terminal, a little amount was found in pods at branch. More ^l5N applied in middle period of flowering was transported to pods at upper terminal and branch than those applied in early period of flowering. It should be further investigated to conclude how will be going on transportation of nitrogen from hulls as preceding of siliqua developing towards maturity of seeds and its difference between ¹⁵N applied in more different periods.
Application of KH₂PO₄ and MgSO₄ with ¹⁵N-urea of surface of pods promoted transportation of ¹⁵N into seeds from hulls, effect of MgSO₄ was more notable.     

Nitrogen Transportation in Oilseed Rape (Brassica napus L.) Plant during Flowering and Early Siliqua Developing

Nitrogen transportation from different organs was investigated by labelling pods, leaves and internodes of upper stem with ¹⁵N-urea during flowering. Labelled plants were harvested one month after flowering and determined the amount of ¹⁵N in relative parts. The results of the experiment show the directions of ¹⁵N applied in different organs during flowering. Transportation of ¹⁵N applied in pods of lower terminal of the main stem and first branch was mainly directed to seeds inside the labelled pods, about 17 % of ¹⁵N entered into seeds 7 days after last labelling, a little transportation each other between the branch and terminal was found, more than 80 % of ¹⁵N applied on leaves during flowering was transported out of the leaves after flowering, 35 % and 67.93 % on average was translocated in pods for early and late flowering, respectively, while 55.97 % of ¹⁵N applied on surface of internodes of upper stem below terminal was found in pods. It was corroborated that nitrogen transportation also occurs within pods by labelling different parts of pods, much greater amount of nitrogen was transported from lower part to upper part of pods than those in opposite direction.     

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.     

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.     

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.     

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.     

Translocation of N in Pods of Oilseed Rape during Siliqua Developing

A pot experiment was conducted to investigate the translocation of N in pods during siliqua developing of oilseed rape using ¹⁵N-urea. The ¹⁵N was applied on the surface of pods at lower stem in three periods after flowering. At maturity the hulls and seeds of pods at different parts of plants were subjected to analyse N content and ¹⁵N abundance and calculate recoveries of N applied.
79.1–84.3 % of labelled N applied were recovered from the total pods including 75.3–80.4 % in labelled pods. A great part of the N was translocated in seeds, the later the labelled N application, the more proportion of N in seeds was. Application of MgSO₄ combined with urea promoted the uptake and translocation of N, but not at a significant level.     

Effect of Soil and Foliar Fertilization on Inoculated and Uninoculated Soybeans

Two experiments of soil N-fertilization and Rhizobium inoculation were conducted in 1981 and 1982 at Giza, Egypt. Soybean was sprayed with a commercial micronutrients mixture, and with urea.
In the first experiment, soil N-fertilization 0, 142.8 and 214.2 kg N/hectare were applied to uninoculated plants, whereas, in the second one, local inoculum was used alone or along with addition of a starter dose of N (47.6 kg N/hectare).
Urea applications were at pod filling period (R₄, R₅ and R₆ stages), whereas, micronutrients mixture was applied at 25 days from planting.
Plant dry weight, leaf area/plant, plant height, pod and seed number/plant, seed weight/plant, seed yield and crude seed protein content increased significantly with nitrogen application to uninoculated soybean plants; whereas the starter dose of N had no significant effect on any of these traits under the inoculated soybean plants.
Foliar application of micronutrients caused significant increases in plant DW, LA, pod and seed number/plant, seed index and seed yield of fertilized and inoculated plants.
Foliar application of urea, to inoculated and uninoculated plants, caused significant increments in plant dry weight, 1A, seed protein content and particular seed index and seed yield.     

Nitrogen Fixation, Growth and Yield of Intercropped Mungbean (yigna radiata L.) and Groundnut (Aracbis bypogaea L.) as Affected by the Genotype

¹⁵N-aided investigations were conducted to ascertain the Nj fixation and the nitrogen (N) contribution by mungbean ( Vigna radiata L.) and groundnut ( Aracbis hypogaea L.) when intercropped with maize ( Zea mays ). The study involved growing seven genotypes of the above legumes with maize in alternate rows in two separate experiments. A sole crop of maize was used as the reference crop to determine N2 fixation by the ¹⁵N methodology. Significant genotypic differences in pod yield and stover N content were observed in intercropped mungbean and groundnut. The percentage N derived from the atmosphere showed a genotypic variation of 31 to 45 % (7 to 10 kg N₂ fixed ha⁻¹O in mungbean and 47 to 69 % (9 to 18 kg N₂ fixed ha⁻¹) in groundnut. Harvest index for N varied from 58 to 77 % in mungbean and 55 to 75 % in groundnut. In groundnut, the uptake of soil N was significantly affected by the genotype. Assuming that the N contribution to the soil by the helow-ground plant parts was negligible, the removal of seeds at maturity resulted in a negative N balance in the soil in all the genotypes of mungbean. In groundnut, some genotypes produced a positive N balance in the soil. Owing to high N₂ fixation capacity and low harvest index for N, groundnut showed a greater N supplementing ability than mungbean.