The relative importance of carbohydrate and nitrogen for the resprouting ability of Quercus crispula seedlings

BACKGROUND AND AIMS: Plants need some kind of stored resources to resprout after shoot destruction. The aim of this study was to determine the relative importance of carbohydrate and nitrogen (N) storage levels for their ability to resprout. METHODS: A shoot clipping experiment was conducted on Quercus crispula seedlings, which were grown in a factorial experimental design, with two light levels (40% and 3% of full light) and three nutrient concentrations (low, medium and high). KEY RESULTS: At the time of shoot clipping (the end of spring leaf expansion), seedlings exposed to 40% light had an average total non-structural carbohydrate (TNC) concentration of 17.0% in their roots compared with 4.9% in the roots of seedlings exposed to 3% light, and the average amount of TNC (TNC pools) in the roots was 203.8 mg and 20.0 mg at 40% light and 3% light, respectively. In contrast, root N concentration averaged 2.3% in the 3% light treatment compared with 1.2% in the 40% light treatment, and it increased with successive rises in nutrient concentrations at both light levels. Regardless of the nutrient status, at the 40% light level >80% of the seedlings resprouted after shoot clipping. Few seedlings, however, resprouted at the 3% light level, particularly in the medium- and high-nutrient treatments. Furthermore, both root TNC concentrations and TNC pools decreased after resprouting, but the amount of root N remained constant. CONCLUSIONS: These results suggest that carbohydrate storage has a stronger influence on resprouting in Quercus crispula than N storage. However, the size of the resprouting shoot was positively correlated with the amount of both N and TNC in roots. The level of N storage is, therefore, also important for the growth of resprouting shoots.     

How periodic growth pattern and source/sink relations affect root growth in oak tree seedlings

Seedlings of Quercus pubescens were grown in root boxes to study the growth pattern of the root system in relation to shoot development. Shoot growth was typically rhythmic. Root elongation was also periodic, in contrast to several previous reports on other Quercus species. Both taproot and lateral root elongation were depressed during expansion of the second leaf flush, with a more pronounced response of lateral root growth. Apical diameter of the taproot followed comparable but less prominent trends than taproot elongation. Modifying source/sink relationships through various defoliation treatments altered the root growth pattern. Ablation of source organs (mature leaves or cotyledons) amplified the decrease in root growth concomitant with leaf expansion. Root growth recovery was even more difficult when both cotyledons and mature leaves had been removed. Ablation of sink aerial organs (young leaves) initially suppressed competition for growth between the shoot and the root, and then caused a gradual decrease in lateral root growth. Antagonism between maximum leaf expansion and root growth reduction during the second flush, and various responses of seedlings with modified source/sink relationships, raise an hypothesis of mutual competition for carbohydrates. The gradual decrease in lateral root growth after ablation of young leaves suggests a long-term carbohydrate limitation, or auxin limitation as auxin sources have been removed.     

Nutrient reserves in roots of fruit trees,in particular carbohydrates and nitrogen

Summary In trees, nutrient reserves built up in the previous year are of primary importance for early spring growth. Despite the relatively great importance of roots for nutrient storage, the root system should not be regarded as a special storage organ. Quantitatively, carbohydrates predominate in these reserves, but qualitatively N and other minerals are of more than minor significance. In roots carbohydrates are usually stored in insoluble form, mainly as starch; sorbitol is the predominant soluble compound in apple and peach. For nitrogen reserves, the soluble form predominates in roots, especially arginine in apple and peach, followed by asparagine. The level of reserves usually becomes maximal early in the winter. During leafing-out the reserves are drawn on until, later in the season, the supply of newly produced or absorbed nutrients exceeds the demand and replenishment occurs. The initial carbohydrate reserves do not determine the amount of new growth, whereas reserve nitrogen is of decisive importance for shoot growth vigour. Environmental factors such as light intensity and temperature affect the level of carbohydrates in roots; the concentration can be reduced by defoliation and summer pruning and increased by ample supply of nitrogen fertilizer in the autumn. The main cultural factors that influence nitrogen reserves are the amount and the time of nitrogen fertilization.     

Interspecific and intraspecific variation in tree seedling survival: effects of allocation to roots versus carbohydrate reserves

We examined interspecific and intraspecific variation in tree seedling survival as a function of allocation to carbohydrate reserves and structural root biomass. We predicted that allocation to carbohydrate reserves would vary as a function of the phenology of shoot growth, because of a hypothesized tradeoff between aboveground growth and carbohydrate storage. Intraspecific variation in levels of carbohydrate reserves was induced through experimental defoliation of naturally occurring, 2-year-old seedlings of four northeastern tree species –Acer rubrum, A. saccharum, Quercus rubra, and Prunus serotina– with shoot growth strategies that ranged from highly determinate to indeterminate. Allocation to root structural biomass varied among species and as a function of light, but did not respond to the defoliation treatments. Allocation to carbohydrate reserves varied among species, and the two species with the most determinate shoot growth patterns had the highest total mass of carbohydrate reserves, but not the highest concentrations. Both the total mass and concentrations of carbohydrate reserves were significantly reduced by defoliation. Seedling survival during the year following the defoliation treatments did not vary among species, but did vary dramatically in response to defoliation. In general, there was an approximately linear relationship between carbohydrate reserves and subsequent survival, but no clear relationship between allocation to root structural biomass and subsequent survival. Because of the disproportionate amounts of reserves stored in roots, we would have erroneously concluded that allocation to roots was significantly and positively related to seedling survival if we had failed to distinguish between reserves and structural biomass in roots. Received: 14 December 1999 / Accepted: 2 June 1999     

The Utilization of Carbohydrate and Nitrogen Reserves in the Spring Growth of Lilac

The spring flush of growth and the utilization of reserve materials in this growth was studied in lilac plants 0, 2, 4 and 6 weeks after bud break. The influence of nitrogen applied the previous season on the storage and utilization of carbohydrate and nitrogen reserves was determined. The plants were separated into buds, stems and roots and analyzed for changes in total available carbohydrates, sugars, hemi-celluloses, total nitrogen, basic and non-basic amino acids and organic acids. The bulk of the carbohydrate reserves occurred as soluble sugars in the roots, although the reserves of sugars and hemicellulose in the stem was important during the first two weeks after bud break. The bulk of the nitrogen reserves were stored as non-basic amino acids in the stems and roots. However, the roots of plants grown under high nitrogen levels contained twice us much total nitrogen as roots grown under low nitrogen. This additional nitrogen which was stored in the roots of high nitrogen plants was released as arginine. The dry weight of buds increased 3–10 fold during the initial two week period and during the next four weeks doubled again. This bud growth was correlated with the stored nitrogen reserves. The high nitrogen plants grew twice as much and utilized more of the reserve carbohydrates in spring growth than low nitrogen plants. Carbohydrates were synthesized in this new growth and the high nitrogen plants utilized this carbohydrate for additional growth while low nitrogen plants transported it to the stems and roots.     

Root soluble carbohydrates of Afzelia africana Sm. seedlings and modifications of mycorrhiza establishment in response to the excision of cotyledons

Stem length, number of secondary lateral roots, shoot dry weight and reducing sugar concentrations of root were significantly reduced when translocation of reserves from cotyledons to the roots of Afzelia africana seedlings was interrupted by complete or partial cotyledon excision. The sucrose but not the glucose concentration of lateral roots also decreased significantly after complete cotyledon excision. Hartig net development rather than fungal sheath formation was affected after inoculation with the early fungal isolate E1 and by both late-stage fungal isolates L1 and L2 after partial or complete cotyledon excision. However, mycorrhizal colonization by the early fungal isolate E2 was not affected by cotyledonary reserves, suggesting that this fungal isolate has a lower carbohydrate requirement than fungal isolates E1, L1 and L2. The late-stage fungal isolates L1 and L2 induced a hypersensitivity reaction by epidermal cell walls of the host plant after complete cotyledon excision, suggesting they are more dependent than the early fungal isolate E1 on available root carbohydrate substrates for ectomycorrhizal colonization. These results are discussed in the light of the hypothesis that early and late-stage fungi were different carbohydrate requirements, and that the time sequence of colonization was related to the root carbohydrate status, which increased with time.     

Seasonal changes in carbohydrate reserves in mature northern<Emphasis Type="Italic"> Populus tremuloides</Emphasis> clones

To assess the changes in seasonal carbohydrate status of Populus tremuloides, sugar and starch concentrations were monitored in roots, stem xylem and phloem and branches of ten different clones. Time of root growth was assessed by extraction of roots from in-growth cores collected five times during the season. Overall the results showed that the main period of root growth in these northern clones was shifted from spring to late summer and fall likely due to the microclimatic conditions of the soil. This increase in root growth was associated with a decline in total non-structural carbohydrate content in the roots during this period. This study also found that the carbohydrate reserves in these clones were being stored as close as possible to the organs of annual growth (leaves and roots). At the time of leaf flush, the largest reduction in stored carbohydrates (3% of dry weight) was observed in the branches of the trees, compared to a slight decline in the stem and roots. Starch and sugar reserves in most tissues were very low in early summer. This suggests that reserves that might be used for the regrowth of foliage after insect defoliation or other disturbances, are relatively small compared to the portion that is needed for maintenance and typical growth developments such as leaf flush.     

The role of the storage carbon of cotyledons in the establishment of seedlings of Hymenaea courbaril under different light conditions

BACKGROUND AND AIMS: Hymenaea courbaril (Leguminosae-Caesalpinioideae) is a tree species with wide distribution through all of the Neotropics. It has large seeds (approx. 5 g) with non-photosynthetic storage cotyledons rich (40 %) in a cell wall polysaccharide (xyloglucan) as a carbon reserve. Because it is found in the understorey of tropical forests, it has been considered as a shade-tolerant, late-secondary species. However, the physiological mechanisms involved in seedling establishment, especially regarding the interplay between storage and light intensity, are not understood. In this work, the ecophysiological role of this carbon cotyledon reserve (xyloglucan) is characterized, emphasizing its effects on seedling growth and development during the transition from heterotrophy to autotrophy under different light conditions. METHODS: Seedlings of H. courbaril were grown in environments with different light intensities, and with or without cotyledons detached before xyloglucan mobilization. Development, growth, photosynthesis and carbon partitioning (dry mass and [14C]sucrose) were analysed in each treatment. KEY RESULTS: The detachment of cotyledons was not important for seedling survival, but resulted in a strong restriction (50 % less) of shoot growth, which was the main sink for the cotyledon carbon reserves. Carbon restriction promoted an early maturation of the photosynthetic apparatus without changes in the net CO2 fixation per unit area. The reduced surface area of the first leaves in seedlings without cotyledons was evidence of limited growth and development of seedlings in low light conditions (22 micromol m(-2) s(-1) photon flux). CONCLUSIONS: There is an increase in the importance of storage xyloglucan in cotyledons for H. courbaril seedling development as light intensity decreases, confirming that this polymer plays a key role in the adaptation of this species to establish successfully in the shadowed understorey of the forest.     

Pea seedling growth and development regulated by cotyledons and modified by irradiance

Growth and development of hydroponically grown pea seedlings ( Pisum sativum L. cv. Alaska) were measured using stem and root length as well as number of leaves and lateral roots. The growth was dependent on the presence of cotyledons and was modulated by the irradiance. All plants were grown in a full nutrient solution. If grown at low irradiance (73 μmol m^-2s^-1) they depended more and for a longer time on the cotyledons than plants grown at high irradiance (220 μmol m^-2s^-1). Low irradiance caused stem elongation but decreased root length and number of lateral roots as compared to plants grown at high irradiance. The dark respiration of the leaves was measured as oxygen uptake. In plants grown at the low irradiance, excision of the cotyledons caused the rate of oxygen uptake to increase by a factor of three, and the increase was sensitive to cyanide. Decotyledonized plants showed a high respiration rate and a diminished leaf growth for their entire life cycle. CO₂ fixation also increased in decotyledonized pea seedlings grown at either irradiance. The mobilization of food reserves from the seeds was positively correlated to seed dry weight, but only if the plants were grown at 73 μmol m^-2s^-1. Increasing dry weight of the seed enhanced top growth, whereas root growth was depressed, so that top and root responds differently with regard to that part of growth which depends on mobilization of reserves from the seed.     

STUDIES ON THE SOLUBLE CARBOHYDRATES AND CARBOHYDRATE PRECURSORS IN GERMINATING SOYBEAN SEED

The total soluble carbohydrate fraction of the cotyledons and embryo axis of germinating soybean seedlings declined rapidly during the first 3 days of germination. This depletion began earlier in the embryo axis than in the cotyledon. The total carbohydrate content of the cotyledons of plants grown in light and plants grown in dark was approximately the same for the first 7 days of germination. Between day 9 and 13 the total carbohydrate content of the cotyledons of soybean seedlings grown in dark was higher than that of plants grown in light. The reducing sugar content of light-grown soybean cotyledons increased approximately 5-fold during the first 9 days of germination, whereas that of dark-grown soybean cotyledons increased more slowly during this interval. Reducing sugars in the embryo increased during the early stages of germination until they approximately equalled the total carbohydrate. Between day 4 and 13, oil was depleted more rapidly in the cotyledons of seedlings grown in light than those grown in the dark. The reserve carbohydrates of soybean embryos and cotyledons consisted primarily of low molecular weight oligosaccharides, particularly sucrose, stachyose, and raffinose. These compounds decreased rapidly during germination. The isocitritase activity in the cotyledons of germinating soybean seeds increased rapidly for the first 6 days of germination and then decreased for the next 7 days. The isocitritase activity of plants grown in the dark was higher than that of the plants grown in light at all stages of development, particularly between day 7 and 11.     

Partitioning of Nitrogen Derived from N2 Fixation and Reserves in Nodulated Medicago sativa L. During Regrowth

Nodul{macron}ted alfalfa plants were grown hydroponically. Inorder to quantify N₂ fixation and remobilization of N reservesduring regrowth the plants were pulse-chase-labelled with ¹⁵N.Starch and ethanol-soluble sugar contents were analysed to examinechanges associated with those of N compounds. Shoot removalcaused a severe decline in N₂ fixation and starch reserves within6 d after cutting. The tap root was the major storage site formetabolizable carbohydrate compounds used for regrowth; initiallyits starch content decreased and after 14 d started to recoverreaching 50% of the initial value on day 24. Recovery of N₂fixation followed the same pattern as shoot regrowth. Afteran initial decline during the first 10 d following shoot removal,the N₂ fixation, leaf area and shoot dry weight increased sorapidly that their levels on day 24 exceeded initial values.Distribution of ¹⁵N within the plant clearly showed that a significantamount of endogenous nitrogen in the roots was used by regrowingshoots. The greatest use of N reserves (about 80% of N incrementin the regrowing shoot) occurred during the first 10 d and thencompensated for the low N₂ fixation. The distribution of N derivedeither from fixation or from reserves of source organs (taproots and lateral roots) clearly showed that shoots are thestronger sink for nitrogen during regrowth. In non-defoliatedplants, the tap roots and stems were weak sinks for N from reserves.By contrast, relative distribution within the plant of N assimilatedin nodules was unaffected by defoliation treatment. Key words: Medicago sativa L., N₂ fixation, N remobilization, N₂ partitioning, regrowth     

The potential for predation induced somatic embryogenesis in storage cotyledons

Using seven tropical rainforest species of north Queensland, Australia, we simulated partial predation and compared the development of intact embryos and embryos from which various proportions had been removed, including in some cases the original root–shoot axis. Embryos of all species contained storage reserve cotyledons and germinate in a hypogeal manner. Species mean embryo masses ranged from 0.4–48.1 g. Partial embryo predation treatments were: ½ embryo treatment; embryos separated into component cotyledons, and ¼ embryo treatment; cotyledons separated as above and subsequently cut in half. Germination was scored as production of roots and shoots, or roots or shoots only. Embryos from all species produced seedlings in all treatments, even after the removal of up to 75 percent of the cotyledonary reserve. Moreover, the proportion germinating were not different between intact embryos and i) separated cotyledons, ii) cotyledon halves that maintained or were adjacent to the embryonic axis (except for the largest seeded species), and iii) cotyledon halves that did not include the root–shoot axis (four species). Thus, production of roots and shoots, or roots or shoots only was largely independent of the presence of the embryonic root–shoot axis – implying that somatic cells in storage cotyledons are capable of differentiating into the full range of cell types typical of shoots and roots in the absence of the root–shoot axis. The generality of this response across all seven species suggests somatic embryogenesis in storage cotyledons may be a more widespread phenomenon in tropical floras than currently considered.     

Diurnal changes in net uptake rate of nitrate are associated with changes in estimated export of carbohydrates to roots

The rate of NO3- uptake by soybean (Glycine max [L.] Merrill) roots generally declines during the night in association with progressive depletion of the nonstructural carbohydrate pool in the shoot as well as the concentration of carbohydrates in roots. To determine if NO3- uptake rate changes in response to variations in translocation rate of carbohydrates from shoot to roots per se or to carbohydrate status of the roots, the night period was interrupted with a low light level from incandescent lamps to alter the diurnal pattern of NO3- uptake by roots and export of carbohydrate from shoots of nonnodulated soybean. Depletion of NO3- from replenished, complete nutrient solutions containing 1 mM NO3- was measured by ion chromatography and rates of NO3- uptake were calculated. Changes in export of carbohydrates from shoot to roots during intervals of the night period were calculated as the differences between rates of disappearance in contents of nonstructural carbohydrates and their estimated rates of utilization in shoot respiration and growth. A positive, significant correlation occurred between changes in calculated rates of carbohydrate export from shoots and NO3- uptake rates. Conversely, there was no significant correlation between concentrations of nonstructural carbohydrates in roots and NO3- uptake rates. These results support the hypothesis that carbohydrate flux from shoot to roots has a direct role in regulation of nitrogen uptake by the whole plant.     

Carbohydrate partitioning and metabolism during acclimatization of micropropagated Calathea

Regulation of carbohydrate metabolism and compartmentation were studied during the acclimatization of tissue cultured Calathea plantlets. At transplantation plants were characterised by a heterotrophic metabolism with roots and stems as the main storage organs for carbohydrates. As acclimatization proceeded, a switch to autotrophic growth was observed: leaves became source organs, which was among others reflected by significant increases of invertase, sucrose synthase and sucrose-P synthase activities. Mobilization of reserves in roots and stems was also observed during the same period. Sucrose and starch accumulation in leaves was positively correlated with increasing light intensity.     

Influence of aluminium on biomass, nutrients, soluble carbohydrates and phenols in beech (Fagus sylvatica)

The effects of aluminium on biomass, nutrients and soluble carbohydrates and phenols were studied in beech ( Fagus sylvatica L.) seedlings. After germination, seedlings with cotyledons and the buds of the first leaf-pair developed, were preconditioned for two weeks and then grown for 31 days in nutrient solutions containing 0.1, 0.5, 1.0 or 2.0 m M A1C1₃. Aluminium did not affect the dry weights of roots but at Al concentrations ≥ 1.0 m M the development of the terminal shoot above the first leaf pair, was reduced by 80% or more. The concentrations of most nutrients (P, Ca, Mg, Zn, Cu) in the plant tissues decreased strongly even at the lowest Al levels, but K increased in the shoots. The tissue concentration of N was not affected of Al. but the distribution between the organs was changed to a higher content of N in the roots. At ≥1.0 m M Al the concentrations of starch in both the shoots and the roots were significantly increased, and at ≥ 0.5 m M the roots contained more of total phenols than untreated seedlings. The elevated concentrations and contents of starch and phenols in the seedlings may partly be related to the reduced shoot growth. The observed effects of Al were marked already at Al levels found in soil waters from beech forests in southern Sweden.     

Correlated responses of root growth and sugar concentrations to various defoliation treatments and rhythmic shoot growth in oak tree seedlings (Quercus pubescens)

Background and Aims

To understand whether root responses to aerial rhythmic growth and contrasted defoliation treatments can be interpreted under the common frame of carbohydrate availability; root growth was studied in parallel with carbohydrate concentrations in different parts of the root system on oak tree seedlings.

Methods

Quercus pubescens seedlings were submitted to selective defoliation (removal of mature leaves, cotyledons or young developing leaves) at appearance of the second flush and collected 1, 5 or 10 d later for morphological and biochemical measurements. Soluble sugar and starch concentrations were measured in cotyledons and apical and basal root parts.

Key Results

Soluble sugar concentration in the root apices diminished during the expansion of the second aerial flush and increased after the end of aerial growth in control seedlings. Starch concentration in cotyledons regularly decreased. Continuous removal of young leaves did not alter either root growth or apical sugar concentration. Starch storage in basal root segments was increased. After removal of mature leaves (and cotyledons), root growth strongly decreased. Soluble sugar concentration in the root apices drastically decreased and starch reserves in the root basal segments were emptied 5 d after defoliation, illustrating a considerable shortage in carbohydrates. Soluble sugar concentrations recovered 10 d after defoliation, after the end of aerial growth, suggesting a recirculation of sugar. No supplementary recourse to starch in cotyledons was observed.

Conclusions

The parallel between apical sugar concentration and root growth patterns, and the correlations between hexose concentration in root apices and their growth rate, support the hypothesis that the response of root growth to aerial periodic growth and defoliation treatments is largely controlled by carbohydrate availability.     

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO₃⁻) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10 mM HCO₃⁻ (−Fe+Bic and −Fe, respectively). After 21 d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO₃⁻ (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO₃⁻ upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H⁺-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15 d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO₃⁻ prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.     

Cassava Response to Water Deficit in Deep Pots: Root and Shoot Growth, ABA, and Carbohydrate Reserves in Stems, Leaves and Storage Roots

Cassava (Manihot esculenta, Crantz) is an important staple crop for tropical climates worldwide, including drought-prone environments where it is valued for its reliable yield. The extent to which stress tolerance involves regulation of growth and carbon balance aided by remobilization of carbohydrate from various plant parts was investigated. Plants were grown in 1-meter high pots to permit observation of deep rooting while they were subjected to four soil water regimes over a 30-d period. Transpiration declined abruptly in conjunction with leaf ABA accumulation and severe leaf abscission. In water stressed plants, growth of all plant parts decreased substantially; however, a basal rate of leaf growth continued to provide some new leaves, and although growth of fibrous lateral roots was reduced, main root elongation to deeper regions was only modestly decreased by stress. In leaf blades and petioles, sugars were the predominant form of nonstructural carbohydrate and about one third was in starch; these reserves were depleted rapidly during stress. In contrast, stems and storage roots maintained relatively high starch concentrations and contents per organ until final harvest. Stems gradually lost starch and had sufficient reserves to serve as a prolonged source of remobilized carbohydrate during stress. The amount of starch stored in stems represented about 35 % of the reserve carbohydrate in the plant at the onset of water stress (T₀), and 6 % of total plant dry mass. We suggest that this pool of carbohydrate reserves is important in sustaining meristems, growing organs, and respiring organs during a prolonged stress and providing reserves for regrowth upon resumed rainfall.     

The Utilization of Carbohydrate and Nitrogen Reserves by Taxus During Its Spring Growth Period

The spring growth and the utilization of carbohydrate and nitrogen reserves in this growth was studied in Taxus media cv. Hicksii plants 0, 2, 4 and 6 weeks after the plants started growing in the spring. The effect of nitrogen applied the previous season on the storage and utilization of the carbohydrate and nitrogen reserves during spring growth was determined. The plants were separated into buds (all new growth), stems, needles (those produced the previous season) and roots and analyzed for changes in total nitrogen, basic and non-basic amino acids, total available carbohydrate, sugars, hemicelluloses, organic acids and chlorophyll. The bulk of the soluble nitrogen reserves were stored as arginine in the stems and old needles. With the onset of spring growth, arginine nitrogen was converted to other amino acids which accumulated in the new growth (buds). The roots, stems and needles of plants grown under high nitrogen levels always contained more total nitrogen than those grown under low nitrogen levels. The bulk of the carbohydrate reserves were stored as hemicelluloses. The plants grown under high nitrogen levels utilized the bulk of the carbohydrate reserves from the roots and smaller amounts from the stems and old needles, while plants grown under low nitrogen levels used only the reserves in the roots. In the low nitrogen plants, carbohydrates accumulated in the needles and stems. Both the carbohydrate and nitrogen reserves were important in the dry weight increase due to spring growth. However, the nitrogen reserves were the limiting factor and the high nitrogen plants grew twice as much, produced more chlorophyll, and utilized more nitrogen and carbohydrate reserve in spring growth than low nitrogen plants. The additional chlorophyll allowed the production of more carbohydrates and these additional carbohydrates were used in increased growth rates, while in the low nitrogen plants the carbohydrate produced was less and accumulated within the plant.     

Effect of light on the development of glyoxysomal functions in the cotyledons of mustard (Sinapis alba L.) seedlings

The degradation of storage fat in the cotyledons of mustard seedlings is unaffected by phytochrome and photosynthesis (irradiation with continuous red or far-red light from sowing of the seeds) although light imposes a strong constraint on the translocation of organic matter from the cotyledons into the seedling axis. Likewise, the development and disappearance of glyoxysomal enzyme activities (isocitrate lyase, malate synthase, citrate synthase) takes place independently of light. It is concluded that the mobilization of storage fat (fatcarbohydrate transformation) is independent of photomorphogenesis. The surplus of carbohydrate produced from fat in the light seems to be converted to starch grains in the plastids, which function as a secondary storage pool in the cotyledons.Abbreviations CS citrate synthase - ICL isocitrate lyase - MS malate synthase