Photosynthate Accumulation Research Articles

Effects of Rewatering after Drought Stress on Photosynthesis and Yield during Flowering and Boll-Setting Stage of Cotton Under-Mulch-Drip Irrigation in Xinjiang

In order to develop water saving irrigation stratagem and increase cotton yield in Xinjiang, we did the irrigation ex- periment in the field, controlled the lower limit of soil relative moisture content in layer of 0–60 cm at 45%, 60%, and 75% (the control) respectively of field water-holding capacity, which was the upper irrigation limit, and studied the effects of rewatering after drought on photosynthesis and yield during flowering-boll stage of cotton under-mulch-drip irrigation. The result showed that drought reduced the parameters of gas exchange. Photochemical quenching coefficient (qP) and PSⅡ photochemical quan- tum yield (ФPSⅡ) were reduced but non-photochemical quenching coefficient (NPQ) was increased significantly under moderate drought. Net photosynthetic rate (Pn) and stomatal conductance (Gs) of three water treatments could be rapidly recovered within three days after rewatering, and the recovery of mild drought treatment was the most rapid. The recovery of ФPSⅡ and qP in three water treatments was similar to that of Pn which achieved the maximum in 2–3 days after rewatering. The NPQ of three water treatments decreased significantly in 1–2 days after rewatering. From early flowering stage to early full boll stage, accumulation of single plant photosynthate was not much different from that of mild drought treatment after rewatering and the control, but the accumulation of single plant photosynthate was decreased significantly from later full boll stage to boll opening stage that let the seed cotton yield in mild drought treatment after rewatering be lower than that in control. Accumulation of single plant photosyn- thate and seed cotton yield in moderate drought treatment after rewatering was always lower than that in mild drought treatment and control.

Effects of Nitrogen Application Rates on Accumulation, Translocation, and Partitioning of Photosynthate in Winter Wheat at Grain Filling Stage

Grain yield is mainly contributed by photosynthate post anthesis in wheat (Triticum aestivum L.), but assimilate ac- cumulation before flowering also plays an important role, especially under stress conditions. The effects of nitrogen fertilizer on assimilation and partitioning of carbohydrate at maturity have been studied in different experiments with different conclusions. To evaluate the dynamic changes of assimilation and carbohydrate partitioning in wheat organs under different nitrogen application rates, a poly-spike cultivar Yumai 49-198 and a large-spike cultivar Lankao Aizao 8 were used in a pot experiment in 2005–2006 growth season. The nitrogen fertilizer was applied (half basic application and half topdressing at jointing) at two levels of 18 g m-2 and 36 g m-2 respectively. Flag leaves were labeled by 14CO2 at pre-anthesis stage. The results indicated that the 14C assimilates photosynthesized at pre-anthesis mainly distributed in stem and sheath, next in grain at maturity. The proportion of 14C partitioned to stem and sheath, grain was 44.31–60.96% and 31.81–40.67% respectively. In comparison, the proportion of 14C partitioned to grain was increased, while to stems and sheath was reduced by increased N application. The percentage of assimilated 14C in stems and sheaths of Lankao Aizao 8 was greater than that of Yumai 49-198. There was 34.94% of the assimilates in grains de- rived from the reallocation of assimilate stored at pre-anthesis and 65.06% from photosynthate post anthesis. Moreover, transloca- tion amount, translocation proportion and contribution of assimilates before flowering to grains decreased with higher nitrogen application rate, while the contribution of assimilates post anthesis and grain weight per spike increased. The results also showed that the percentage of post anthesis assimilation to grains was 77.84% and 56.29% for Lankao Aizao 8 and Yumai 49-198, respec-tively, indicating that assimilates photosynthesized post anthesis in Lankao Aizao 8 was greater than that in Yumai 49-198. Finally, grain yield in 36 g m-2 N treatment was higher than that in 18 g m-2 N treatment. Meanwhile, increase range in grain yield of Lankao Aizao 8 both in treatments of 36 g m-2 and 18 g m-2 was greater than that of Yumai 49-198, indicating that the effect of nitrogen fertilizer on Lankao Aizao 8 was significantly greater than that of Yumai 49-198.

Guard cell apoplastic photosynthate accumulation corresponds to a phloem-loading mechanism

Apoplastic phloem loaders have an apoplastic step in the movement of the translocated sugar, prototypically sucrose, from the mesophyll to the companion cell-sieve tube element complex. In these plants, leaf apoplastic sucrose becomes concentrated in the guard cell wall to nominally 150 mM by transpiration during the photoperiod. This concentration of external sucrose is sufficient to diminish stomatal aperture size in an isolated system and to regulate expression of certain genes. In contrast to apoplastic phloem loaders and at the other extreme, strict symplastic phloem loaders lack an apoplastic step in phloem loading and mostly transport raffinose family oligosaccharides (RFOs), which are at low concentrations in the leaf apoplast. Here, the effects of the phloem-loading mechanism and associated phenomena on the immediate environment of guard cells are reported. As a first step, carbohydrate analyses of phloem exudates confirmed basil (Ocimum basilicum L. cv. Minimum) as a symplastic phloem-loading species. Then, aspects of stomatal physiology of basil were characterized to establish this plant as a symplastic phloem-loading model species for guard cell research. [(14)C]Mannitol fed via the cut petiole accumulated around guard cells, indicating a continuous leaf apoplast. The (RFO+sucrose+hexoses) concentrations in the leaf apoplast were low, <0.3 mM. Neither RFOs (<10 mM), sucrose, nor hexoses (all, P >0.2) were detectable in the guard cell wall. Thus, differences in phloem-loading mechanisms predict differences in the in planta regulatory environment of guard cells.

Vertical migration of the toxic dinoflagellate Gymnodinium catenatum under different concentrations of nutrients and humic substances in culture

Vertical migration behaviour by the chainforming dinoflagellate Gymnodinium catenatum Graham was investigated using vertically-stratified laboratory columns. Under surface nutrient-deplete conditions, with nutrients added only at depth, 100% of cells underwent vertical migration (VM), starting downwards migration 3 h before the end of the light period and beginning upwards migration 3 h before the start of the light period. Cells in nutrient-replete columns showed no VM, but they were more dispersed in the upper layer during the dark compared to the light period. When surface layers (S) were nitrate-deplete (−N) and enriched with humic substances (H) contained in Huon River water and bottom waters (B) were nutrient replete (R) (SH −NB R), the pattern of VM was altered—50% of cells underwent migration and 50% remained at the pycnocline. In columns with nitrate-replete and humic-enriched surface layers (SH RB R), most cells underwent VM, while 30% remained at the surface. Cells in SH −NB R columns showed increased N quotas and intra-cellular nitrate concentrations after 4 days, indicating nitrate uptake by G. catenatum in bottom layers. The concomitant increase in particulate organic nitrogen (PON) with the decrease in external nitrate concentrations in bottom layers provide convincing evidence that VM by G. catenatum facilitates nutrient retrieval at depth. However, addition of humic substances (a potential source of organic nitrogen) to surface layers did not ameliorate G. catenatum N depletion sufficiently to preclude the need for NO 3 − uptake at depth. Furthermore, there was no detectable pattern of increasing carbon (C) quota during the day (photosynthate accumulation) or increasing N quota during the night (nitrate assimilation). Toxic dinoflagellate G. catenatum blooms are commonly associated with nitrate depletion in surface waters in south-east Tasmanian waters (Australia). Therefore, vertical migration, facilitating N uptake at depth, could play an important role in this organism's ecological strategy, enabling it to exploit environments where light and nutrients are vertically separated.

Calculation of the Root/Shoot Ratio in the Models of Higher Plant Organogenesis

A new method for calculating the assimilate distribution between plant shoots and roots in dynamic models of production process for agricultural crops is suggested. The method is based on direct calculation of the dynamics of photosynthate accumulation and absorption rates of nitrogen compounds in the plant root system. The hypothesis underlying this method is that all mobile compounds entering the plant are completely utilized for the production of structured biomass. Unlike the method of distribution keys, which is widely used in similar models, the suggested procedure accounts for adaptive plant responses to both uncontrolled weather conditions and mineral nutrition. The suggested method was implemented as software within the framework of Agrotool (version 3) simulation system. Verification of the method in many years' field experiments with barley confirmed its efficiency and showed a satisfactory accuracy of model calculations.

13C-photosynthate accumulation in Japanese pear fruit during the period of rapid fruit growth is limited by the sink strength of fruit rather than by the transport capacity of the pedicel

In Japanese pear, the application of GA3+4 during the period of rapid fruit growth resulted in a marked increase in pedicel diameter and bigger fruit at harvest. To elucidate the relationship between pedicel capacity and fruit growth and to determine the main factor responsible for larger fruit size at harvest, fruit growth and pedicel vascularization after GA application were examined and the carbohydrate fluxes were monitored in a spur unit by non-invasive techniques using 13C tracer. Histological studies of fruit revealed that GA increased the cell size of the mesocarp but not the cell number and core size. The investigation of carbon partitioning showed that an increase in the specific rate of carbohydrate accumulation in fruit or the strength of fruit should be responsible for an increase of fruit weight in GA-treated trees. Observation of pedicel vascularization showed that an increase in pedicel cross-sectional area (CSA) by GA application mainly resulted from phloem and xylem CSA, but it is unlikely that an increase in the transport system is the direct factor for larger fruit size. Therefore, it can be concluded that larger fruit size resulting from GA application during the period of rapid fruit growth caused an increase in the cell size of the mesocarp and increased carbon partitioning to the fruit. Although GA is closely involved with pedicel vascularization, it seems that photosynthate accumulation in fruit is limited by the sink strength of fruit rather than by the transport capacity of the pedicel.

Leaf responses of micropropagated apple plants to water stress: nonstructural carbohydrate composition and regulatory role of metabolic enzymes

We examined changes in nonstructural carbohydrate biosynthesis and activities of related enzymes in leaves of micropropagated apple plants (Malus domestica Borkh. cv. 'NaganoFuji') in response to water stress, with particular emphasis on the enzymes associated with sorbitol, sucrose and starch metabolism. Water stress resulted in the accumulation of photosynthates in leaves, mainly sorbitol, sucrose, glucose and fructose, accompanied by a reduction in starch concentration. Correlation and path analysis indicated that water stress affected the partitioning of newly fixed carbon among terminal products. In response to water stress, ADP-glucose-pyrophosphorylase (ADPGPPase) activity decreased, becoming a critical and limiting step in shifting partitioning of photosynthetically fixed carbon. Amylase and ADPGPPase affected sucrose and sorbitol metabolism, mainly by regulating substrate supply; however, competition for limited substrate had a greater effect on the biosynthesis of sorbitol than of sucrose. Starch metabolism was also strictly regulated by ADPGPPase and amylase, whereas other related enzymes were downstream of the pathway for synthesis and degradation of carbohydrates and thus had relatively little effect on starch metabolism. Sorbitol dehydrogenase and sucrose phosphate synthase were critical regulators of sorbitol and sucrose metabolism, respectively.

Environmental sex determination in response to light and biased sex ratios in Equisetum gametophytes

Summary Sexual differentiation of Equisetum (horsetails) gametophytes is influenced by environmental conditions, and wild populations tend to be female biased. We show that photon irradiance has a very significant and reproducible effect on sex determination in three species of Equisetum grown in vitro. Under our experimental conditions, high light levels (PAR = 24–48 µmol m−2 s−1) induce most gametophytes to differentiate as female, whereas only males are observed at PAR &lt; 6 µmol m−2 s−1. Addition of sugar to the culture medium, however, promotes male development, suggesting that the effect of increasing photon irradiance is not related to the accumulation of photosynthates. According to evolutionary theory, environmental sex determination can cause population sex ratios to deviate from unity, and is favoured when the environment consists of patches that differentially affect fitness as a male or a female. However, in two out of three species, we found that the fitness of males increases faster than the fitness of females with increasing light levels, contrary to the predictions of the Charnov and Bull model. We conclude that environmental sex determination in response to light cannot alone account for the female bias in natural populations of Equisetum gametophytes.

Characterization of mRNAs that accumulate during illumination of excised leaves of big bluegrass ( Poa secunda)

Summary Photosynthate accumulation during illumination of excised leaves provides a useful system to study some aspects of carbohydrate metabolism. The objectives of this study were to identify and characterize mRNAs that show regulated abundance during illumination of excised leaves of big bluegrass (Poa secunda). Differential display PCR identified mRNAs of interest. RNA samples from excised leaves were tested with 45 primer combinations after 0, 0.5, 2, 8, and 24 h of light exposure. Of approximately 2500 cDNA amplification products examined, only six different sequences showed repeatable patterns of regulation during the time course of these experiments. Three full-length cDNAs were isolated and none appear to be directly related to carbohydrate metabolism. The deduced amino acid sequences of the three cDNA products show homology to the thiamin biosynthesis proteins, metallothionene-like proteins and ribosomal proteins of other species. The abundance of metallothinene-like protein mRNA, in particular, showed strong up-regulation during illumination of detached leaves. The abundance of these three mRNAs in attached leaves was further evaluated under low-temperature and dehydration treatments-conditions also known to influence photosynthate/carbohydrate accumulation. The abundance of the metallothinene-like protein was strongly affected by dehydration, whereas the thiamin biosynthesis and ribosomal protein mRNAs were only somewhat affected by low temperatures.

Net photosynthetic rate in peanut (Arachis hypogaea L.): Influence of leaf position, time of day, and reproductive-sink

Net photosynthetic rate (PN) was studied in field-grown peanut cv. GG 2 in relation to leaf position, time of day, reproductive-sink, and phenophase. In general, PN remained higher in the upper leaves (first from top to the fourth) than in the lower leaves (fifth to eighth). The mean PN of the leaves situated upper and the leaves lower in the canopy increased from the morning, reached a maximum during noon hours, and decreased thereafter. Between 09:00 to 10:00 h, PN, stomatal conductance (gs), and transpiration rate (E) in the upper leaves were higher than in the lower leaves, but between 12:00 and 13:00 h, these activities increased significantly in the lower leaves. Highest PN was found during pod-development phase. Removal of flowers, and hence of active reproductive-sink, decreased plant height and number of leaves, and initiated accumulation of photosynthates in the leaves. The PN per unit leaf area in plants with reproductive-sink (WRS) was similar to those without reproductive-sink (WORS). However, leaf area of WORS plants decreased significantly, mainly due to the reduction in number of leaves. No feed-back inhibition of PN (per unit leaf area) was found despite accumulation of photosynthates in the leaves as a result of removal of the active reproductive-sink.

Leaflet photosynthesis rate and carbon metabolite accumulation patterns in nitrogen-limited, vegetative soybean plants

Prolonged inorganic nitrogen (NO3 (-)+NH4 (+)) limitation of non-N2-fixing soybean plants affected leaflet photosynthesis rates, photosynthate accumulation rates and levels, and anaplerotic carbon metabolite levels. Leaflets of nitrogen-limited (N-Lim), 27-31-day-old plants displayed ≈ 15 to 23% lower photosynthesis rates than leaflets of nitrogen-sufficient (N-Suff) plants. In contrast, N-Lim plant leaflets displayed higher sucrose and starch levels and rates of accumulation, as well as higher levels of carbon metabolites associated with sucrose and starch synthesis, e. g., glycerate-3-phosphate and glucose phosphates, than N-Suff plant leaflets. Concurrently, levels of soluble protein, chlorophyll, and anaplerotic metabolites, e.g., malate and phosphoenolpyruvate, were lower in leaflets of N-Lim plants than N-Suff plants, suggesting that the enzymes of the anaplerotic carbon metabolite pathway were lower in activity in N-Lim plant leaflets. Malate net accumulation rates in the earliest part of the illumination period were lower in N-Lim than in N-Suff plant leaflets; however, by the midday period, malate accumulation rate in N-Lim plant leaflets exceeded that in leaflets of N-Suff plants. Further, soluble protein accumulation rates in leaflets of N-Suff and N-Lim plants were similar, and the rate of dark respiration, measured in the early part of the dark period, was higher in N-Lim plant leaflets than in N-Suff plant leaflets. It was concluded that during prolonged N-limitation, foliar metabolite conditions favored the channelling of a large proportion of the carbon assimilate into sucrose and starch, while assimilate flow through the anaplerotic pathway was diminished. However, in some daytime periods, there was a normal level of carbon assimilate channelled through the anaplerotic pathway for ultimate use in amino acid and protein synthesis.

Change of Sucrose Synthase Activity in Developing Endosperm of Rice Cultivars

Sucrose synthase (SS, EC 2.4.1.13) in rice (Oryza sativa L.) endosperm acts as the first step in the sucrose‐starch conversion pathway and is thought to have some relation to photosynthate accumulation and grain development. This study investigated genotypic differences in the change of SS activity in developing endosperm using four rice cultivars with different grain sizes and grain‐filling rates. The difference in SS activity between grain positions within a panicle was also examined. In addition to SS activity, activities of acid invertase (AI, EC 3.2.1.26) and UDP‐glucose pyrophosphorylase (UDPGP, 2.7.7.9) were observed in the same samples used for SS activity assay. In every cultivar and grain position, SS activity showed a maximum value at the middle of the linearly increasing period of grain dry weight, and decreased thereafter. Mean SS activity per gram fresh weight across sampling times and grain positions was not significantly different among cultivars. A significant difference among cultivars was detected in SS activity per grain. As for the difference between grain positions, the activities both per gram fresh weight and per grain were significantly higher in grains on primary branches showing a higher grain‐filling rate. The changes of AI and UDPGP activities did not correspond with the change of grain dry weight. These results suggest that SS activity in developing rice endosperm plays a role in the regulatory system of grain development, but does not have any relation to genetic variations in grain size and grain‐filling rate.

Influence of phosphorus on nitrogen fixation in chickpea cultivars

Abstract Phosphorus (P) is a major nutrient factor influencing nitrogen (N) accumulation and partitioning of photosynthates in plants, especially the symbiotic N2‐fixation in legumes. This study was conducted to investigate how P application (0, 20, 40, and 60 kg P2O5/ha) affects symbiotic N2‐fixation of three cultivars (C 235, Pusa 408, and Pusa 417) of chickpea (Cicer arietinum L.). Application of P in general significantly increased leaf area, shoot dry weight, and the rate of acetylene (C2H2) reduction. Phosphorus concentration of shoots and roots, soluble sugar content of nodules, and shoot N accumulation were also significantly increased, especially by P at the 40 kg P2O5/ha rate. The P concentration in nodules was, however, not affected by different levels of P. The Pusa 417 cultivar responded better than the others to the P treatments. Phosphorus‐deficient plants accumulated sugar in their leaves. The interaction effect was found significant on leaf area, shoot dry weight, nodule number, and shoot...

The architecture of plant vasculature and transport as seen with magnetic resonance microscopy

Water and photosynthate transport through plants has been studied extensively for the past three centuries. Few techniques are available that are capable of providing both physiological and anatomical information, and most are destructive in nature. We report the use of high resolution magnetic resonance microscopy (MRM) for the study of intact plant vasculature. Both two- (2-D) and three-dimensional (3-D) image acquisition protocols are employed wherein the plant vasculature can be readily distinguished from surrounding parenchymal tissue. In the 3-D image sets, the vasculature has been digitally segmented, allowing isolation of only the intact vascular architecture. The paths of water and photosynthate transport into several plant specimens have been visualized in this manner. Images of sugar beets, plants that store high concentrations of sucrose within the parenchyma, show contrast patterns between vasculature and parenchyma that are opposite to those seen in images acquired of an apple, fig, okra pod, kiwi fruit, and potato, plants that do not store high concentrations of sucrose. This suggests that transport and accumulation of photosynthates may be partially responsible for contrasts seen within images acquired of these plant specimens. Key words: transport, transpiration, sugar, MRI, magnetic resonance imaging, plants.

Seasonal Investigations of Soluble Carbohydrates and Pigment Levels in Antarctic Bryophytes and Lichens

Levels of soluble carbohydrates, moisture, and pigments in the major bryophytes and lichens from the Windmill Islands, continental Antarctica, were monitored over a 14-month period. Gas-liquid chromatography revealed little seasonal change in soluble carbohydrate levels. Water content of vegetation varied throughout the season with maximum hydration occurring over the summer months. Pigment levels also varied seasonally with a decrease in total chlorophyll and chlorophyll a/b ratios during winter. Levels of total carotenoids increased over summer in response to high ambient irradiation. In contrast with the seasonality of soluble carbohydrates reported in some cryptogams from subpolar regions, the lack ofany significant seasonal changes in the Antarctic bryophytes and lichens may be due to the extreme climate and rapid temperature fluctuations in the continental Antarctic environment. Bryophytes and lichens form a dominant component of vegetation at high latitudes due to their ability to withstand extreme polar environments (Longton 1988; Tenhunen et al. 1992). An important factor in the resistance of these poikilohydric plants is considered to be the accumulation and maintenance of relatively high levels of cell solutes including lipids, amino acids, and soluble carbohydrates (Farrar 1976, 1978; Karunen & Salin 1982; Levitt 1980; Longton 1988). Although it has long been recognized that soluble carbohydrates confer frost resistance to higher plant cells by increasing their tolerance to osmotic and thermal stress (Carpenter & Crowe 1988; Levitt 1980), the significance of soluble carbohydrates in the frost resistance of polar bryophytes and lichens is unclear. Studies from subpolar regions have indicated seasonal trends in carbohydrate levels of mosses and lichens with the accumulation of photosynthates and inorganic nutrients during the periods preceding winter (Hicklenton & Oechel 1977; Smith 1978; Tearle 1987). These differences were high enough to suggest a role in frost resistance. In the latter study, maritimeantarctic lichens were found to have much higher soluble carbohydrate levels than those reported in lichens from temperate regions. Given the hostile nature of the antarctic environment, vegetation on continental Antarctica may similarly be expected to contain high levels of cell solutes in response to cold and desiccation stress. However, Rastorfer (1972) reported that many moss species are frost resistant despite low soluble sugar contents. Furthermore an initial survey offrigid-antarctic (sensu Longton 1988) cryptogams (Roser et al. 1992) showed soluble carbohydrate levels to be comparable to those found in temperate cryptogams and much lower than those reported by Tearle (1987) for maritime-antarctic cryptogams. However, as the former survey involved a single sampling over summer the possibility remained that seasonal increases in soluble carbohydrate levels may occur. In this paper the results of a long-term monitoring of the seasonal cycle of soluble carbohydrates in several of the dominant continental antarctic moss and lichen species are presented for the first time. To give some parallel measures of other growth paameters results are also given for seasonal variations in the moisture content and pigment levels of the plants. This information is important not only to clarify the adaptive physiology of plants in the extreme antarctic habitat but also in terms of the nutrients made available to the antarctic terrestrial ecosystem. The flush of soluble carbohydrates during the spring thaw is thought to contribute to the increase in soil microbial activity over this period in the maritime antarctic (Smith 1985; Tearle 1987; Wynn-Williams 1982). In continental Antarctica where the terrestrial biomass is much less, the nutrient input from cryptogamic vegetation is likely to be the major source of nutrients in areas away from bird colonies.

Premature Leaf Chlorosis in Cucumber Associated with High Starch Accumulation

Summary Premature leaf chlorosis is a physiological disorder observed in winter-grown cucumber plants and is visually distinct from senescence-related chlorosis. Yellow leaves are characterized by high levels of starch and most of the soluble sugars, including glucose, fructose, galactose, galactinol and inositol. Levels of stachyose were found to be similar in healthy and chlorotic leaves. Electron micrographs of yellow leaves showed that plastids were filled with starch and that only traces of the thylakoid membrane structure remained. Starch levels in cucumber leaves followed a diurnal cycle and morning levels were higher following a low-night-temperature treatment (5 °C minimum) as compared with a high-night-temperature treatment (20 °C minimum). These results are consistent with the hypothesis that this form of chlorosis is due to an accumulation of photosynthate in the source leaf and an overaccumulation of starch in the chloroplast. Reduced export from the source leaf in response to low night temperature may be one of the factors responsible for the symptoms.

The Use of the 11 C Technique to Measure Plant Responses to Herbivorous Soil Nematodes

An advantage of the short half-life (20_3 min) isotope method is the simultaneous measurement of several crucial plant processes without hindering or destroying whole-plant function. The technique was used to examine the effects of the herbivorous soil nematode, Meloidogyne javanica (Treub) Chitwood, on carbon assimilation and redistribution in tomato (Lycopersicum esculentum L.) and in two ecotypes [grazing adapted (GA) and non-grazing adapted (NGA)], of an African C4 grass, Panicum coloratum L. Preliminary tests, based on nematode eggs and galls, showed that M. javanica reproduced differentially on both P. coloratum ecotypes and suppressed GA shoot growth (weight), but had little effect on fresh root weight. In tomatoes, control plants had a higher pool of labile C in the roots than the nematode-infected plants. With P. coloratum, there were no differences in parameters between ecotypes. Plants with herbivorous nematodes had a lower stem sink activity, root activity and root transport speed than control plants. The technique proved valuable for measuring instantaneous changes in photosynthate accumulation and movement induced by herbivorous soil nematodes. Key-words: Carbon allocation, phytophages, root herbivory, soil nematodes

トマトにおける葉の光合成, 転流&amp;bull;分配の経時的変化と果実肥大に対する葉位別寄与度

Changes in rates of photosynthesis, translocation, and distribution pattern of 14C-assimilates in leaves during their development and the contribution of individual leaves to the accumulation of photosynthates in various sinks were investigated by using tomato plants.The photosynthetic rate of the 3rd and 7th leaf gradually decreased with their ages, however, the amounts of photosynthates produced per leaf gradually increased with the increase of leaf area. Therefore, the amounts of photosynthates reached maximum just before full expansion of each leaf.Most of assimilates were distributed to near sink as a main sink. Furthermore, the relationship between source and sink likely changed with the developmental stages of roots, shoot and fruits resulting in difference in sink strengths. Thus, competitiveness among sinks changed according to the relative gradients between them and the source.The contribution of each leaf to the accumulation of assimilates by each sink was calculated by the total amount of assimilates and the sum of the distribution of 14C-assimilates from each leaf. The inflorescence was supplied 60-80% of its accumulation by 2 to 4 adjacent leaves. Furthermore, the maximum contribution rate from one leaf seemed to be about 30%. The peak efficiency of a leaf to supply a sink corresponded to the time when the sink was enlarging most rapidly.

Effects of late-autumn fertilizer dressing on accumulation of photosynthates in tea (Camellia sinensis) and its contribution to spring tea quality

SUMMARYTwo-year-old tea bushes were given NPK fertilizer on 12 November 1986 and 14CO2 on 22–23 December 1986 and 9–10 January 1987. Late-autumn fertilizer dressing stimulated photosynthate accumulation in the whole bush, especially in overwintering leaves and roots. Large amounts of photosynthates in overwintering leaves provide the nutrition required for early spring budding. Lateautumn dressing also accelerated the transport of photosynthates from leaves to roots in winter, where photosynthates, with absorbed nitrogen, synthesized more animo acids, especially theanine and phenylalanine. The re-use of photosynthates stored in the roots of the dressed bushes during shoot growth the following spring was also facilitated by late-autumn dressing. The contents of amino acids and caffeine in the shoots of dressed bushes were much higher than those in the control, whereas the content of polyphenol was lower than in the control. The results indicate that late-autumn dressing improves the quality of spring green tea.

Variations in amounts of carbohydrates, amino acids and adenine nucleotides in mulberry tree (Morus alba L.) stems during transitional phases of growth.

Quantitative changes in carbohydrates, amino acids and adenine nucleotides in the stems of mulberry trees (Morus alba L., cv. Shin-ichinose) were followed from spring to early summer and from autumn to early spring. Both ATP and ADP content of stems increased before bud break, whereas the content of sucrose, the most abundant sugar among the stem carbohydrates, decreased. The sucrose content fell to its lowest value at the beginning of May, and then increased rapidly, whereas the starch content decreased suggesting consumption of reserve carbohydrate and simultaneous accumulation of current photosynthate. This was confirmed by studies in which reserve carbohydrates were labeled with (14)CO(2). Proline content of stems increased from the time of leaf shedding until early spring. Although it was the most abundant amino acid at the time of bud break, proline rapidly decreased as new shoots developed and was hardly detectable by the beginning of May. The asparagine and arginine contents increased transiently following bud break, and then decreased toward summer. Transient increases in glutamine and arginine were noted at the time of leaf shedding.