Starch Accumulation In Leaves Research Articles

Over-activation of cold tolerance in arabidopsis causes carbohydrate shortage compared with Chorispora bungeana

Many plants cope with cold stress by developing acquired freezing tolerance (AFT) through cold acclimation (CA), and some species have strong basal freezing tolerance (BFT) independent of CA. Although CA has been extensively studied, its potential in agricultural applications is still unclear. Here, carbohydrate metabolism and transcriptome in AFT plant Arabidopsis and BFT plant Chorispora bungeana were compared with each other. The results showed that, although both species were able to accumulate soluble sugars during CA, leaf starch accumulation in the daytime was almost blocked in Arabidopsis while it was greatly enhanced in C. bungeana, revealing that Arabidopsis experienced carbohydrate shortage during CA. Transcriptome and pathway enrichment analysis found that genes for photosynthesis antenna proteins were generally repressed by cold stress in both species. However, cold-up-regulated genes were enriched in protein translation in Arabidopsis, whilst they were enriched in carotenoid biosynthesis, flavonoid biosynthesis, and beta-amylases in C. bungeana. Furthermore, weighted gene co-expression network analysis (WGCNA) showed that the inhibition of starch accumulation was associated with down-regulation of genes for photosynthesis antenna proteins and up-regulation of genes for protein translation, DNA repair, and proteasome in Arabidopsis but not in C. bungeana. Taken together, our results revealed that over-activation of common tolerant mechanisms resulted in insufficient carbohydrate supplies in Arabidopsis during CA, and photoprotective mechanisms played important roles in cold adaptation of C. bungeana. These findings uncovered the drawback of CA in improving freezing tolerance and highlighted photoprotection as a possible solution for agricultural applications.

Custom-Developed Reflection-Transmission Integrated Vision System for Rapid Detection of Huanglongbing Based on the Features of Blotchy Mottled Texture and Starch Accumulation in Leaves.

Huanglongbing (HLB) is a highly contagious and devastating citrus disease that causes huge economic losses to the citrus industry. Because it cannot be cured, timely detection of the HLB infection status of plants and removal of diseased trees are effective ways to reduce losses. However, complex HLB symptoms, such as single HLB-symptomatic or zinc deficiency + HLB-positive, cannot be identified by a single reflection imaging method at present. In this study, a vision system with an integrated reflection-transmission image acquisition module, human-computer interaction module, and power supply module was developed for rapid HLB detection in the field. In reflection imaging mode, 660 nm polarized light was used as the illumination source to enhance the contrast of the HLB symptoms in the images based on the differences in the absorption of narrow-band light by the components within the leaves. In transmission imaging mode, polarization images were obtained in four directions, and the polarization angle images were calculated using the Stokes vector to detect the optical activity of starch. A step-by-step classification model with four steps was used for the identification of six classes of samples (healthy, HLB-symptomatic, zinc deficiency, zinc deficiency + HLB-positive, magnesium deficiency, and boron deficiency). The results showed that the model had an accuracy of 96.92% for the full category of samples and 98.08% for the identification of multiple types of HLB (HLB-symptomatic and zinc deficiency + HLB-positive). In addition, the classification model had good recognition of zinc deficiency and zinc deficiency + HLB-positive samples, at 92.86%.

Detection of citrus Huanglongbing (HLB) based on the HLB-induced leaf starch accumulation using a home-made computer vision system

Citrus Huanglongbing (HLB) is a highly destructive and transmissible citrus disease spread by insects. As it has no effective treatment, there is an urgent need for a rapid HLB detection method that can be applied in orchards to remove the diseased trees. In this research, the contribution of two symptoms, based on HLB-induced starch accumulation, were evaluated to HLB detection using a home-made computer vision system with two imaging modes. The reflection imaging mode was used to detect blotchy mottles symptoms. A 660 nm light source was used and the absorption of different wavelengths by chlorophyll and lutein was measured. The transmission imaging was designed to detect abnormal starch accumulation within the leaf. An image was taken with 590 nm polarised light penetrating the leaf, then the angle of linear polarisation (AoLP) was calculated by the Stokes vector. The AoLP reflects the ability of the internal leaf components to rotate polarised light. The polarisation angle reflects the starch content of the leaves and determines their disease status. Multi-layer perceptron (MLP), random forest (RF), and logistic regression (LR) classifiers were then evaluated. The RF classifier performed better in the reflection experiment, with a classification accuracy of 96.67%. In the transmission experiment, the LR classifier had 88.33% recognition rate. The results show that HLB-induced starch accumulation contributes to the visual detection of HLB. This research supports the high accuracy and portability of HLB detection equipment and it has great practical importance for preventing and controlling of HLB disease. • A home-made computer vision system with two imaging modes was designed. • Computer vision enhanced two symptoms caused by HLB-induced starch accumulation. • Reflection imaging was effective in highlighting blotchy mottles symptoms of HLB. • The optical activity of starch in HLB + leaf was detected by transmission imaging. • The contribute of HLB-induced starch accumulation to HLB detection was confirmed.

Overexpression of thioredoxin m in chloroplasts alters carbon and nitrogen partitioning in tobacco.

In plants, there is a complex interaction between carbon (C) and nitrogen (N) metabolism, and its coordination is fundamental for plant growth and development. Here, we studied the influence of thioredoxin (Trx) m on C and N partitioning using tobacco plants overexpressing Trx m from the chloroplast genome. The transgenic plants showed altered metabolism of C (lower leaf starch and soluble sugar accumulation) and N (with higher amounts of amino acids and soluble protein), which pointed to an activation of N metabolism at the expense of carbohydrates. To further delineate the effect of Trx m overexpression, metabolomic and enzymatic analyses were performed on these plants. These results showed an up-regulation of the glutamine synthetase–glutamate synthase pathway; specifically tobacco plants overexpressing Trx m displayed increased activity and stability of glutamine synthetase. Moreover, higher photorespiration and nitrate accumulation were observed in these plants relative to untransformed control plants, indicating that overexpression of Trx m favors the photorespiratory N cycle rather than primary nitrate assimilation. Taken together, our results reveal the importance of Trx m as a molecular mediator of N metabolism in plant chloroplasts.

Foliar nutrient and carbohydrate in Aralia elata can be modified by understory light quality in forests with different structures at Northeast China

Many non-wood forest product (NWFP) plants are shade-obligate species, but current understanding about their foliar response to understory spectrum is quite scarce. To monitor understory light condition at large scale faces significant obstacles from heavy canopy shade and high cost of sensors arrangement. Therefore, we employed a novel methodology to meter the relative light ratio between plots under canopy and in the open-air. In this study, a number of 34 plots of natural Aralia elata populations were investigated for forest structure across six types of forests at Northeast China. Light properties of relative intensity, photosynthetic photon flux rate (PPFD), spectra in red, green, and blue wavelengths, and relative ratio of red/green, red/blue, and green/blue were measured at the height of 1.3m. Leaves of A. elata were collected to determined concentrations of nitrogen (N), phosphorus (P), starch, and soluble sugars. We found that relative blue light ratio was different among forest-types, but it had little further effect on leaf traits in A. elata . Instead, higher ratios of relative green light and green/blue depressed leaf P concentration. Increases in PPFD and light intensity promoted leaf N and P concentrations, respectively. The red/green ratio had adverse relationships with leaf P and starch concentrations in A. elata . In conclusion, due to the variation understory light condition, sites with low canopy density would benefit leaf N concentration and those with larger canopies can promote leaf starch accumulation in A. elata .

Row orientation effects on Syrah grapevine performance during winter growing season

ABSTRACT The sunlight and heating effects on leaves and grapes are directly influenced by row orientation in vineyards. Row orientation studies have not been addressed under double pruning management, a technique used to transfer the wine grape harvest from wet summer to dry winter season in Brazilian Southeast. Effects of grapevine row orientation (north/south - NS and east/west - EW) of vertically trellised and shoot positioned Vitis vinifera L. Syrah grafted onto 1103 Paulsen were investigated in the South of Minas Gerais State. The vegetative vigor was increased in NS oriented vines, probably due to high photosynthesis as suggested by the highest leaf starch accumulation. The leaf and stem water potential were slight affected by row orientation. NS orientation increased the cluster weight, but cluster number and yield per vine were not affected by treatments. Berries from NS oriented vines also showed the highest values of anthocyanins and total phenols. Under NS orientation there was a reduction on tartaric acid and soluble sugar in berries probably diluted by increased cluster weight. This study showed that vineyard under NS orientation improved grapevine vigor and promoted better phenolic maturity in wine grapes harvested during the winter season than EW orientation.

Identification and Gene Fine Mapping of Starch Accumulation and Early Senescent Leaf Mutant esl10 in Rice

ABSTRACTA novel starch accumulation and early senescent leaf mutant esl10 was identified among progenies of the rice (Oryza sativa L.) indica maintainer line Xinong 1B raised from seeds treated with ethyl methane sulfonate (EMS). Under paddy field conditions, leaf starch accumulation commenced at the three‐leaf stage in the mutant esl10 and the leaves began to yellow at the four‐leaf stage, gradually extending from the tip to the middle of the leaf. The yellowing phenotype was most obvious at the tillering stage and persisted until maturity. Compared with the wild type, photosynthetic pigment concentrations and net photosynthetic rate of esl10 were significantly lower, whereas the concentrations of reactive oxygen species and malondialdehyde (MDA) were higher. Moreover, catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD) activities decreased in leaves at the tillering stage. Quantitative real‐time polymerase chain reaction showed that the expression of genes associated with starch metabolism pathway changed. Excessive accumulation of leaf starch may have caused the leaf premature senescence, finally influencing grain yield and quality of esl10. Genetic analysis showed that esl10 was controlled by a dominant nuclear gene (tentatively called ESL10). ESL10 was mapped between the single‐nucleotide polymorphism markers SNP585 and SNP498 on chromosome 7 with a physical distance of 416.29 kb including 56 annotated genes. The results provide a foundation for gene cloning and functional analysis of ESL10.

Receptor protein kinase FERONIA controls leaf starch accumulation by interacting with glyceraldehyde-3-phosphate dehydrogenase

Cell expansion is coordinated by several cues, but available energy is the major factor determining growth. Receptor protein kinase FERONIA (FER) is a master regulator of cell expansion, but the details of its control mechanisms are not clear. Here we show that FER interacts with cytosolic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH, GAPC1 and GAPC2), that catalyzes a key reaction in glycolysis, which contributes to energy production. When there is an FER deficiency, there are corresponding decreases in the enzyme activity of GAPDH and increased amounts of starch. More importantly, gapc1/2 mutants mimic fer4 mutants. These data indicate that FER regulated starch content is an evolutionarily conserved function in plants that connects the cell expansion and energy metabolism pathways.

Mesophyll conductance in leaves of Japanese white birch (Betula platyphylla var. japonica) seedlings grown under elevated CO2 concentration and low N availability.

To test the hypothesis that mesophyll conductance (gm ) would be reduced by leaf starch accumulation in plants grown under elevated CO2 concentration [CO2 ], we investigated gm in seedlings of Japanese white birch grown under ambient and elevated [CO2 ] with an adequate and limited nitrogen supply using simultaneous gas exchange and chlorophyll fluorescence measurements. Both elevated [CO2 ] and limited nitrogen supply decreased area-based leaf N accompanied with a decrease in the maximum rate of Rubisco carboxylation (Vc,max ) on a CO2 concentration at chloroplast stroma (Cc ) basis. Conversely, only seedlings grown at elevated [CO2 ] under limited nitrogen supply had significantly higher leaf starch content with significantly lower gm among the treatment combinations. Based on a leaf anatomical analysis using microscopic photographs, however, there were no significant difference in the area of chloroplast surfaces facing intercellular space per unit leaf area among treatment combinations. Thicker cell walls were suggested in plants grown under limited N by increases in leaf mass per area subtracting non-structural carbohydrates. These results suggest that starch accumulation and/or thicker cell walls in the leaves grown at elevated [CO2 ] under limited N supply might hinder CO2 diffusion in chloroplasts and cell walls, which would be an additional cause of photosynthetic downregulation as well as a reduction in Rubisco activity related to the reduced leaf N under elevated [CO2 ].

Prevention of natural flowering in pineapple (Ananas comosus) by shading and urea application

The year-round production of pineapple (Ananas comosus var. comosus) is often interrupted by natural flowering during winter in Taiwan. A stable and promising technique for preventing natural flowering is required. In this study, we have tested the effect of shading and urea application on the flowering of pineapple. Shading 90% of sun light(s) before mid-November delayed the natural flowering of pineapple and the delay was affected by the plant age. For pineapples planted less than 11 month before mid-November, applying 1% urea plus shading treatment (SN) completely inhibited natural flowering. All the flowering-inhibited plants could be forced to flower by applying calcium carbide. Long-term shading might result in a decreased number of fruitlets within a fruit. However, 6 weeks of recovery before forcing flowering was sufficient for plants to produce fruits with quality equal to that of the control plants. In winter, pineapple plants that were prone to flowering tended to accumulate more leaf starch and increase their C/N ratio. The SN treatment increased the leaf nitrogen concentration and thus effectively maintained a low leaf C/N ratio. Furthermore, flowering-inhibited plants exhibited a constantly low level of leaf starch during the winter and their flowering forced by calcium carbide did not accompany with leaf starch accumulation.

Enhanced Rice Growth is Conferred by Increased Leaf ADP-Glucose Pyrophosphorylase Activity

Enhanced Rice Growth is Conferred by Increased Leaf ADP-Glucose Pyrophosphorylase Activity Modification of leaf starch levels may be employed in attempts to increase cereal yield. Few studies have examined leaf starch as a plant biomass limiting factor. Here we test the hypothesis that rice plant productivity may be increased by increasing leaf starch. Starch biosynthesis is controlled by the heterotetrameric rate-limiting enzyme ADP-glucose pyrophosphorylase (AGPase). Rice variety Nipponbare was transformed with a modified form of the maize endosperm AGPase large subunit gene, Sh2r6hs, as well as with the small subunit gene, Bt2, under control of a rice RuBisCO small subunit promoter. RNA sequencing results indicated that Sh2r6hs and Bt2 transcript levels were each greater than 20 times that of the native genes. Increased total AGPase activity was correlated with higher leaf starch accumulation at the end of the day.

Carbohydrate and Nutritional Responses to Stem Girdling and Drought Stress with Respect to Understanding Symptoms of Huanglongbing in Citrus

The most important worldwide problem in citrus production is the bacterial disease Huanglongbing (HLB; citrus greening) caused by a phloem-limited bacterium Candidatus Liberibacter asiaticus. The earliest visible symptoms of HLB on leaves are vein yellowing and an asymmetrical chlorosis referred to as “blotchy mottle,” thought to be the result of starch accumulation. We tested the hypothesis that such visible symptoms are not unique to HLB by stem girdling 2-year-old seedlings of two citrus rootstocks with and without drought stress in the greenhouse. After 31 days, girdling had little effect on shoot growth but girdling increased the relative growth rate of shoots in drought-stressed trees. Starch content in woody roots of non-girdled trees was three to 19 times higher than in girdled trees. In non-girdled trees, drought stress induced some starch accumulation in roots, but there were no effects of drought stress on root starch or sucrose in girdled trees. Girdling induced a 4-fold greater starch content in leaves on well-watered trees but leaf sucrose content was unaffected. Girdling reduced leaf transpiration in well-watered trees but net assimilation of CO2 was unaffected by girdling or leaf starch accumulation. Leaves on girdled trees clearly had visible blotchy mottle symptoms but no symptoms developed on non-girdled trees. The increase in leaf starch, up to 50% dry weight (DW), resulted in an increase in leaf DW per leaf area (LA) and an artificial reduction of many leaf nutrients on a DW basis. Most of these differences disappeared when expressed on a LA basis. Leaf boron (B), however, was inversely related to leaf starch when both were expressed on a LA basis. In the absence of HLB, girdling increased leaf starch, decreased root starch, and duplicated the asymmetric blotchy mottled visual leaf symptoms that have been associated with HLB-infected trees. This supports our contention that such symptoms generally attributed to HLB are not uniquely related to HLB infection, but rather are directly related to starch accumulation and secondarily to nutrient deficiencies in leaves.

Overexpression of plastidial thioredoxin f leads to enhanced starch accumulation in tobacco leaves

Starch, the most abundant storage carbohydrate in plants, has been a major feedstock for first-generation biofuels. Growing fuel demands require, however, that the starch yields of energy crops be improved. Leaf starch is synthesised during the day and degraded at night to power nonphotosynthetic metabolism. Redox regulation has been associated with the coordination of the enzymes involved in starch metabolism, but neither the signals nor mechanisms that regulate this metabolism are entirely clear. In this work, the thioredoxin (Trx) f and m genes, which code for key enzymes in plastid redox regulation, were overexpressed from the plastid genome. Tobacco plants overexpressing Trx f, but not Trx m, showed an increase of up to 700% in leaf starch accumulation, accompanied by an increase in leaf sugars, specific leaf weight (SLW), and leaf biomass yield. To test the potential of these plants as a nonfood energy crop, tobacco leaves overexpressing Trx f were subjected to enzymatic hydrolysis, and around a 500% increase in the release of fermentable sugars was recorded. The results show that Trx f is a more effective regulator of photosynthetic carbon metabolism in planta than Trx m. The overexpression of Trx f might therefore provide a means of increasing the carbohydrate content of plants destined for use in biofuel production. It might also provide a means of improving the nutritional properties of staple food crops.

Simultaneous boosting of source and sink capacities doubles tuber starch yield of potato plants

An important goal in biotechnological research is to improve the yield of crop plants. Here, we genetically modified simultaneously source and sink capacities in potato (Solanum tuberosum cv. Desirée) plants to improve starch yield. Source capacity was increased by mesophyll-specific overexpression of a pyrophosphatase or, alternatively, by antisense expression of the ADP-glucose pyrophosphorylase in leaves. Both approaches make use of re-routing photoassimilates to sink organs at the expense of leaf starch accumulation. Simultaneous increase in sink capacity was accomplished by overexpression of two plastidic metabolite translocators, that is, a glucose 6-phosphate/phosphate translocator and an adenylate translocator in tubers. Employing such a 'pull' approach, we have previously shown that potato starch content and yield can be increased when sink strength is elevated. In the current biotechnological approach, we successfully enhanced source and sink capacities by a combination of 'pull' and 'push' approaches using two different attempts. A doubling in tuber starch yield was achieved. This successful approach might be transferable to other crop plants in the future.

Photosynthetic traits around budbreak in pre-existing needles of Sakhalin spruce (Picea glehnii) seedlings grown under elevated CO2 concentration assessed by chlorophyll fluorescence measurements

To assess the effects of elevated CO(2) concentration ([CO(2)]) on the photosynthetic properties around spring budbreak, we monitored the total leaf sugar and starch content, and chlorophyll fluorescence in 1-year-old needles of Sakhalin spruce (Picea glehnii Masters) seedlings in relation to the timing of budbreak, grown in a phytotron under natural daylight at two [CO(2)] levels (ambient: 360 μmol mol(-1) and elevated: 720 μmol mol(-1)). Budbreak was accelerated by elevated [CO(2)] accompanied with earlier temporal declines in the quantum yield of PSII electron transport (Φ(PSII)) and photochemical quenching (q(L)). Plants grown under elevated [CO(2)] showed pre-budbreak leaf starch content twice as high with no significant difference in Φ(PSII) from ambient-CO(2)-grown plants when compared at the same measurement [CO(2)], i.e., 360 or 720 μmol mol(-1), suggesting that the enhanced pre-budbreak leaf starch accumulation might not cause down-regulation of photosynthesis in pre-existing needles under elevated [CO(2)]. Conversely, lower excitation pressure adjusted for the efficiency of PSII photochemistry ((1 - q(P)) F(v)'/F(m)') was observed in plants grown under elevated [CO(2)] around budbreak when compared at their growth [CO(2)] (i.e., comparing (1 - q(P)) F(v)'/F(m)' measured at 720 μmol mol(-1) in elevated-CO(2)-grown plants with that at 360 μmol mol(-1) in ambient-CO(2)-grown plants), which suggests lower rate of photoinactivation of PSII in the elevated-CO(2)-grown plants around spring budbreak. The degree of photoinhibition, as indicated by the overnight-dark-adapted F(v)/F(m), however, showed no difference between CO(2) treatments, thereby suggesting that photoprotection during the daytime or the repair of PSII at night was sufficient to alleviate differences in the rate of photoinactivation.

Effect of Pot Size on Various Characteristics Related to Photosynthetic Matter Production in Soybean Plants

Despite the wide uses of potted plants, information on how pot size affects plant photosynthetic matter production is still considerably limited. This study investigated with soybean plants how transplantation into larger pots affects various characteristics related to photosynthetic matter production. The transplantation was analyzed to increase leaf photosynthetic rate, transpiration rate, and stomatal conductance without affecting significantly leaf intercellular CO2concentration, implicating that the transplantation induced equal increases in the rate of CO2diffusion via leaf stomata and the rate of CO2fixation in leaf photosynthetic cells. Analyses of Rubisco activity and contents of a substrate (ribulose-1,5-bisphosphate (RuBP)) for Rubisco and total protein in leaf suggested that an increase in leaf Rubisco activity, which is likely to result from an increase in leaf Rubisco content, could contribute to the transplantation-induced increase in leaf photosynthetic rate. Analyses of leaf major photosynthetic carbohydrates and dry weights of source and sink organs revealed that transplantation increased plant sink capacity that uses leaf starch, inducing a decrease in leaf starch content and an increase in whole plant growth, particularly, growth of sink organs. Previously, in the same soybean species, it was demonstrated that negative correlation exists between leaf starch content and photosynthetic rate and that accumulation of starch in leaf decreases the rate of CO2diffusion within leaf. Thus, it was suggested that the transplantation-induced increase in plant sink capacity decreasing leaf starch content could cause the transplantation-induced increase in leaf photosynthetic rate by inducing an increase in the rate of CO2diffusion within leaf and thereby substantiating an increase in leaf Rubisco activity in vivo. It was therefore concluded that transplantation of soybean plants into larger pots attempted in this study increased the plant photosynthetic matter production by increasing mainly sink capacity that uses leaf starch for whole plant growth, particularly, growth of sink organs.

The role of transitory starch in C3, CAM, and C4 metabolism and opportunities for engineering leaf starch accumulation

Essentially all plants store starch in their leaves during the day and break it down the following night. This transitory starch accumulation acts as an overflow mechanism when the sucrose synthesis capacity is limiting, and transitory starch also acts as a carbon store to provide sugar at night. Transitory starch breakdown can occur by either of two pathways; significant progress has been made in understanding these pathways in C(3) plants. The hydrolytic (amylolytic) pathway generating maltose appears to be the primary source of sugar for export from C(3) chloroplasts at night, whereas the phosphorolytic pathway supplies carbon for chloroplast reactions, in particular in the light. In crassulacean acid metabolism (CAM) plants, the hydrolytic pathway predominates when plants operate in C(3) mode, but the phosphorolytic pathway predominates when they operate in CAM mode. Information on transitory starch metabolism in C(4) plants has now become available as a result of combined microscopy and proteome studies. Starch accumulates in all cell types in immature maize leaf tissue, but in mature leaf tissues starch accumulation ceases in mesophyll cells except when sugar export from leaves is blocked. Proper regulation of the amount of carbon that goes into starch, the pathway of starch breakdown, and the location of starch accumulation could help ensure that engineering of C(4) metabolism is coordinated with the downstream reactions required for efficient photosynthesis.

Starch accumulation in the leaves of root-restricted pepper affects plant growth by a feedback-inhibition of the photosynthesis

The mechanism behind the reduced growth occurring in plants subjected to root restriction is still not fully understood. Therefore, this investigation was planned to determine the morphological and physiological changes induced in response to root volume reduction and to determine the time frame within which these changes occurred. In particular, this research focused on the effect of root restriction on growth, leaf gas exchange parameters, carbohydrate production and water relations in pepper (Capsicum annuum L.). Our results show that the reduced growth is mainly linked to a feedback inhibition of the photosynthesis, caused by a concurrent limited stomatal conductance (probably driven by both stomatal factors and hormonal substances) together with a strong accumulation of starch in the leaves.

Photosynthesis affects following night leaf conductance in Vicia faba

Night-time stomatal opening in C(3) plants may result in significant water loss when no carbon gain is possible. The objective of this study was to determine if endogenous patterns of night-time stomatal opening, as reflected in leaf conductance, in Vicia faba are affected by photosynthetic conditions the previous day. Reducing photosynthesis with low light or low CO(2) resulted in reduced night-time stomatal opening the following night, irrespective of the effects on daytime stomatal conductance. Likewise, increasing photosynthesis with enriched CO(2) levels resulted in increased night-time stomatal opening the following night. Reduced night-time stomatal opening was not the result of an inability to regulate stomatal aperture as leaves with reduced night-time stomatal opening were capable of greater night-time opening when exposed to low CO(2). After acclimating plants to long or short days, it was found that night-time leaf conductance was greater in plants acclimated to short days, and associated with greater leaf starch and nitrate accumulation, both of which may affect night-time guard cell osmotic potential. Direct measurement of guard cell contents during endogenous night-time stomatal opening will help identify the mechanism of the effect of daytime photosynthesis on subsequent night-time stomatal regulation.

Effect of Growing Soybean Plants Under Continuous Light on Leaf Photosynthetic Rate and Other Characteristics Concerning Biomass Production

The present study investigated various characteristics concerning photosynthetic source capacity and biomass production of intact soybean plants grown under daily 10 h photoperiod as controls or under continuous light without darkness as CL plants from sowing. It was shown that while total photosynthetic source capacity and total dry matter production were larger in CL plants than in control plants, photosynthetic rate per unit leaf area and dry matter production of reproductive organs (pods) were smaller in CL plants than in control plants. It was also shown that CL plants had similar leaf intercellular CO2 concentration despite having lower leaf stomatal conductance and had lower activation state of Rubisco and similar content of leaf Rubisco as compared to control plants. With leaf microsomal membranes, three phosphatase activities, which have been found to increase under limitation of inorganic phosphate, were shown to be higher in CL plants than in control plants. Content of starch, a major photosynthetic end product in leaf was higher in CL plants than in control plants, showing that CL plants were subjected to a surplus source, an imbalance of photosynthetic source/sink balance. There are previous findings that inorganic phosphate stimulates the activation of Rubisco by promoting the binding of activator CO2 to the uncarbamylated inactive Rubisco. There is also evidence for the accumulation of starch in leaf under limitation of inorganic phosphate. Therefore, these results suggest that under continuous light that gives a surplus source, although plant total photosynthetic capacity and total biomass production are likely to increase, the efficiency of plant photosynthetic matter production is likely to decrease because of a lowered activation state of Rubisco that is likely to result from the limitation of inorganic phosphate. It is thus suggested that for the efficient improvement of plant biomass production, well-balanced improvement of source and sink would be essential.