Influence of moisture stress during growth on14CO2 fixation and translocation inSolanum tuberosum L.

Moisture stressing of potato plants resulted in reduced¹⁴CO₂ fixation and translocation of labelled photosynthates from leaves to tubers. A majority of the label was recovered in the sugar fraction of both leaves and tubers. The amount of labelled¹⁴C recovered in the organic acid fraction of tubers of normally irrigated plants was significantly higher than in tubers which had been moisture stressed. In the other fractions, the differences were not significantly different. Injection of uniformly labelled sucrose into the basal portion of attached tubers of stressed and non-stressed plants showed greater translocation of labelled carbon by tubers of stressed plants from basal to the apical portion and also into the stems as compared to non-stressed plants.     

The effect of oxygen concentration on the sugar content of potato tubers stored at low temperature

Summary Mature potato tubers of the varietyMajestic were stored, at 1°C, in concentrations of oxygen from 0 to 100% for a period of one month. The contents of sucrose and reducing sugar and the CO₂ production of the tubers were measured. Concentrations of oxygen of 3% and below delayed the accumulation of sugars in the tubers compared with that in air. In N₂ the accumulation was prevented, while the CO₂ production continued at a low rate. At oxygen concentrations above 3% the sucrose level rose to a maximum after three weeks and then slowly fell, while the reducing sugar content increased throughout. Under these conditions carbon dioxide production increased rapidly to a peak at about 7 days and then slowly fell to near the initial level.     

Relationships of hollow heart in Irish potatoes to carbohydrate reabsorption and growth rate of tubers

Tubers of Irish Cobbler that were hollow grew faster than non-hollow tubers on the same plant. However, tubers of varieties without hollow heart grew just as rapidly as tubers of the variety with hollow heart. Therefore tuber growth rate was related to hollow heart occurring within a variety but could not account for differences between varieties. When plant foliage was pruned the C-¹⁴ label from sucrose was translocated from the tuber to the top of the plant. Our studies suggest hollow heart can occur in small tubers under the following conditions: (i) moisture stress in the tubers resulting in conversion of starch to sugar, followed by a rapid influx of water into the tuber resulting in rapid enlargement of the perimedullary zone and a separation in the pith that later develops into hollow heart, and/or (ii), following injury to some cells in the tuber due to reabsorption of minerals and carbohydrates or depletion of food reserves followed by tuber enlargement. It seems probable however that hollow heart that is initiated in large tubers is only associated with excessively rapid tuber enlargement without the involvement of reabsorption or depletion of food reserves.     

Effects of the Temperature Lowered in the Daytime and Night-time on Sugar Accumulation in Sugarcane

Abstract

Sugarcane (Saccharum spp.) is a major crop grown for sucrose production. In Japan, its sucrose concentration is highest in winter. We examined the effects of the temperature lowered in the daytime and night-time (LDT and LNT, respectively) on sugar assimilation. Since photosynthetic and respiration rates change with temperature, we assumed that plants under LNT (LNT plants) would have low respiration rates and thus high sugar yields, whereas those under LDT (LDT plants) would have low rates of photosynthesis and thus low sugar yields. However, because of their acclimatisation to the reduced temperatures, LNT and LDT plants had sugar yields that were similar, or superior, to those of control plants. Sugar yield depends on biomass and sugar concentration; the stems of LNT and LDT plants did not grow as tall as those of the controls, but the sucrose concentrations in their stems were higher than in the controls. ¹³C analysis revealed no difference in the partitioning of photosynthates to the soluble sugar fraction between control plants and those treated with low temperature. Control plants had higher glucose concentrations in the stem than treated plants, in which new photosynthates appeared to be partitioned preferentially into sucrose. Low temperature enhanced the sucrose concentration in the sugarcane stem not by improving the carbon budget, but by promoting the partitioning of carbon to stored sucrose.     

The effect of 2,4-d on tuberization and starch content of potato tubers produced on stem segments culturedin vitro

The effect of 2,4-D on tuberization, yield and the starch content of potato tubers produced on stem segments was examined. Potato stem segments were cultured in nutrient agar containing 2,4-D concentrations ranging from 10^?7 M to 2 × 10^?3 M. The stem segments were incubated in the dark at 25° C and examined after 15 days. The degree of tuberization on stem segments cultured in media containing 10^?7 M and 10^?6 M 2,4-D was higher than on the control stem segments. Mainly long stolons were observed on stem segments cultured in media containing 10^?4 M and 2 × 10^?3 M 2,4-D. The percent starch (dry wt. basis) in stolons was higher than that in tubers. However, the total starch content of tubers per stem segment cultured in media containing 10^?7 M and 10^?6 M 2,4-D was significantly higher than that of stolons obtained from stem segments cultured in media containing higher concentrations of 2,4-D. The total starch content of tubers, except those produced on stem segments cultured in media containing 10^?7 M 2,4-D, decreased steadily with increasing concentration of 2,4-D in the culture media.     

The effect of storage factors on membrane permeability and sugar content of potatoes and decay byErwinia carotovora var.atroseptica andFusarium roseum var.Sambucinum

Russet Burbank and WC230-14 potato tubers were stored at 0 C (32 F) and 5 C (41 F) in air, air plus 4% CO₂ and air plus 8% CO₂ for a 175 day storage period. Four times during this period, tubers were removed and inoculated withErwinia carotovora var.atroseptica (van Hall) Dye orFusarium roseum var.sambucinum (L. K.) Sn. and H. and stored at 17 C (62.6 F). Tuber samples were also reconditioned for two weeks at 17C(62.6 F) and then inoculated. Tubers were evaluated for rate of membrane permeability, free glucose, free fructose, and sucrose content and the rate of tuber decay by the two pathogens. Relative to 5 C (41 F), 0 C (32 F) storage increased sugar content, membrane permeability and the rate of tuber breakdown. Increasing CO₂ during storage at 0 C (32 F) and 5 C (41 F) increased each of the above parameters. Reconditioning tended to alleviate the adverse effects of 0 C (32 F) storage and increasing CO₂ levels, but varietal differences existed. A significant and high correlation was obtained between the rate ofErwinia decay, membrane permeability, and sucrose content of the tubers.     

Partitioning of photoassimilates by potato plants (Solanum tuberosum l.) as influenced by irradiance: II. Partitioning patterns by four clones grown under high and low irradiance1

This paper is the second in a three-part series describing the influence of varied irradiance on growth and photoassimilate partitioning by potato plants. Four clones (Russet Burbank, Lemhi Russet, A66107-51, and A6948-4) were grown under two light regimes: a) high light levels (HL) of 500 to 1200 μE m^-2 s^-1, varying with changes in natural sunlight and time of day, and b) low light levels (LL) at approximately one quarter of high light (21 to 28%). Three weeks after tuber initiation, the most recently-matured leaf was labelled with¹⁴CO₂, and plants were harvested: 1) one day after labelling, and 2) two weeks after labelling. Plants of all clones responded to the low light levels in a similar way by: 1) changing some morphological characteristics, 2) decreasing biomass accumulation and tuber yield, and 3) changing the sink-source relationship by promoting growth of leaves and stems at the expense of tubers. However, there were evident clonal differences in reactions to growth under low light; e.g., Lemhi Russet appeared to be most sensitive to light stress, while clones A66107-51 and A6848-4 were much less sensitive. No matter what the prior light history (HL or LL), clone A6948-4 was able to maintain higher rates of photosynthesis than the other clones at all light levels between 200 and 1200 μE m^-2 s^-1. This study showed that the potential exists to breed for cuttivars that can maintain higher rates of photosynthesis and higher tuber yield under low light levels.     

The pattern of assimilate movement in potato plants

Summary Leaves at nodes 5, 7 and 9 (numbered from the base) on separate batches of plants were supplied with¹⁴CO₂ at flowering and to further batches of plants 20 and 40 days after flowering. Of the tubers formed on a plant 20% arose from that portion of the stem within an arc of ±45 from the supply leaf but they contained 47% of the activity detected in all of the tubers.     

Influence of heat stress on dry matter production and photo-assimilate partitioning by four potato clones

Partitioning patterns of¹⁴C labeled assimilates were studied to determine their relationship to dry matter accumulation and distribution in four potato clones (Desiree, DTO-28, LT-1 and Russet Burbank). Plants placed in growth chambers at 35/25 C day/night temperature and 12-hour photo-period two weeks after tuber initiation were compared with plants grown continuously at 25/12 C. Two weeks after temperature treatments were begun, the most recently expanded leaf was labeled with¹⁴CO₂ for 30 minutes, and plants were harvested 20 hours or 15 days later. High temperature reduced total dry matter production and altered dry matter distribution in favor of vines at the expense of tubers. Partitioning of¹⁴C assimilates generally followed the pattern of dry matter distribution. Potato clones exhibited variation in¹⁴C assimilate export from labeled leaves and in partitioning to vines and tubers. Assimilate partitioning to tubers was not consistently higher in clones considered heat tolerant.     

Growth rate and carbohydrate metabolism of potato tubers exposed to high temperatures

Summary The effect of high tuber temperature (30 °C) on the growth rate and carbohydrate metabolism of tubers was studied with 3 cultivars differing in heat tolerance. Subjecting individual tubers to 30°C for 6 days caused cessation of tuber growth. During this period, non-treated tubers (20°C) on the same plant increased in volume. At 30°C, incorporation of¹⁴C-labelled assimilates into the ethanol-insoluble fraction (mainly starch) as well as the starch content was significantly reduced. In contrast, the incorporation of¹⁴C-labelled assimilates into the sugar fraction was not affected by high tuber temperature. At 30°C the activity of some of the enzymes involved in starch metabolism was depressed. Varietal differences in responses of tuber growth rate and carbohydrate metabolism to high tuber temperature were insignificant. From these preliminary results it is concluded that high soil temperatures may decrease starch content of potato tubers directly by inhibition of the conversion of sugars into starch.     

Effect of leaf age on photosynthesis,carbon transport and carbon allocation in potato plants

Summary Photosynthetic characteristics, carbon allocation and partitioning of newly-fixed¹⁴C among the various carbohydrate fractions were studied in leaves of potato plants (Solanum tuberosum L. cv. Désirée) of different ages. The higher photosynthetic rate of young leaves was associated with higher levels of starch and reducing sugars. After 24 hours, in young leaves the fixed¹⁴C had been partitioned mainly to the residue and starch fractions, while in older leaves there was an increase in partitioning to sucrose and reducing sugars. The activities of the various sink organs were found to be dependent upon their distance from the source leaf. Tuber activity, however, was affected similarly by all fully expanded leaves. Although young fully expanded leaves are thought to be the major source of assimilates for tuber growth, it seems that a vast potential for contributing to plant productivity and tuber yield lies also in the older leaves, which translocate most of their photoassimilates to the tubers.     

Temperature,cyanide, and oxygen effects on the respiration,chip color,sugars, and organic acids of stored tubers

The possibility that sugar accumulation of potatoes stored at low temperatures may be linked to activation of cyanide-resistant respiration (CRR) was investigated. After a lag period of several days, continuous HCN treatment stimulated CO₂ production of tubers stored in 20% O₂. At 1°C in 20% O₂, HCN treatment increased respiration over that effected by low temperature treatment. After several weeks of treatment, cyanide-stimulated CO₂ production was greater at 1°C than at 10°C. Sucrose and malate levels of HCN treated tubers were sometimes higher than those of the 10°C control tubers, but they were always lower than those of the 1°C control tubers. This indicated that CRR alone could not account for the sugar increases at 1°C. Storage in 2% O₂ blocked the increase in CO₂ production and changes in constituents associated with HCN treatments in 20% O₂. HCN treatment had no significant effect on chip color. The level of CRR was measured in freshly cut slices from Monona, Norchip, and Kennebec tubers previously stored at 10°, 5°, or 1°C for several months. Slices from tubers previously stored at 1°C had increased CRR, but there was no difference in CRR between the 5°C and 10°C treatments. Sugars accumulated at 5°C, again indicating that sugar accumulation in potatoes stored at low temperatures was at least partially independent of the activation of CRR.     

Overexpression of a Maize SPS Gene Improves Yield Characters of Potato under Field Conditions

Abstract

We analyzed the yield characters of field-grown transgenic potato plants (Solanum tuberosum) carrying a maize gene for sucrose-phosphate synthase (SPS), the key enzyme in sucrose synthesis. The SPS activity in the leaves of transgenic plants (line Ag1203) was 2 times that of the control (cv. May Queen). There was no difference in the photosynthetic CO₂ uptake rates between Ag1203 and May Queen plants, and the leaf starch content of Ag1203 was lower. These observations indicate that the introduction of a foreign SPS gene improved the supply of photosynthate from source (leaves) to sink (tubers). Additionally, leaf senescence of the transgenic potato plants was delayed relative to that of May Queen. The average tuber weight and total yield of Ag1203 plants were at least 20% higher, and the tuber sucrose content, which is related to eating quality, was also higher. Increased translocation of photosynthate and longer period of photosynthetic activity in the leaves may have increased the yield of Ag1203. These results suggest that introduction of the SPS gene improved the yield characters and quality of potato tubers under field conditions.     

Effects of elevated CO2 concentration on bulbil germination and early seedling growth in Chinese yam under different air temperatures

The present study investigated the effects of elevated carbon dioxide concentration ([CO₂]) and air temperature on the germination of seed bulbils and the seedling vigour of two Chinese yam lines. Plants were grown under two [CO₂] levels, ambient and elevated (ambient + 200 μmol mol^?1), and two mean air temperature regimes, 22.2 °C (ambient + 1.4 °C) and 25.6 °C (ambient + 5.2 °C). Elevated [CO₂] did not affect bulbil germination under both air temperature regimes. During the early growth stage, the dry weight (DW) of leaves, vines, shoots, roots, belowground parts (roots + tubers) and whole plants were higher under elevated [CO₂] than ambient [CO₂] for both lines under the low- and high-temperature regimes. The values of vigour indexes (index I = germination % × seedling length and index II = germination % × seedling DW) were also higher under elevated [CO₂] than ambient [CO₂] for both lines. These results indicated that Chinese yam seedlings respond positively to elevated [CO₂] during the early growth stage. The above:belowground DW ratios were lower under elevated [CO₂] than ambient [CO₂] in seedlings with very small new tubers for both yam lines, indicating that elevated [CO₂] strongly affected the root growth in the early growth stage. The DWs of post-treatment seed bulbils were higher in the elevated [CO₂] under both air temperature regimes. The results showed that Chinese yam used a smaller amount of the reserves in seed bulbils under elevated [CO₂] than under ambient [CO₂].     

The degree of starch phosphorylation as influenced by phosphate deprivation of potato (Solanum tuberosum L.) plants

Summary The levels of starch phosphorylation in potato tubers were investigated in relation to fertilization with phosphorus (P) of field-grown and greenhouse-grown plants. The field-grown plants received 0, 15 or 30 kg P ha⁻¹. Starch from plants grown without P-fertilizer contained 15.6 nmol P (mg starch)⁻¹ whereas starch from plants grown with 30 kg P ha⁻¹ contained 20.6 nmol P (mg starch)⁻¹. The greenhouse-grown plants were cultured in inert media and received nutrient solutions containing 0, 3, 12 or 24 mg P l⁻¹, respectively. Plants grown with no P-fertilizer produced tuber starch with phosphorylation levels reduced to approximately 30% of the level found in plants grown with an ample supply of P. Thus, the level of starch phosphorylation can be modified by limiting the P-supply through the root system. Application of foliar P-fertilizer to the greenhouse-grown plants had no significant effect on the phosphorylation of the tuber starch.     

子粒发育过程中糖分转化量对Sh_2甜玉米种子活力的影响

分析Sh_2甜玉米品系(4份自交系和其测交组合)子粒发育过程中果糖、蔗糖含量及种子百粒重、种子物质利用率和种子活力等指标,探讨Sh_2甜玉米子粒发育过程中糖分转化机制对种子活力的影响。结果表明,在Sh_2甜玉米子粒发育过程中,淀粉不断累积,从授粉至收获果穗(乳熟期),子粒中蔗糖果糖含量,且4个品系间存在显著差异。蔗糖含量是从授粉后7 d高位迅速下降,到35 d左右保持稳定,后期又有所下降;果糖是早期高,中期稳定,后期下降。在发育早期,子粒中糖分含量为淀粉含量的9.17～21.59倍;到发育后期,子粒中糖分含量是淀粉含量的1.27～3.02倍。相关分析表明,种子活力指数与种子物质利用率正相关,蔗糖转化量与子粒淀粉含量呈显著负相关(P0.05),果糖转化量与种子物质利用率呈显著正相关(P0.01),种子活力指数与蔗糖转化量、果糖转化量相关不显著。     

甜菜不同类型品种植株中锰含量及其分配特点的研究

本文对甜菜植株中锰含量的变化及其分配特点进行了初步研究.结果表明:(1)甜菜锰代谢最强的时期,是在叶丛快速生长期.这与氮、磷代谢特点相一致。生育期植株中锰的含量,因品种类型不同有所差异。(2)甜菜吸收和累积锰量最多的时期,是叶丛快速生长期至决根,糖分增长期;锰在叶中的分配量,在整个生育期都占绝对优势。(3)蔗糖与锰的含量,在叶片中存在着正相关关系;在叶柄中却呈负相关关系。     

Effects of elevated atmospheric CO2 concentration on morphology of leaf blades in Chinese yam

ABSTRACT

The effects of elevated carbon dioxide concentration on the morphology of leaf blades in two Chinese yam lines under different temperature conditions were determined. Plants were grown under two [CO₂] levels, ambient (about 400 µmol mol^?1) and elevated (ambient + 200 µmol mol^?1) in the daytime, and two mean air temperature regimes, approximately ambient temperature (22.2°C) and high temperature (25.6°C). The palisade layer was thicker under elevated [CO₂] than under ambient [CO₂] in both temperature regimes, and the whole yam leaf blade was thicker under elevated [CO₂] than under ambient [CO₂] in the approximately ambient temperature regime. The numbers of chloroplasts per palisade cell and spongy cell as well as per unit profile area of palisade cell, number of starch grains per chloroplast, profile area of the starch grain, and starch-to-chloroplast area ratio in both palisade and spongy cells were higher under elevated [CO₂] than under ambient [CO₂] in both temperature regimes. Furthermore, the stomatal density on the abaxial side of the leaf blade in Chinese yam was greater under elevated [CO₂] than under ambient [CO₂] under both temperature regimes, and stomatal-pore length was higher under elevated [CO₂] than under ambient [CO₂] in the approximately ambient temperature regime. These results indicate that elevated [CO₂] positively affects the photosynthetic apparatus. The results of this study provide information for understanding the response characteristics of the leaf blade under elevated [CO₂] and a possible explanation for the positive photosynthetic responses of Chinese yam to elevated [CO₂] in our previous study.

List of Abbreviations:[CO₂]: carbon dioxide concentration     

Effect of free-air CO2 enrichment on the storage of carbohydrate fixed at different stages in rice (Oryza sativa L.)

Increasing global atmospheric CO₂ concentrations are expected to influence crop production. To investigate the effect on rice (Oryza sativa L.), plants were grown under ambient CO₂ (AMB) or free-air CO₂-enrichment (FACE) at CO₂ concentrations ranged from 275 to 365 μmol mol⁻¹ above AMB. We supplied ¹³CO₂ to the plants at different growth stages so we could examine the contribution of carbohydrate stored during the vegetative stage or newly fixed carbohydrate produced during the grain-filling stage to ear weight at grain maturity. In plants supplied with ¹³C at the panicle-initiation or pre-heading stages, plants grown under FACE had more starch in the stems at heading, but there was no difference in stem ¹³C content. Furthermore, there were no differences between treatments in whole-plant ¹³C contents at heading and grain maturity. In contrast, plants supplied with ¹³C at the grain-filling stage had more ¹³C in the whole plant and the ears at grain maturity under FACE than under AMB, indicating that the increased amount of photosynthate produced at the grain-filling stage under CO₂ enrichment might be effectively stored in the grains. Furthermore, regardless of when the ¹³C was supplied, plants had more ¹³C in starch in the ears at grain maturity under FACE than under AMB. Therefore, CO₂ enrichment appears to promote partitioning of photosynthate produced during both vegetative and grain-filling stages to the grains.     

Comparative performance of three small seed tuber sizes and standard size seed tubers planted at similar stem densities

Summary Small seed tubers of 1–5 g, 5–10 g and 10–20 g were planted at the same sprout densities as standard size seed tubers of 40–60 g in order to give similar stem densities. Early ground cover by foliage, total yield, and yield of tubers >45 mm were consistently greater in plots planted with larger seed tubers. The effect of seed tuber size on yield and tuber number per stem varied between years but 1–5 g seed tubers always gave lower yields per stem than larger seed tubers. Reducing the spacing between rows from 90 cm to 60 cm and maintaining the same sprout density was more effective in increasing yields from small seed tubers than increasing sprout density from 20 to 40 sprouts per m² by reducing plant spacing within the row.