Critical approaches in the catalytic transformation of sugar isomerization and epimerization after Fischer-History,challenges,and prospects

The transformation of aldose to ketose or common sugars into rare saccharides,including rare ketoses and aldoses,is of great value and interest to the food industry and for saccharidic biomass utilization,medicine,and the synthesis of drugs.Nowadays,high-fructose corn syrup(HFCS)is industrially produced in more than 10 million tons annually using immobilized glucose isomerase.Some low-calorie saccharides such as tagatose and psicose,which are becoming popular sweeteners,have also been produced on a pilot scale in order to replace sucrose and HFCS.However,current catalysts and catalytic processes are still difficult to utilize in biomass conversion and also have strong substrate dependence in producing high-value,rare sugars.Considering the specific reaction properties of saccharides and catalysts,since the pioneering discovery by Fischer,various catalysts and catalytic systems have been discovered or developed in attempts to extend the reaction pathways,improve the reaction efficiency,and to potentially produce commercial products.In this review,we trace the history of sugar isomerization/epimerization reactions and summarize the important breakthroughs for each reaction as well as the difficulties that remain unresolved to date.

Consumption of sugary beverages,genetic predisposition and the risk of depression:a prospective cohort study

Background The associations between sugary beverages and genetic predisposition to depression risk remain unclear.Aims This study aimed to investigate the associations of sugar-sweetened beverages(SSBs),artificially sweetened beverages(ASBs)and natural juices(NJs)with depression and to assess whether these associations were modified by genetic predisposition.Methods We used data from the UK Biobank of 180599 individuals aged 39-72 years who were depression-free at baseline.Dietary intake of SSBs,ASBs and NJs was accessed by a 24-hour dietary recall between 2009 and 2012.The Polygenic Risk Score for depression was estimated and categorised as low(lowest tertile),intermediate(tertile 2)and high(highest tertile),.Cox proportional hazard and substitution models were conducted to evaluate hazard ratios(HRs)and 95%Cls.Results Over the 12-year follow-up,4915 individuals developed depression.Higher consumption(>2 units/day)of SSBs(HR:1.26,95%CI 1.12 to 1.43)and ASBs(HR:1.40,95%Cl 1.23 to 1.60)were both associated with an increased risk of depression.However,moderate consumption(>0-1 units/day)of NJs was associated with a lower risk of depression(HR:0.89,95%CI 0.83 to 0.95).Furthermore,genetic predisposition did not modify these associations(p interaction>0.05).In substitution models,the HRs for depression risk were 0.94(95%CI 0.89 to 0.99)and 0.89(95%CI 0.85 to 0.94),respectively,when 1 unit/day of SSBs or ASBs was replaced by an equivalent intake of NJs.Conclusions Higher consumption of SSBs and ASBs was associated with an increased risk of depression;in contrast,moderate consumption of NJs was inversely associated with a lower risk of depression.In theory,substituting SSBs and ASBswith NJs would suppose a reduction of depression risk.

Ingenious liquid-observed vapor exchange (LOVE) NMR method revealing how sugars protect dry protein structure

Recently,Gary et al.published an article elucidating how sugars contribute to the protection of dry protein structure.They utilized an ingenious liquid-observed vapor exchange(LOVE)nuclear magnetic resonance(NMR)method,providing valuable insights into the protection mechanism of sugars during the drying process.The details of their study can be found in the article available at https://doi.org/10.1021/acs.biochem.2c00692.

Genome-Wide Discovery and Expression Profiling of the SWEET Sugar Transporter Gene Family in Woodland Strawberry (Fragaria vesca) under Developmental and Stress Conditions: Structural and Evolutionary Analysis

The SWEET(sugar will eventually be exported transporter)family proteins are a recently identified class of sugar transporters that are essential for various physiological processes.Although the functions of the SWEET proteins have been identified in a number of species,to date,there have been no reports of the functions of the SWEET genes in woodland strawberries(Fragaria vesca).In this study,we identified 15 genes that were highly homolo-gous to the A.thaliana AtSWEET genes and designated them as FvSWEET1–FvSWEET15.We then conducted a structural and evolutionary analysis of these 15 FvSWEET genes.The phylogenetic analysis enabled us to categor-ize the predicted 15 SWEET proteins into four distinct groups.We observed slight variations in the exon‒intron structures of these genes,while the motifs and domain structures remained highly conserved.Additionally,the developmental and biological stress expression profiles of the 15 FvSWEET genes were extracted and analyzed.Finally,WGCNA coexpression network analysis was run to search for possible interacting genes of FvSWEET genes.The results showed that the FvSWEET10 genes interacted with 20 other genes,playing roles in response to bacterial and fungal infections.The outcomes of this study provide insights into the further study of FvSWEET genes and may also aid in the functional characterization of the FvSWEET genes in woodland strawberries.

Nitrogen-Doped Amorphous Carbon Homojunction from Palmyra Sugar as a Renewable Solar Cell

An a-C/a-C:N junction,which used palmyra sugar as the carbon source and ammonium hydroxide(NH4OH)as the dopant source,was successfully deposited on the ITO glass substrate using the nano-spraying method.The current-voltage relationship of the junction was found to be a Schottky-like contact,and therefore the junction shows the characteristic rectifiers.This means the a-C and a-C:N are semiconductors with different types of conduction.Moreover,the samples showed an increase in current and voltage value when exposed to visible light(bright state)compared to the dark condition,thereby,indicating the creation of electron-hole pairs during the exposure.It was also discovered that the relationship between current and voltage for the a-C/a-C:N junction sample formed a curve that satisfies the rule of the photovoltaic effect when exposed to visible light from a light bulb.The exposure of this sample to direct sunlight at AM 1.5 conditions produced a curve that meets the rules for the emergence of the photovoltaic effect with higher characteristics for the current-voltage relationship.Thus,the a-C/a-C:N junction sample is a solar cell successfully fabricated using a sample method and has a maximum efficiency of 0.0013%.

Transcriptome Sequencing for Sugar and Flavonoid Metabolism in Prunus persica‘Jinxiangyu’

In this study,high performance liquid chromatography(HPLC)and RNA-seq transcriptome sequencing were used to study the changes in soluble sugar components and flavonoids in Prunus persica‘Jinxiangyu’at different developmental stages(20–90 d after flowering)and screen the key genes regulating the formation of soluble sugar and flavonoids in the fruits.The results showed that 60–85 d after flowering was the key stage of quality formation of Prunus persica‘Jinxiangyu’,and the content of soluble sugar,soluble solid,fructose,and sucrose in the fruit increased significantly during this period.The sugar content of ripe fruits was mainly fructose and sucrose.The content of kaempferol glycoside was low in the fruit.Quercetin glycoside content was higher in the young fruit stage and decreased with fruit maturity.There were no anthocyanin compounds in the fruit.The expression levels of genes involved in flavonoid metabolism(ANS,DFR,F3H,FLS,4CL1,etc.)were low in the fruit.A total of 181 differentially expressed genes were identified during fruit development to participate in five sugar metabolism pathways,among which the SDH gene had a higher expression level,which continuously rised in the later stage of fruit development.It mainly promoted the accumulation of fructose content in the later stage of fruit development.The expression levels of SPS1,SS,and SS1 genes were continuously up-regulated,which played a key role in sucrose regulation.The higher expression levels of SUS3 and INVA genes in the early stage of fruit development promoted the degradation of sucrose.

Assessment of Physico-Chemical and Microbial Quality of Sugarcane Juice Sold by Street Vendors in Three Regions of Bangladesh

Sugar cane juice is a popular refreshing drink in most part of Bangladesh. It has great taste and health benefits;also it is available most of the public places at reasonable prices which consumed by road side customers including general public, shopping personals, tourists, students. In our country, street vendors crushing sugarcane between roller crusher and sold without any heat treatment or preservative, also served with or without added ice and lemon juice. The study aimed to identify and compare the physico-chemical and microbial quality of sugarcane juice. The chemical qualities of juices including moisture, PH, ash, total soluble solid, total sugar, reducing sugar and titrable acidity were found slightly different in Mymensingh, Gazipur and Narayangonj areas. The highest and lowest value of moisture, ash, PH, total soluble solids, total sugar, reducing sugar and titrable acidity were found in 84.33% - 79.26% (Gazipur-Mymensingh), 0.57% - 0.04% (Mymensingh-Gazipur), 5.9 - 2.9 (Gazipur-Narayangonj), 17.48% - 4.98% (Mymensingh-Narayangonj), 21.9% - 6.56% (Mymensingh-Gazipur), 3.7 - 2.1 (Gazipur-Mymensingh) and 0.523% - 0.007% (Narayangonj-Gazipur) respectively. For microbiological analysis, the total viable count of sugar cane juice in Mymensingh, Gazipur and Narayangonj were ranged from 0.6 × 105 - 43.6 × 105 cfu/ml, 4.6 × 105 - 21.6 × 105 cfu/ml and 3.6 × 105 - 36.6 × 105 cfu/ml respectively, where the permitted value is 1.0 × 104 cfu/ml, whereas the total coliform count was ranged from 0.4 × 105 - 6.4 × 105 cfu/ml, 0.6 × 105 - 8.4 × 105 cfu/ml and 0.00 - 8.4 × 105 cfu/ml, where the permitted value is 100 cfu/ml and total fungal count was ranged from 5.5 × 105 - 56.5 × 105 cfu/ml, 21.5 × 105 - 54.5 × 105 cfu/ml and 32.5 × 105 - 68.5 × 105 cfu/ml, where the permitted value is 1000 cfu/ml. According to the Gulf standard, the microbiological parameters of all the collected sugar cane juice were out of the permitted standards, so that a serious health outbreak can be caused anytime.

Overview on Soil Compaction and Sugar Beet Growth

With the advancement of agricultural mechanization,soil compaction has become a serious environmental problem.Soil compaction can increase soil bulk density and firmness,reduce porosity and permeability,and deteriorate soil structure,ultimately inhibit sugar beet growth and reduce both root yield and sugar content.However,few farmers recognize the link between soil compaction and these adverse effects.Soil compaction has a cumulative effect,with significant differences observed in the vertical range of compaction accumulation.The most significant soil compaction occurs in the topsoil of 0-10 cm,and the influence depth can reach 70 cm,but it is small in deep soil,and the inflection point is at a soil depth of 10 cm.The degree of soil compaction is related to soil type,water content,tractor shaft load,tyre type,tyre pressure and operation speed,etc.Therefore,in the production process of sugar beet,it is advisable to avoid high-humidity operations,use low pressure tyres,reduce the number of tractor-units passes over the farmland,and implement agricultural and agronomic measures to minimize soil compaction.These practices will help protect the soil environment and ensure sustainable production of sugar beets.

Analysis of The Effect of Comprehensive Nursing Intervention on Improving Blood Sugar Levels and Treatment Compliance in Elderly Patients with Diabetes

Objective: To analyze the effect of comprehensive nursing intervention on improving blood glucose levels and treatment compliance in elderly patients with diabetes. Methods: One hundred and forty-eight elderly patients with diabetes were selected and randomly divided into a control group and an observation group, with 74 cases each. The control group received routine nursing intervention and the observation group received comprehensive nursing intervention. The blood sugar levels, treatment compliance, and nursing satisfaction of the two groups of patients before and after intervention were compared. Results: After the intervention, the fasting plasma glucose (FPG) (t = 7.729), 2 hours postprandial glucose (PPG) (t = 8.343), and HbA1c (t = 6.929) levels of patients in the observation group were significantly lower than those in the control group (P < 0.001). The observation group (71/95.95%) had a higher compliance rate than the control group (54/72.97%) (χ^(2)=14.877, P < 0.001). The comprehensive nursing satisfaction rate of the observation group (73/98.65%) was higher than that of the control group (56/75.68%) (χ^(2)=17.451, P < 0.001). Conclusion: In caring for elderly patients with diabetes, comprehensive nursing intervention effectively reduced patients’ blood sugar levels and improved treatment compliance and nursing satisfaction.

Composite Panels from the Combination of Rice Husk and Wood Chips with a Natural Resin Based on Tannins Reinforced with Sugar Cane Molasses Intended for Building Insulation: Physico-Mechanical and Thermal Properties

The objective of this work is to develop new biosourced insulating composites from rice husks and wood chips that can be used in the building sector. It appears from the properties of the precursors that rice chips and husks are materials which can have good thermal conductivity and therefore the combination of these precursors could make it possible to obtain panels with good insulating properties. With regard to environmental and climatic constraints, the composite panels formulated at various rates were tested and the physico-mechanical and thermal properties showed that it was essential to add a crosslinker in order to increase certain solicitation. an incorporation rate of 12% to 30% made it possible to obtain panels with low thermal conductivity, a low surface water absorption capacity and which gives the composite good thermal insulation and will find many applications in the construction and real estate sector. Finally, new solutions to improve the fire reaction of the insulation panels are tested which allows to identify suitable solutions for the developed composites. In view of the flame tests, the panels obtained are good and can effectively combat fire safety in public buildings.

Fruit Photosynthesis and Assimilate Translocation and Partitioning: Their Characteristics and Role in Sugar Accumulation in Developing Citrus unshiu Fruit

Dynamics of dry- or fresh-weight of fruit, peel photosynthetic rate and chlorophyll content, and the characteristics of translocation and distribution of radiolabelled assimilates from leaf or fruit were examined in developing satsuma mandarin (Citrus unshiu Marc. cv. Miyagawa wase) fruit from primary stage of fruit enlargement up to fruit full ripe. Change in fruit photosynthetic rate was some what related to the change in the chlorophyll content of peel. Fruit photosynthetic rate markedly declined as chlorophyll degradation occurred in the peel. Before full ripe stage of the fruit, photosynthates produced by a 14C-fed leaf were mainly distributed to juice sacs even during periods when dry matter accumulation in peel was more rapid than that in juice sacs. At the full ripe stage, peel photosynthetic rate approached zero and peel became the major sink of leaf photosynthates. Most of the peel assimilates, however, remained in situ for up to 48 h after feeding 14CO 2 to the fruit, only a small portion being transported to other parts of fruit. The percentage of fruit photosynthates exported decreased with fruit development and ripening, but the peak rate of export to juice sacs amount to as high as 12%. The sugar content and dry weights of peel and juice sacs in shaded fruit were lower than that in the control fruit. These results show that peel assimilate was mainly consumed in peel respiration and growth and thus the dependence on leaf photosynthates decreased. Part of this assimiate was used in sugar accumulation in juice sacs of fruit.

Variation of Sugar, Acid and Vitamin C Contents in Fruit Development in Different Types of Kiwifruit

The variation of sugar, acid and vitamin C contents in fruits of red flesh kiwifruit （Actinidia chinensis） ＂Hongyang＂ and green fresh kiwifruit （A. deliciosa） ＇Jinkui＇ were investigated during fruit development. The results showed that the to- tal sugar soluble contents of ＂Hongyang＇ and ＇Jinkui＂ during fruit development ex- isted different variations. With the upward trend of ＇Hongyang＇ fruit development, 95 days after full bloom （DAFB）, the total soluble sugar accumulation was relatively slow, and then rose rapidly until harvest with the maximum content （6.87%）. While ＇Jinkui＇ fruit showed a fluctuant process, rising in 50 DAFB, then declining, then rising rapidly and decreasing slightly right before harvest. The variation of fruit titrat- able acid between them was more consistent, which was increased and then de- creased. The only difference was that the titratable acid content of ＇Jinkui＇ fruit de- creased slowly from the late of fruit development to fruit ripening, similar to the maximum value, but that of ＇Hongyang＇ fruit decreased rapidly in the late. Titrat- able acid contents of them in the maturity were 1.08% and 1.20%, respectively. The trends of sugar acid ratio for ＇Hongyang＇ and ＇Jinkui＇ fruit were quite different. ＇Hongyang＇ fruit increased slowly and then rapidly; ＇Jinkui＇ changed from decreas- ing to increasing, followed by slight decreasing in mature stage. In addition, the two kiwifruit varieties had a similar change trend of Vc content during fruit development, which changed from rapid increasing to declining, followed by slight growing in the harvest. The changing tendency of ＇Jinkui＇ fruit was later than that of ＇Hengyang＇.

Studies on Membrane Function and Sugar Components of Ultradried Seeds

The effects of ultradry storage on the activity of ATPase and fluidity of plasma membrane in Chinese cabbage (Brassica pekinensis (Lour.) Rupr.) and elm ( Ulmus pumila L.) seeds were investigated. The results indicated that no significant differences in the activity of ATPase and the micro- viscosity of plasma membrane of ultradried (UD) seeds could be found as compared to the control seeds stored under -20 degreesC, although there was a little adverse effect on the seeds with extreme dehydration. The results were consistent with higher vigor level of UD seeds. This implied that ultradry seed storage could protect the integrity of the membrane, maintain its physiological function and improve the storability of seeds. The relationship between sugar and desiccation tolerance of UD seeds was analysed using the HPLC. The results showed that the ratio of reducing to nonreducing sugar was lower in UD seeds than that in control. The content of sucrose and stachyose in elm and Chinese cabbage UD seeds was related to their desiccation tolerance, while no stachyose was detected in corn (Zea mays L.) seeds. This could be one of the reasons for its sensitivity to desiccation.

Dynamic Variation in Sugar,Acid,and ASA Contents of ‘Ganmi 6' Kiwifruit(Actinidia eriantha Benth) Fruits

[Objective] The variation of sugar, acid and AsA contents in fruits of ‘Ganmi 6＇ kiwifruit （Actinidia eriantha Benth） were investigated during fruit develop- ment. [Method] Kiwi fruits were randomly taken as materials every 15 days since 20 days after full bloom （DAFB） to 170 DAFB until in mature stage. [Result] The results showed that during fruit development of ‘Ganmi 6＇, the total sugar soluble contents had a rising trend with relatively stable at 95 DAFB, then rose until har- vest with the maximum content （10.35%）. The titratable acid content showed a trend of increasing, then declining, then increase to the harvest content （1.10%）. From the sugar acid ratio, we can knew it decreased in 95 DAFB, then up to the max （9.38）. The changes of AsA contents showed double ‘S＇ shape, decreased af- ter the first increased rapidly, slightly increased and then decreased in the early harvest. [Conclusion] It provided a theoretical basis for scientific cultivation methods to explore the nutrients regulation.

Effect of Wheat Based Diet Supplemented with Xylanase on Blood Sugar and Total Protein in Serum of Geese

[Objective] The effects of wheat based diet supplemented with xylanase on blood sugar and total protein in serum of geese were studied. [ Method ] By using the randomized design of single factor, the 1-day-old healthy goslings were divided into 6 groups and fed with corn based diet, wheat based diet and wheat based diet supplemented with xylanase at different concentrations respectively, the contents of blood sugar and total protein in serum were determined. [ Result] The wheat based diet supplemented with xylanase could increase the blood sugar and total protein in serum of geese and wheat based diet supplemented with 0.2% xylanase generated the best effect, which was higher than those of corn based diet group. As for the concentration of protein in serum, wheat based diet supplemented with 0.2% xylanase was significantly different from corn based diet and wheat based diet. [ Conclusion] The wheat based diet supplemented with xylanase could enhance geese production.

The effect of exogenous sugar solution and high concentration of CO_2 on the contents of sugar and protein of Betula platyphylla leaves

The content of total sugar, sucrose, fructose and protein in the leaves of3-yr.-old Betula platyphylla was measured after the treatment by three exogenous sugar solutions(sucrose, fructose, glucose) and three high concentrations of CO_2 (700, 1 400, 2 100 μL/L·L^(-1))for about a month in 1998. The results showed that spraying three exogenous sugar solutionsincreased markedly the content of sugar and protein of leaves under 700 μL·L^(-1) and 1 400μL·L^(-1) CO_2 The effect of spraying exogenous sucrose solution was the best among the threeexogenous sugars. The treatment of spraying exogenous sugar solution and 2 100 μL·L^(-1) CO_2constrained the accumulation of total sugar and protein of leaves. There was no difference inprotein content of leaves when spraying glucose and fructose solutions under 700 μL·L^(-1) and 1400 μL·L^(-1) CO_2. The treatment of 2 100 μL·L^(-1) CO_2 concentration significantly increasedthe contents of total sugar, sucrose, fructose, and protein of leaves compared with that of the 700μL·L^(-1) and 1 400 μL·L^(-1) CO_2 except the plants spraying fructose solution. There waspositive correlation between the content of sugar of leaves and CO_2 concentration when sprayingsame exogenous sugar solution.

Varietal Characteristics and Nutrition Characteristics of Several New Varieties of High Biomass Sugarcanes for Sugar and Energy

[Objective] The aim was to study the varietal characteristics of six new varieties of high biomass sugarcanes for sugar and energy namely GT02-833,GT97-69,GT02-351,GT03-2287,B9 and GT02-770,as well as the nutrition characteristics of them under drip irrigation conditions. [Method] Industrial and agronomic characters,total N,total P,total K and chlorophyll content were determined. [Result] Cane yield,total biomass yield and sugar content of six varieties were more than 180,200 and 25 t/hm2 respectively,which were higher than that of the control Xintaitang 22. The total nitrogen and total phosphorus contents of six varieties were high and persistent from Jul to Nov,but they decreased sharply in Dec. Total potassium content of all varieties increased from Jul to Dec. Chlorophyll content of all varieties were high from Aug to Oct,but they decreased sharply in Nov. Total nitrogen,total phosphorus and total potassium content of GT02-833,GT97-69 and B9 were higher than that of CK. [Conclusion] GT02-833,GT97-69 and B9 had characteristic of efficient use of nutrients,thus should be extended as elite varieties.

Comparisons of Nectar Quantity and Sugar Concentration of Pomegranate Blossom in a Day

[Objective] The aim was to research the rules of nectar quantity and sugar concentration of perfect and staminate flowers in a day. [Method] Based on nine Tianguang Yan pomegranate trees, nectar quantity and sugar concentration of per- fect and staminate flowers were measured and analyzed in morning and afternoon. [Result] Average nectar quantity and sugar concentration differed insignificantly in morning and afternoon of perfect flowers, which could also be applied to staminate flowers. However, average nectar quantity of perfect flower was 64.09 μI and of staminate flower was 44.07 μl. It is obvious that the two were of extremely signifi- cant differences （t=4.642, P〈0.01）, and the former was significantly higher by 45,43%. On the other hand, average sugar concentration of perfect flower was 48.44% and of staminate flower was 37.16%. The two were of extremely significant differences and the former is higher by 30.36%, compared with the latter. These suggested that nectar quantity and sugar concentration would maintain unchanged in different periods for a day, if nectars are not consumed by pollinators, such as bees and butterflies. In the same period, nectar quantity and sugar concentration of per- fect flowers were higher than those of staminate flowers. [Conclusion] The research provides references for benefits increase of bee farmers and fruit farmers, as well as exploration of bee pollination.

Effect of Sugar on the Process of Cold-Acclimation-Induced Freezing Tolerance of Populus tomentosa

Populus tomentosa seedlings for cold-acclimating were pretreated wit h or without 20% saccharose. Changes in the concentrations of total soluble sugar , the survival rates, and freezing tolerance of seedlings during cold acclimatio n were investigated. The results showed that cold acclimation increased the conc entrations of total soluble sugar, the survival rates and freezing tolerance. Co ld acclimation, combined with the saccharose-pretreatment, enhanced the above- ment ioned effect of cold acclimation, and obviously increased the concentrations of total soluble sugar, the survival rates and freezing tolerance of seedlings. Fur ther analysis found that the concentrations of total soluble sugar in branches i ncreased greater than that in leaves during both cold acclimation with or withou t the pretreatment of saccharose. Moreover, an increase of the concentrations of total soluble sugar in branches and leaves was closely related to the freezing tolerance of seedlings. The results indicate the accumulation of soluble sugar i n seedlings induced by cold acclimation may be involved in the induction of free zing tolerance .

Effects of Plant Growth Regulators on the Contents of Reducing Sugar and Starch in Potato(Solanum tuberosum L.)

[Objective] The aim was to investigate the effects of plant growth regulators on contents of reducing sugar and starch in potato（Solanum tuberosum L.）.[Method]A potato cultivar named ＇Holand-212＇ with three treatments by spraying Diethyl aminoethyl hexanoate（DTA-6）,Uniconazole（S3307）and SOD mimics（SODM）were employed to compare differences of the contents of reducing sugar and starch in potato leaves,stolons and tubers in a field experiment.[Result]DTA-6 treatment could significantly reduce the contents of starch and reducing sugar in potato stolons in the period of 100-110 d after seeding,and it could also reduce the content of reducing sugar in tubers,but there is an opposite result in leaves in the same period,significantly.S3307 could extremely significantly increase the content of starch,and can promote the transfer of starch in stolons,in addition,it also could reduce the content of reducing sugar in tubers,and extremely significantly increase the content of starch in leaves at the 110 d after sowing.Moreover,there is a similar effect between SODM and S3307.[Conclusion]The research results are significant for understanding mechanisms of plant growth regulators and promoting application of plant growth regulator in potato.