The Biomass, Fibre and Sucrose Dilemma in Realising the Agronomic Potential of Sugarcane
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The Biomass, Fibre and Sucrose Dilemma in Realising the Agronomic Potential of Sugarcane

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Event / Evento: II Workshop on Sugarcane Physiology for Agronomic Applications ...

Event / Evento: II Workshop on Sugarcane Physiology for Agronomic Applications

Speaker / Palestrante: Frederick C. Botha (Sugar Research Australia)
Date / Data: Oct, 29-30th 2013 / 29 e 30 de outubro de 2013
Place / Local: CTBE/CNPEM Campus, Campinas, Brazil
Event Website / Website do evento: www.bioetanol.org.br/sugarcanephysiology

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The Biomass, Fibre and Sucrose Dilemma in Realising the Agronomic Potential of Sugarcane Presentation Transcript

  • 1. Enter title here for Powerpoint July 1 2013 The biomass, fibre and sucrose dilemma in realising the agronomic potential of sugarcane Extra details Botha here Frikkie 29 October 2013
  • 2. Outline • Background – – – – • • • • The ‘Sugarcane Triangle’ Biomass composition of the culm Genetic composition and selection pressure Supply and demand in sugarcane Is sugarcane the ideal biomass crop? Carbon partitioning in the culm and seedling What do we know about control? Conclusions
  • 3. Sugarcane Triangle ‘The Sugarcane Triangle, is the relationship between biomass, fibre and sucrose. Many believe that Devil is at play here and therefore call the area also as Devil's Triangle. The facts however are quite far from what is generally said or believed to be true. There are many publications, stories and myths created through sheer imagination. True to say that in some cases, conclusions got blurred’.
  • 4. Yield improvement in sugarcane 110 A B 14 100 12 90 10 TSH 70 8 60 6 50 4 40 2 30 1920 TCH/TSH TCH 80 1940 1960 YEAR 1980 2000 0 1920 9 C 7 5 1920 1940 1945 1960 YEAR 1970 YEAR 1980 1995 2000
  • 5. Components of the sugarcane stalk (commercial varieties) Sugarcane Dry matter (30%) Water (70%) • Fibre plus sucrose ~30%. When this goes much above 30% it is non-plant matter or poor cane!! • High fibre plus high sucrose- impossible • Breeders and cropping systems always try to balance ratio of fibre:sucrose • Very complex physiological processes controlling this ratio Fibre and sucrose make up 95% of the dry matter in the culm. The remaining dry matter is probably crucial for survival and cannot be used to enhance sugar content
  • 6. The two main progenitor species of “sugarcane” Saccharum officinarum Yield Vigour Tillering Canes Roots Sucrose Fibre Abiotic Biotic Saccharum spontaneum High Moderate Poor Thick Shallow High (sweet canes) Low Susceptible to frost, drought, salt Susceptible to most disease and insects Poor yielding Very good Heavy Thin Deep Low High Resistant to frost, drought, salt Resistant to most disease and insects
  • 7. The Sugarcane Cell Wall (Fibre) • The cell wall of sugarcane comprises cellulose (28%), hemicellulose (58%), and pectin (8%) • Type II walls which means that glucuronoarabinoxylans (GAX) is the major cellulose/crosslinking glycan (CLG) • The ratio between these different chemical components of fibre depends upon multiple factors, including: o o o o o genotype, climate conditions, location and rate of growth, amount and type of fertilizers used on the crop physical and chemical composition of the soil o Once the secondary wall is formed no further expansion growth is possible
  • 8. Sink and Source relationship • Solute passage through plasmodesmata is passive. Therefore, symplastic transport cannot, by itself, establish a solute concentration gradient! • Experimental manipulation of source/sink ratios generally indicates that meristematic sinks are source limited, whereas cell expansion and storage sinks are sink limited(Smith and Stitt, 2007).
  • 9. Biomass accumulation CO2 + E R1 Biomass production R2 (CH2O)n R1 > R2 = Biomass accumulation R1 = photosynthesis R2 = respiration Plants respire approximately one-half of their fixed photosynthate in providing energy and precursors for biochemical processes. Respiration us therefore a significant drain on the carbon available for partitioning into storage. Sugarcane ???? The energy and reducing equivalents produced during these steps serve as vital co-mediators in a multitude of other chemical reactions necessary for normal cell function. Significant carbon losses occur during over-maturation and post-harvest respiration of mature harvested cane (up to 10% of harvested sucrose) Sucrolysis in the sugarcane culm is key for identify strategies and targets for traditional breeding or genetic engineering to develop more desirable attributes in sugarcane
  • 10. Biomass partitioning CO2 R4 (CH2O)nx R3 (CH2O)n + E R5 R6 CO2 (R3-R4):(R5-R6) = Biomass partitioning (CH2O)ny Biomass partitioning Sucrolysis is sugarcane generally poorly studied. Probably would differ significantly from other species (symport off loading and very high sucrose levels) The sucrose storing capacity of sugarcane is characterised by pronounced substrate cycles, sometimes called futile cycles because they involve both the continuous synthesis and degradation of sucrose and the recycling of metabolic intermediates between the pools of hexose phosphates and triose phosphates in the cytosol
  • 11. Energy cane vs sugarcane 80 Tonnes DW/ha 70 60 Sugarcane Energycane 50 40 30 20 10 0 Sucrose Fiber Total Fernando Reinach: Canavialis Brazil
  • 12. Sink strength/priority drives carbon partitioning R1>R2 R1 Source (supply) R2 Sink 1 (culm) Sink 2 (roots) R2>R1
  • 13. Supply and demand CO2 Supply Demand SUCROSE Demand P SUCROSE H2O Nutrients X Supply
  • 14. Name Plant group Sugarcane varieties Net assimilation rate µmol m-2 s-1 29-61 40 Australian varieties 8 Japanese varieties N14 NiF4 Lahaina and H varieties CP73-1547 Q138, Q183 6 Brazilian varieties Other Species Chitton,Pindar, HQ409 16-54 25-44 46* 34.3 45-51* 31 30.5,35.5 41.3-60.7 Saccharum sinense Saccharum robustum Saccharum spontaneum Sorghum bicolor Zea mays C4 plants C3 Crop Plants Reference Bull 1969 Irvine 1967, 1975 Nose & Nakama 1990 Allison et al. 1997 Du et al.1999a Meinzer & Zhu 1998 Vu et al. 2006 Inman-Bamber et al. 2008 Galon et al. 2009 45.8 Meinzer & Zhu 1998 49.2* 33.4-48.2 42.5 52.4 30-70 20-40 Meinzer & Zhu 1998 Nose et al. 1994 Ziska & Bunce 1997 Ziska & Bunce 1997 Larcher 2003 Larcher 2003
  • 15. Nitrogen use efficiency should be a key focus in sugarcane • In maize, maximum photosynthetic rates (~57 mol m 2 s 1) are observed at a leaf N of 80mmolm 2 , whereas sugarcane requires about 125 mmol m 2 to exhibit the same peak A value. • The reason for the PNUE differences between sugarcane and maize are unclear • If sugarcane could be bred to have similar PNUE as maize, then A could be increased about 25% at a leaf N of 80 mmol m 2 • The key to high photosynthetic performance in sugarcane, therefore, is to maintain a high leaf N status or increase the PNUE. Maintaining a high leaf N status is a major problem because it promote growth over sugar accumulation and thus reduce crop quality (‘Energy cane’ production)
  • 16. Percentage allocation of mobilised carbon from the internode to the developing shoot, roots and respiration. Values are the mean of three replicates ± SE. Dark Time (days) Shoot Roots 0 0 0 7 43.2 ± 1.4 32.0 ± 3.3 14 45.3 ± 1.5 12.3 ± 2.5 21 38.3 ± 1.3 13.3 ± 2.1 Dark/Light Respiration Shoot Roots Respiration 0 0 0 0 24.8 ± 2.4 43.2 ± 1.4 32.0 ± 3.3 24.8 ± 2.4 44.4 ± 2.8 41.6 ± 1.1 14.8 ± 2.8 43.7 ± 5.8 48.4 ± 5.3 47.8 ± 1.8 17.7 ± 2.1 34.5 ± 3.3
  • 17. 0 R² = 0.9849 4000 Time (min) 2000 0 2 4 Time (min) 6 8 % Label 0 HCl 120 100 80 60 40 20 0 Sucrose Glu/Fru A+O Insol 90 NaH214CO3 • • • • • 180 6000 150 8000 90 10000 120 12000 60 % Label CO2 uptake 100 90 80 70 60 50 40 30 20 10 0 30 C- Pulse feeding Uptake (Bq) 14 Time (h) 180 Labeling done on leaf 6 Uptake of CO2 was linear during the first 5 min of labelling (R2 0.98) Fixation rate was 45 µmol C/m2/s. Label is rapidly mobilised from the leaf All the label is exported as sucrose
  • 18. Sink strength -2 0 +1 Labelled leaf [Sucrose] +4 +7 +8 +11 [Sucrose] Sink strength = 1 > 3 > 4= 0 > 7 > 8 = -1 > 11 > -2 > -3
  • 19. Carbon partitioning 0 50 100 0 50 100 0 50 100 6 weeks Fibre 6 hours R1 Respiration R2 -3 Sugar 3 R3 0 200 400 600 Carbon distribution (Bq) Sucrose 30% Label lost 25% 3 0 -3 20% % Carbon distribution 15% 10% 5% 0% 0 10 20 Time (days) 30 40
  • 20. Carbon partitioning 42% 50% 8% Respiration R1 Sucrose R2 R3 -3 30% Sugar 3 30% 40% 5% 20% Fibre 75%
  • 21. Cellular partitioning HP to TP • The dominating metabolic flux is sucrose synthesis, sucrose breakdown, Hex-P and TP cycling Metabolic modelling indicate that: • CIN and Hexokinases have the largest flux control coefficients • Vacuolar loading would have a large positive influence • Reloading of the phloem would be important Sucrose Synthesis TP to HP Respiration Hexokinase 0 2 4 6 8 10 Internode 7 Internode 9 Internode 3 CO2 release Fibre Synthesis Starch Synthesis
  • 22. sucrose sucrose APOPLAST CWI CYTOSOL PPi PFP G1P G6P F6P PFK Pi F1,6P2 sucrose cycling triose-hexose phosphate cycling fructos glucose e UTP UGPase PPi SPS UDPGlc sucrose-6-P sucrose SUSY NI DHAP 3-PGA fructose VACUOLE MITOCHONDRIA glucose fructose glucose AI sucrose TCA cycle and respiration (CO2 production) sucrose
  • 23. SuSy (Synthesis : Breakdown) The SPS/SuSy story 2.5 2 1.5 1 The contributions by SPS and SuSy to synthesis 0.5 0 3 5 7 Internode # 9 Internode 14C-Glc/ 14C-Frc Calculated enzyme ratio SPS/SuSy 3 5 8 15 2.2 1.5 1.1 1.0 0.9 2.5 >20 SPS only
  • 24. Hexokinase activities • • • • Rapid mobilisation of glucose and fructose At least 5 hexokinase like activities with fructokinase dominating The role of FRK2 in sugarcane metabolism is not clear. The only way that this enzyme could play a meaningful part in fructose phosphorylation was if the fructose concentration was less than 0.2 mM (even in young internodes the concentration exceeds this limit by more than 100 times. Is this enzyme involved in sugar signalling?
  • 25. Impact of reduced PFP activity FLUX (nmol min-1 mg protein-1) Suc to fruc 0.85 1.56 100.43 254.87 14.56 13.22 4.37 1.52 0.70 0.13 90.12 42.3 9.56 5.67 901.33 456.11 88.99 50.87 1.68 0.92 0.42 1.28 OPU506 4 2 0 Internode 6 600 Hexose concentration ( mol g-1 DW) WT Internode 3 Triose-P to Hex-P 9.98 13.40 Triose-P cycling 6 Gluc to Suc 500 * * 400 * 300 503 * Q3 200 100 0 WT TC 501 504 505 506 Genotype 507 508 400 350 300 250 200 150 100 50 0 4000 3500 3000 2500 2000 1500 1000 500 0 Q4 * * 502 * 7000 6000 5000 4000 3000 * 2000 1000 0 WT TC 501 502 503 504 505 506 Genotype 507 508 Q3 Q4 Sucrose concentration ( mol g-1 DW) WT Internode 3+4 Internode 6+7 OPu506 Internode 3+4 Internode 6+7 Carbon cycling
  • 26. Reducing neutral invertase activity 3.0 2.5 Flux into sucrose nmol/ min/mg protein Maturing Internode Young Internode 80 NCo310 U1 U2 2.0 1.5 1.0 0.5 40 0.0 0.30 Young Int Maturing Int Young Int Maturing Int 20 0.25 0 Neutral Invertase SuSy • • • • Acid Inv CW Inv Neutral Invertase SuSy Acid Inv Recovery of CIN – GM clones problematic Increase in sucrose content 30% reduction in biomass accumulation 50% reduction in bud germination CW Inv Flux into glucose nmol/ min/mg protein nmol/ min/mg protein 60 NCo310 U1 U2 0.20 0.15 0.10 0.05 0.00
  • 27. Conversion of vacuolar sucrose Internode 3 9 12 3 9 12 3 9 12 3 9 12 3 9 12 Frucrose Sucrose Kestose Kestotetraose detector response] 1-2-6-12 700 Polymer Clone 2 K2 = 1,1 - 2 200 K3 = 1,1,1 - Clone 1 control 600 500 nmol/gram 3 400 -50 1-2-5-1 Total Sugars 600 1 1-2-3-5 Clone Sucrose DP3 NCO 310 800 1-2-2-4 Kestopentaose 1'000 nC NCo310 2153 2121 400 2 300 200 100 0 3 6 9 12 Internode 13 16
  • 28. The Sugarcane story ST Vac kestose PP Suc Suc/ H2O Suc Suc H H H-P T-P Respiration H2O S P Fibre • Maintaining a sucrose gradient crucial for biomass production • Sucrose concentration in the culm between 0.5 and 0.9 M. • Two major carbon cycles occur even in mature internodes • CIN plays an important role in sucrose hydrolysis • What is the signalling and control pathways (FK)? • Rapid labelling of Suc and much slower for kestose; slow loading or no loading? • Fibre and respirqtion the dominant demands in young tissue
  • 29. The sugarcane CO story Tops 2 Sucrose H Sucrose storage Leaf • Under high input conditions biomass accumulation is driven by the solar radiation • A constant radiation use efficiency is not achieved throughout the crop cycle (reduced growth phenomenon (RGP)). • Lower photosynthetic capacity because of leaf nitrogen limitations and poor PNUE • Sucrose feedback control by the sink tissues • Increased respiration • Active growth under especially under limited water and nutrient supply reduce availability of C for sucrose storage = high fibre:sucrose • Reduces available carbon for stalk and root growth H Sucrose Fibre Stalk Respiration Roots • Initial growth phase has a limited time window and water stress or limited sunlight will reduce internode growth. • Mild stress conditions increases sucrose (high sucrose :fibre). • Vigorous growth (high nitrogen levels enough water) will achieve the opposite (high fibre:sucrose). • Sucrose accumulation can suppress photosynthesis (lower yield, vigour ratoonability)
  • 30. Conclusions Sugarcane is one of the world’s most productive crops and its exceptional ability to produce biomass makes it very attractive in a biomass-dependent economy. Surprisingly, the reported photosynthetic capacities of sugarcane are low relative to other typical C4 species and frequently are equivalent to that of C3 crops. Several factors contribute to this phenomenon including lower photosynthetic capacity because of leaf nitrogen limitations and feedback control by the sink tissues that accumulate exceptionally high sugar levels. The distribution of carbon between sucrose and fibre in the stalk is not constant. In young actively growing tissue the majority of carbon is allocated to fibre and energy production for growth. However, a redirection of carbon to sucrose occurs during internode maturation. Several potential control mechanisms have been studied abut no clear picture is evident An early switch to sucrose storage has a negative impact on biomass yield. Key targets for further improvement of sugarcane should be improving photosynthetic nitrogen use efficiency, or altering sink-source partitioning of carbon and nitrogen.
  • 31. http://www.wiley.com/WileyCDA/WileyTitle/productCd-0813821215.html CONTENTS 1. Sugarcane: The Crop, the Plant, and Domestication 2. Anatomy and Morphology 3. Developmental Stages (Phenology) 4. Ripening and Postharvest Deterioration 5. Mineral Nutrition of Sugarcane 6. Photosynthesis in Sugarcane 7. Respiration as a Competitive Sink for Sucrose Accumulation in Sugarcane Culm: Perspectives and Open Questions 8. Nitrogen Physiology of Sugarcane 9. Water Relations and Cell Expansion of Storage Tissue 10. Water, Transpiration, and Gas Exchange 11. Transport Proteins in Plant Growth and Development 12. Phloem Transport of Resources 13. Cell Walls: Structure and Biogenesis 14. Hormones and Growth Regulators 15. Flowering 16. Stress Physiology: Abiotic Stresses 17. Mechanisms of Resistance to Pests and Pathogens in Sugarcane and Related Crop Species 18. Source and Sink Physiology 19. Biomass and Bioenergy 20. Crop Models 21. Sugarcane Yields and Yield-Limiting Processes 22. Systems Biology and Metabolic Modeling 23. Sugarcane Genetics and Genomics 24. Sugarcane Biotechnology: Axenic Culture, Gene Transfer, and Transgene Expression