Basic mechanism of secondary cell wall formation in softwood tracheids

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1 Basic mechanism of secondary cell wall formation in softwood tracheids Stig L. Bardage Department of Forest Products: Wood Science SWEDEN

2 The structure of annual rings and thereby the structure of tracheids is influenced by external factors: - Temperature - Nutrient availability - Water - Climat - Sun light - Others

3 Genetically controlled growth and inwintering Birch with different proveniences planted at Ultuna in a North to South row.

4 Background The differentiation of tracheids in the xylem of conifers occurs from the cambium with four arbitrary phases: Cell division in the cambium and formation of primary wall Surface growth/expansion of daughter cells to the size of mature tracheids Formation of the secondary wall Lignifications of the cell wall (Wardrop and Harada, 1963)

5 Hosoo et al. (2005) were able to demonstrate that the deposition of cellulose microfibrils onto the developing secondary wall of tracheids occurs during daylight and that hemicelluloses and maybe also lignin precursor are deposited during the night.

6 A particular annual ring of spruce Fibres in a radial row are more genetically related with each other, originate from the same mother cell in the cambium Earlywood Latewood Wall area of tracheids along a radial row across an annual ring: IMAGE ANALYSIS

7 Measurements on other annual rings Spruce 1.5 m - annual ring 38 CELL WALL AREA and LUMEN AREA Cell wall Lumen Square microns Tracheid number

8 Spruce 1.5 m - annual ring 20 CELL WALL AREA and LUMEN AREA Cell wall Lumen Square microns Tracheid number

9 Spruce 1.5 m - annual ring 38 CELL WALL AREA and LUNEN AREA Cell wall Lumen Square microns Tracheid number

10 Pine 1.5 m - annual ring 19 CELL WALL AREA and LUMEN AREA Cell wall Lumen Square microns Tracheid number

11 Pine 1.5 m - annual ring 10 CELL WALL AREA and LUMEN AREA Cell wall Lumen Square micrometers Tracheid number

12 Deposition of cellulose microfibrils onto the developing secondary wall of tracheids occurs during daylight and that hemicelluloses and lignin precursor are deposited during the night (Hosoo et al., 2005). Latitude and availability of sun light may influenced annual ring formation. Earlywood/Latewood Context During biosynthesis the geometry softwood tracheids is already determined and completed before formation of the secondary cell wall (Larson, 1994). The speed and ratio of secondary wall formation will be determined by external factors but the intrinsic mechanism of cell wall deposition may be in operation trough the whole growing season. Hypothesis Given constant conditions with regard to availability of water, nutrients, temperature, and cyclic equal day/night intervals, secondary cell wall deposition will occur in a constant manner. As a direct consequence of that, the transverse wall area of tracheids in a radial row across a growth ring is expected to be the same.

13 Study of factors affecting secondary cell wall deposition (for forestry, wood biomass production) and annual ring formation solely through measurement of transverse wall area on single rows

14 Experimental approach 1. Norway spruce (Picea abies) plants grown under controlled conditions in growth cabinets. 2. Norway spruce plants grown outdoors

15 First growth period Three months in continuous light at 20 C humidity 75% (optimal growth conditions for all Norway spruce provenances). All other factors are constant. Inwintering = eight weeks of long nights (16 h) at 20 C, then one week of long nights at 10 C, one week of long nights at 5 C, one week in darkness at 2 C, one week of long nights at 10 C, after which second growth period. Second growth period Group 1: Group 2: Group 3: Constant conditions: 16h day and 8h darkness Day length : from 16h to 22h, and back to 16h Effect of temperature: 16h day at 25 C and 8h darkness at 15 C (10 C) All other factors are constant. Third growth period Group 4: Planted outdoors (analysis matched to meteorological data)

16 First growth period

17 Inwintering: start - Sept. 2010

18 Expected result Group 1: Constant conditions: 16h day and 8h darkness Transverse cell wall area Tracheids

19 Expected result Group 2: : Day length variation Transverse cell wall area Tracheids

20 Expected result Group 3: Effect of temperature Transverse cell wall area? Less tracheids formed? Smaller transverse cell wall area? Tracheids

21 Expected result Group 4: Planted outdoors (2 years) 1600 Example Cell wall Lumen Cell wall area Tracheid number Analysis against meteorological data

22 Other experimental set-ups Effect of photoperiod: grow the plants under continuous light with correspondingly reduced light intensity Effect of reduced total light energy Effects of drought Formation of latewood Others

2005. The effect of day length on diurnal differences in the innermost surface of the S2 layer in differentiating

23 What do you think? Thank You! David Clapham SLU - Forest Genetics Stig Bardage SLU - Wood Products Hosso Y, Yoshida M, Imai T,and Okuyama T The effect of day length on diurnal differences in the innermost surface of the S2 layer in differentiating tracheids. J Wood Sci (2005) 51: Wardrop, A. B. and Harada, H The formation and structure of the cell wall in fibres and tracheids. Journal of Experimental Botany. Vol 16 No

The secondary meristem result in growth in a lateral direction, such as the increase in girth of a tree.

Chapter 9b-Stems and Material Transport Woody plants produce wood tissue and bark through the activity of secondary meristems: The secondary meristem result in growth in a lateral direction, such as the