1Plant Form & Function #2,Secondary GrowthBio 1B, Fall ’08Professor Carlson2Primary vs. Secondary growthPrimary growth increases length of stem axis:• new cells originate from meristems at tips of roots& shootsSecondary growth increases width of stem ortrunk• new cells originate from vascular cambium3Monocot Stems & Trunks• Majority of monocots do not have secondary growth• Large palm trees (e.g., coconut trees) do not havetrue secondary growth, but rather produce “woody”tissue from primary growth that make up the trunk• Certain monocots (e.g., Agavaceae family) have aspecialized type of secondary growth that is differentthan eudicot secondary growth• Monocot secondary growth information will NOT berequired for the exam4Eudicot Secondary Growth• The following slides onsecondary growth refer toeudicots and not monocots567Annual vs Perennial Plants• Annual: plant that goes through entire lifecycle with flowering, fruit production, anddeath within one year. Secondary growth doesnot occur in annual plants• Perennial: plant that lives multiple years andmay have a below ground stem called a rhizome(e.g., goldenseal) or an above ground trunk andbranches (e.g., shrubs and trees)8Meristems and Cell Production• Apical Meristems (Figs. 35.11, 35.12, 35.13, 35.16; Lab manual 4.1, 4.2,4.3)– primary tissues– increase length of shoot and root axis• Vascular Cambium Meristems (Figs. 35.11, 35.12, 35.19, 35.20, 35-21; Lab manual 4.6-4.11)– secondary tissues for wood production– increase in girth/width• Cork Cambium Meristems (Figs. 35.19, 35.22; Lab manual 4.5, 4.6,4.9, 4.10, 4.11)– secondary tissues for cork & bark production– increase in girth/width910Secondary growth in young stems:tissues from outer to center (Fig 35-11)• Periderm• Cork cambium• Ground tissue (cortex)• Primary phloem• Secondary phloem• Vascular cambium• Secondary xylem• Primary xylem• Ground tissue (pith)11121314Secondary Growth in Eudicots(Figs. 35.11, 35.12, 35.19, 35.20, 35.22; Lab manual 4.6-4.11)• increases width/girth of stem/trunk• feature of eudicots and gymnosperms• occurs in both roots and stems• new cells develop from vascular cambium15Vascular Cambium Development(Figs. 35.11, 35.13, 35.17, 35.19-20, 35-22; Lab manual 4.6-4.11)• cambium develops from cells betweenprimary xylem and primary phloem withinbundles• cambium also develops within parenchymacells in regions between bundles• these regions merge to form a continuousring of cells that is one layer thick1617181920Secondary Growth in Eudicots(Figs. 35.11, 35.12, 35.19, 35.20, 35.22; Lab manual 4.6-4.11)• Bark (Fig. 35.18, 35.21, 35.23)– tissue outside of vascular cambium– made up of secondary phloem & cork• Vascular Cambium– single layer of cells in ring in stem/trunk• secondary xylem formed to inside of cambium to produce wood• secondary phloem forms to the outside of cambium• Wood– tissue inside of vascular cambium• all cells internal to the vascular cambium are secondary xylem exceptfor a small amount of primary xylem2122Secondary growth in tree trunks:tissues from outer to center (Fig 35-11, 35-19, 35-22)• Periderm• Cork cambium• Secondary phloem• Vascular cambium• Secondary xylem (sapwood)• Secondary xylem (heartwood)232425Phloem Cell Types(Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3– 4.11)• Contains sieve cells, sieve tubes, and companion cells• Sieve tube member: elongated food-conducting plant cellwith clusters of pores at both ends allowing sap to flow toadjacent cells• Sieve tube members are stacked end-to-end to form sievetubes• Companion cell: specialized cell found adjacent to sievetube member262728Phloem Transports Sugars (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3–4.11)• Plant vascular tissue that transports sugars fromthe photosynthetic leaves DOWN to other parts ofthe plant including the roots where sugars areconverted into starch for storage• In the early Spring, in many tree species innorthern latitudes, the starch in the roots isbroken down into sugars which are transported UPthe tree in the phloem to the small branches toprovide nutrients for developing leaves & shoots29Most Typical Function of Phloem• Phloem cells transports photosynthatein the form of sugar both up and downthe tree30Functions of Xylem• The main function of xylem is to transport water andminerals absorbed by the roots up the tree• Some tall tree species (e.g., redwoods & Douglas firs)are known to absorb water from fog through openstomata in leaves. In these circumstances, themovement of water in the xylem is downward in tree• There are also examples where the xylem fluidtransports sugars upward in the tree, e.g., in the Springin sugar maples when the starches stored in the rootsare converted to sugars which are transported up thetree by xylem to provide food and energy for thedeveloping buds and leaves31Xylem Transports Water & Minerals (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3–4.11)• plant vascular tissue provides longitudinaltransport of water & minerals up (vertically)from roots and in some species the water istransported from leaves down the tree• tracheid & vessel cell types• dead at functional maturity• provide structural support32Xylem (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig.4.3–4.11)Plant vascular tissue typically provides longitudinaltransport of water & minerals UP from rootsUnder conditions of high air humidity, there aresome tree species e.g., the coastal redwood andthe Douglas fir, that can absorb water from theair through stomata on the leaf surface andtransport this fluid DOWN the tree in the xylem;this is based on research done by Professor ToddDawson in the Department of Integrative Biologyat UC Berkeley33Xylem Transport of Fluids (Fig 35.10, 35.11, 35.14, 35.17-20, 35.22; Lab Man. Fig. 4.3–4.11)• The main activity of the xylem is to transportwater and minerals up the tree from the roots• However, in some species of trees, e.g., the SugarMaple (Acer saccharum) in eastern USA & easternCanada, glucose can be transported upward in thexylem from the roots to the leaves and developingstems in the early Spring; maple syrup is typicallytapped in early Spring when the sap is moving upwardfrom the roots to the developing leaves.34Brassinosteroid HormonesSupport Growth of XylemTracheids & Vessels35Xylem Cell Types (Fig 35.10, 35.11, 35.14,
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