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Hydraulic architecture and physiology of Loblolly Pine genotypes: Potential effects of abnormal lignin .
MOURA, CATARINA*,1, MAHERALI, HAFIZ1, ADDINGTON, ROBERT1, O'MALLEY, DAVID2, JACKSON, ROBERT1, 1 Duke University, Durham, NC2 North Carolina State University, Raleigh, NC
ABSTRACT- A recessive mutant allele is responsible for a deficient activity of the enzyme cinnamyl alcohol dehydrogenase (CAD), resulting in the formation of abnormal lignin. Since lignins are important for mechanical support and water transport, this mutation potentially affects several aspects of hydraulic structure and whole-plant physiology. Three genotypes (cad-null mutant, heterozygote, and wild-type) of Pinus taeda were studied to examine the relationship between hydraulic structure and function. Based on measurements of the xylem tension at which 50% percent of hydraulic conductivity was lost (50), branches of the cad-n trees were the most vulnerable to xylem cavitation (50 = -2.58 MPa) followed by heterozygotes (50 = -3.24 MPa) and wild-types (50 = -3.40MPa). However, both saturated hydraulic conductivity (KH) and specific-hydraulic conductivity (KS) were lower in the cad mutants, contradicting the generally observed trade-off between safety and efficiency. Nevertheless, leaf-specific hydraulic conductivity (KL) was similar across genotypes as a result of a higher Huber value (sapwood to leaf area ratio, AS/AL) in the mutants than in the heterozygotes and wild-types. To understand the basis of the hydraulic differentiation among genotypes, this study also includes measurements of the anatomical and biomechanical properties of these trees.
KEY WORDS: Pinus taeda, lignin biosynthesis, xylem structure and function, water transport