Physiological responses to water stress and waterlogging in Nothofagus species.

Gas exchange and water relations were investigated in Nothofagus solandri var. cliffortioides (Hook. f.) Poole (mountain beech) and Nothofagus menziesii (Hook. f.) Oerst (silver beech) seedlings in response to water stress and waterlogging. At soil matric potentials (Psi(soil)) above -0.005 MPa, N. solandri had significantly higher photosynthetic rates (A), and stomatal and residual conductances (g(sw) and g(rc)), and lower predawn xylem water potentials (Psi(predawn)) than N. menziesii. The relative tolerance of plants to water stress was defined in terms of critical soil matric potential (Psi(cri)) and lethal xylem water potential (Psi(lethal)). The estimated values of Psi(cri) and Psi(lethal) were -1.2 and -7 MPa, respectively, for N. solandri, and -0.7 and -4 MPa, respectively, for N. menziesii. Photosynthesis was sustained to a xylem water potential (Psi(xylem)) of -7 MPa in N. solandri compared with -4 MPa in N. menziesii. Following rewatering, both A and Psi(xylem) recovered quickly in N. solandri, whereas the two variables recovered more slowly in N. menziesii. During the development of water stress, nonstomatal inhibition significantly affected A in both N. solandri and N. menziesii. Nothofagus menziesii was more susceptible to inhibition of A by waterlogging than N. solandri. However, the tolerance of N. solandri to severe waterlogging was also limited as a result of a failure to form adventitious roots, suggesting a lack of adaptation to these conditions. The differences in tolerance to water stress and waterlogging between the two species are consistent with the distribution patterns of N. solandri and N. menziesii in New Zealand.

Seed orchards in development.

This paper reviews the role of seed orchards as output systems for genetic improvement programs. In this paper, technological changes since the 1950s are examined, with emphasis on recent developments. The need to equate the type of seed orchard to the type of forestry practiced is recognized, as is the significance of the relationship between seed orchards and other output systems for genetically improved material.

Gibberellin A(4/7) and the Promotion of Flowering in Pinus radiata: Effects on Partitioning of Photoassimilate within the Bud during Primordia Diferentiation.

Gibberellin A(4/7) mixture (GA(4/7)), a highly effective promoter of early and enhanced flowering in the Pinaceae, caused a significant reallocation of dry matter and (14)C-photosynthate within terminal buds of Pinus radiata D. Don within 8 days of hormone treatment. Treatment with GA(4/7) to terminal shoots of vigorous, potentially flowering mature grafted propagules reduced the flow of photoassimilated (14)C and dry matter into the terminal bud as a whole, but significantly increased the dry matter and (14)C allocated within the bud to developing long-shoot primordia (potential seed-cone buds). This was accomplished at the expense of the structural tissues, the apical dome region, and the vegetative branch buds. Although GA(3) caused a similar reallocation of dry matter within the terminal bud, it was significantly less effective than GA(4/7) thus appears to have, in addition to any nutrient diversion abilities, a distinct morphogenic function in sexual differentiation.

Changes in Cytokinins and Gibberellin-Like Substances in Pinus radiata Buds during Lateral Shoot Initiation and the Characterization of Ribosyl Zeatin and a Novel Ribosyl Zeatin Glycoside.

Based on detection and quantitation by bioassay, endogenous gibberellin-like substances (GAs) and cytokinins (CKs) in Pinus radiata D. Don buds during sequential shoot initiation shift from less polar to more polar forms (GAs) and from conjugated to free forms (CKs). As the terminal bud moves from the production of "short shoots" (needle fascicles) to "long shoots" (lateral branches or female conebuds), a more polar GA appears while a glucoside-conjugate of zeatin riboside is reduced, and zeatin riboside levels increase markedly.Permethyl derivatives of the two highly active CK fractions were examined by capillary gas chromatography-mass spectrometry after separation by C(18) reverse phase high performance liquid chromatography. The mass spectra indicated the presence of: 9-beta-d-ribofuranosyl-6-(4-hydroxy-3-methyl-but-2-enylamino)purine (zeatin riboside) and 9-[hexosyl(probably glucosyl)-beta-d-ribofuranosyl]-6-(4-hydroxy-3-methyl-but-2- enylamino)purine (a glycoside of zeatin riboside in which the glycosyl moiety is attached directly to the ribosyl moiety at an unknown position).

Spring shoot growth in douglas-fir may be initiated by gibberellins exported from the roots.

Trials conducted under controlled environments demonstrated that the delay of bud activity of Douglas-fir (Pseudotsuga menziesii) seedlings occasioned by low temperature of the soil could be eliminated by application of gibberellic acid. Analyses of field-grown plants showed a parallel increase in bud activity, level of gibberellin-like compounds in xylem sap, and soil temperature during February and March.

A diffusible auxin from Pinus radiata pollen and its possible role in stimulating ovule development.

Germinated pollen of Pinus radiata contains an auxin which is active in the Avena coleoptile test. It differs from all other hormones detected in pine pollen in that it is readily able to diffuse out from the pollen into an agar medium. It is suggested that, following pollination in vivo, the auxin may diffuse from the germinated pollen-tube onto the nucellus, thereby triggering the processes which allow ovule and gametophyte development to proceed. The auxin is water-soluble and may be an indole derivative.