Metrosideros polymorpha, a dominant tree species in Hawaiian ecosystems, occupies a wide range of habitats. Complementary field and common-garden studies of M. polymorpha populations were conducted across an altitudinal gradient at two different substrate ages to ascertain if the large phenotypic variation of this species is determined by genetic differences or by phenotypic modifications resulting from environmental conditions. Several characteristics, including ecophysiological behavior and anatomical features, were largely induced by the environment. However, other characteristics, particularly leaf morphology, appeared to be mainly determined by genetic background. Common garden plants exhibited higher average rates of net assimilation (5.8 μmol CO m s) and higher average stomatal conductance (0.18 mol HO m s) than their field counterparts (3.0 μmol CO m s, and 0.13 mol HO m s respectively). Foliar δC of most common-garden plants was similar among sites of origin with an average value of -26.9‰. In contrast, mean values of foliar δC in field plants increased substantially from -29.5‰ at low elevation to -24.8‰ at high elevation. Leaf mass per unit area increased significantly as a function of elevation in both field and common garden plants; however, the range of values was much narrower in common garden plants (211-308 g m for common garden versus 107-407 g m for field plants). Nitrogen content measured on a leaf area basis in common garden plants ranged from 1.4 g m to 2.4 g m and from 0.8 g m to 2.5 g m in field plants. Photosynthetic nitrogen use efficiency (PNUE) decreased 50% with increasing elevation in field plants and only 20% in plants from young substrates in the common garden. This was a result of higher rates of net CO assimilation in the common garden plants. Leaf tissue and cell layer thickness, and degree of leaf pubescence increased significantly with elevation in field plants, whereas in common garden plants, variation with elevation of origin was much narrower, or was entirely absent. Morphological characteristics such as leaf size, petiole length, and internode length decreased with increasing elevation in the field and were retained when grown in the common garden, suggesting a potential genetic basis for these traits. The combination of environmentally induced variability in physiological and anatomical characteristics and genetically determined variation in morphological traits allows Hawaiian M. polymorpha to attain and dominate an extremely wide ecological distribution not observed in other tree species.

The rise of sap in mangroves has puzzled plant physiologists for many decades. The current consensus is that negative pressures in the xylem exist which are sufficiently high to exceed the osmotic pressure of seawater (2.5 MPa). This implies that the radial reflection coefficients of the mangrove roots are equal to unity. However, direct pressure probe measurements in xylem vessels of the roots and stems of mangrove (Rhizophora mangle) grown in the laboratory or in the field yielded below‐atmospheric, positive (absolute) pressure values. Slightly negative pressure values were recorded only occasionally. Xylem pressure did not change significantly when the plants were transferred from tap water to solutions containing up to 1700 mOsmol kg−1 NaCl. This indicates that the radial reflection coefficient of the roots for salt, and therefore the effective osmotic pressure of the external solution, was essentially zero as already reported for other halophytes. The low values of xylem tension measured with the xylem pressure probe were consistent with previously published data obtained using the vacuum/leafy twig technique. Values of xylem tension determined with these two methods were nearly two orders of magnitude smaller than those estimated for mangrove using the pressure chamber technique (−3 to −6MPa). Xylem pressure probe measurements and staining experiments with alcian blue and other dyes gave strong evidence that the xylem vessels contained viscous, mucilage‐ and/or protein‐related compounds. Production of these compounds resulting from wound or other artifactual reactions was excluded. The very low sap flow rates of about 20–50 cm h−1 measured in these mangrove plants were consistent with the presence of high molecular weight polymeric substances in the xylem sap. The presence of viscous substances in the xylem sap of mangroves has the following implications for traditional xylem pressure measurement techniques, development of xylem tension, and longdistance water transport: (1) high external balancing pressures in the pressure chamber are needed to force xylem sap to the cut surface of the twig; (2) stable tensions much larger than 0.1 MPa can be developed only occasionally because viscous solutions provide nucleation sites for gas bubble formation; (3) the frequent presence of small gas bubbles in viscous solutions allows water transport by interfacial, gravity‐independent streaming at gas/water interfaces and (4) the increased density of viscous solutions creates (gravity‐dependent) convectional flows. Density‐driven convectional flows and interfacial streaming, but also the very low radial reflection coefficient of the roots to NaCl are apparently the means by which R. mangle maintains water transport to its leaves despite the high salinity of the environment.

Cyclic nucleotide gated channels (CNGCs) that are regulated by calmodulin (CaM) have been shown to play essential roles in signal transduction, metabolism, and growth in animals. By contrast, very little is known about the subcellular location and the function of these channels in plants. Here we report on the effects of antisense suppression of the expression of AtCNGC10, a putative K+ channel, and the immunolocalization of the protein using an AtCNGC10-specific antiserum. In Arabidopsis thaliana leaves, AtCNGC10 was localized to the plasma membrane of mesophyll and parenchyma cells. Antisense AtCNGC10 plants had 40% of the AtCNGC10 mRNA levels and virtually undetectable protein levels relative to wild type plants. Antisense expression of AtCNGC10 did not affect the mRNA levels of AtCNGC13, the most closely related CNGC family member in the genome. Relative to wild type Columbia, antisense AtCNGC10 plants flowered 10 days earlier, and had a 25% reduction in leaf surface area, thickness and palisade parenchyma cell length. Their roots responded more slowly to gravitropic changes and the chloroplasts accumulated more starch. We propose that AtCNGC10, through interactions with CaM and cGMP, modulates cellular K+ balance across the plasma membrane, and that perturbations of this K+ gradient affect numerous growth and developmental processes.

The ontogenetic course followed by somatic embryos of interior spruce is highly dependent on the media concentration of abscisic acid (ABA). Little or no organized development occurs in the absence of ABA and as the level of ABA is increased, a range of embryo types is produced. “Shooty embryo” structures predominate in many callus lines at low levels of ABA (1‐10 μM), while 10‐20 μM ABA promotes the formation of bipolar embryos that germinate precociously. When ABA is increased to 30‐40 μM, precocious germination is inhibited and opaque cotyledonary embryos characteristic of their zygotic counterparts are formed which enter a period of quiescence. Only “mature” somatic embryos contain significant amounts of storage proteins and the level to which these proteins accumulate is dependent on the concentration of ABA. Indole‐butyric acid (IBA) included with ABA increases the number of mature embryos. Root elongation, which was used as a measure of embryo quality, was never observed from shooty embryo Structures and was 2‐3 fold higher in mature embryos compared to those that germinated precociously.

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