The effects of soil salt-alkaline (SA) stress on leaf physiological processes are well studied in the laboratory, but less is known about their effect on leaf, bark and branch chlorenchyma and no reports exist on their effect on C 4 enzymes in field conditions. Our results demonstrated that activities of C 4 enzymes, such as phospholenolpyruvate carboxylase (PEPC), NADP-malic enzyme (NADP-ME), pyruvate orthophosphate dikinase (PPDK), and NADP-dependent malate dehydrogenase (NADP-MDH), could also be regulated by soil salinity/alkalinity in poplar (Populus alba × P. berolinensis) trees, similarly as the already documented changes in activities of antioxidative enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione reductase (GR), pigment composition, photosynthesis, and respiration. However, compared with 50-90% changes in a leaf and young branch chlorenchyma, much smaller changes in malondialdehyde (MDA), antioxidative enzymes, and C 4 enzymatic activities were observed in bark chlorenchyma, showing that the effect of soil salinity/alkalinity on enzymatic activities was organ-dependent. This suggests that C 4 enzymatic ratios between nonleaf chlorenchyma and leaf (the commonly used parameter to discern the operation of the C 4 photosynthetic pathway in nonleaf chlorenchyma), were dependent on SA stress. Moreover, much smaller enhancement of these ratios was seen in an improved soil contrary to SA soil, when the fresh mass (FM) was used as the unit compared with a calculation on a chlorophyll (Chl) unit. An identification of the C 4 photosynthesis pathway via C 4 enzyme difference between chlorenchyma and leaf should take this environmental regulation and unit-based difference into account.

A stem-girdling experiment was carried out on an evergreen conifer, the Korean pine (Pinus koraiensis Sieb. et Zucc.), in mid summer in Northeast China. A 50 % higher respiration rate at the upper part of the stem was observed 3 d after stem girdling, and a stable higher rate (1.2-2.8 times) one week later. However, no higher soluble sugar or starch contents were found in the upper bark of the girdled stems in measurements over three weeks. These findings indicate that most of the newly-formed photosynthates were consumed by the high respiratory activity; this is also implied by the strong correlation between the photosynthetic photon flux over the canopy (PPF) and respiration at the upper parts of girdled stems. Moreover, the maximum PPF and cumulative PPF one day before measurement (PPFmax-Y and CPPF-Y, respectively) were closely correlated with the respiratory difference between the upper and the lower parts, but no such correlation was found with the instantaneous PPF (PPF-I) and cumulative PPF on the current day from sunrise to measured time point (CPPF-C). This shows that photosynthates newly formed by canopy needles need at least one day for transportation in order to increase the stem respiration at tree breast height.Additional key words: long-distance transport; photosynthetic photon flux; seasonal course; soluble sugar; starch.--Photosynthates are utilized mainly for synthesis of new organs, maintenance of the plant body, defence, and supporting symbiotic micro-organisms (Chapin et al. 1990). An important effect of tree-girdling is to stop the flow of newly-formed photosynthates to the lower part of the girdled stem; girdling can therefore be used to distinguish between the roles of newly-formed and stored photosynthates in respiration from stems and roots (Högberg et al. 2001). The issues are: how much of the newly-formed photosynthates from canopy photosynthesis are consumed in the enhanced respiratory activity resulting from girdling; and what is the functional difference between stored and newly-formed photosynthates in respiratory activity? From the girdling technique together with gas exchange measurements and photosynthate analysis, these questions may be answered.Newly-formed photosynthates deriving from the canopy are determined by the total photosynthetic photon flux (PPF) impinging on a plant. If newly-formed photosynthates are more important for respiration (Högberg et al. 2001), the photosynthetic photon flux (PPF) will positively correlate with the respiratory differences between the upper and the lower parts of girdled stems. Moreover, long-distance transport of photosynthates from the canopy to low stems will take time, which will be observable in the processes of symplasmic and apoplasmic ---

Plantlet regeneration through shoot formation from young leaf explant-derived callus of Camptotheca acuminata is described. Calli were obtained by placing leaf explants on Woody plant medium (WPM) supplemented with various concentrations of 6-benzyladenine (BA) and naphthaleneacetic acid (NAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Callus induction was observed in all media evaluated. On the shoot induction medium, the callus induced on the WPM medium containing 19.8 µM BA and 5.8 µM NAA was the most effective, providing high shoot regeneration frequency (70.3 %) as well as the highest number of shoots (11.2 shoots explant -1 ). The good rooting percentage and root quality (98 %, 5.9 roots shoot -1 ) were achieved on WPM medium supplemented with 9.6 µM indole-3-butyric acid (IBA). 96 % of the in vitro rooted plantlets with well developed shoots and roots survived transfer to soil.