The internal conductance from intercellular spaces to the sites of carboxylation ( g i ) has only been measured in a few tree species and not in conifers, despite the fact it may impose a large limitation on photosynthesis. The present study provides the first estimates of g i for a coniferous species, and examines variation in g i with height and its relationships to anatomical, biochemical and physiological traits. Measurements were made on upper and lower canopy current-year needles of 50-year-old Douglas-fir ( Pseudotsuga menziesii (Mirb.) Franco). Needle thickness and specific leaf area decreased by 30% from the top to bottom of the canopy. These anatomical/morphological changes were accompanied by modest variation in allocation of N to chlorophyll and the chlorophyll a / b ratio. Allocation of N to Rubisco did not vary with height, but the ratio of Rubisco to chlorophyll did owing to the aforementioned changes in allocation to chlorophyll. The value of g i was estimated in one tree from concurrent measurements of carbon isotope discrimination and net photosynthesis. To examine the variation in g i among trees a second independent method based on day respiration and the difference between the chloroplastic and intercellular photocompensation points (photocompensation point method) was used. Estimates of g i obtained by the two methods agreed well with values varying between 0.14 and 0.20 mol m ---. It is estimated that g i limits photosynthesis by approximately 20% as compared to an approximately 30% stomatal limitation (under well-watered conditions). The value of g i scaled approximately with maximum rates of photosynthesis, which were significantly greater in upper canopy needles. Nevertheless, g i did not vary significantly with canopy height, owing to greater variability in g i than photosynthesis.Key-words : carbon isotope discrimination; chlorophyll; internal resistance; needle anatomy; needle morphology; photocompensation point; photosynthesis; Rubisco.Abbreviations : A , rate of photosynthesis; a i , carbon isotope fractionation during diffusion/hydration into water; A n , rate of light-saturated photosynthesis measured at C a = 360 m mol mol -1 ; A pn , rate of photosynthesis assuming g i and g s are infinite (i.e. at a C c of 360 m mol mol -1 ); A on , rate of photosynthesis assuming infinite g i and g s as measured (i.e. at a C c = C i ); b , carbon isotope fraction due to Rubisco and PEP carboxylation; C a , ambient CO 2 concentration; C e , CO 2 concentration of air entering chamber; C i , intercellular CO 2 concentration; C i *, intercellular CO 2 concentration at which the chloroplastic CO 2 concentration = G *; C c , chloroplastic CO 2 concentration; D obs , observed carbon isotope discrimination; D i , carbon isotope discrimination estimated for a shoot with infinite transfer conductance; d o , carbon isotope discrimination of air leaving chamber without a shoot enclosed; d e , carbon isotope discrimination of air leaving chamber with a shoot enclosed; f , carbon isotope fractionat...

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Shoot tips from accessions of wild cherry (Prunus avium L.) selected from British woodland, and also the P. avium rootstock cvs. F12/1 and Charger, were successfully established in vitro, and most were easily micropropagated on Murashige and Skoog (MS)-based media. In one accession, adventitious shoots occasionally developed from the extrafioral nectaries positioned at the base of leaf petioles of the initial explants. Micropropagation of cv. Charger was improved by culture on a Quoirin and Lepoivre and Woody Plant-based medium, and by supplementing the medium with 1-phenyl-3-(1, 2, 3-thiadiazol-5yl)urea (thidiazuron). Poor shoot production by F12/1 on 1, 3, 5-trihydroxybenzene (phloroglucinol)-free media was not improved by up to 18 months of regular subculture. Study of cv. F12/1 showed that shoots produced on a MS-based medium with 1 mM phloroglucinol, 0.49 #M indolebutyric acid, 4.4 #M benzyladenine (BA) and 0.29 #M gibberellic acid (GA3), were easier to root over several subcultures than shoots produced on a similar medium with no GA3 and only 2.2 #M BA, but only in a rooting medium supplemented with 1 mM phloroglucinol.

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