Seasonal patterns of leaf photosynthetic and secondary xylem vascular traits in current-year stems of three Sorbus species with contrasting growth habits.

Seasonal effects of environmental variables on photosynthetic activity and secondary xylem formation provide data to demonstrate how environmental factors together with leaf ageing during the season control tree growth. In this study, we assessed physiological responses in photosynthetic behaviour to seasonal climate changes, and also identified seasonal differences in vascular traits within differentiating secondary xylem tissue from three diploid species of the taxonomically complex genus Sorbus. From sampling day 150, a clear physiological segregation of S. chamaemespilus from S. torminalis and S. aria was evident. The shrubby species S. chamaemespilus could be distinguished by a higher photosynthetic capacity between days 150 and 206. This was reflected in its associations with net CO2 assimilation rate (PN), maximum photochemical efficiency of PSII (F(v)/F(m)), variable-to-initial fluorescence ratio (F(v)/F(0)), potential electron acceptor capacity ('area') in multivariate space, and also its associations with log-transformed vessel area and log-transformed relative conductivity between days 239 and 268. The maximum segregation and differentiation among the examined Sorbus species was on sampling day 206. The largest differences between S. torminalis and S. aria were found on day 115, when the latter species clearly showed closer associations with high values of vessel density and transpiration (E). Sampling day clusters were arranged along an arch-like gradient that reflected the positioning of the entire growing season in multivariate space. This arch-like pattern was most apparent in the case of S. chamaemespilus, but was also observed in S. torminalis and S. aria.

Changes in leaf organisation, photosynthetic performance and wood formation during ex vitro acclimatisation of black mulberry (Morus nigra L.).

Changes in anatomical organisation of the leaf, photosynthetic performance and wood formation were examined to evaluate the temporal and spatial patterns of acclimatisation of micropropagated slow-growing black mulberry (Morus nigra L.) plantlets to the ex vitro environment. Leaf structure differentiation, the rates of net photosynthesis (P(n)), transpiration (E) and stomatal conductance (g(s)), and secondary xylem growth were determined in the course of a 56-day acclimatisation. Differentiation of palisade parenchyma was observed 7 days after transfer. At this stage, the rates of P(n), E and g(s) reached maximum values, after which the rates of all three gas exchange parameters gradually decreased. The highest proportion of woody area occupied by vessels was also observed 7 days after transfer. An important feature of developing woody tissue is the difference in patterns of vessel distribution from the characteristic differentiation patterns of earlywood and latewood vessels in mature wood of ring-porous trees. Vessels with lumen areas over 3000 microm(2) were only differentiated in acclimatised plantlets, whereas vessels in stems sampled on days 0 and 7 had very small lumen areas of up to 560 microm(2). Full acclimatisation, observed 56 days after transfer to the ex vitro environment, was associated with the rapid growth of new in vivo formed leaves, very low rates of E and g(s), and much increased secondary xylem tissue within the stem area.

Micropropagation of mature wych elm (Ulmus glabra Huds.).

Explants of mature vigorous donor trees of wych elm ( Ulmus glabra Huds.) that had not been previously exposed to Dutch elm disease were investigated for the influence of phytohormones and media on shoot multiplication rates and organogenic capacity. The regenerates were micropropagated from cultures that originated from 15-year-old progeny of plus trees. Two plus trees aged over 70 years showed recalcitrant responses. Thidiazuron in combination with 6-benzylaminopurine (BAP) induced a significantly higher number of shoots per explant than the most optimal BAP treatment (5.88 vs. 3.05 shoots). Woody plant medium and Dubovský minimal medium had no significant effects on shoot formation and multiplication rates. All plantlets raised in vitro were phenotypically normal and successfully hardened to ex vitro conditions. Two experimental field plots with 3-year-old in vitro-propagated trees were established.

Regeneration of Acer caudatifolium Hayata plantlets from juvenile explants.

Juvenile and fully mature Acer caudatifolium Hayata explants were assayed for their organogenic capacity. A protocol for multiple shoot culture formation and in vitro plant regeneration was developed for juvenile axillary bud cultures. Mature explants failed in shoot regeneration. Shoot multiplication was achieved by releasing apical dominance of the single elongated shoot on woody plant medium (WPM) supplemented with 0.7 mg l(-1) 6-benzylaminopurine and 0.05 mg l(-1) alpha-naphthaleneacetic acid. The highest rooting percentage was recorded on half-strength WPM containing 1.0 mg l(-1) indole-3-butyric acid. Regenerated plantlets were successfully hardened to ex vitro conditions and continued to grow after transfer to soil. No morphological aberrations were observed in the regenerates.