Maria Laura Traversi

Intra-annual dynamics of non-structural carbohydrates in the cambium of mature conifer trees reflects radial growth demands

The presence of soluble carbohydrates in the cambial zone, either from sugars recently produced during photosynthesis or from starch remobilized from storage organs, is necessary for radial tree growth. However, considerable uncertainties on carbohydrate dynamics and the consequences on tree productivity exist. This study aims to better understand the variation in different carbon pools at intra-annual resolution by quantifying how cambial zone sugar and starch concentrations fluctuate over the season and in relation to cambial phenology. A comparison between two physiologically different species growing at the same site, i.e., the evergreen Picea abies Karst. and the deciduous Larix decidua Mill., and between L. decidua from two contrasting elevations, is presented to identify mechanisms of growth limitation. Results indicate that the annual cycle of sugar concentration within the cambial zone is coupled to the process of wood formation. The highest sugar concentration is observed when the number of cells in secondary wall formation and lignification stages is at a maximum, subsequent to most radial growth. Starch disappears in winter, while other freeze-resistant non-structural carbohydrates (NSCs) increase. Slight differences in NSC concentration between species are consistent with the differing climate sensitivity of the evergreen and deciduous species investigated. The general absence of differences between elevations suggests that the cambial activity of trees growing at the treeline was not limited by the availability of carbohydrates at the cambial zone but instead by environmental controls on the growing season duration.

Responses to changes in Ca2+ supply in two Mediterranean evergreens, Phillyrea latifolia and Pistacia lentiscus, during salinity stress and subsequent relief.

BACKGROUND AND AIMS Changes in root-zone Ca(2+) concentration affect a plants performance under high salinity, an issue poorly investigated for Mediterranean xerophytes, which may suffer from transient root-zone salinity stress in calcareous soils. It was hypothesized that high-Ca(2+) supply may affect differentially the response to salinity stress of species differing in their strategy of Na(+) allocation at organ level. Phillyrea latifolia and Pistacia lentiscus, which have been reported to greatly differ for Na(+) uptake and transport rates to the leaves, were studied. Methods In plants exposed to 0 mM or 200 mM NaCl and supplied with 2.0 mM or 8.0 mM Ca(2+), under 100 % solar irradiance, measurements were conducted of (a) gas exchange, PSII photochemistry and plant growth; (b) water and ionic relations; (c) the activity of superoxide dismutase and the lipid peroxidation; and (d) the concentration of individual polyphenols. Gas exchange and plant growth were also estimated during a period of relief from salinity stress. Key Results The performance of Pistacia lentiscus decreased to a significantly smaller degree than that of Phillyrea latifolia because of high salinity. Ameliorative effects of high-Ca(2+) supply were more evident in Phillyrea latifolia than in Pistacia lentiscus. High-Ca(2+) reduced steeply the Na(+) transport to the leaves in salt-treated Phillyrea latifolia, and allowed a faster recovery of gas exchange and growth rates as compared with low-Ca(2+) plants, during the period of relief from salinity. Salt-induced biochemical adjustments, mostly devoted to counter salt-induced oxidative damage, were greater in Phillyrea latifolia than in Pistacia lentiscus. CONCLUSIONS An increased Ca(2+) : Na(+) ratio may be of greater benefit for Phillyrea latifolia than for Pistacia lentiscus, as in the former, adaptive mechanisms to high root-zone salinity are primarily devoted to restrict the accumulation of potentially toxic ions in sensitive shoot organs.

Chlorophyll Fluorescence Imaging for the Noninvasive Assessment of Anthocyanins in Whole Grape (Vitis vinifera L.) Bunches

The distribution of anthocyanins in grape (Vitis vinifera L.) bunches from the Sangiovese cultivar was measured nondestructively by chlorophyll fluorescence imaging using two excitation light bands at 550 and 650 nm in sequence. The pixel intensity in the derived logarithm of the fluorescence excitation ratio image was directly related, by an exponential function (r2 = 0.93), to the anthocyanin concentration of berry extracts. The method will be useful for the assessment of the heterogeneity of anthocyanin accumulation in berries that is known to depend on physiologic and climatic factors. It can also represent a new, rapid and noninvasive technique for the assessment of grape ripening and the appropriate time of harvest.

Do tree-ring traits reflect different water deficit responses in young poplar clones (Populus × canadensis Mönch ‘I-214’ and P. deltoides ‘Dvina’)?

Poplar clones are known to display a wide range of tolerance to drought and water-use efficiency, but the effects of water deficit on stem growth and tree-ring characteristics are rarely taken into account. This study was conducted in order to investigate whether the main tree-ring traits correlate with irrigation regimes during the growing season in ‘I-214’ and ‘Dvina’ 4-year-old poplar clone saplings grown in concrete tanks, during three consecutive years. Total carbon, stable carbon isotope, Klason lignin and α-cellulose contents were analyzed to characterize wood biochemistry; ring width, wood density, mean vessel density and mean vessel lumen area were analyzed to characterize wood anatomy to assess the influence of irrigation regime. In both clones, wood formed in 2005 was more enriched in 13C, suggesting drought-induced stomatal closure. Wood formed in 2006 was less variable in δ13C in relation to irrigation regimes. ‘Dvina’ showed higher Klason lignin content and wood density than ‘I-214’, whatever the irrigation regime, despite the larger ring widths. ‘Dvina’ has the potential to recover promptly after drought stress, but at the expense of poor wood technological properties, while ‘I-214’ could continue to grow more uniformly under limited water availability, though at a lower rate.

Transcript Accumulation Dynamics of Phenylpropanoid Pathway Genes in the Maturing Xylem and Phloem of Picea abies during Latewood Formation

In temperate regions, latewood is produced when cambial activity declines with the approach of autumnal dormancy. The understanding of the temporal (cambium activity vs dormancy) and spatial (phloem, cambial region, maturing xylem) regulation of key genes involved in the phenylpropanoid pathway during latewood formation represents a crucial step towards providing new insights into the molecular basis of xylogenesis. In this study, the temporal pattern of transcript accumulation of 12 phenylpropanoid genes (PAL1, C4H3/5, C4H4, 4CL3, 4CL4, HCT1, C3H3, CCoAOMT1, COMT2, COMT5, CCR2) was analyzed in maturing xylem and phloem of Picea abies during latewood formation. Quantitative reverse transcription-polymerase chain reaction analyses revealed a well-defined RNA accumulation pattern of genes involved in the phenylpropanoid pathway during latewood formation. Differences in the RNA accumulation patterns were detected between the different tissue types analyzed. The results obtained here demonstrated that the molecular processes involved in monolignol biosynthesis are not restricted to the cambial activity timeframe but continued after the end of cambium cell proliferation. Furthermore, since it has been shown that lignification of maturing xylem takes place in late autumn, we argue on the basis of our data that phloem could play a key role in the monolignol biosynthesis process.

Effect of Water Deficit on Expression of Stress-related Genes in the Cambial Region of Two Contrasting Poplar Clones

In this study we investigated the effect of prolonged water shortage in the cambial region of two poplar clones, Dvina (Populus deltoides) and I-214 (Populus x canadensis) that differ in their response to water deficit. For this purpose we monitored growth parameters in Dvina and I-214 plants under well-watered and water-stress conditions and after rewatering and analyzed the content of malondialdehyde (MDA) and proline and the expression level of genes coding for antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; ascorbate peroxidase, APX; glutathione reductase, GR) and metallothioneins (MT) by quantitative real-time RT-PCR (RT-qPCR). Water deficit resulted in a significant increase of osmotically active solutes in both clones. No significant increase of MDA level was observed in Dvina, whereas a significant enhancement of lipid peroxidation was detected in I-214, in which also a strong fivefold increase of proline was detected. Transcript analysis of stress-related genes indicated a different ability of the two clones to modulate antioxidant genes under stress. In particular, MT3b was strongly upregulated by water deficit in Dvina thus suggesting an important role for this gene in the maintenance of cellular redox homeostasis in the clone. On the whole, the two clones exhibited changes at the transcription and physiological levels in the cambial region that suggest the occurrence of different strategies of plant protection from prolonged water deficit.

Can sugar metabolism in the cambial region explain the water deficit tolerance in poplar

In two poplar species with contrasting growth performance, sugar metabolism in xylem and cambial regions can explain their different grades of tolerance to drought and their recovery rates following water deficits.