Majken Pagter

Changes in carbohydrates, ABA and bark proteins during seasonal cold acclimation and deacclimation in Hydrangea species differing in cold hardiness

Cold injury is frequently seen in the commercially important shrub Hydrangea macrophylla but not in Hydrangea paniculata. Cold acclimation and deacclimation and associated physiological adaptations were investigated from late September 2006 to early May 2007 in stems of field-grown H. macrophylla ssp. macrophylla (Thunb.) Ser. cv. Blaumeise and H. paniculata Sieb. cv. Kyushu. Acclimation and deacclimation appeared approximately synchronized in the two species, but they differed significantly in levels of mid-winter cold hardiness, rates of acclimation and deacclimation and physiological traits conferring tolerance to freezing conditions. Accumulation patterns of sucrose and raffinose in stems paralleled fluctuations in cold hardiness in both species, but H. macrophylla additionally accumulated glucose and fructose during winter, indicating species-specific differences in carbohydrate metabolism. Protein profiles differed between H. macrophylla and H. paniculata, but distinct seasonal patterns associated with winter acclimation were observed in both species. In H. paniculata concurrent increases in xylem sap abscisic acid (ABA) concentrations ([ABA](xylem)) and freezing tolerance suggests an involvement of ABA in cold acclimation. In contrast, ABA from the root system was seemingly not involved in cold acclimation in H. macrophylla, suggesting that species-specific differences in cold hardiness may be related to differences in [ABA](xylem). In both species a significant increase in stem freezing tolerance appeared long after growth ceased, suggesting that cold acclimation is more regulated by temperature than by photoperiod.

Winter warming delays dormancy release, advances budburst, alters carbohydrate metabolism and reduces yield in a temperate shrub

Global climate models predict an increase in the mean surface air temperature, with a disproportionate increase during winter. This study documents that even a very modest temperature increase during the colder periods of a plants annual cycle may delay dormancy release and advance bud burst and flowering in blackcurrant, but the magnitude of the responses varies between genotypes differing in chilling requirement. Winter warming additionally has a large carryover effect into the growing season by reducing fruit yield the following summer.

Phenotypic differences in development of cold hardiness in three latitudinal populations of Acer platanoides L.

Abstract Variation in cold hardiness, assessed using the electrolyte leakage method, of three 6–7-year-old seedling populations of Acer platanoides (L.) originating from Sweden, Denmark and Germany (northern, central and southern population, respectively) was investigated in a Danish field trial during autumn and early winter. Simultaneously, autumnal changes in cold hardiness, stem water content and annual height growth were investigated in field-grown 3-year-old seedlings of the Danish population. The variation in cold hardiness among populations was structured as a moderate latitudinal cline, with the northern population cold acclimating earlier and/or faster than the other populations. Among the central and southern populations the latitudinal gradient was not apparent, resulting in approximately the same percentages of frost damage in the autumn. In early winter no differentiation in cold hardiness was observed among the three populations. In the Danish population cold acclimation was correlated with reduced water content and seedlings that grew longer in the autumn tended to dehydrate late. The results are discussed in relation to the transfer of A. platanoides seeds.

Metabolic fingerprinting of dormant and active flower primordia of Ribes nigrum using HR-MAS NMR

Global warming may modify the timing of dormancy release and spring growth of buds of temperate fruit crops. Environmental regulation of the activity-dormancy cycle in perennial plants remains poorly understood at the metabolic level. Especially, the fine-scale metabolic dynamics in the meristematic zone within buds has received little attention. In this work we performed metabolic profiling of intact floral primordia of Ribes nigrum isolated from buds differing in dormancy status using high-resolution magic angle spinning (HR-MAS) NMR. The technique proved useful in monitoring different groups of metabolites, e.g., carbohydrates and amino acids, in floral primordia and allowed metabolic separation of primordia from endo- and ecodormant buds. In addition, due to its nondestructive character, HR-MAS NMR may provide novel insights into cellular compartmentation of individual biomolecules that cannot be obtained using liquid-state NMR. Out results show that HR-MAS NMR may be an important method for metabolomics of intact plant structures.

Direct and indirect effects of shoot- and/or root-chilling stress ongrowth, photosynthesis, and osmotic root water uptake in Kalanchoe blossfeldiana Poelln. ‘Molly’

Summary Kalanchoe blossfeldiana is the most extensively cultivated flowering potted plant for indoor use in Europe, and it is also used outdoors as a patio and bedding plant. Increased chilling tolerance in K. blossfeldiana is desirable, as it would enhance the marketing potential for outdoor use and allow more energy-efficient greenhouse production. In this study, the effects of shoot-chilling, root-chilling, or whole plant-chilling (4°C/20°C, 20°C/4°C, or 4°C/4°C air temperature /root-zone temperature, respectively) on K. blossfeldiana Poelln. ‘Molly’ were compared in order to identify the most sensitive physiological processes related to the impairment of growth under low temperatures. As controls, plants were grown at 20°C/20°C. All three chilling treatments severely inhibited plant growth and decreased the net photosynthetic rate (Pn). Inhibition of Pn in root-chilled plants was due to stomatal closure, while in shootchilled plants it was related both to stomatal and non-stomatal effects. A low air temperature also caused the accumulation of soluble carbohydrates and cellular membrane damage in the leaves. Root- or whole plant-chilling significantly reduced the composite root hydraulic conductance (CRHC), whereas the decrease in osmotic root water uptake of shoot-chilled plants was unrelated to changes in CRHC. Impaired water uptake led to partial leaf wilting of root-chilled plants at 20°C/4°C. We conclude that the sensitivity of Kalanchoe to low temperatures is linked to both direct and indirect effects of shoot-and/or root-chilling on photosynthetic carbon metabolism and osmotic water uptake by the roots.