Veerle Verdoodt

Changes in sugar content and fatty acid composition of in vitro sugar beet shoots after cold acclimation: influence on survival after cryopreservation

To cryopreserve sugar beet shoot tips using an encapsulation-dehydration technique, cold hardening of in vitro plants was needed to obtain high survival rates after freezing. Cold acclimation not only enhanced dehydration and freezing tolerance, but also induced several changes in sugar beet shoots. Plants contained greater amounts of sucrose, D-glucose and D-fructose and the fatty acid composition of lipids changed. Furthermore, the unsaturation level of membrane lipids, estimated by the (C18:2 + C18:1)/C16:0 ratio, increased after cold hardening. These changes were correlated with better survival rates after cryopreservation.

Impact of developmental stage on CAM expression and growth in an Aechmea hybrid under greenhouse conditions

Summary Besides environmental factors, expression of crassulacean acid metabolism (CAM) and the related production of malic acid may depend on plant developmental stage. This topic has not yet been investigated under commercial greenhouse conditions. In CAM plant cultivation, malic acid is a central determinant of plant growth, but can also cause physiological leaf damage problems. Here, we present data on diurnal leaf malic acid contents, relative water content dynamics, and measurements of growth at four stages of the plant growth cycle (i.e., ex vitro-acclimated plantlets, 6-month, 12-month, and 18-month-old plants) of Aechmea ‘Maya’. The results obtained showed that Aechmea ‘Maya’ was an obligate CAM plant at all developmental stages during cultivation. Nevertheless, there was some developmental control on the expression of CAM. Under the same environmental conditions, 6-month-old plants accumulated significantly higher amounts of malic acid in their leaves, thus supporting higher growth rates, than in the other growth stages. This larger malic acid pool implied a higher risk of physiological leaf damage, but since remobilisation of malic acid in the early morning remained unaffected during growth, physiological leaf damage might occur throughout vegetative growth.

Interaction between physiological age and cold treatment on the composition and concentration of carbohydrates in chicory roots (Cichorium intybus L.)

Summary The concentration of free sugars (glucose, fructose and sucrose) and inulin was measured in chicory roots (Cichorium intybus L. var. foliosum cv. Flash) during two growing seasons. Roots were harvested approximately every 2 weeks between June and October. They were either used immediately for sugar analysis or after a cold treatment. After the final harvest, samples were taken during the whole storage period of several months. The evolution pattern of free sugars and inulin during the growing season was very similar to previously reported data. When the long storage period after the vegetative growing year was considered, the changes in free sucrose (increase), and inulin bound glucose and fructose (decrease) mainly occurred at the first 60 days of storage. The apex was not necessary for perception of the cold signal. From the start of the growing season, cold treatment caused a strong decrease in free glucose and increases in free fructose and sucrose. Thus, still very young roots reacted to cold treatment by hydrolysis of inulin. Even at this young stage, the apex was not necessary for perception of the cold signal.

Physiological responses by Billbergia zebrina (Bromeliaceae) when grown under controlled microenvironmental conditions

Sucrose, the most commonly used carbon source in conventional in vitro culture, and limited air exchange in the culture containers are factors that affect the growth of in vitro-cultured plants. They may induce physiological disorders and decrease the survival rate of plants after transfer to ex vitro conditions. The aim of the present study was to analyze the effects of gas exchange and sucrose concentration on Billbergia zebrina plantlets during in vitro propagation. In vitro-established B. zebrina plantlets were transferred to culture media containing 0, 15, 30, 45, or 60 g L-1 sucrose. Two different culture-container sealing systems were compared: lids with a filter (permitting gas exchange) and lids with no filter (blocking fluent gas exchange). Carbohydrate and chlorophyll (Chl a+b) concentrations were analyzed in plantlets at 45-days of culture. The addition of sucrose to the medium reduced the Chl a+b concentration in the plantlets. On the other hand, additional sucrose had a positive effect on the carbohydrate stock formation of the plantlets. The results showed that a photoautotrophic system (air exchange and a sugar-free medium) improves the in vitro propagation of B. zebrina without creating physiological disorders. Key words: Bromeliad, In vitro plant, photoautotrophic growth, physiological disorders, sucrose.