Contour ? Figure4 cuatro reveals the changes in AsA

_t content of source leaves of potato plants acclimatised for 14 days in cabinets with artificial diurnal dark/light cycles. The cabinets were off-phased so that plants at different stages in their lighting regime were available at any given time. The AsA_t content of source leaves was monitored for dos4 h in plants sampled simultaneously from the two cabinets. At the end of the dark phase, leaf AsA_t content was approximately 12 mg/100 gFW and it progressively increased following artificial sunrise. After 10 h of light, the leaf AsA_t content increased to approximately 30 mg/100 gFW after which it leveled off. Following artificial sunset the AsA_t level gradually fell back to approximately 12 mg/100 gFW within 6–10 h.

Changes in AsA_t content of potato leaves as a function of light. Environment chambers were on a 10 h dark – 14 h light cycle as indicated by the brown and yellow panels respectively. At the times shown, source leaves (leaves on the lower four nodes tagged of each stem) were removed from each of three plants, ground in liquid nitrogen and extracted in 5% MPA, 5 mM TCEP (9:1 v/w) prior to quantification by HPLC. Values are represented as mean ± SE, n = 3.

Glasshouse adult herbs have been transferred to from-phased regulated ecosystem compartments (boards An excellent and you will B) 2 weeks before the beginning of the check out

Table ? Table1 1 shows the AsA_t content of source leaves and tuberising stolons collected at h from the light-phase or dark-phase plants (after collection of phloem exudate for 90 min in a prehumidified atmosphere in leaves). In the table are also reported the chromatographic AsA_t peak areas from phloem exudates collected from source leaves and tuberising stolons of the same plants. The exudate data are reported as peak areas as the exact volume of exudate collected could not be established. Whilst the leaves from light-phase plants contained over twice the AsA_t level of leaves from dark-phase plants, no significant difference was found in the AsA_t content of tuberising stolons from the two sets of plants. The AsA_t peak area in chromatograms of light-phase leaf exudates was 1.8-fold larger than that obtained from dark-phase leaves. In tuberising stolons the increase in exudate peak area was more pronounced (4.6-fold).

Table step 1

Glasshouse grown plants were transferred to off-phased controlled environment chambers 14 days prior to the start of the experiment. Environment chambers were on a 10 h dark – 14 h light cycle (see Fig. 4). At h source leaves and tuberising stolons were removed from 3 plants and a sub-sample used for tissue AsA_t quantification. For the determination of AsA_t in leaf phloem exudates, petioles were re-cut under water and placed into EDTA or CaCl₂ exudation buffer for 90 min in a prehumidified chamber in the dark. For determination of stolon phloem exudates the cut end of the stolon attached to the plant was re-cut under water and placed in the appropriate exudation solution. Values are represented as mean ± SE, n = 6. mAUt = milli absorbance units (?245 nm) ? time.

The correlation between leaf AsA_t content and the AsA_t levels of phloem exudates was also investigated in glasshouse-grown plants following the supply of a range of AsA biosynthetic precursors using the flap technique . Figure ? Figure5 5 shows the chromatographic AsA_t peak area of exudates from leaves pre-treated for 24 h with 20 mM MES pH 5.5, 2 mM CaCl₂ alone (control) or containing precursors at a final concentration of 25 mM. Incubation with D -glucose ( D -Glc) resulted in a slight (10%) reduction in leaf AsA_t content compared with the control but no significant change in AsA_t was detected in the exudates. By contrast, supply of L -galactose ( L -Gal) or L -galactono-1,4-lactone ( L -GalL) increased the AsA_t content of leaves (4.9 and 6.2-fold respectively) and, more substantially, of exudates (10.8 and 11.2-fold respectively). With all treatments, the replacement of EDTA with CaCl₂ in collection wells resulted in a significant reduction of AsA_t peak area in the exudate chromatograms.