Differences in regulation of carbohydrate metabolism during early fruit development between domesticated tomato and two wild relatives

Early development and growth of fruit in the domesticated tomato Solanum lycopersicum cultivar Money Maker and two of its wild relatives, S. peruvianum LA0385 and S. habrochaites LA1777, were studied. Although small differences exist, the processes involved and the sequence of events in fruit development are similar in all three species. The growth of developing fruits is exponential and the relative growth rate accelerates from 5 days after pollination (DAP 5) to DAP 8, followed by a decline during further development. Growth is positively correlated to the standard ¿Brix plus starch¿¿ in the period DAP 8¿DAP 20. Carbohydrate composition and levels of sugars and organic acids differ in fruits of the wild accessions compared to domesticated tomato. The wild accessions accumulate sucrose instead of glucose and fructose, and ripe fruits contain higher levels of malate and citrate. The enzymes responsible for the accumulation of glucose and fructose in domesticated tomatoes are soluble invertase and sucrose synthase. The regulation of initial carbohydrate metabolism in the domesticated tomato differs from that in the wild species, as could be concluded from measuring activities of enzymes involved in primary carbohydrate metabolism. Furthermore, changes in the activity of several enzymes, e.g., cell wall invertase, soluble invertase, fructokinase and phosphoglucomutase, could be attributed to changes in gene expression level. For other enzymes, additional control mechanisms play a role in the developing tomato fruits. Localization by in-situ activity staining of enzymes showed comparable results for fruits of domesticated tomato and the wild accessions. However, in the pericarp of S. peruvianum, less activity staining of phosphogluco-isomerase, phosphoglucomutase and UDP-glucosepyrophosphorylase was observed

In situ analysis of enzymes involved in sucrose to hexose-phosphate conversion during stolon-to-tuber transition of potato

An in situ study of enzymes involved in sucrose to hexose-phosphate conversion during in vitro stolon-to-tuber transition of potato (Solanum tuberosum L. cv. Bintje) was employed to follow developmental changes in spatial patterns. In situ activity of the respective enzymes was visualized by specific activity-staining techniques and they revealed distinct spatially and developmentally regulated patterns. Two of the enzymes studied were also subject to in situ investigations at the transcriptional level. During the stages of stolon formation high hexokinase (EC 2.7.1.1) and acid (cell wall-bound) invertase (EC 3.2.1.26) activities were restricted to the mitotically active (sub)apical region, suggesting a possible importance of these enzymes for cell division. At the onset of tuberization sucrose synthase (EC 2.4.1.13) and fructokinase (EC 2.7.1.4) were strongly induced (visualized at transcriptional and translational level) and the acid invertase activities disappeared from the swelling subapical region as expected. The high degree of similarity in the spatial pattern and the temporal induction of sucrose synthase and fructokinase suggests a tightly co-ordinated coarse (up)regulation, which may be subject to a sugar-modulated mechanism(s) by which genes involved in the metabolic sucrose-starch converting potential are co-ordinately regulated during tuber growth. The overall activity of uridine-5-diphosphoglucose pyrophosphorylase (EC 2.7.7.9) was present in all tissues during stolon and tuber development, implying that its coarse control is not subject to (in)direct developmental regulation

Developmental changes in enzymes involved in the conversion of hexose phosphate and its subsequent metabolites during early tuberization of potato

A highly synchronized in vitro tuberization system, based on single-node cuttings containing an axillary bud, was used to investigate the activity patterns of enzymes involved in the conversion of hexose phosphates and related products during stolon-to-tuber transition of potato (Solanum tuberosum L.). At tuberization the activity of enzymes involved in glycolysis and the oxidative pentose phosphate pathway (OPPP) showed a small but clear increase. This increase reflects a higher capacity of respiratory(-related) metabolism, presumably due to the onset of rapid cell division in the apical part of the tuberizing stolon. During the phase of successive tuber growth these enzymes decreased in activity, suggesting that the concomitant massive starch accumulation is not accompanied by a large increase in respiration. A high degree of positive correlation between the activities of these enzymes could be observed, implying that the level of respiratory metabolism-related enzymes is co-ordinately regulated by the same mechanism of coarse control. The activity pattern of pyrophosphate:fructose-6-phosphate phosphotransferase (PFP) showed no developmental change and does not resemble the activity pattern of the enzymes participating in respiratory(-related) metabolism. Instead, its level of activity is very likely the result of metabolic regulation. The level of the content of the metabolites UDP-glucose (UDPGlc) and glucose-6-phosphate (Glc6P) decreased after the onset of tuberization. This decline indicates that tuber induction is not accompanied by an appreciable increase in the level of the cytosolic hexose phosphate (hexose-P) content but that it rather remains on a low level, which might be a prerequisite in order to maintain a high net rate of sucrose degradation during tuber development. In contrast to UDPGlc and Glc6P, the content of fructose-1,6-bisphosphate (Fru1,6bisP) showed an increase after tuber induction. The overall activities of ADP-glucose pyrophosphorylase (AGPase) and starch phosphorylase (STP) both showed a large increase after tuber initiation, which is consistent with their presumed role in the process of starch synthesis and accumulation during rapid tuber growth

Functional genomic analysis of potato tuber life-cycle

Potato tuber life-cycle is composed of many individual developmental stages including tuber formation, tuber development, dormancy and sprouting. We have used cDNA-AFLP fingerprinting to analyse gene expression in 24 individual stages of development, over the period from stolon formation through sprouting. In addition to these developmental stages, different tissues were analysed to assess tissue specificity and various controls were incorporated to determine process specificity. In total around 18000 transcript derived cDNA fragments (TDFs) were visualised from which circa 2600 were included in a statistical analysis allowing general conclusions about gene expression during development. More than 200 process specific TDFs were isolated and sequenced throughout the potato tuber life-cycle. The sequence similarities of these TDFs to known genes give an insight into the kinds of processes occurring during tuberisation, dormancy and sprouting