Sink Metabolism in Tomato Fruit

Abstract

Fruit of domesticated tomato (Lycopersicon esculentum) accumulate primarily glucose and fructose, whereas some wild tomato species, including Lycopersicon chmielewskii, accumulate sucrose. Genetic analysis of progeny resulting from a cross between L. chmielewskii and L. esculentum indicated that the sucrose-accumulating trait could be stably transferred and that the trait was controlled by the action of one or two recessive genes. Biochemical analysis of progeny resulting from this cross indicated that the sucrose-accumulating trait was associated with greatly reduced levels of acid invertase, but normal levels of sucrose synthase. Invertase from hexose-accumulating fruit was purified and could be resolved into three isoforms by chromatofocusing, each with isoelectric points between 5.1 and 5.5. The invertase isoforms showed identical polypeptide profiles on sodium dodecyl sulfate polyacrylamide gel electrophoresis, consisting of a primary 52 kilodalton polypeptide and two lower molecular mass polypeptides that appear to be degradation products of the 52 kilodalton polypeptide. The three invertase isoforms were indistinguishable based on pH, temperature, and substrate concentration dependence. Immunological detection of invertase indicated that the low level of invertase in sucrose-accumulating fruit was due to low levels of invertase protein rather than the presence of an invertase inhibitor. Based on comparison of genetic and biochemical data we speculate that a gene either encoding tomato fruit acid invertase or one required for its expression, plays an important role in determining sucrose accumulation. In addition, sucrose is metabolically less active than hexose (24) and may be less accessible for loss through respiration, contributing to higher levels of accumulation. It is significant to note that storage organs accumulating very high levels of sugars do so by accumulating sucrose (6,7,13,27 Sugar DeterminationFor sugar determination, 3 g of tissue was ground with a polytron in cold 80% ethanol and boiled twice for 20 min in a water bath. After each boiling, samples were centrifuged 10 min at 10,000 rpm, the supernatants pooled and brought to a final volume of 20 mL with 80% ethanol. Total reducing sugars were measured using Nelson's arsenomolybdate reagent (23). To determine sucrose concentration, samples were incubated with yeast invertase (Sigma) and total reducing sugar was determined as described above. Sucrose levels were inferred by the difference in reducing sugar levels assayed with and without invertase treatment. The validity of this technique was confirmed by HPLC analysis of sugar composition in some samples. Extraction and Purification of InvertaseSix hundred grams of fresh ripe tomato pericarp tissue was homogenized in 400 mL of 10 mM Na citrate buffer (pH 4.5) containing 5 mM f3-mercaptoethanol and 0.5% soluble PVP. The homogenate was centrifuged at 10,000 rpm for 30 min and the pellet washed in extraction buffer (without PVP) and recentrifuged. The pellet was resuspended in 200 ...

Base genética do hábito de crescimento e florescimento em tomateiro e sua importância na agricultura

“…Hábito de crescimento e impacto no brix O acúmulo de açúcares, um dos componentes do TSS (ou °brix), nos frutos de tomateiro, envolve vários fatores ambientais e mecanismos fisiológicos, tais como assimilação de CO 2 pelas folhas (fontes), transporte de açúcares no floema, descarregamento no fruto (dreno) e metabolismo dos açúcares nesse órgão (YELLE et al, 1991). Como o hábito de crescimento regula, em última análise, o número relativo de folhas (fontes) com relação aos frutos (drenos), esse pode ter um grande impacto no brix.…”

Sucrose protects cell wall invertase but not vacuolar invertase against proteinaceous inhibitors

“…Both invertase types exist in different isoforms [3][4][5]. Sequence comparisons indicate a common evolutionary origin [4].…”

“…However, VI and CWI can be clearly distinguished based on structural and kinetic properties. Purified VI have Kin values ranging from 5 to 10 raM, or even higher [3], whereas CWI exhibit Km values of 0.5-1.0 mM [5][6][7]. Furthermore, the pI of VI is around 5, whereas CWI are basic proteins with a pI around 9.5 [3,7,8].…”

Enzyme Activity Profiles during Fruit Development in Tomato Cultivars andSolanum pennellii

“…Invertase serves to convert Suc into hexoses (NguyenQuoc and Foyer, 2001). The decrease of GlcK and FruK activity and the maintenance of invertase activity are accompanied by a progressive increase of hexoses and decline of Suc as tomato fruits mature (Ho, 1984;Yelle et al, 1991;.…”