Biochemical basis of high-temperature inhibition of ethylene biosynthesis in ripening tomato fruits

Biggs, M. S., Woodson, W. R. and Handa, A. K. 1988. Biochemical basis of high-temperature inhibition of ethylene biosynthesis in ripening tomato fruits. Physiol. Plant. 72: 572578
Incubation of fruits of tomato ( Lycopersicon esculentum Mill. cv. Rutgers) at 34°C or above resulted in a marked decrease in ripening-associated ethylene production. High temperature inhibition of ethylene biosynthesis was not associated with permanent tissue damage, since ethylene production recovered following transfer of fruits to a permissive temperature. Determination of pericarp enzyme activities involved in ethylene biosynthesis following transfer of fruits from 25°C to 35 or 40°C revealed that 1-aminocyclopropane-l-carboxylic acid (ACC) synthase (EC 4.4.1.14) activity declined rapidly while ethylene forming enzyme (EFE) activity declined slowly. Removal of high temperature stress resulted in more rapid recovery of ACC synthase activity relative to EFE activity. Levels of ACC in pericarp tissue reflected the activity of ACC synthase before, during, and after heat stress. Recovery of ethylene production following transfer of pericarp discs from high to permissive temperature was inhibited in the presence of cycloheximide, indicating the necessity for protein synthesis. Ethylene production by wounded tomato pericarp tissue was not as inhibited by high temperature as ripening-associated ethylene production by whole fruits.     

Water deficit, root demography, and the causes of internal blackening in field-grown tomatoes:(Lycopersicon esculentum Mill.)

An internal blackening disorder may cause substantial losses in the value of tomatoes grown for processing. The disorder resembles an internal form of blossom-end rot and appears to be more common in dry seasons. In an experiment to test whether the internal blackening is caused by water deficit and whether it is indeed blossom-end rot, plots of cv. Cannery Row were irrigated to keep the soil moisture deficit <50 mm and others were sheltered from rain and not irrigated from early flowering onwards. Shoot growth (total and fruit dry mass) was measured destructively at intervals, and root growth and death nondestructively using minirhizotrons. There was a greater incidence of internal blackening and blossom-end rot, and lower Ca concentrations, in the fruit of non-irrigated plants. Root growth and root death were accelerated in these plants around the time that internally-blackened fruit were set. Although the internal blackening syndrome shared some features with blossom-end rot some differences were apparent in this experiment. It is suggested that internal blackening could have resulted from increased root competition for photosynthate, leading to abnormal seed development. Root turnover was appreciable (30–40% of the roots survived 28 days). This suggests there may be substantial errors in contemporary models of dry matter partitioning in tomato crops.     

Expression of thiol proteases decreases in tomato ovaries after fruit set induced by pollination or gibberellic acid

The modulation of the expression of thiol proteases during both senescence and development was investigated Proteolytic activity and some thiol proteases were analyzed in unpollinated tomato (Lycopersicon esculentum Mill. cv. Rutgers) ovaries during presenescence and during early fruit development induced by treatment with gibberellic acid (GA) or by natural pollination. Proteolytic activity in extracts was tested on azocasein and by observing degradation of the ribulose-1,5-bisphosphate carboxylase large subunit in western blots. There was no correlation between total activity and protein content. Thiol proteases were analyzed by western blot with antibodies raised against papain and a recombinant tomato C14 thiol protease. A 58-kDa polypeptide was recognized by both antibodies and two more polypeptides of 47 and 36 kDa were detected with the second one. All these polypeptide levels increased in untreated unpollinated ovaries at the presenescent stage. Natural pollination or GA treatment of unpollinated ovaries resulted in decreases of these polypeptides at an early developmental stage. The same pattern was observed for the levels of C14 mRNA. Our results suggest that the expression of C14 thiol protease occurs in unpollinated ovaries at the presenescent stage and that it can be suppressed by factors that induce fruit set and development.     

Nitrogen isotope composition of tomato (Lycopersicon esculentum Mill. cv. T-5) grown under ammonium or nitrate nutrition

Studies that quantify plant δ¹⁵N often assume that fractionation during nitrogen uptake and intra-plant variation in δ¹⁵N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetum Mill. cv. T-5) at NH₄⁺ or NO^?₃ concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole-plant δ¹⁵N was not significantly different from source δ¹⁵ N for plants grown on either nitrogen form. No intra-plant variation in δ¹⁵N was observed for plants grown with NH⁺₄. In contrast. δ¹⁵N of leaves was as much as 5.8% greater than that of roots for plants grown with NO^?₃. The contrasting patterns of intra-plant variation are probably caused by different assimilation patterns. NH⁺₄ is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO^?₃ assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ¹⁵N of NO^?₃ to become enriched relative to organic nitrogen; the δ¹⁵N of NO^?₃ was 11.1 and 12.9% greater than the δ¹⁵N of organic nitrogen in leaves and roots, respectively. Leaf δ¹⁵N may therefore be greater than that of roots because the NO^?₃ available for assimilation in leaves originates from a NO^?₃ pool that was previously exposed to nitrate assimilation in the root.     

NaCl-induced accumulation of tonoplast and plasma membrane H+-ATPase message in tomato

NaCl-induced changes in the accumulation of message for the 70 kDa subunit of the tonoplast H⁺-ATPase and plasma membrane H⁺-ATPase were studied in hydroponically grown plants of Lycopersicon esculentum Mill. cv. Large Cherry Red. There was increased accumulation of message for the 70 kDa (catalytic) subunit of the tonoplast H⁺-ATPase in expanded leaves of tomato plants 24 h after final NaCl concentrations were attained. This was a tissue-specific response; levels of this message were not elevated in roots or in young, unexpanded leaves. The NaCl-induced accumulation of this message was transient in the expanded leaves and returned to control levels within 7 days. The temporal and spatial patterns of NaCl-induced accumulation of message for the plasma membrane H⁺-ATPase differed from the patterns associated with the 70 kDa subunit of the tonoplast H⁺-ATPase. NaCl-induced accumulation of the plasma membrane H⁺-ATPase message occurred in both roots and expanded leaves. Initially accumulation of the plasma membrane H⁺-ATPase message was greater in root tissue than in expanded leaves, but increased to higher levels in expanded leaves after 7 days. These results suggest that increased expression of the tonoplast H⁺-ATPase is an early response to salinity stress and may be associated with survival mechanisms, rather than with long-term adaptive processes.     

Reduction, assimilation and transport of N in normal and gibberellin-deficient tomato plants

A fast-growing normal and a slow-growing gibberellin-deficient mutant of Lycopersicon esculentum (L.) Mill. cv. Moneymaker were used to test the hypothesis that slow-growing plants reduce NO₃^? in the root to a greater extent than do fast-growing plants. Plants that reduce NO₃^? in the root may grow more slowly due to the higher energetic and carbon costs associated with root-based NO₃^? reduction compared to photosynthetically driven shoot NO₃^? reduction. The plants were grown hydroponically with a complete nutrient solution containing 10 mM NO₃^? and the biomass production, gas exchange characteristics, root respiratory O₂ consumption, nitrate reductase activity and translocation of N in the xylem were measured. The gibberellin-deficient mutants accumulated more total N unit^?1 dry weight than did the faster-growing normal plants. There were no significant differences between the genotypes in the rates of photosynthesis expressed on a leaf dry weight basis. The plants differed in the proportion of photosynthetic carbon available to growth due to a greater proportion of daily photo-synthate production being consumed by respiration in the slow-growing genotype. This difference in allocation of carbon was associated with differences in the specific leaf area and specific root length. In addition, a greater leaf weight ratio in the fast-growing than in the slow-growing plants indicates a greater investment of carbon into biomass supporting photosynthetic production in the former. We did not find differences in the activity or distribution of nitrate reductase or in the N composition of the xylem sap between the genotypes. We thus conclude that the growth rate was determined by the efficiency of carbon partitioning and that the site of NO₃^? reduction and assimilation was not related to the growth rate of these plants.     

The influence of plant age on wound induction of proteinase inhibitors in tomato

Proteinase inhibitors can be induced by wounding in shoots of tomato ( Lycopersicon esculentum [L.] Mill. cv. Moneymaker). These inhibitors are toxic to insects, but their ecological importance is not clear. Published work suggests that proteinase inhibitors may be wound-inducible in tomato only while the plants are young (less than 30 days). In the present investigation the influence of plant age on wound-inducible proteinase inhibitor was re-assessed using tomato plants grown in an outdoor polythene tunnel, with natural lighting and without supplementary heat. In contrast to previous findings, proteinase inhibitor was shown to be induced by wounding in plants of all ages. However, the systemic efficacy of wounds was much reduced in mature plants, possibly because such plants have outgrown the range of the wound-signalling system.     

Effect of temperature on biomass allocation in tomato (Lycopersicon esculentum)

Temperature may influence dry matter partitioning between fruits and vegetative plant parts either directly or indirectly through its influence on development, flower and/or fruit abortion. The objective of the present work was to investigate whether there is any direct effect of temperature on dry matter partitioning between fruits and vegetative plant parts in tomato. A greenhouse experiment was conducted, with alternating 3-week periods of high (23°C) and low (18°C) temperature setpoint. Dry matter partitioning during these 3-week periods was determined from destructive plant harvests at two levels of fruit pruning (3 and 7 fruits per truss). Indirect temperature effects on dry matter partitioning were excluded by fruit pruning.
On average, the fraction of dry matter distributed to the fruits during a 12-week period, starting with the flowering of the fifth truss (28 days after planting), was 0.53 (3 fruits per truss) and 0.70 (7 fruits per truss). These ratios were also calculated for every 3-week period separately and did not depend on the average temperature (18–24°C) during that period.
It is concluded that dry matter distribution in tomato is not significantly affected by temperature directly, which means that the temperature effect (18–24°C) on the generative sink strength is not much different from the temperature effect on the vegetative sink strength.     

Salt stress increases ferredoxin-dependent glutamate synthase activity and protein level in the leaves of tomato

Ferredoxin-dependent glutamate synthase (EC 1.4.7.1) catalyzes an essential step in the pathway of glutamate biosynthesis. Exposing detached tomato ( Lycopersicon esculentum ) leaves for 6 h to 12 g l⁻¹ NaCl resulted in a significant two-fold increase in the activity of ferredoxin-dependent glutamate synthase extracted from the leaves. Western blot studies demonstrated that salt treatment also increased the ferredoxin-dependent glutamate synthase content of the leaves. A similar effect of salt on the concentration of this enzyme was found in the leaves of hydroponically-grown tomato plants. The induction of ferredoxin-dependent glutamate synthase under salt stress may provide the glutamate required for the proline synthesis which is a common response to salt stress.     

Growth analysis of wild-type and photomorphogenic-mutant tomato plants

A custom designed growth-measuring apparatus, controlled by a microcomputer has been used to study extension growth kinetics of wild-type and photomorphogenic-mutant tomato ( Lycopersicon esculentum Mill.) plants with and without end-of-day farred light (EODFR). The following photomorphogenic mutants were used. Far-red insensitive ( fri ^.1): deficient in phytochrome A (phyA); temporarily red light-insensitive ( tri ^.3): deficient in phytochrome Bl (phyB1), and their isogenic wild type (WT) cv. MoneyMaker. aurea (au) : deficient in phytochrome chromophore biosynthesis; high-pigment-1 ( hp-1 ): exhibiting exaggerated phytochrome responses, and their isogenic WT cv. Ailsa Craig. The stem elongation rate (SER) during a 24-h period of all the genotypes studied shows a similar pattern, having two dramatic transients, one shortly after the onset of the light period (a sharp decline in SER) and another shortly after the start of the dark period (a sharp increase in SER). These transients are probably associated with water relations as a consequence of opening and closure of the stomata. The fastest SER occurs during the dramatic oscillations early in the dark period. Between the genotypes there are large quantitative differences in SER. All the genotypes tested exhibited a strong EODFR response, resulting in a relative promotion of SER during the first period after the start of EODFR and in the subsequent light and dark periods. These results indicate that phyA, absent in the fri ^.1 mutant, does not play a major role in SER of light-grown tomato plants, whereas phyB 1, absent in the tri ^.3 mutant, is partly responsible for the compact stature of WT plants. An additional phytochrome other than phy A and phy B1 must therefore be capable of eliciting the EODFR response.