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The growth of tomato fruit is the result of cell division early in development followed by cell expansion until the onset of ripening. We have utilized the mRNA differential display technique to clone genes differentially expressed in 10- and 20-day-old tomato fruit, when most fruit cells are undergoing a transition to growth by cell expansion. Of 1753 total bands observed using 30 independent primer sets, 31 differential display bands were obtained only in either 10-or 20-day - old fruit RNAs. Seven differentially expressed bands from 10-day-old fruit RNAs and six from 20-day-old fruit RNAs were cloned and characterized by sequence analysis and mRNA expression patterns in developing fruit, leaf and root tissues. Two clones had sequence similarities to 3-deoxy-D-arabino-heptulosonate-7-phosphate (DAHP) synthase or threonine deaminase genes, while the remaining clones did not correspond to previously characterized genes. Steady state levels of mRNAs corresponding to seven clones were upregulated between 10 and 20 days of fruit development, while two clones were downregulated during growth and ripening. Most clones also hybridize to mRNA species present in leaf and root tissues. Collectively, these results suggest a transition in gene expression between 10- and 20-day-old fruit development.
Abstract
Water availability is one of the principal environmental limitations of crop productivity throughout the world. The water deficits, which are a consequence of either continuous or transitory periods of drought, cause significant yield reductions on presently cultivated land, and greatly restrict the cultivation of crops on over one-third of the earth’s land surface considered to be arid or semiarid (25). These restrictions on yield potential are rapidly becom ing of great concern in the face of the food demands of an ever increasing world population. The problem becomes complicated further by the fact that supplies of suitable irrigation water are dwindling rapidly, and that the costs of irrigation are becoming prohibitive. As a result, studies on the effects of water stress on plant survival and yield are attracting added interest in plant science research.
Abstract
Salinity is a significant limiting factor to agricultural productivity, impacting about 9 × 108 ha of the land surface on the earth, an area about 3 times greater than all of the land that is presently irrigated (17, 18). Reduced productivity occurs as a result of decreased yields on land that is presently cultivated [about one-third of all irrigated land is considered to be affected by salt (18, 45)], as well as due to the restriction of significant agricultural expansion into areas that presently are not cultivated. In the United States, salinity is a major limiting factor to agricultural productivity, and as the quality of irrigation water continues to decline this problem will become more acute (1, 56). About 1.8 million ha of land are salt-affected in California (56), the major agricultural state in the nation. Annual losses to crop production in the salt-affected areas, including the Imperial, Coachella, and San Joaquin valleys, are substantial and are increasing at a significant rate each year (56).
Effects of hot water treatment (HWT) on metabolism of mango (Mangifera indica cv. Okrong) fruit during low-temperature storage (LTS) and subsequent room temperature fruit ripening (RTFR) were examined. Mature-green ‘Okrong’ mango fruit were treated by immersing in hot (50 ± 1 °C) or ambient (30 ± 1 °C) water for 10 min, stored either at 8 or 12 °C for 15 days, followed by transfer to room temperature (30 ± 2 °C) for 5 days. Rate of ethylene production was significantly reduced by HWT during LTS and RTFR in all treatments. HWT increased catalase activity, suppressed ascorbate peroxidase activity, and had no effect on glutathione reductase activity during the ripening phase but showed a slight stimulatory effect during LTS. HWT altered RNA transcripts of manganese–superoxide dismutase, pectate lyase, β-galactosidase, and β-1,3-glucanase, which exhibited increases during LTS. RTFR of LTS fruit caused reduction in transcript levels of these genes, except pectate lyase. Total protein patterns were altered by all treatments during LTS and RTFR, but HWT arrested loss of several proteins during RTFR. Taken together, results provide strong evidence that HWT increases the storage period of mango by extending fruit shelf life through the regulation of a myriad of metabolic parameters, including patterns of antioxidant and cell wall hydrolase genes and protein expression during storage at low and ambient temperatures.
Transgenic `Rutgers' 37-81^ tomato (Lycopersicon esculentum Mill.) homozygous for a pectin methylesterase (PME) antisense gene, which lowers PME activity and increases levels of soluble solids, was compared to azygous (a segregating line of 37-81^ with 0 copies of the introduced gene) and wild-type `Rutgers' in the field during Summer 1992 and 1993 to determine the effects of the introduced PME antisense gene on tomato plant growth, fruit set, fruit yield, and fruit processing attributes. Fresh and dry weight accumulation in transgenic plants was similar to wild-type `Rutgers' and azygous 37-81^ lines during 1992 and 1993, indicating that the introduced PME antisense gene did not affect biomass accumulation. Transgenic plants showed an increase in fruit number and yield in 1992 compared to wild-type `Rutgers' and azygous 37-81^, but no differences were observed among the three genotypes in 1993. Average fruit weight did not show significant differences among the three genotypes in 1992, but was lower in azygous and transgenic plants than wild-type plants in 1993. Transgenic fruit had higher soluble and total solids and higher pH than control fruit, but shelf life was somewhat shorter in transgenic fruit. Overall, these data indicate that introduction of the PME antisense gene, which improves the processing quality of tomatoes, does not adversely affect fruit yield or vegetative growth of plants.
We have introduced an antisense pectin methylesterase (PME) gene into Rutgers tomato to elucidate its role in fruit development and ripening. In greenhouse trials tomato fruits from transformant 37-81^ homozygous for the antisense PME gene ripened normally and contained higher levels of soluble solids than wild-type Rutgers fruits (Tieman et al. (1992) Plant Cell 4:667-679). Field trials of transgenic 37-81^ homozygous and azygous for the antisense PME gene and wild-type Rutgers were conducted during the summer of 1992. Field grown fruits from homozygous 37-81^ plants have significantly higher levels of soluble solids and total solids and a higher fruit pH than Rutgers or 37-81^ azygous fruits. Average fruit weight did not differ significantly in the three genotypes, but 37-81^ (homozygous) plants had a higher total fruit yield than Rutgers or 37-81^ azygous plants. Plant fresh and dry weights did not differ significantly among the three plant types.