Harry W. Janes

Sucrose regulation of ADP-glucose pyrophosphorylase subunit genes transcript levels in leaves and fruits.

ADP-glucose pyrophosphorylase (AGPase, EC2.7.7.27) is a key regulatory enzyme in starch biosynthesis. The enzyme is a heterotetramer with two S and two B subunits. In tomato, there are three multiple forms of the S subunit gene. Agp S1, S2 and B are highly expressed in fruit from 10 to 25 days after anthesis. Agp S3 is only weakly expressed in fruit. Sucrose significantly elevates expression of Agp S1, S2 and B in both leaves and fruits. Agp S1 exhibits the highest degree of regulation by sucrose. In fact, sucrose may be required for Agp S1 expression. For excised leaves incubated in water, no transcripts for Agp S1 could be detected in the absence of sucrose, whereas it took up to 16 h in water before transcripts were no longer detectable for Agp S2 and B. Neither Agp S3 nor the tubulin gene is affected by sucrose, demonstrating that this response is specifically regulated by a carbohydrate metabolic signal, and is not due to a general increase in metabolism caused by sucrose treatment. Truncated versions of the promoter for Agp S1 indicate that a specific region 1.3-3.0 kb upstream from the transcription site is responsible for sucrose sensitivity. This region of the S1 promoter contains several cis-acting elements present in the promoters of other genes that are also regulated by sucrose.

Respiratory Upsurge in Blueberries and Strawberries as Influenced by Ethylene and Acetaldehyde

The effects of acetaldehyde and ethylene were compared in the induction of a respiratory rise in blueberry and strawberry fruits. The increase in CO2 production in blueberries caused by acetaldehyde was more pronounced than that caused by ethylene. Acetaldehyde induced a climacteric-like respiration in straw-berries, while ethylene had no effect. The results suggest that the action of acetaldehyde and ethylene involves different mechanisms.

PCR cloning and characterization of multiple ADP-glucose pyrophosphorylase cDNAs from tomato

Four ADP-glucose pyrophosphorylase (AGP) cDNAs were cloned from tomato fruit and leaves by the PCR techniques. Three of them (agp S1, agp S2, and agp S3) encode the large subunit of AGP, the fourth one (agp B) encodes the small subunit. The deduced amino acid sequences of the cDNAs show very high identities (96-98%) to the corresponding potato AGP isoforms, although there are major differences in tissue expression profiles. All four tomato AGP transcripts were detected in fruit and leaves; the predominant ones in fruit are agp B and agp S1, whereas in leaves they are agp B and agp S3. Genomic southern analysis suggests that the four AGP transcripts are encoded by distinct genes.

The influence of light period on carbon partitioning, translocation and growth in tomato.

Abstract Carbon partitioning, translocation and growth were examined in young tomato (Lycopersicon esculentum Mill.) plants grown for 38 days under a 12-h light period and a photosynthetic photon flux density (PPFD) of 150 μmoles m−2 s−1 and then transferred and grown under 8-, 16- or 20-h light periods for an additional 7 days under similar PPFD. The third leaf from the base of the plant was used for carbon partitioning and translocation studies. The longer the length of the light period, the greater were the net assimilation rate (NAR), relative growth rate (RGR) and amount of carbon fixed and translocated. The shoot-to-root ratio and leaf area ratio (LAR) decreased with an increase in the light period. No significant differences were observed in photosynthetic rate among the three light treatments. From the total amount of carbon fixed, a certain amount stayed in the leaf independent of light period and the surplus was translocated. The 8-h light treatment had the highest accumulation rates of hexose, and starch. The starch accumulation rate in the 8- and 16-h light treatments were twice as high as that in the 20-h light treatment. The amount of hexose, sucrose and starch at any one time increased with an increase in the length of the light period. The carbon fixed in excess of demand was stored in the leaf as starch, and this accumulated over time in the 20-h light treatment. The leaves appeared to have a maximum capacity to store starch.

Expression of the ipt gene with the AGPase S1 promoter in tomato results in unbranched roots and delayed leaf senescence

Transgenic tomato plants were produced with the isopentenyl transferase gene (ipt) ligated to a promoter that is active exclusively in sink tissue. Initially, transgenic plants had smaller, round-scale leaves, swollen stems, and exhibited early development of lateral shoots compared to wild type. Expression of the ipt gene resulted in the formation of unbranched roots on cuttings and delayed senescence in excised leaves. Callus and root formation occurred on excised leaves and leaf discs during dark incubation. The retention percentage of chlorophyll, as well as cytokinin in excised leaves or discs was significantly greater than wild type. Transgenic tomato fruit had elevated levels of cytokinins in the first days after fruit set and these levels were maintained longer during fruit development.

Alternative production strategies for greenhouse tomatoes using supplemental lighting

Abstract The yield response of greenhouse tomatoes ( Lycopersicon esculentum Mill. ‘Vendor’) was examined under both natural light conditions (light available from the sun) and with the addition of 6.48 moles m −2 day −1 supplemental light from a high-pressure sodium (HPS) source. Tomato crop yield significantly increased as plant population density increased when HPS lighting was employed. No significant yield increase was obtained with increased plant density under natural light conditions. Four production strategies (representing four combinations of plant density and the number of trusses produced per plant) were tested. A significant yield increase was obtained with HPS lighting relative to the unlit control for all of the production strategies used. Similar total yields were obtained regardless of the production strategy when HPS lighting was used.

Computer Simulation of a Single Truss Tomato Cropping System

ABSTRACT THE development of a computer simulation model for greenhouse tomato crop management is discussed. The management model, based on a crop production model, will determine a production schedule designed to provide a continuous yield, optimize greenhouse space utilization, and predict production rates throughout the year.

Senescence in Isolated Carnation Petals: Differential Response of Various Petal Portions to ACC, and Effects of Uptake of Exudate From Excised Gynoecia*

Summary Exogenously-applied ACC accelerates loss of fresh weight in bases and mid portions of isolated petals excised from young carnations, but petal tops show little or no response to uptake of ACC. Petal tops do acquire greater ability to convert ACC to ethylene with age. Senescence is promoted more rapidly in excised petals taking up exudate from excised gynoecia taken from whole carnations aged 6 days than from gynoecia aged 1 day.

Effect of temperature perturbations on tomato (Lycopersicon esculentum Mill.) quality and production scheduling

Summary Controlled environment experiments were conducted to evaluate the effect of a 2-week change in air temperature imposed after first fruit-set on tomato production scheduling and on the quality of vine-ripened fruit. Experiments were conducted with hydroponically-grown tomato (Lycopersicon esculentum Mill., cv. ‘Laura’). Air temperature was altered from control day/night temperature values of 23°/18°C for a 2-week period starting 10 d after fruit-set. Plants were returned to the 23°/18°C temperature and a minimum of eight fruits per treatment were harvested at three ripening stages, breaker (when 25% of the fruit skin had acquired a red tint), breaker plus 3 d, and breaker plus 6 d. A perturbation of ± 5°C (28°/23°C and 18°/13°C) was used in two Experiments (E1 and E2) and ± 7°C (30°/25°C and 16°/11°C) was used in a third Experiment (E3). Fruits were more responsive to an increase than to a decrease in temperature. Reductions in days to harvest (from 3.1 – 8.5 d) and fruit fresh weight at later stages of vine-ripening were observed for the high temperature treatments. Colour indices, soluble solids contents (SSC), acidity and viscosity at each ripening stage were significantly affected by high temperature treatments. The results indicate that short-term temperature perturbations following first fruit-set can influence the rates at which changes occurred in the external appearance of fruit (colour) and in their internal characteristics. The results can be used to improve environmental control and management strategies for tomato growers.

The relationship between the activity and the activation state of RuBP carboxylase and carbon exchange rate as affected by sink and developmental changes

The purpose of this study was to explore if sink manipulations which affect leaf carbon exchange rate (CER) are mediated by ribulose 1,5-bisphosphate (RuBP) carboxylase activity. Tomato leaf (Lycopersicon esculentum Mill. cv. Vendor) RuBP carboxylase was assayed using a rapid extraction method. Over a diurnal period, leaf CER fluctuated independent of carboxylase activity. Differences in leaf CER induced by fruit pruning in one leaf-one cluster plants were not accompanied by changes in carboxylase activity.During leaf expansion, carboxylase activity and percent enzyme in the active form paralleled the increase and then decrease in leaf carbon exchange rate. Differences in leaf CER induced by root warming at ambient air temperature, were accompanied by parallel changes in carboxylase activity.These results suggest that modifications in leaf CER are not mediated exclusively through changes in carboxylase activity, but rather that modifications in carboxylase activity coincide with overall changes in leaf physiology and morphology in response to sink demand.