The Agrobacterium vitis T-6b oncoprotein induces auxin-independent cell expansion in tobacco

Among the Agrobacterium T-DNA genes, rolB, rolC, orf13, orf8, lso, 6b and several other genes encode weakly homologous proteins with remarkable effects on plant growth. The 6b oncogene induces tumors and enations. In order to study its properties we have used transgenic tobacco plants that carry a dexamethasone-inducible 6b gene, dex-T-6b. Upon induction, dex-T-6b plants develop a large array of morphological modifications, some of which involve abnormal cell expansion. In the present investigation, dex-T-6b-induced expansion was studied in intact leaves and an in vitro leaf disc system. Although T-6b and indole-3-acetic acid (IAA) both induced expansion and were non-additive, T-6b expression did not increase IAA levels, nor did it induce an IAA-responsive gene. Fusicoccin (FC) is known to stimulate expansion by increasing cell wall plasticity. T-6b- and FC-induced expansion were additive at saturating FC concentrations, indicating that T-6b does not act by a similar mechanism to FC. T-6b expression led to higher leaf osmolality values, in contrast to FC, suggesting that the T-6b gene induces expansion by increasing osmolyte concentrations. Metabolite profiling showed that glucose and fructose played a major role in this increase. We infer that T-6b disrupts the osmoregulatory controls that govern cell expansion during development and wound healing.     

The Agrobacterium oncogene AB-6b causes a graft-transmissible enation syndrome in tobacco

Agrobacterium 6b oncogenes induce tumours and modify plant growth in various ways. Here we show that the AB-6b gene from strain AB4 placed under 2x35S promoter control (2x35S-AB-6b) induces a complex enation syndrome in transgenic Nicotiana tabacum plants, that also occurs in a few rare cases of genetic enations. In Arabidopsis thaliana, 2x35S-AB-6b induced radially symmetrical tubes on the abaxial side of the leaves, which must therefore be considered as the Arabidopsis equivalents of enations on other plant species. Tobacco and Arabidopsis 2x35S-AB-6b leaves contained small, supernumerary densely packed cells between the spongy mesophyll and the abaxial epidermis, close to vascular strands arising at an early stage of leaf development. On tobacco, the 2x35S-AB-6b enation syndrome could be transmitted across graft junctions to growing tissues of untransformed plants, both acropetally and basipetally. We propose that the AB-6b gene encodes the synthesis of one or more enation factor(s) that are transported by the phloem and modify the growth of developing tissues.     

Abnormal accumulation of sugars and phenolics in tobacco roots expressing the Agrobacterium T-6b oncogene and the role of these compounds in 6b-induced growth

The Agrobacterium T-DNA oncogene 6b induces tumors and modifies the growth of transgenic plants by an unknown mechanism. We have investigated changes in roots of tobacco seedlings that express a dexamethasone-inducible T-6b (dex-T-6b) gene. On induction medium with sucrose, intact or isolated dex-T-6b roots accumulated sucrose, glucose, and fructose and changed their growth, contrary to noninduced roots. Root fragments bridging agar blocks with or without sucrose accumulated sugars at the site of sucrose uptake, resulting in local growth. Induced root fragments showed enhanced uptake of 14C-labeled sucrose, glucose, and fructose. When seedlings were placed on sucrose-free induction medium, sugar levels strongly decreased in roots and increased in cotyledons. Collectively, these results demonstrate that 6b stimulates sugar uptake and retention with drastic effects on growth. Apart from sugars, phenolic compounds also have been found to accumulate in 6b tissues and have been proposed earlier to play a role in 6b-induced growth. Induced dex-T-6b roots accumulated high levels of 5-caffeoylquinic acid (or chlorogenic acid [CGA]), but only under conditions where endogenous sugars increased. Inhibition of phenylalanine ammonia-lyase with the competitive inhibitor 2-aminoindan-2-phosphonic acid (AIP) abolished CGA accumulation without modifying sugar accumulation or affecting the 6b phenotype. We conclude that the absorption, retention, and abnormal accumulation of sugars are essential factors in 6b-induced growth changes, whereas phenylpropanoids only marginally contribute to the 6b seedling phenotype.     

Expression of Pokeweed Antiviral Protein in Transgenic Plants Induces Virus Resistance in Grafted Wild-Type Plants Independently of Salicylic Acid Accumulation and Pathogenesis-Related Protein Synthesis

Pokeweed antiviral protein (PAP), a 29-kD protein isolated from Phytolacca americana, inhibits translation by catalytically removing a specific adenine residue from the large rRNA of the 60S subunit of eukaryotic ribosomes. Transgenic tobacco (Nicotiana tabacum) plants expressing PAP or a variant (PAP-v) were shown to be resistant to a broad spectrum of plant viruses. Expression of PAP-v in transgenic plants induces synthesis of pathogenesis-related proteins and a very weak (<2-fold) increase in salicylic acid levels. Using reciprocal grafting experiments, we demonstrate here that transgenic tobacco rootstocks expressing PAP-v induce resistance to tobacco mosaic virus infection in both N. tabacum NN and nn scions. Increased resistance to potato virus X was also observed in N. tabacum nn scions grafted on transgenic rootstocks. PAP expression was not detected in the wild-type scions or rootstocks that showed virus resistance, nor was there any increase in salicylic acid levels or pathogenesis-related protein synthesis. Grafting experiments with transgenic plants expressing an inactive PAP mutant demonstrated that an intact active site of PAP is necessary for induction of virus resistance in wild-type scions. These results indicate that enzymatic activity of PAP is responsible for generating a signal that renders wild-type scions resistant to virus infection in the absence of increased salicylic acid levels and pathogenesis-related protein synthesis.     

Regulatory network of microRNA399 and PHO2 by systemic signaling

Recently, we showed that microRNA399s (miR399s) control inorganic phosphate (Pi) homeostasis by regulating the expression of PHO2 encoding a ubiquitin-conjugating E2 enzyme 24. Arabidopsis (Arabidopsis thaliana) plants overexpressing miR399 or the pho2 mutant overaccumulate Pi in shoots. The association of Pi translocation and coexpression of miR399s and PHO2 in vascular tissues suggests their involvement in long-distance signaling. In this study, we used reciprocal grafting between wild-type and miR399-overexpressing transgenic plants to dissect the systemic roles of miR399 and PHO2. Arabidopsis rootstocks overexpressing miR399 showed high accumulation of Pi in the wild-type scions because of reduced PHO2 expression in the rootstocks. Although miR399 precursors or expression was not detected, we found a small but substantial amount of mature miR399 in the wild-type rootstocks grafted with transgenic scions, which indicates the movement of miR399 from shoots to roots. Suppression of PHO2 with miR399b or c was less efficient than that with miR399f. Of note, findings in grafted Arabidopsis were also discovered in grafted tobacco (Nicotiana benthamiana) plants. The analysis of the pho1 mutant provides additional support for systemic suppression of PHO2 by the movement of miR399 from Pi-depleted shoots to Pi-sufficient roots. We propose that the long-distance movement of miR399s from shoots to roots is crucial to enhance Pi uptake and translocation during the onset of Pi deficiency. Moreover, PHO2 small interfering RNAs mediated by the cleavage of miR399s may function to refine the suppression of PHO2. The regulation of miR399 and PHO2 via long-distance communication in response to Pi deficiency is discussed.     

Long-distance signaling and the control of branching in the rms1 mutant of pea

The ramosus (rms) mutation (rms1) of pea (Pisum sativum) causes increased branching through modification of graft-transmissible signal(s) produced in rootstock and shoot. Additional grafting techniques have led us to propose that the novel signal regulated by Rms1 moves acropetally in shoots and acts as a branching inhibitor. Epicotyl interstock grafts showed that wild-type (WT) epicotyls grafted between rms1 scions and rootstocks can revert mutant scions to a WT non-branching phenotype. Mutant scions grafted together with mutant and WT rootstocks did not branch despite a contiguous mutant root-shoot system. The primary action of Rms1 is, therefore, unlikely to be to block transport of a branching stimulus from root to shoot. Rather, Rms1 may influence a long-distance signal that functions, directly or indirectly, as a branching inhibitor. It can be deduced that this signal moves acropetally in shoots because WT rootstocks inhibit branching in rms1 shoots, and although WT scions do not branch when grafted to mutant rootstocks, they do not inhibit branching in rms1 cotyledonary shoots growing from the same rootstocks. The acropetal direction of transport of the Rms1 signal supports previous evidence that the rms1 lesion is not in an auxin biosynthesis or transport pathway. The different branching phenotypes of WT and rms1 shoots growing from the same rms1 rootstock provides further evidence that the shoot has a major role in the regulation of branching and, moreover, that root-exported cytokinin is not the only graft-transmissible signal regulating branching in intact pea plants.     

Long‐distance ABA transport can mediate distal tissue responses by affecting local ABA concentrations

Environmental stresses that perturb plant water relations influence abscisic acid (ABA) concentrations, but it is unclear whether long‐distance ABA transport contributes to changes in local ABA levels. To determine the physiological relevance of ABA transport, we made reciprocal‐ and self‐grafts of ABA‐deficient flacca mutant and wild‐type (WT) tomato plants, in which low phosphorus (P) conditions decreased ABA concentrations while salinity increased ABA concentrations. Whereas foliar ABA concentrations in the WT scions were rootstock independent under conditions, salinity resulted in long‐distance transport of ABA: flacca scions had approximately twice as much ABA when grafted on WT rootstocks compared to flacca rootstocks. Root ABA concentrations were scion dependent: both WT and flacca rootstocks had less ABA with the flacca mutant scion than with the WT scion under conditions. In WT scions, whereas rootstock genotype had limited effects on stomatal conductance under conditions, a flacca rootstock decreased leaf area of stressed plants, presumably due to attenuated root‐to‐shoot ABA transport. In flacca scions, a WT rootstock decreased stomatal conductance but increased leaf area of stressed plants, likely due to enhanced root‐to‐shoot ABA transport. Thus, long‐distance ABA transport can affect responses in distal tissues by changing local ABA concentrations.     

Trypsin inhibitor activity in mature tobacco and tomato plants is mainly induced locally in response to insect attack,wounding and virus infection

Wounding of plants by insects is often mimicked in the laboratory by mechanical means such as cutting or crushing, and has not been compared directly with other forms of biotic stress such as virus infection. To compare the response of plants to these types of biotic and abiotic stress, trypsin inhibitor (TI) activity induced locally and systemically in mature tobacco (Nicotiana tabacum L.) and tomato (Lycopersicon esculentum L.) plants was followed for 12 days. In tobacco, cutting, crushing and insect feeding all induced comparable levels of TI activity of approx. 5 nmol·(mg leaf protein)^?1 in wounded leaves, while tobacco mosaic virus (TMV) infection of tobacco induced 10-fold lower amounts in the infected leaves. In tomato, feeding by insects also led to the induction of a level of TI activity of 5 nmol·(mg leaf protein)^?1. In contrast, both cutting and crushing of tomato leaves induced 10-fold higher amounts. These data show that biotic stress, in the form of insect feeding and TMV infection, and abiotic stress, in the form of wounding, have different effects on local levels of induced TI activity in mature tobacco and tomato plants. Irrespective of the type of wounding, in neither tobacco nor tomato could systemic induction of TI activity be observed in nearby unwounded leaves, which suggests that systemic induction of TI activity in mature tobacco and tomato plants is different from systemic TI induction in seedlings. Wounding of tobacco leaves, however, did increase the responsiveness to wounding elsewhere in the plant, as measured by an increased induction of TI activity.     

Relationship between hydraulic conductance and citrus dwarfing by the Flying Dragon rootstock (Poncirus trifoliata L. Raft var. monstruosa)

This work studied the hydraulic characteristics and physiological behavior of two trifoliate orange (Poncirus trifoliata L. Raft) varieties—Flying Dragon (FD) and Rubidoux (RT)—with contrasting size-controlling potential when used as rootstocks for citrus trees. Thus, Valencia orange scions growing on RT root system develop about 40 % more biomass than scions on FD. The anatomical study of xylem root tissue of both rootstocks showed that the number of vessels per cross-sectional area in RT almost doubled that found in FD, whereas diameter distribution did not vary significantly. Hydraulic resistance determined in rootstocks, and bud union segments were, respectively, 2- and 3.4-fold higher in trees on FD than in trees on RT. Root systems accounted for 46.5 and 55.2 % of whole-plant hydraulic resistance, whereas bud union segments represented 7.5 and 14.6 % of this parameter, the dwarfing rootstock (FD) having the highest values. Reduced hydraulic conductance in plants on FD rootstock diminished water potential in high evaporative demand periods, causing a reduction in stomatal conductance with respect to plants on RT. This leads to lower net photosynthetic CO₂ assimilation, which may affect biomass production. Translocation of ¹³C-labeled photoassimilates from leaves to roots was lower in plants on FD than in plants on RT, indicating that in the dwarfing rootstock (FD) there may be a vascular resistance to sucrose transport at the budding union level. Findings show that reduced hydraulic conductance may be the main cause of rootstock-induced dwarfing in citrus grafted onto FD.     

Epidemiology of tobacco leaf curl virus in India

The incidence of disease caused by tobacco leaf curl geminivirus (TbLCV) in ten tobacco growing areas of India ranged from 1.2% to 77%. The highest incidence of disease was observed in Andhra Pradesh (77%) followed by Gujarat (59%), Karnataka (17%), Bihar (11.6%) and West Bengal (5.4%). Under field conditions, an average of 32 adult whiteflies (Bemisia tabaci) per plant were recorded in Andhra Pradesh followed by Gujarat (20), Karnataka (12), Bihar (8) and West Bengal (5). In sequential sowings at Bangalore, all the plants were infected within 90 days in plots planted from February to June. Infection in plots planted later was progressively less. There was a positive correlation between whitefly catches and the final incidence of leaf curl disease in plantings. TbLCV was transmitted by Bemisia tabaci to 35 plant species, including Beta vulgaris, Capsicum annuum, Carica papaya, Cymopsis tetragonoloba, Lycopersicon esculentum, Sesamum indicum, Phaseolus vulgaris and Petunia hybrida. Forty five TbLCV isolates from different parts of India induced four distinct types of symptoms on tobacco cultivars Samsun and Anand 119. Group 1 isolates caused severe curling and cup-shaped enations; group II isolates induced pale green leaves, pit-like depressions and thorny enations: group III isolates caused leathery leaves, narrow and tiny protruding enations between the veins, and group IV isolates induced irregular thickening and swelling of veins and green flap-like enations on veins. Nylon net covers protected tobacco seedlings in nursery beds for 45 days. Ricinus communis and Helianthus annuus sown around the tobacco nursery bed as barrier crops attracted adult whiteflies and decreased the number found on tobacco.     

Photosynthetic capacity is differentially affected by reductions in sedoheptulose-1,7-bisphosphatase activity during leaf development in transgenic tobacco plants

The impact of reduced sedoheptulose-1,7-bisphosphatase (SBPase) activity on photosynthetic capacity and carbohydrate status was examined during leaf expansion and maturation in antisense transgenic tobacco (Nicotiana tabacum L. cv Samsun) plants. In wild-type plants, photosynthetic capacity was lowest in young expanding leaves and reached a maximum in the fully expanded, mature leaves. In contrast, the transgenic antisense SBPase plants had the highest photosynthetic rates in the young expanding leaves and lowest rates in the mature leaves. In the mature, fully expanded leaves of the transgenic plants photosynthetic capacity was closely correlated with the level of SBPase activity. However, in the youngest leaves of the SBPase antisense plants, photosynthetic rates were close to, or higher than, those observed in wild-type plants, despite having a lower SBPase activity than the equivalent wild-type leaves. Reductions in SBPase activity affected carbohydrate levels in both the mature and young developing leaves. The overall trend was for decreased SBPase activity to lead to reductions in carbohydrate levels, particularly in starch. However, these changes in carbohydrate content were also dependent on the developmental status of the leaf. For example, in young expanding leaves of plants with the smallest reductions in SBPase activity, the levels of starch were higher than in wild-type plants. These data suggest that the source status of the mature leaves is an important determinant of photosynthetic development.     

Tobacco transformants with strongly decreased expression of pyrophosphate:fructose-6-phosphate expression in the base of their young growing leaves contain much higher levels of fructose-2,6-bisphosphate but no major changes in fluxes

The role of pyrophosphate:fructose-6-phosphate 1-phosphotransferase (PFP) in developing leaves was studied using wild-type tobacco (Nicotiana tabacum L.) and transformants with decreased expression of PFP. (i) The leaf base, which is the youngest and most actively growing area of the leaf, had 2.5-fold higher PFP activity than the leaf tip. T3 transformants, with a 56-95% decrease in PFP activity in the leaf base and an 87-97% decrease in PFP activity in the leaf tip, were obtained by selfing and re-selfing individuals from two independent transformant lines. (ii) Other enzyme activities also showed a gradient from the leaf base to the leaf tip. There was a decrease in PFK and an increase in fructose-6-phosphate,2-kinase and plastidic fructose-1, 6-bisphosphatase, whereas cytosolic fructose-1,6-bisphosphatase activity was constant. None of these gradients was altered in the transformants. (iii) Fructose-2,6-bisphosphate (Fru2,6bisP) levels were similar at the base and tip of wild-type leaves in the dark. Illumination lead to a decrease in Fru2,6bisP at the leaf tip and an increase in Fru2,6bisP at the leaf base. Compared to wild-type plants, transformants with decreased expression of PFP had up to 2-fold higher Fru2,6bisP at the leaf tip in the dark, similar levels at the leaf tip in the light, 15-fold higher levels at the leaf base in the dark, and up to 4-fold higher levels at the leaf base in the light. (iv) To investigate metabolic fluxes, leaf discs were supplied with 14CO2 in the light or [14C]glucose in the light or the dark. Discs from the leaf tip had higher rates of photosynthesis than discs from the leaf base, whereas the rate of glucose uptake and metabolism was similar in both tissues. Significantly less label was incorporated into neutral sugars, and more into anionic compounds, cell wall and protein, and amino acids in discs from the leaf base. Metabolism of 14CO2 and [14C]glucose in transformants with low PFP was similar to that in wild-type plants, except that synthesis of neutral sugars from 14CO2 was slightly reduced in discs from the base of the leaf. (v) These results reveal that the role of PFP in the growing cells in the base of the leaf differs from that in mature leaf tissue. The increase in Fru2,6bisP in the light and the high activity of PFP relative to cytosolic fructose-1,6-bisphosphatase in the base of the leaf implicate PFP in the synthesis of sucrose in the light, as well as in glycolysis. The large increase in Fru2,6bisP at the base of the leaf of transformants implies that PFP plays a more important role in metabolism at the leaf base than in mature leaf tissue. Nevertheless, there were no major changes in carbon fluxes, or leaf or plant growth in transformants with below 10% of the wild-type PFP activity at the leaf base, implying that large changes in expression can be compensated by changes in Fru2,6-bisP, even in growing tissues.     

Growth and Water Relations of Wilty Mutants of Tomato (Lycopersicon esculentum Mill.)

In contrast to some previous reports on the growth of the ABA-deficientwilty mutants of tomato, growth was at least as rapid in themutants as in the wild type, as long as an adequate plant waterstatus was maintained by growing the plants under mist. Moreover,shoot extension was greater and the rate of leaf productionmore rapid in the mutants. Stomatal changes in response to environmentand to time in the light-dark cycle were generally similar inboth wilty mutants and the wild type, though the wild-type weregenerally more closed. Grafting experiments confirmed that thegenotype of the shoot was dominant in determining stomatal aperture,though wild-type rootstocks could cause a slight reduction inthe stomatal conductance of mutant leaves. The effect on plantwater relations of draughting only part of the root system wasinvestigated in a ‘split-root’ experiment. Withholdingwater from only part of the root system was found to lower significantlythe mean leaf water potential, even though the potential evaporationrate was kept very small. Key words: Abscisic acid, stomata, tomato     

Bioassay and attributes of a growth factor associated with crown gall tumors

An improved bioassay is described for a factor that promotes tumor growth which was first obtained from extracts of pinto bean leaves with crown gall tumors. Sixteen primary pinto bean leaves per sample are inoculated with sufficient Agrobacterium tumefaciens to initiate about 5 to 10 tumors per leaf and treated with tumor growth factor at day 3 after inoculation. The diameters of 30 to 48 round tumors (no more than 3 randomly selected per leaf) are measured per test sample at day 6. Mean tumor diameter increased linearly with the logarithm of the concentration of tumor growth factor applied. The tumor growth factor was separated by column chromatography from an ultraviolet light-absorbing compound previously reported to be associated with fractions having maximal tumor growth factor activity. Partly purified tumor growth factor showed no activity in a cytokinin bioassay or an auxin bioassay, and negligible activity in gibberellin bioassays. Representatives of these three classes of growth factors did not promote tumor growth. Extracts from crown gall tumors on primary pinto bean leaves, primary castor bean leaves, Bryophyllum leaves, carrot root slices, and tobacco stems showed tumor growth factor activity, whereas extracts from healthy control tissues did not. Extracts from actively growing parts of healthy pinto beans, Bryophyllum, and tobacco, however, showed tumor growth factor activity. Tumor growth factor is proposed to be a normal plant growth factor associated with rapidly growing tissues. Its synthesis may be activated in nongrowing tissues by infection with Agrobacterium sp.     

The Occurence of δ-Tocopherylquinone in Higher Plants and Its Relation to Senescence

δ-Tocopherylquinone (δTQ) content was determined in tobacco and yellow maple leaves, green ivy leaves and cactus tissues. It was found that the concentration of δ-TQ was highest in mature or senescent tissues, such as white tobacco leaves (0.02 μmole/g dry wt) while its detection was uncertain in young, green leaves from the apex of tobacco plants. Fractionation by centrifugation of senescent tobacco leaves showed that the osmiophilic globule fraction was enriched in δ-TQ. Electron microscope studies of young, mature and senescent tobacco tissues showed progressive changes in the size and number of osmiophilic globules. After chloroplast breakdown in senescent tobacco leaves, these globules became the predominant constituents of the organelle. δ-TQ which is associated with osmiophilic globules may play a role in the development of plants, particularly during senescence.     

Cotton shoot plays a major role in mediating senescence induced by potassium deficiency

The objective of this study was to determine the roles of shoot and root in the regulation of premature leaf senescence induced by potassium (K) deficiency in cotton (Gossypium hirsutum L.). Two contrasting cultivars (CCRI41, more sensitive to K deficiency; and SCRC22, a less sensitive cultivar) were selected for self- and reciprocal-grafting, using standard grafting (one scion/one rootstock), Y grafting (two scions/one rootstock) and inverted Y grafting (one scion/two rootstocks) at the seedling stage. Standard grafting was studied in the field in 2007 and 2008. There were no obvious differences in senescence between CCRI41 and SCRC22 scions while supplied with sufficient K. However, SCRC22 scions showed significantly greater K content, SPAD values (chlorophyll content), soluble protein content and net photosynthetic rates than CCRI41 scions while grown in K deficient solution or soil, regardless of rootstock cultivars, grafting types, growth stage and growth conditions. Also, SCRC22 scions had greater yield and less variation in boll weight either between upper- and lower sympodials, or between proximal and distal fruit positions from the main stem in the field under K deficiency, probably owing to reduced leaf senescence. Although the effect of rootstocks on leaf senescence under K deficiency was significant in some cases, the scion cultivars explained the highest percentage of variations within grafting treatments. The shoot-to-root feedback signal(s), rather than high shoot demand for K nutrition, was involved in the shoot regulation of premature senescence in cotton plants, achieved possibly by altering root K uptake.     

Developmental and environmental regulation of tissue- and cell-specific expression for a pea protein farnesyltransferase gene in transgenic plants

Farnesylation mediates membrane targeting and in vivo activities of several key regulatory proteins such as Ras and Ras-related GTPases and protein kinases in yeast and mammals, and is implicated in cell cycle control and abscisic acid (ABA) signaling in plants. In this study, the developmental expression of a pea protein farnesyl-transferase (FTase) gene was examined using transgenic expression of the β-glucuronidase (GUS) gene fused to a 3.2 kb 5′ upstream sequence of the gene encoding the pea FTase β subunit. Coordinate expression of the GUS transgene and endogenous tobacco FTase β subunit gene in tobacco cell lines suggests that the 3.2 kb region contains the key FTase promoter elements. In transgenic tobacco plants, GUS expression is most prominent in meristematic tissues such as root tips, lateral root primordia and the shoot apex, supporting a role for FTase in the control of the cell cycle in plants. GUS activity was also detected in mature embryos and imbibed embryos, in accordance with a role for FTase in ABA signaling that modulates seed dormancy and germination. In addition, GUS activity was detected in regions that border two organs, e.g. junctions between stems and leaf petioles, cotyledons and hypocotyls, roots and hypocotyls, and primary and secondary roots. GUS is expressed in phloem complexes that are adjacent to actively growing tissues such as young leaves, roots of light-grown seedlings, and hypocotyls of dark-grown seedlings. Both light and sugar (e.g. sucrose) treatments repressed GUS expression in dark-grown seedlings. These expression patterns suggest a potential involvement of FTase in the regulation of nutrient allocation into actively growing tissues.